HOT LINE DETECTION DEVICE
Technical Field
[0001] The present invention relates to a hot line detection device which detects
whether an optical line created by connecting the respective one end of two optical
fibers is in a hot line state or not.
Background Art
[0002] In the optical fiber communication technology field, a hot line detection
device, which detects whether an optical line created by optical fibers for optical
communication, housed in an optical termination box installed in a station, building,
house or the like, is in the hot line state or not, has been known. For such a hot line
detection device, a hot line detection device which can detect a hot line state without
bending the optical fiber, for example, has been proposed (e.g. see Patent Document
1). Here a hot line state refers to a state in which the optical line transmits light
normally.
[0003] This hot line detection device can detect a hot line state without bending the
optical fiber, so a break in the optical fiber by bending the optical fiber, and the
generation of transmission errors due to a temporary increase in transmission loss, can
be prevented.
[0004] Fig. 20 is a diagram depicting a configuration of a conventional hot line
detection device according to Patent Document 1. As Fig. 20 shows, the conventional

hot line detection device has a fusion reinforcing sleeve 42' which protects a fused
portion 2' which was created by fusing a respective one end of two optical fibers 1'
and 1' constituting the optical line A', and leaks the light leaking from the fused
portion 2', a case 40' which houses the fusion reinforcing sleeve 42' and leads each
optical fiber 1' and 1' out, and a photo-detection portion 50' which is inserted into the
opening of the case 40' so as to detect the light leaked from the fused portion 2'
through the fusion reinforcing sleeve 42' using a light receiving element (not
illustrated).
[0005] To fuse the respective one end of the two optical fibers 1' and 1', the two
optical fibers 1' and 1' are normally fused so that the connection loss due to axial
discrepancy and angular discrepancy of an optical axis of the two optical fibers 1' and
1' is minimized. Therefore the connection loss is about 0.2 dB at a 1310 nm
wavelength in the fused portion 2' shown in Fig. 20.
[0006] However in the case of optical communication, the power of the light that
propagates the optical fiber spreads over a wide range, and could decrease to about -
20 dBm, and in such a case, the power of the light leaked from the fused portion 2'
becomes low. Furthermore the distance between the light receiving element installed
outside the fusion reinforcing sleeve 42' and the fused portion 2' is long. For these
reasons, the power of the light that reaches the light receiving surface of the light
receiving element drops, and as a result, the light receiving efficiency decreases and
the S/N ratio decreases, which makes it difficult to detect a hot line.
[0007] It is an object of the present invention to provide a hot line detection device
which can perform more stable hot line detection.
[0008] Patent Document 1: Japanese Patent Application Laid-open No. 2007-85934
Disclosure of the Invention
[0009] A hot line detection device according to an aspect of the present invention is
a hot line detection device for detecting whether an optical line, including two optical
fibers, is in a hot line state or not, including: a light leakage generation portion which
is formed by connecting the two optical fibers so that a refractive index distribution in
a portion of connection of the two optical fibers is different from a refractive index
distribution of another portion in an optical axis direction, and which leaks a part of a
light propagating a core of one optical fiber into a clad of the other optical fiber; and a
light receiving element which adheres to an outer circumferential surface of the clad
of the other optical fiber via a transparent adhesive layer so as to detect a light leaked
by the light leakage generation portion.
Brief Description of the drawings
[0010] [Fig. 1] Fig. 1 is a diagram depicting a general configuration of a hot line
detection device according to Embodiment 1 of the present invention.
[Fig. 2] Fig. 2A to Fig. 2D are diagrams depicting the refractive index
distribution in the case of using a single mode fiber as the optical fibers, where Fig.
2A shows a general configuration of the optical fibers, Fig. 2B shows the refractive
index distribution of the B-B cross-section in Fig. 2A, Fig. 2C shows the refractive
index distribution of the C-C cross-section in Fig. 2A, and Fig. 2D shows the
refractive index distribution of the D-D cross-section in Fig. 2A.
[Fig. 3] Fig. 3A to Fig. 3D are diagrams depicting the refractive index

distribution in the case of using a GI type multi-mode fiber as the optical fibers, where
Fig. 3A shows the general configuration of the optical fibers, Fig. 3B shows the
refractive index distribution of the B-B cross-section in Fig. 3A, Fig. 3C shows the
refractive index distribution of the C-C cross-section in Fig. 3A, and Fig. 3D shows
the refractive index distribution of the D-D cross-section in Fig. 3A.
[Fig. 4] Fig. 4A and Fig. 4B are diagrams depicting a hot line detection
device according to Embodiment 2 of the present invention.
[Fig. 5] Fig. 5A is a diagram depicting a general configuration of a hot line
detection device according to Embodiment 3 of the present invention, Fig. 5B is a
cross-sectional view of the B-B cross-section of the optical fiber, and Fig. 5C is a
cross-sectional view of the C-C cross-section of the light leakage generation optical
fiber.
[Fig. 6] Fig. 6A and Fig. 6B are enlarged views of the fused portion shown
in Fig. 5.
[Fig. 7] Fig. 7A is a diagram depicting a general configuration of a hot line
detection device according to Embodiment 4 of the present invention, Fig. 7B is a
cross-sectional view of the B-B cross-section in Fig. 7A, Fig. 7C shows the refractive
index distribution of the B-B cross-section, Fig. 7D is a cross-sectional view of the D-
D cross-section in Fig. 7A, and Fig. 7E shows the refractive index distribution of the
D-D cross-section.
[Fig. 8] Fig. 8A is a diagram depicting an optical path of an SI type multi-
mode fiber, Fig. 8B is a diagram depicting an optical path of a GI type multi-mode
fiber, Fig. 8C is a diagram depicting the optical path near the fused portion at the right

side in Fig. 7 A, and Fig. 8D is a diagram depicting the optical path near the fused
portion at the left side in Fig. 7A.
[Fig. 9] Fig. 9A is a diagram depicting a general configuration of a hot line
detection device according to Embodiment 5 of the present invention, Fig. 9B is a
cross-sectional view of the B-B cross-section in Fig. 9 A, Fig. 9C shows the refractive
index distribution of the B-B cross-section, Fig. 9D is a cross-sectional view of the D-
D cross-section in Fig. 9 A, and Fig. 9E shows the refractive index distribution of the
D-D cross-section.
[Fig. 10] Fig. 10 is a diagram depicting a general configuration of a hot line
detection device according to Embodiment 6 of the present invention.
[Fig. 11] Fig. HA to Fig. 11D are diagrams depicting the refractive index
distribution in the case of using a single mode fiber as the optical fibers, where Fig.
HA shows a general configuration of the optical fibers, Fig. 11B shows the refractive
index distribution of the B-B cross-section in Fig. HA, Fig. 11C shows the refractive
index distribution of the C-C cross-section in Fig. HA, and Fig. 11D shows the
refractive index distribution of the D-D cross-section in Fig. HA.
[Fig. 12] Fig. 12A to Fig. 12D are diagrams depicting the refractive index
distribution in the case of using a GI type multi-mode fiber as the optical fibers, where
Fig. 12A shows the general configuration of the optical fibers, Fig. 12B shows the
refractive index distribution of the B-B cross-section in Fig. 12A, Fig. 12C shows the
refractive index distribution of the C-C cross-section in Fig. 12A, and Fig. 12D shows
the refractive index distribution of the D-D cross-section in Fig. 12A.
[Fig. 13] Fig. 13 is a diagram depicting a general configuration of a hot line

detection device according to Embodiment 7 of the present invention.
[Fig. 14] Fig. 14 is a diagram depicting a general configuration of a hot line
detection device according to Embodiment 8 of the present invention.
[Fig. 15] Fig. 15A is a diagram depicting a general configuration of a hot
line detection device according to Embodiment 9 of the present invention, and Fig.
15B is a diagram depicting a general configuration of a comparison example of the
hot line detection device according to Embodiment 9 of the present invention.
[Fig. 16] Fig. 16 is a diagram depicting a general configuration of a hot line
detection device according to Embodiment 10 of the presente invention.
[Fig. 17] Fig. 17A is a diagram depicting a general configuration of a hot
line detection device according to Embodiment 11 of the present invention, and Fig.
17B is a diagram depicting a general configuration of a comparison example of the
hot line detection device according to Embodiment 11 of the present invention.
[Fig. 18] Fig. 18A is a diagram depicting a general configuration of a hot
line detection device according to Embodiment 12 of the present invention, and Fig.
18B is a diagram depicting a general configuration of a comparison example of the
hot line detection device according to Embodiment 12 of the present invention.
[Fig. 19] Fig. 19 is a diagram depicting a general configuration of a hot line
detection device according to Embodiment 13 of the present invention.
[Fig. 20] Fig. 20 is a diagram depicting a configuration of a conventional
hot line detection device.

Best Mode for Carrying Out the Invention
[0011] (Embodiment 1)
Fig. 1 is a diagram depicting a general configuration of a hot line detection
device according to Embodiment 1 of the present invention. As Fig. 1 shows, this hot
line detection device is a hot line detection device for detecting whether an optical
line A formed by connecting a respective one end of the two optical fibers 1 and 1 is
in the hot line state or not, and has the optical fibers 1 and 1, a light leakage
generation portion 3, a light receiving element chip 5 (an example of a light receiving
element), a current-voltage conversion circuit 100, a determination unit 200 and a
display unit 300. In the diagrams depicting the configuration of a hot line detection
device other than Fig. 1, the current-voltage conversion circuit 100, determination unit
200 and display unit 300 are omitted.
[0012] The light leakage generation portion 3 is formed in a connected portion by
connecting the optical fibers 1 and 1 so that the refractive index distribution of the
connected portion of the two optical fibers 1 and 1 is different from the refractive
index distribution of the other portion in the optical axis direction, and leaks a part of
the light propagating the core of one optical fiber 1 (optical fiber 1 at the right side in
the example shown) into the clad 12 of the other optical fiber 1 (optical fiber 1 at the
left side in the example shown).
[0013] The light receiving element chip 5 adheres to an outer circumferential
surface of the clad 12 of the other optical fiber 1, that is, to an outer circumferential
surface of a wire 10 constituted by the core 11 and the clad 12, via a transparent
adhesive layer 4 (an example of a transparent adhesive layer) constituted by
transparent adhesive, so as to detect light leaked by the light leakage generation

portion 3.
[0014] The optical fibers 1 and 1 are connected by fusing the respective one end,
and a fused portion 2 is formed in the connected portion of the optical fibers 1 and 1,
and a light leakage generation portion 3 is formed in this fused portion 2. The bold
arrow marks in Fig. 1 show light propagating directions.
[0015] The current-voltage conversion circuit 100 is constituted by an operational
amplifier, for example, and converts a current signal, which is output from the light
receiving element chip 5, into a voltage signal.
[0016] The determination unit 200 is constituted by a microcomputer or IC
(Integrated Circuit) enclosing a resistor, capacitor, amplification circuit or the like, for
example, and determines whether the optical line A is in the hot line state or not based
on the voltage signal which is output from the current-voltage conversion circuit 100,
and has the display unit 300 display the determination result. The display unit 300 is
constituted by a liquid crystal display panel or a light emitting diode, for example, and
displays the determination result by the determination unit 200.
[0017] In the present embodiment, quartz glass fiber, which excels in propagation
loss, transmission bandwidth and such environmental resistance as mechanical
strength, for example, are used for the optical fibers 1 and 1. In the present
embodiment, a single mode fiber is used for the quartz glass fiber. This, however, is
an example, and a step-index type (SI type) multi-mode fiber, grated-index type (GI
type) multi-mode fiber, or other special fibers which can form the light leakage
generation portion 3 may be used, instead of a single mode fiber. For the optical
fibers 1 and 1, a multi-component glass fiber, or plastic fiber, for example, may be
used instead of quartz glass fiber.

[0018] As Fig. 1 shows, coating 13 is removed in the fused portion 2 side of the
optical fibers 1 and 1 respectively, where the wire 10 is exposed. The light receiving
element chip 5 adheres to the outer circumferential surface of the wire 10, that is, the
outer circumferential surface of the clad 12 via the transparent adhesive layer 4, so
that the light receiving surface faces the clad 12 side of the other optical fiber 1.
[0019] Here in optical fibers 1 and t, the length of the portion where the outer
circumferential surface of the wire 10 is exposed is about 10 mm, and the light
receiving element chip 5 is disposed at a predetermined length (e.g. about 2 to 5 mm)
away from the light leakage generation portion 3 in the optical axis direction of the
other optical fiber 1.
[0020] As a light that propagates the optical fiber 1, a light of which wavelength is
1550 nm, a light of which wavelength is 1310 nm, or a light of which wavelength is
850 nm, for example, is assumed, and the transparent adhesive layer 4 is formed by an
epoxy resin or acrylic resin adhesive, which is transparent to light having these
wavelengths. The transparent adhesive layer 4 need not be formed by a material
having a refractive index that is higher than the clad 12, but may be formed by a
material having an intermediate refractive index between air and the clad 12.
[0021] For the light receiving element chip 5, a photodiode chip, for example, can
be used. If the wavelength of the light which propagates the optical fiber 1, that is,
the light used for optical communication, is in a 1µm band wavelength area (e.g.
1510 nm, 1310 nm), then an InGaAs photodiode chip which has a high light receiving
sensitivity in a 1 urn band wavelength area can be used.
[0022] If the wavelength of the light which propagates the optical fiber 1 is light in
a 0.8 µm band width area (e.g. 850 nm), then an Si photodiode chip, which has a high

light receiving sensitivity in the 0.8 [xm band wavelength area, can be used.
[0023] If the light which propagates the optical fiber 1 is a light in a 1 µm band
wavelength area and 0.8 µm band wavelength area, then a light receiving element
chip 5 having a high light receiving sensitivity in each wavelength area can be set
individually.
[0024] Now the refractive index distribution of the optical line A will be described
with reference to Fig. 2A to Fig. 2D. Fig. 2A to Fig. 2D are diagrams depicting the
refractive index distribution in the case of using a single mode fiber as the optical
fibers 1 and 1, Fig. 2A shows the skeleton framework of the optical fibers 1 and 1, Fig.
2B shows the refractive index distribution of the B-B cross-section in Fig. 2A, Fig. 2C
shows the refractive index distribution of the C-C cross-section in Fig. 2A, and Fig.
2D shows the refractive index distribution of the D-D cross-section in Fig. 2A. The x
direction is the direction which intersects orthogonally with the optical axis direction.
[0025] Fig. 2B and Fig. 2D show the refractive index distribution of portions which
are not melted when the optical fibers 1 and 1 are fused, and show a step-formed
refractive index distribution, which is an original refractive index distribution of the
optical fibers 1 and 1.
[0026] Whereas in the refractive index distribution in Fig. 2C, the refractive index
gradually decreases as the area moves away from the center, and includes an area in
which the refractive index is lower than the refractive index nl of the core 11, and is
higher than the refractive index n2 of the clad 12. The length of this area in the x
direction is longer than the core diameter (diameter) of the optical fibers 1 and 1. The
refractive index distribution in the case of using this SI type multi-mode fiber for the
optical fibers 1 and 1 is also the same as the refractive index distribution in Fig. 2B to

Fig. 2D.
[0027] Fig. 3A to Fig. 3D are diagrams depicting the refractive index distribution
in the case of using a GI type multi-mode fiber for the optical fibers 1 and 1, where
Fig. 3A shows the general configuration of the optical fibers 1 and 1, Fig. 3B shows
the refractive index distribution of the B-B cross-section in Fig. 3A, Fig. 3C shows the
refractive index distribution of the C-C cross-section in Fig. 3A, and Fig. 3D shows
the refractive index distribution of the D-D cross-section in Fig. 3 A.
[0028] Fig. 3B and Fig. 3D show the refractive index distribution of portions which
did not melt when the optical fibers 1 and 1 are fused, and show a refractive index
distribution gradually decreasing with a square distribution from the center to the
outside, which is an original refractive index distribution of the optical fibers 1 and 1.
Whereas in the refractive index distribution in Fig. 3C, the refractive index gradually
decreases as the area moves away from the center, and includes an area in which the
refractive index is lower than the refractive index nl of the core 11 and is higher than
the refractive index n2 of the clad 12. The length of this area in the x direction is
longer than the diameter of the core of the optical fibers 1 and 1.
[0029] Here the light leakage generation portion 3 is formed by fusing the optical
fibers 1 and 1, as shown in Fig. 2A and Fig. 3A, so that an intermediate refractive
index area lla, in which the refractive index is higher than the refractive index n2 of
the clad 12 and is lower than the refractive index nl of the core 11 in the other
portions in the optical axis direction, is formed near the fused portion 2.
[0030] To fuse the respective one end of the optical fibers 1 and 1, the end faces of
the respective one end of the optical fibers 1 and 1 are butted, and heated and melted
by an arc discharge or the like, and are then cooled down so that the two optical fibers

1 and 1 are connected.
[0031] Thereby during the heating and melting, the core 11 and the clad 12 change
from a solid phase to a liquid phase, even for a short time, and are mixed, and an area
having an intermediate refractive index between the refractive index of the core 11
and the refractive index of the clad 12 is formed. The intermediate refractive index
area lla can be formed to have a desired size by appropriately changing the
conditions (e.g. temperature, time) during fusing from the conditions by which
connection loss is minimized.
[0032] In Fig. 3, optical paths of the leaked light generated in the light leakage
generation portion 3 are shown by arrow marks. In other words, out of the leaked
light generated in the light leakage generation portion 3, the ray PI, of which
supplementary angle of incidence in the boundary between the clad 12 and air is
greater than the total reflection critical supplementary angle, is leaked from the clad
12 and emitted outside, but rays P2 and P3, of which supplementary angle of
incidence is smaller than the total reflection critical supplementary angle, are totally
reflected by the boundary between air and the clad 12.
[0033] If quartz glass fibers are used for the optical fibers 1 and 1 as this
embodiment, the difference of the refractive indexes between the clad 12 and air is
large, therefore the a large percent of the leaked light generated in the light leakage
generation portion 3 is totally reflected by the boundary between the clad 12 and air,
and most of the leaked light propagates as rays P2 and P3.
[0034] The ray P2 indicates a ray which propagates through the wire 10 while
repeating the total reflection. The difference of the refractive indexes between the
clad 12 and the transparent adhesive layer 4 is smaller than the difference of the

refractive indexes between the clad 12 and air, therefore a small percent of light is
totally reflected by the interface between the clad 12 and the transparent adhesive
layer 4, and most of the light which reached the interface of the clad 12 and the
transparent adhesive layer 4 reaches the light receiving surface of the light receiving
element chip 5.
[0035] The ray P3 indicates a ray which is totally reflected only once by the
boundary of the clad 12 and air, then transmits through the interface of the clad 12 and
the transparent adhesive layer 4, and reaches the light receiving surface of the light
receiving element chip 5. In Fig. 1, an example of the ray P3, which is totally
reflected only once, is shown, but the present invention is not limited to this, and the
ray P3 may be totally reflected a plurality of times by the boundary between the clad
12 and air, then transmit through the interface of the clad 12 and the transparent
adhesive layer 4, and reach the light receiving surface of the light receiving element
chip 5.
[0036] As described above, the hot line detection device according to the present
embodiment has a light leakage generation portion 3 which is formed in a connected
portion by connecting the optical fibers 1 and 1, so that the refractive index
distribution of the connected portion of the two optical fibers 1 and 1 is different from
the refractive index distribution of the other portion in the optical axis direction, and
leaks a part of the light propagating the core of one optical fiber 1 into the clad 12 of
the other optical fiber 1.
[0037] Therefore compared with the prior art shown in Fig. 20, in which the optical
fibers 1' and 1' are fused so that the connection loss is minimized, the absolute
quantity of the leaked light can be increased. Also in the case of the hot line detection

device according to the present embodiment, the light receiving element chip 5
adheres to the outer circumferential surface of the clad 12 of the other optical fiber 1
via the transparent adhesive layer 4. Therefore compared with the case of the prior art
shown in Fig. 20, where the fusion reinforcing sleeve 42' or the like intervenes, the
distance between the light receiving element chip 5 and the outer circumferential
surface of the clad 12 can be decreased, and the efficiency of the leaked light reaching
the light receiving element chip 5 can be improved.
[0038] Furthermore, air does not intervene between the light receiving element chip
5 and the outer circumferential surface of the clad 12 of the other optical fiber 1, so
considerable leaked light can enter from the clad 12 to the transparent adhesive layer
4, of which refractive index is greater than that of air, and the efficiency of the leaked
light reaching the light receiving element chip 5 can be improved.
[0039] As a result, the hot line can be detected regardless the intensity of power of
the light propagating the optical line A. In other words, the hot line can be detected
not only when the power of the light propagating the optical line A is high, but also
when the power of the light is low, and more stable hot line detection becomes
possible.
[0040] If the distance between the light receiving element chip 5 and the light
leakage generation portion 3 is too short, the light intensity distribution of the leaked
light from the light leakage generation portion 3 may directly influence the output
current from the light receiving element chip 5, and the output current of the light
receiving element chip 5 may disperse.
[0041] However according to the present embodiment, the light receiving element
chip 5 is disposed at a predetermined length (e.g. about 2 to 5 mm) distant from the

light leakage generation portion 3 in the optical axis direction. Therefore by the
leaked light generated in the light leakage generation portion 3 repeating total
reflection, the light intensity distribution is equalized, and dispersion of the output
current of the light receiving element chip 5 can be suppressed, and as a result, stable
output from the light receiving element chip 5 can be obtained.
[0042] Also in the hot line detection device of the present embodiment, the light
leakage generation portion 3 is formed by fusing the optical fibers 1 and 1 so as to
form the intermediate refractive index area lla. Therefore the refractive index
distribution locally changes in the light propagation direction, and the light intensity
distribution also changes as the light passes through the fused portion 2, and a part of
the light can be leaked from the core 11 to the clad 12 as leaked light from the light
leakage generation portion 3.
[0043] Therefore by adjusting the size of the intermediate refractive index area lla,
to control the refractive index distribution when the optical fibers 1 and 1 are fused,
the leaked light required for hot line detection can be obtained. In other words,
according to the hot line detection device of the present embodiment, the leaked light
can be guided to the light receiving element chip 5 without adding a separate element
for light leakage generation.
[0044] (Embodiment 2)
Fig. 4A and Fig. 4B are diagrams depicting a hot line detection device
according to Embodiment 2 of the present invention. The basic configuration of the
hot line detection device of the present embodiment is generally the same as
Embodiment 1. The difference is as follows. First before fusing the two optical fibers
1 and 1, the respective one end is independently fused, as shown in Fig. 4A, so that

the refractive index distribution of the connected portion is different from the other
portion, and is different from the original refractive index distribution of the optical
fibers 1 and 1. Then as Fig. 4B shows, the respective one end of the optical fibers 1
and 1 are fused with each other to form the fused portion 2, so that the light leakage
generation portion 3 is formed. Illustration and description of the other configuration,
which is the same as Embodiment 1, are omitted.
[0045] As described in Embodiment 1, the intermediate refractive index area lla is
formed by the cores 11 and 11 and the clads 12 and 12 being mixed as the optical
fibers 1 and 1 melt when the respective one end of the two optical fibers 1 and 1 are
fused with each other, but the intermediate refractive index area lla cannot be
increased so much merely by changing the conditions of fusion.
[0046] Whereas in the present embodiment, before fusing the respective one end of
the two optical fibers 1 and 1 with each other, as shown in Fig. 4A, the respective one
end of each optical fiber 1 is transformed to a sphere of which diameter is greater than
the diameter of the wire 10, so that the core diameter of each optical fiber 1
continuously changes in the optical axis direction.
[0047] Therefore according to the hot line detection device of the present
embodiment, the light leakage generation portion 3 can be formed with more certainty,
and the range of the area, where the light leakage generation portion 3 is formed in the
cross-section that intersects the optical axis direction orthogonally, can be increased,
and the quantity of leaked light required for the hot line detection can be further
increased.
[0048] (Embodiment 3)

The basic configuration of a hot line detection device of Embodiment 3 is
generally the same as Embodiment 1, and the difference is that, as Fig. 5 shows, the
light leakage generation portion 3 is formed by connecting the respective one end of
the optical fibers 1 and 1 so as to sandwich a light leakage generation optical fiber 6,
of which core diameter is different from those of the optical fibers 1 and 1.
Illustration and description of the other configuration, which is the same as
Embodiment 1, are omitted.
[0049] Fig. 5A is a diagram depicting a general configuration of a hot line
detection device according to Embodiment 3 of the present invention, Fig. 5B is a
cross-sectional view of the B-B cross-section of the optical fiber 1, and Fig. 5C is a
cross-sectional view of the C-C cross-section of the light leakage generation optical
fiber 6.
[0050] Fig. 6A and Fig. 6B are enlarged views of the fused portion 2 shown in Fig.
5. The light leakage generation optical fiber 6 is formed by quartz glass fiber, just
like the optical fibers 1 and 1. The outer diameter of the clad 62 of the light leakage
generation optical fiber 6 is the same as the outer diameter of the clads 12 and 12 of
the optical fibers 1 and 1. In other words, the outer diameter of the wire 60 of the
light leakage generation optical fiber 6 is the same as the outer diameter of the wires
10 and 10 of the optical fibers 1 and 1.
[0051] The core diameter (diameter) of the core 61 of the light leakage generation
optical fiber 6 is greater than the core diameter of the cores 11 and 11 of the optical
fibers 1 and 1. Both ends of the light leakage generation optical fiber 6 are fused with
the respective one end of the optical fibers 1 and 1, so that the optical axis thereof
matches with the optical axes of the optical fibers 1 and 1.

[0052] Here both ends of the light leakage generation optical fiber 6 are fused with
the respective one end of the optical fibers 1 and 1, whereby the fused portions 2 and
2 are formed respectively. The core diameter changes from small to large in the
optical axis direction of the optical fibers 1 and 1, at the fused portion 2 (fused portion
2 at the right side in Fig. 5) between one optical fiber 1 (optical fiber 1 at the right
side in Fig. 5) and the light leakage generation optical fiber 6 as the boundry,
therefore little connection loss is generated and the light leakage .generation portion 3
is not formed.
[0053] However in the fused portion 2 (fused portion 2 at the left side in Fig. 5)
between the light leakage generation optical fiber 6 and the other optical fiber 1
(optical fiber 1 at the left side in Fig. 5), the core diameter changes from large to small
in the optical axis direction of the optical fibers 1 and 1, at the fused portion 2 as the
boundary, therefore the light leakage generation portion 3 is formed in the fused
portion 2.
[0054] In the light leakage generation optical fiber 6 and the other optical fiber 1
are single mode fibers, the quantity of leaked light in the light leakage generation
portion 3 changes according to the difference between the light distribution state
(intrinsic mode), which is determined by the refractive index distribution on the cross-
section which intersects orthogonally with the optical axis direction of the light
leakage generation optical fiber 6, and the refractive index distribution of the cross-
section which intersects orthogonally with the optical axis direction of the other
optical fiber 1.
[0055] If the light leakage generation optical fiber 6 and the other optical fiber 1
are multi-mode fibers, the quantity of leaked light changes according to the area

difference between the sectional area of the core 61 of the light leakage generation
optical fiber 6 and the sectional area of the core 11 of the other optical fiber 1.
Therefore the quantity of leaked light increases as the area difference of the core 11
increases regardless whether single mode fibers or multi-mode fibers are used for the
light leakage generation optical fiber 6 and the other optical fiber 1.
[0056] Therefore in the case of the hot line detection device of the present
embodiment, the light leakage generation portion 3 can be formed by selecting an
appropriate core diameter of the light leakage generation optical fiber 6, which is
sandwiched between the respective one end of the two optical fibers 1 and 1, and
fusing both ends of the light leakage generation optical fiber 6 with the respective one
end of the two optical fibers 1 and 1. This makes it possible to secure the quantity of
the leaked light required for the hot line detection, and to form the light leakage
generation portion 3 without changing the conditions of fusion.
[0057] In the case of the hot line detection device of the present embodiment, the
refractive index of the core 61 of the light leakage generation optical fiber 6 and the
refractive index of the core 11 of the other optical fiber 1 are the same, and a part of
the light flows from the core 61 of the light leakage generation optical fiber 6 to the
clad 12 of the other optical fiber 1, as bold arrows in Fig. 6A show.
[0058] However if the refractive index of the core 61 of the light leakage
generation optical fiber 6 is different from the refractive index of the core 11 of the
other optical fiber 1, the quantity of leaked light generated in the light leakage
generation portion 3 can be increased, and hot line can be detected more accurately.
[0059] For example, in the case of using an SI type multi-mode fiber for the optical
fibers 1 and 1 and the light leakage generation optical fiber 6, if the refractive index of

the other optical fiber 1, of which core diameter is small, is lower than the refractive
index of the optical fiber for the light leakage generation 6, of which core diameter is
large, refraction occurs in the fused portion 2 between the light leakage generation
optical fiber 6 and the other optical fiber 1. Therefore as Fig. 6B shows, light spreads
wider in the wire 10 of the other optical fiber 1, and light of which supplementary
angle of incidence in the boundary of the core 11 and the clad 12 of the other optical
fiber 1 is greater than the critical supplementary angle of total reflection is refracted,
and enters the clad 12 of the other optical fiber 1, so the quantity of the leaked light
increases.
[0060] According to the present embodiment, the core diameter of the light leakage
generation optical fiber 6 is greater than the core diameter of the optical fibers 1 and 1,
but the present invention is not limited to this. In other words, a light leakage
generation optical fiber 6, of which core diameter is smaller than those of the optical
fibers 1 and 1, may be used, and in this case, the light leakage generation portion 3 is
formed on the fused portion 2 between one optical fiber 1 and the light leakage
generation optical fiber 6, and the light leakage generation portion 3 is not generated
on the fused portion 2 between the light leakage generation optical fiber 6 and the
other optical fiber 1.
[0061] (Embodiment 4)
Fig. 7A is a diagram depicting a general configuration of a hot line
detection device according to Embodiment 4 of the present invention, Fig. 7B is a
cross-sectional view of the B-B cross-section in Fig. 7A, Fig. 7C shows the refractive
index distribution of the B-B cross-section, Fig. 7D is a cross-sectional view of the D-
D cross-section in Fig. 7A, and Fig. 7E shows the refractive index distribution of the

D-D cross-section.
[0062] The basic configuration of the hot line detection device of the present
embodiment is generally the same as Embodiment 3. The difference is that, as Fig. 7
shows, the light leakage generation portion 3 is formed by connecting the respective
end of the optical fibers 1 and 1, so as to sandwich a light leakage generation optical
fiber 7, of which core diameter is the same as those of the optical fibers 1 and 1 and
the refractive index of the core 71 is different from the core 11 of the optical fibers 1
and 1. Illustration and description of the other configuration, which is the same as
Embodiment 1, are omitted.
[0063] The light leakage generation optical fiber 7 is constituted by quartz glass
fiber, just like the optical fibers 1 and 1. Here the outer diameter of the clad 72 of the
light leakage generation optical fiber 7 is the same as the outer diameter of the clads
12 and 12 of the optical fibers 1 and 1. In other words, the outer diameter of the wire
70 of the light leakage generation optical fiber 7 is the same as the outer diameter of
the wires 10 and 10 of the optical fibers 1 and 1. The core diameter of the core 71 of
the light leakage generation optical fiber 7 is also the same as the core diameter of the
cores 11 and 11 of the optical fibers 1 and 1. Both ends of the light leakage
generation optical fiber 7 in the optical axis direction are fused with each one end of
the optical fibers 1 and 1 respectively, so that the optical axis thereof matches with the
optical axis of the optical fibers 1 and 1. In the present embodiment, an SI type multi-
mode fiber is used for the optical fibers 1 and 1, and a GI type multi-mode fiber, of
which numerical aperture (NA) is the same as those of the optical fibers 1 and 1, is
used for the light leakage generation optical fiber 7, for example.
[0064] Both ends of the light leakage generation optical fiber 7 and the respective

one end of the optical fibers 1 and 1 are fused, whereby the fused portions 2 and 2 are
formed respectively, and in the optical axis direction of the optical fibers 1 and 1, the
SI type multi-mode fiber changes into GI type multi-mode fiber, at the fused portion 2
(fused portion 2 at the right side in Fig. 7A) between one optical fiber 1 (optical fiber
1 at the right side in Fig. 7A) and the light leakage generation optical fiber 7 as the
boundary. Thereby the light leakage generation portion 3 is formed in the fused
portion 2 at the right side.
[0065] On the other hand, in the boundary at the fused portion 2 (fused portion 2 at
the left side in Fig. 7A) between the light leakage generation optical fiber 7 and the
other optical fiber 1 (optical fiber 1 at the left side in Fig. 7A) in the optical axis
direction of the optical fibers 1 and 1, the GI type multi-mode fiber changes into SI
type multi-mode fiber, therefore the light leakage generation portion 3 is not formed.
This aspect will now be described with reference to Fig. 8A to Fig. 8D.
[0066] Fig. 8A is a diagram depicting an optical path of the SI type multi-mode
fiber, Fig. 8B is a diagram depicting an optical path of the GI type multi-mode fiber,
Fig. 8C is a diagram depicting the optical path near the fused portion 2 at the right
side in Fig. 7A, and Fig. 8D is a diagram depicting the optical path near the fused
portion 2 at the left side in Fig. 7A.
[0067] The SI type multi-mode fiber has a step-formed refractive index distribution
where the portion of the core 11 is high and the portion of the clad 12 is low, as
shown in Fig. 7C, so the light having a maximum supplementary angle of incidence
exists at any position in the diameter direction (x direction) of the optical fiber 1, as
the bold arrows in Fig. 8A show.
[0068] The GI type multi-mode fiber, on the other hand, has a refractive index

distribution of the core 11, which changes in the convex curve facing up with the
refractive index nl at the peak, as shown in Fig. 7E, so the supplementary angle of
incidence of the light changes according to the position in the diameter direction (x
direction) of the optical fiber 7, as the bold arrows in Fig. 8B show.
[0069] In other words, in the case of the light leakage generation optical fiber 7
constituted by the GI type multi-mode fiber, light of which supplementary angle of
incidence is large exists in the core 71 in a portion near the center of the core 71, but
only light of which supplementary angle of incidence is small exists in an edge
portion near the clad 72, therefore the locus of the light vacillates in sine wave form.
[0070] As a consequence in the core 71 of the light leakage generation optical fiber
7 constituted by the GI type multi-mode fiber, light of which supplementary angle of
incidence is large enters the edge portion near the clad 72 from one optical fiber 1
constituted by the SI multi-mode fiber, as shown in Fig. 8C, then the light does not
remain within the core 71, and leaks to the clad 72.
[0071] On the other hand, as shown in Fig. 8D, even if light enters from the light
leakage generation optical fiber 7, constituted by the GI type multi-mode fiber, to the
other optical fiber 1 constituted by the SI multi-mode fiber, loss is not generated.
[0072] As described above, according to the hot line detection device of the present
embodiment, the light leakage generation optical fiber 7 constituted by the GI type
multi-mode fiber is sandwiched by the optical fibers 1 and 1 constituted by the SI type
multi-mode fibers, therefore the quantity of the leaked light required for the hot line
detection can be secured with more certainty, and the light leakage generation portion
3 can be formed without changing the conditions of the fusion.

[0073] In the present embodiment, an SI type multi-mode fiber is used for the
optical fibers 1 and 1, and a GI type multi-mode fiber of which NA is the same as the
optical fibers 1 and 1 is used for the light leakage generation optical fiber 7, but the
present invention is not limited to this.
[0074] In other words, an SI type multi-mode fiber may be used for the optical
fibers 1 and 1, and an SI type multi-mode fiber, of which core diameter is the same as
the optical fibers 1 and 1 and the NA is different from (smaller than) the optical fibers
1 and 1, may be used for the optical fiber for the light leakage generation 7.
[0075] A GI type multi-mode fiber may be used for the optical fibers 1 and 1, and
an SI type multi-mode fiber of which core diameter and NA are both the same as
those of the optical fibers 1 and 1 may be used for the light leakage generation optical
fiber 7.
[0076] In this case, the light leakage generation portion 3 is formed in the fused
portion 2 between the other optical fiber 1 and the light leakage generation optical
fiber 7, where the SI type multi-mode fiber changes into GI type multi-mode fiber,
and the light leakage generation portion 3 is not formed in the fused portion 2 between
the one optical fiber 1 and the light leakage generation optical fiber 7.
[0077] (Embodiment 5)
Fig. 9A is a diagram depicting a general configuration of a hot line
detection device according to Embodiment 5 of the present invention, Fig. 9B is a
cross-sectional view of the B-B cross-section in Fig. 9A, Fig. 9C shows the refractive
index distribution of the B-B cross-section, Fig. 9D is a cross-sectional view of the D-
D cross-section in Fig. 9A, and Fig. 9E shows the refractive index distribution of the

D-D cross-section.
[0078] The basic configuration of the hot line detection device of the present
embodiment is generally the same as Embodiment 1, but the difference is that, as Fig.
9A shows, the light leakage generation portion 3 is formed by connecting the
respective one end of the optical fibers 1 and 1 so as to sandwich a fiber 8 which is
constituted by a same material (quartz glass) as the clads 12 and 12 of the optical
fibers 1 and 1 and of which refractive index is uniform.
[0079] Here the refractive index of the fiber 8 is set to the same value as the
refractive index of the clads 12 and 12 of the optical fibers 1 and 1. Illustration and
description of the other configuration, which is the same as Embodiment 1, are
omitted.
[0080] According to the hot line detection device of the present embodiment, the
fused portions 2 and 2 are formed by fusing both ends of the fiber 8 and the respective
one end of the optical fibers 1 and 1, and light, other than the light that reaches the
core 11 of the other optical fiber 1, out of the light which spread and entered from the
core 11 of one optical fiber 1 to the fiber 8, becomes leaked light.
[0081] Thus according to the hot line detection device of the present embodiment,
the light leakage generation portion 3 is formed by the optical fibers 1 and 1
sandwiching the fiber 8, which is constituted by the same material as the clads 12 and
12 of the optical fibers 1 and 1, and of which refractive index is uniform.
[0082] Therefore the required quantity of leaked light can be secured with more
certainty, and the light leakage generation unit 3 can be formed without changing the
conditions of fusion.

[0083] (Embodiment 6)
Fig. 10 is a diagram depicting a general configuration of a hot line detection
device according to Embodiment 6 of the present invention. As Fig. 10 shows, the
hot line detection device of the present embodiment is characterized in that a plurality
of light receiving element chips 51 and 52, which can independently detect a plurality
of (two in this case) lights having different wavelength bands, are disposed.
[0084] In the present embodiments, a composing element the same as that of
Embodiments 1 to 5 is denoted with the same reference numeral, for which
description is omitted. The optical fibers 1 and 1 are the same as those of
Embodiment 1. In the optical fibers 1 and 1, the length of the portion where the outer
circumferential surface of the wire 10 is exposed is about 10 mm, which is the same
as Embodiment 1. The light receiving element chips 5 are disposed at a
predetermined length (e.g. about 2 to 5 mm) distant from the light leakage generation
portion 3 in the optical axis direction of the other optical fiber 1, just like Embodiment
1.
[0085] As light that propagates the optical fibers 1 and 1, two lights having
different wavelength bands, such as light of which wavelength is 1550 nm and light of
which wavelength is 850 nm, are assumed. Two lights having different band
wavelengths are not limited to these, but light of which wavelength is 1310 nm and
light of which wavelength is 850 nm, for example, may be used. Fig. 10 shows the
case of using the light of which wavelength is 1550 nm and the light of which
wavelength is 850 nm.
[0086] The transparent adhesive layer 4 is constituted by epoxy resin or acrylic
resin, which are adhesives transparent to light have these wavelengths.

[0087] For each light receiving element chips 51 and 52, photodiode chips, of
which crystal materials are different from each other, can be used. Here it is assumed
to use the light of which wavelength is 1550 nm and light of which wavelength is 850
nm for the light that propagates the optical fiber 1, that is, light used for optical
communication. Therefore for the light receiving element chip 51, an InGaAs
photodiode chip which has high light receiving sensitivity in a 1.5 µm band
wavelength area is used.
[0088] For the light receiving element chip 52, an Si photodiode chip which has
high light receiving sensitivity in an 0.8 urn band wavelength area is used. The Si
photodiode has no light receiving sensitivity for light in a 1 µm band. The InGaAs
photodiode has light receiving sensitivity for a 1.3 µm band and 1.5 µm band light,
and has very low light receiving sensitivity for a 0.8µm band light.
[0089] Now the refractive index distribution of the optical line A will be described
with reference to Fig. 11A to Fig. 11D. Fig. 11A to Fig. 11D are diagrams depicting
the refractive index distribution in the case of using a single mode fiber as the optical
fiber, where Fig. 11A shows a general configuration of the optical fibers 1 and 1, Fig.
11B shows the refractive index distribution of the B-B cross-section in Fig. 11 A, Fig.
11C shows the refractive index distribution of the C-C cross-section in Fig. 11 A, and
Fig. 11D shows the refractive index distribution of the D-D cross-section in Fig. 11 A.
[0090] In Fig. 11A to Fig. 11D, a single mode fiber is used for the optical fibers 1
and 1. Description on the refractive index distribution in Fig. 11B to Fig. 11D, which
is the same as the refractive index distribution in Fig. 2B to Fig. 2D, is omitted.
[0091] Fig. 12A to Fig. 12D are diagrams depicting the refractive index distribution
in the case of using a GI type multi-mode fiber for the optical fibers 1 and 1, where

Fig. 12A shows the general configuration of the optical fibers 1 and 1, Fig. 12B shows
the refractive index distribution of the B-B cross-section in Fig. 12A, Fig. 12C shows
the refractive index distribution of the C-C cross-section in Fig. 12A, and Fig. 12D
shows the refractive index distribution of the D-D cross-section in Fig. 12A.
[0092] Description of the refractive index distribution in Fig. 12B to Fig. 12D,
which is the same as the refractive index distribution in Fig. 3B to Fig. 3D, is omitted.
[0093] Most of the leaked light generated in the light leakage generation portion 3
propagates through the wire 10 while repeating total reflection, pass through the
interface between the clad 12 and the transparent adhesive layers 4 and 4, and reach
the light receiving surfaces of the light receiving element chips 51 and 52. In Fig. 10,
a dashed line arrow shows an example of the traveling path of the ray PI of the light
of which wavelength is 1310 nm, out of the leaked light generated in the light leakage
generation portion 3, and the solid line arrow shows an example of the traveling path
of the ray P2 of the light of which wavelength is 850 nm.
[0094] According to the hot line detection device of the present embodiment
described above, a plurality of light receiving element chips 51 and 52, which can
independently detect a plurality of lights having different band wavelengths, are
disposed. Therefore in addition to the effect of Embodiment 1, hot line can be easily
detected for each of the plurality of lights for the optical line A where a plurality of
lights having different band wavelengths propagate.
[0095] The detection sensitivity of the light receiving element chip 51 or 52 is
determined by the total of four aspects (1) to (4): (1) light receiving sensitivity of the
light receiving element chip 51 or 52 with respect to the detection target wavelength;
(2) quantity of the leaked light having each detection target wavelength in the light

leakage generation portion 3; (3) efficiency of the leaked light having the detection
target wavelength reaching the light receiving element chip 51 or 52; and (4) area of
the light receiving surface of the light receiving element chip 51 or 52.
[0096] Here according to the hot line detection device of the present embodiment,
detection target wavelength and crystal material are different between the light
receiving element chips 51 and 52, so the values of the light receiving sensitivity (1)
and the area of the light receiving surface (4) are different between the two light
receiving element chips 51 and 52. The quantity of the leaked light having each
detection target wavelength in the light leakage generation portion 3 (2) is about the
same, so if the light receiving sensitivity (1) and the area of the light receiving surface
(4) are different between the two light receiving element chips 51 and 52, the
detection sensitivities of the light receiving element chips 51 and 52 can be balanced
to approximately a same value by adjusting the reach efficiency (3).
[0097] According to the hot line detection device of the present embodiment, it is
preferable to dispose the light receiving element chip 51 having lower detection
sensitivity closer to the light leakage generation portion 3 when the plurality of light
receiving element chips 51 and 52 are disposed. Thereby the difference of detection
sensitivities between the light receiving element chips 51 and 52 can be decreased so
that detection sensitivities of the light receiving element chips 51 and 52 can be
balanced to approximately a same value, and the hot line can be detected more
accurately for each light.
[0098] (Embodiment 7)
Fig. 13 is a diagram depicting a general configuration of a hot line detection
device according to Embodiment 7 of the present invention. The basic configuration

of the hot line detection device of the present embodiment is roughly the same as that
of Embodiment 6. The difference is that, as Fig. 13 shows, the light receiving element
chips 51 and 52 are disposed so that the distance of the light receiving element chips
51 and 52 from the light leakage generation portion 3 ("specified length" described in
Embodiment 1) become the same. Here the light receiving element chip 51 and the
light receiving element chip 52 are disposed so as to face each other, sandwiching the
other optical fiber 1. A composing element the same as that in Embodiments 1 to 6 is
denoted with a same reference numeral, for which description is omitted.
[0099] In the case of the hot line detection device of Embodiment 6, a plurality of
light receiving element chips 51 and 52 are disposed along the optical axis direction
of the other optical fiber 1. Therefore a part of the light having a detection target
wavelength to be detected by the light receiving element chip 52 disposed at the
downstream side (left side in Fig. 10) enters the light receiving element chip 51
disposed at the upstream side. This may decrease the leaked light having the
detection target wavelength which reaches the light receiving element chip 52, drop
the efficiency of the leaked light reaching the light receiving element chip 52, and
decrease the output current.
[0100] Whereas in the hot line detection device of the present embodiment, the
plurality of light receiving element chips 51 and 52 are disposed so that the respective
distance from the light leakage generation portion 3 become the same. Hence the
efficiency of leaked light, reaching the light receiving chips 51 and 52 respectively,
can be roughly the same.
[0101] In Fig. 13, not only the ray PI of the light having a detection target
wavelength, but also the ray P2 having a detection target wavelength of the light

receiving element chip 52 enters the light receiving element chip 51. However the ray
P2, which passes through the light path reaching the light receiving element chip 51,
is originally a ray P2 which does not reach the light receiving element chip 52, and
does not decrease the efficiency of the leaked light reaching the light receiving
element chip 52.
[0102] If the distance between the light receiving element chips 51 and 52 and the
light leakage generation portion 3 is too short, it is possible that the light intensity
distribution of the leaked light from the light leakage generation portion 3 directly
influences the output current of the light receiving element chips 51 and 52, and the
output current of the light receiving element chips 51 and 52 disperse. Therefore it is
preferable to set the predetermined length so that the light generated in the light
leakage generation portion 3 totally reflects at least once, and reaches the light
receiving element chips 51 and 52. Thereby the light intensity distribution is
equalized, and dispersion of the output current of the light receiving element chips 51
and 52 can be suppressed, and stable output of the light receiving element chips 51
and 52 can be implemented.
[0103] (Embodiment 8)
Fig. 14 is a diagram depicting a general configuration of a hot line detection
device according to Embodiment 8 of the present invention. The basic configuration
of the hot line detection device of the present embodiment is roughly the same as that
of Embodiment 6. The difference is that the optical line A is a two-way
communication optical line, and as Fig. 14 shows, the light receiving element chips 51
and 52 and the light receiving element chips 51 and 52 are disposed on both sides of
the light leakage generation portion 3 in the optical axis direction. In the present

embodiment, a composing element the same as that of Embodiments 1 to 7 is denoted
with the same reference numeral, for which description is omitted.
[0104] As Fig. 14 shows, in the present embodiment, a plurality of (two in this
case) lights which propagate from right to left and have mutually different wavelength
bands, and a plurality of (two in this case) lights which propagate from left to right
and have mutually different wavelength bands propagate the optical fibers 1 and 1.
The light paths of the former plurality of lights are indicated by solid line arrows, and
the light paths of the latter plurality of lights are indicated by broken line arrows.
[0105] According to the hot line detection device of the present embodiment, the
light receiving element chips 51 and 52 disposed at the right side receive the leaked
light propagating the light paths indicated by the broken line, that is, from left to right,
and the light receiving element chips 51 and 52 disposed at the left side receive the
leaked light propagating the light paths indicated by the solid ine, that is, from right to
left.
[0106] Hence each of the light receiving element chips 51, 52, 51 and 52, can
prevent the light, of which propagating direction is the opposite of the detection target
light, from being reached.
[0107] In Fig. 14, it is preferable that the light receiving element chips 51 and 52 at
the left side, and the light receiving element chips 51 and 52 at the right side, are
disposed symmetrically with respect to the cross-section that contains the fused
portion 2. In the present embodiment, the optical line A in a line where lights having
a plurality of wavelength bands are transmitted both ways, but it is not necessary that
lights having a same number of wavelength bands are transmitted in both directions,
and lights having a different number of wavelength bands may be transmitted in each

direction. And only light with one wavelength band may be transmitted in both
directions.
[0108] The method for forming the light leakage generation portion 3 in
Embodiments 6 and 7 is not limited to the forming method described in Embodiment
1, but the light leakage generation portion 3 may be formed using the method of
Embodiment 2.
[0109] The light leakage generation portion 3 may be formed by connecting the
respective one end of the optical fibers 1 and 1 so as to sandwich the light leakage
generation optical fiber 6, of which core diameter is different from that of optical
fibers 1 and 1, as shown in Embodiment 3.
[0110] The light leakage generation portion 3 may be formed by connecting the
respective one end of the optical fibers 1 and 1 so as to sandwich the light leakage
generation optical fiber 7, of which core diameter is the same as that of the optical
fibers 1 and 1, and the refractive index is different from that of the core 11 of the
optical fibers 1 and 1, as shown in Embodiment 4.
[0111] The light leak generation portion 3 may also be formed by connecting the
respective one end of the optical fibers 1 and 1 so as to sandwich a fiber which is
constituted by a same material (quartz glass) as the clads 12 and 12 of the optical
fibers 1 and 1, and of which refractive index is uniform, as shown in Embodiment 5.
[0112] (Embodiment 9)
Fig. 15A is a diagram depicting a general configuration of a hot line
detection device according to Embodiment 9 of the present invention. Fig. 15B is a
diagram depicting a general configuration of a comparison example of the hot line

detection device according to Embodiment 9 of the present invention. In the present
embodiment, a composing element the same as that of Embodiments 1 to 8 is denoted
with the same reference numeral, for which description is omitted.
[0113] The basic configuration of the hot line detection device of the present
embodiment is the same as that of the hot line detection device of Embodiment 1.
The difference is that an area of the transparent adhesive layer 4, which contacts the
clad 12 of the other optical fiber 1, is limited so that the leaked light from the light
leakage generation portion 3 does not leak into the air via the transparent adhesive
layer 4, in the space between the light receiving element chip 5 and the light leakage
generation portion 3.
[0114] As Fig. 15B shows, in the case of the comparison example, the transparent
adhesive layer 4 spreads wide toward the light leakage generation portion 3 side in the
optical axis direction of the optical fibers 1 and 1. Therefore in the space between the
light receiving element chip 5 and the light leakage generation portion 3, a part of the
leaked light from the light leakage generation portion 3 leaks to the outside (into the
air) via the transparent adhesive layer 4. This decreases the efficiency of the leaked
light reaching the light receiving element chip 5.
[0115] As Fig. 15A shows, in the case of the hot line detection device of the
present embodiment, on the other hand, the contact area of the clad 12 of the other
optical fiber 1 and the transparent adhesive layer 4 is limited so that the leaked light
from the light leakage generation portion 3 is not leaked into the air via the
transparent adhesive layer 4, in the space between the light receiving element chip 5
and the light leakage generation portion 3.
[0116] In concrete terms, as Fig. 15 A shows, the size of the contact area of the clad

12 of the other optical fiber 1 and the transparent adhesive layer 4 is smaller than the
size of this area shown in Fig. 15B.
[0117] To implement this, the coating amount of adhesive to be the transparent
adhesive layer 4, and the load applied when the light receiving element chip 5 is
adhered, are appropriately set. In the present embodiment, the size of the contact area
of the transparent adhesive layer 4 and the clad 12 is set to be a size slightly larger
than the size of the light receiving element chip 5, but the present invention is not
limited to this. In other words, the contact area of the transparent adhesive layer 4 and
the clad 12 may be formed to have the same size as the light receiving surface of the
light receiving element chip 5. In the present embodiment, the size of the light
receiving surface of the light receiving element chip 5 and the size of the light
receiving element chip 5 are approximately the same.
[0118] As described above, according to the hot line detection device of the present
embodiment, not only can the effect of Embodiment 1 be implemented, but also the
efficiency of the leaked light reaching the light receiving element chip 5 can be
further improved since the size of the contact area of the transparent adhesive layer 4
and the clad 12 is limited.
[0119] (Embodiment 10)
Fig. 16 is a diagram depicting a general configuration of a hot line detection
device according to Embodiment 10 of the present invention. The basic configuration
of the hot line detection device of the present embodiment is roughly the same as that
of Embodiment 1. The difference is that, as Fig. 16 shows, a part of the light
receiving surface of the light receiving element chip 5 is an effective light receiving
area 5a in which the light receiving sensitivity is approximately uniform, and the size

of the contact area of the transparent adhesive layer 4 and the clad 12 is set to be
smaller than the size of the light receiving element chip 5, and is larger than the
effective light receiving area 5 a. Description on the other configuration, which is the
same as Embodiment 9, is omitted.
[0120] By this configuration, the amount of using adhesive for forming the
adhesive layer 4 can be decreased, and efficiency of light reaching the light receiving
element chip 5 can be improved.
[0121] (Embodiment 11)
Fig. 17A is a diagram depicting a general configuration of a hot line
detection device according to Embodiment 11 of the present invention. Fig. 17B is a
diagram depicting a general configuration of a comparison example of the hot line
detection device according to Embodiment 11 of the present invention. In the present
embodiment, a comprising element the same as that of Embodiments 1 to 10 is
denoted with the same reference numeral, for which description is omitted.
[0122] The basic configuration of the hot line detection device of the present
embodiment is roughly the same as that of the hot line detection device of
Embodiment 9. The difference is that, as Fig. 17A shows, a reflection portion 6x,
which is constituted by a metal film, for reflecting the leaked light generated in the
light leakage generation portion 3, and which limits the size of the contact area of the
transparent adhesive layer 4 and the clad 12 at the light leakage generation portion 3
side, is coated on the outer circumferential surface of the other optical fiber 1 in the
space between the light receiving element chip 5 and the light leakage generation
portion 3.

[0123] Here the reflection portion 6x is coated throughout the entire circumference
of the clad 12 in the circumferential direction. In other words, the reflection portion
6x is formed to be concentric with the clad 12.
[0124] For the material of the metal film constituting the reflection portion 6x, a
metal material of which reflectance is higher, with respect to the light propagating the
optical fiber 1, can be used. The light used for optical communication is normally
infrared light of which wavelength is 850 nm, 1310 nm or 1550 nm, for example.
Hence it is preferable to use Au, Ag, Al and Cu, for example, for the metal material,
and it is especially preferable to use Au, which is superb in oxidation resistance.
[0125] Therefore according to the hot line detection device of the present
embodiment, the leaked light generated in the light leakage generation portion 3 can
be reflected by the reflection portion 6x constituted by a metal film. Therefore
compared with the comparison example shown in Fig. 17B, where the contact area of
the transparent adhesive layer 4 and the clad 12 spreads widely toward the light
leakage generation portion 3 side, the efficiency of the leaked light reaching the light
receiving element chip 5 can be further improved. Even if the adhesive spreads
toward the light leakage generation portion 3 side during manufacture, the contact
area of the transparent adhesive layer 4 and the clad 12 is limited by the reflection
portion 6x, so a drop in efficiency of the leaked light reaching the light receiving
element chip 5 can be prevented.
[0126] (Embodiment 12)
Fig. 18A is a diagram depicting a general configuration of a hot line
detection device according to Embodiment 12 of the present invention. Fig. 18B is a
diagram depicting a general configuration of a comparison example of the hot line

detection device according to Embodiment 12 of the present invention. In the present
embodiment, a composing element the same as that of Embodiments 1 to 11 is
denoted with the same reference numeral, for which description is omitted.
[0127] The basic configuration of the hot line detection device of the present
embodiment is roughly the same as that of the hot line detection device of
Embodiment 9. The difference is that, as Fig. 18A shows, a reflection portion 7x,
which is constituted by a porous glass film for totally reflecting the leaked light
generated in the light leakage generation portion 3, and which limits the size of the
contact area of the transparent adhesive layer 4 and the clad 12, at the light leakage
generation portion 3 side, is coated on the outer circumferential surface of the other
optical fiber 1 in the space between the light receiving element chip 5 and the light
leakage generation portion 3.
[0128] Here the reflection portion 7x is coated throughout the entire circumference
of the clad 12 in the circumferential direction. In other words, the reflection portion
7x is formed to be concentric with the clad 12.
[0129] For the porous glass film constituting the reflection portion 7x, a porous
glass film, of which average refractive index (equivalent refractive index) is about
1.01 to 1.05, close to the refractive index of air, that is 1, can be used. In other words,
for the porous glass film, a porous glass film, of which refractive index is sufficiently
lower than the refractive index of the transparent adhesive layer 4 and the refractive
index of the clad 12, can be used.
[0130] For the material of the porous glass film, silica aerogel, for example, can be
used.

[0131] Therefore according to the hot line detection device of the present
embodiment, the leaked light generated in the light leakage generation portion 3 can
be totally reflected by the reflection portion 7x. Thus compared with the comparison
example shown in Fig. 18B, where the contact area of the transparent adhesive layer 4
and the clad 12 spreads widely toward the light leakage generation portion 3 side, the
efficiency of the leaked light reaching the light receiving element chip 5 can be
further improved. Even if the adhesive spread toward the light leakage generation
portion 3 side during manufacture, the contact area of the transparent adhesive layer 4
and the clad 12 is limited by the reflection portion 7x, so a drop in efficiency of the
leaked light reaching the light receiving element chip 5 can be prevented.
[0132] (Embodiment 13)
Fig. 19 is a diagram depicting a general configuration of a hot line detection
device according to Embodiment 13 of the present invention. In the present
embodiment, a composing element the same as that of Embodiments 1 to 12 is
denoted with the same reference numeral, for which description is omitted.
[0133] The basic configuration of the hot line detection device of the present
embodiment is roughly the same as Embodiment 11. The difference is that, as Fig. 19
shows, the reflection portion 6x extends over the optical fibers 1 and 1. In the present
embodiment, the reflection portion 6x is formed extending over the optical fibers 1
and 1, but it is sufficient if the reflection portion 6x is formed at least roughly on the
entire area between the transparent adhesive layer 4 and the light leakage generation
portion 3 in the optical axis direction of the optical fibers 1 and 1.
[0134] In the case of the hot line detection device of Fig. 17A described in
Embodiment 11, a portion where the clad 12 of the other optical fiber 1 is exposed

exists between the reflection portion 6x and the light leakage generation portion 3.
Therefore depending on the operating environment, condensation may be generated
on the surface of the clads 12 and 12. If such condensation is generated, a part of the
leaked light generated in the light leakage generation portion 3 may leak into the air
via water drops, because the refractive index of water is about 1.3, and the refractive
index difference between the clad 12 and water is smaller than the refractive index
difference between the clad 12 and air, and as a result, the efficiency of the leaked
light reaching the light receiving element chip 5 may drop.
[0135] Whereas in the hot line detection device of the present embodiment, the
reflection portion 6x is formed on the entire area between the transparent adhesive
layer 4 and the leakage generation portion 3. Therefore the generation of
condensation on the surface of the clad 12 of the other optical fiber 1 in the space
between the transparent adhesive layer 4 and the leakage generation portion 3 can be
prevented. As a result, leakage of the leaked light generated in the light leakage
generation portion 3 into the air via water drops can be prevented, and a drop in
efficiency of the leaked light reaching the light receiving element chip 5 can be
prevented.
[0136] The same effect can also be implemented by using the reflection portion 7x
described in Embodiment 12, instead of the reflection portion 6x of the present
embodiment.
[0137] The technical characteristics of the above mentioned hot line detection
device are summarized as follows.
[0138] (1) The hot line detection device according to an aspect of the present
invention is a hot line detection device for detecting whether an optical line, including

two optical fibers, is in a hot line state or not, including: a light leakage generation
portion which is formed by connecting the two optical fibers so that a refractive index
distribution in a portion of connection of the two optical fibers is different from a
refractive index distribution of another portion in an optical axis direction, and which
leaks a part of a light propagating a core of one optical fibers into a clad of the other
optical fiber; and a light receiving element which adheres to an outer circumferential
surface of the clad of the other optical fiber via a transparent adhesive layer so as to
detect a light leaked by the light leakage generation portion.
[0139] According to this configuration, the light leakage generation portion, for
leaking a part of the light propagating the core of one optical fiber into the clad of the
other optical fiber, is disposed. Therefore compared with a configuration where two
optical fibers are fused so that the connection loss is minimized, the absolute quantity
of leaked light can be increased.
[0140] The light receiving element chip adheres to the outer circumferential surface
of the clad of the other fiber via the transparent adhesive layer. Therefore the distance
between the light receiving element chip and the outer circumferential surface of the
clad of the other optical fiber can be decreased. As a result, the efficiency of the
leaked light reaching the light receiving element can be improved.
[0141] Further, compared with the configuration where air intervenes between the
light receiving element chip and the outer circumferential surface of the clad of the
other optical fiber, more leaked light enters from the clad to the transparent adhesive
layer, which has a higher refractive index than air, and the efficiency of the leaked
light reaching the light receiving element can be improved. As a result, more stable
hot line detection can be implemented.

[0142] (2) In the above hot line detection device, it is preferable that the light
leakage generation portion is formed by fusing the two optical fibers so as to create an
intermediate refractive index area of which refractive index is higher than the
refractive index of the clad of the other portion, and is lower than the refractive index
of the core of the other portion.
[0143] According to this configuration, the light leakage generation portion can be
formed without adding a separate element for light leakage generation.
[0144] (3) In the above hot line detection device, it is preferable that the light
leakage generation portion is formed by individually melting one end of the one
optical fiber and one end of the other optical fiber before fusing the two optical fibers
so that the refractive index distribution of each of the one ends becomes different
from the refractive index distribution of the other portion, and then fusing the one
ends together.
[0145] According to this configuration, the light leakage generation portion can be
formed with more certainty, and the range of the area, where the light leakage
generation portion is formed in the cross-section that intersects orthogonally with the
optical axis direction, can be wider, and more quantity of leaked light required for hot
line detection can be further increased.
[0146] (4) In the above hot line detection device, it is preferable that the light
leakage generation portion is formed by connecting the two optical fibers sandwiching
a light leakage generation optical fiber, which has a core diameter different from that
of the two optical fibers.
[0147] According to this configuration, the light leakage generation portion can be

formed by selecting an appropriate core diameter of the light leakage generation
optical fiber, which is inserted between the two optical fibers. Therefore the quantity
of the leaked light required for hot line detection can be secured with more certainty,
and the light leakage generation portion can be formed without changing the
conditions of fusion.
[0148] (5) In the above hot line detection device, it is preferable that the refractive
index of the core of the light leakage generation optical fiber is different from the
respective refractive index of the cores of the two optical fibers.
[0149] According to this configuration, the light leakage generation portion can be
constructed by selecting an appropriate light leakage generation optical fiber, of
which refractive index is different from the refractive index of the respective cores of
the two optical fibers.
[0150] (6) In the above hot line detection device, it is preferable that the light
leakage generation portion is formed by connecting the two optical fibers sandwiching
a light leakage generation optical fiber, of which core diameter is the same as that of
the two optical fibers and refractive index of the core is different from that of the two
optical fibers.
[0151] According to this configuration, the light leakage generation portion can be
formed by selecting an appropriate optical fiber, of which core diameter is the same as
that of the two optical fibers, and the refractive index of the core is different from that
of the two optical fibers. Therefore the quantity of the leaked light required for hot
line detection can be secured with more certainty, and the light leakage generation
portion can be formed without changing the conditions of fusion.
[0152] (7) In the hot line detection device, it is preferable that the light leakage

generation portion is formed by connecting the two optical fibers sandwiching a fiber
which is constituted by a same material as the clads of the two optical fibers, and of
which refractive index is uniform.
[0153] According to this configuration, the light leakage generation portion is
formed by sandwiching the fiber, which is constituted by a same material as the clads
of the two optical fibers and of which refractive index is uniform, between two optical
fibers. Therefore the quantity of the leaked light required for hot line detection can be
secured with more certainty, and the light leakage generation portion can be formed
without changing the conditions of fusion.
[0154] (8) In the above hot line detection device, it is preferable that the light
receiving element is a plurality of light receiving elements which can independently
detect a plurality of lights which are different in at least one of a band wavelength and
a transmission direction.
[0155] According to this configuration, a plurality of light receiving elements,
which can independently detect a plurality of lights which are different in at least one
of wavelength band and transmission direction, are disposed. Therefore hot line
detection can be performed independently for a plurality of lights which are different
in at least one of band wavelength and transmission direction.
[0156] (9) In the above hot line detection device, it is preferable that the plurality
of light receiving elements are disposed to have a same distance from the light
leakage generation portion.
[0157] According to this configuration, the efficiency of leaked light reaching each
light receiving element can be approximately the same.

[0158] (10) In the above hot line detection device, it is preferable that the plurality
of light receiving elements are disposed so that the light receiving element having a
lower detection sensitivity is disposed closer to the light leakage generation portion.
[0159] According to this configuration, the difference of detection sensitivity of
each light receiving element can be decreased, and the hot line detection can be
performed with more certainty for each of the plurality of lights which are different in
at least one of band wavelength and transmission direction.
[0160] (11) In the above hot line detection device, it is preferable that the optical
line is a two-way communication optical line, and the plurality of light receiving
elements are disposed on both sides of the light leakage generation portion in the
optical axis direction.
[0161] According to this configuration, light, of which transmission direction is the
opposite of the detection target light of each light receiving element, can be prevented
from reaching the light receiving element.
[0162] (12) In the above hot line detection device, it is preferable that an area of
the transparent adhesive layer, which contacts the clad of the other optical fiber, is
limited so that the leaked light from the light leakage generation portion does not leak
into an air via the transparent adhesive layer, in a space between the light receiving
element and the light leakage generation portion.
[0163] According to this configuration, the contact area of the transparent adhesive
layer and the clad of the other optical fiber is limited. Therefore the leaked light from
the light leakage generation portion can be prevented from leaking into the air via the
transparent adhesive layer in the space between the light receiving element and the

light leakage generation portion. As a result, the efficiency of the leaked light
reaching the light receiving element chip can be further improved, and more stable hot
line detection can be implemented.
[0164] (13) It is preferable that the above hot line detection device further
includes: a reflection portion, which is disposed on an outer circumferential surface of
the other optical fiber so as to limit the area, and which is constituted by a metal film
that reflects the leaked light generated in the light leakage generation portion, in the
space between the light receiving element and the light leakage generation portion.
[0165] According to this configuration, the size of the contact area of the
transparent adhesive layer and the clad of the other optical fiber is limited by the
reflection portion constituted by a metal film, so leakage of the light from the other
optical fiber into air via the adhesive layer can be prevented, and the efficiency of the
leaked light reaching the light receiving element can be further improved. Even if
adhesive spreads toward the light leakage generation portion side during manufacture,
the size of the contact area of the adhesive layer and the other optical fiber is limited
by the reflection portion, so a drop in efficiency of the leaked light reaching the light
receiving element can be prevented.
[0166] (14) It is preferable that the above hot line detection device further
includes: a reflection portion which is disposed on an outer circumferential surface of
the other optical fiber so as to limit the area, and is constituted by a porous glass film
which totally reflects the leaked light generated in the light leakage generation portion,
in the space between the light receiving element and the light leakage generation
portion.
[0167] According to this configuration, the size of the contact area of the

transparent adhesive layer and the clad of the other optical fiber is limited by the
reflection portion constituted by a porous glass film, so leakage of the light from the
other optical fiber into air via the adhesive layer can be prevented, and efficiency of
the leaked light reaching the light receiving element can be further improved. Even if
the adhesive spreads toward the light leakage generation portion side during
manufacture, the size of the contact area of the adhesive layer and the other optical
fiber is limited by the reflection portion, so a drop in efficiency of the leaked light
reaching the light receiving element can be prevented.
[0168] (15) In the above hot line detection device, it is preferable that the
reflection portion is formed so as to cover an outer circumference of the clad of the
other optical fiber, in a space between the transparent adhesive layer and the light
leakage generation portion.
[0169] According to this configuration, the generation of condensation on the
surface of the clad of the other optical fiber in the space between the transparent
adhesive layer and the light leakage generation portion can be prevented. Since direct
contact of the clad and water drops, due to condensation, can be prevented, the
leakage of the leaked light generated in the light leakage generation portion into air
via water drops can be prevented. As a result, a drop in efficiency of the leaked light
reaching the light receiving element can be prevented.

Claims
1. A hot line detection device for detecting whether an optical line, including
two optical fibers, is in a hot line state or not, comprising:
a light leakage generation portion which is formed by connecting the two
optical fibers so that a refractive index distribution in a portion of connection of the
two optical fibers is different from a refractive index distribution of another portion in
an optical axis direction, and which leaks a part of a light propagating a core of one
optical fiber into a clad of the other optical fiber; and
a light receiving element which adheres to an outer circumferential surface
of the clad of the other optical fiber via a transparent adhesive layer so as to detect a
light leaked by the light leakage generation portion.
2. The hot line detection device according to Claim 1, wherein
the light leakage generation portion is formed by fusing the two optical
fibers so as to create an intermediate refractive index area of which refractive index is
higher than the refractive index of the clad of the other portion, and is lower than the
refractive index of the core of the other portion.
3. The hot line detection device according to Claim 2, wherein
the light leakage generation portion is formed by individually melting one
end of the one optical fiber and one end of the other optical fiber before fusing the two
optical fibers so that the refractive index distribution of each of the one ends becomes

different from the refractive index distribution of the other portion, and then fusing
the one ends together.
4. The hot line detection device according to Claim 1, wherein
the light leakage generation portion is formed by connecting the two optical
fibers sandwiching a light leakage generation optical fiber, which has a core diameter
different from that of the two optical fibers.
5. The hot line detection device according to Claim 4, wherein
the refractive index of the core of the light leakage generation optical fiber
is different from the respective refractive index of the cores of the two optical fibers.
6. The hot line detection device according to Claim 1, wherein
the light leakage generation portion is formed by connecting the two optical
fibers sandwiching a light leakage generation optical fiber, of which core diameter is
the same as that of the two optical fibers and refractive index of the core is different
from that of the two optical fibers.
7. The hot line detection device according to Claim 1, wherein
the light leakage generation portion is formed by connecting the two optical
fibers sandwiching a fiber which is constituted by a same material as the clads of the

two optical fibers, and of which refractive index is uniform.
8. The hot line detection device according to any one of Claim 1 to Claim 7,
wherein
the light receiving element is a plurality of light receiving elements which
can independently detect a plurality of lights which are different in at least one of a
wavelength band and a transmission direction.
9. The hot line detection device according to Claim 8, wherein
the plurality of light receiving elements are disposed to have a same
distance from the light leakage generation portion.
10. The hot line detection device according to Claim 8, wherein
the plurality of light receiving elements are disposed so that the light
receiving element having a lower detection sensitivity is disposed closer to the light
leakage generation portion.
11. The hot line detection device according to Claim 9 or Claim 10, wherein
the optical line is a two-way communication optical line, and
the plurality of light receiving elements are disposed on both sides of the
light leakage generation portion in the optical axis direction.

12. The hot line detection device according to any one of Claim 1 to Claim 11,
wherein
an area of the transparent adhesive layer, which contacts the clad of the
other optical fiber, is limited so that the leaked light from the light leakage generation
portion does not leak into an air via the transparent adhesive layer, in a space between
the light receiving element and the light leakage generation portion.
13. The hot line detection device according to Claim 12, further comprising:
a reflection portion, which is disposed on an outer circumferential surface of
the other optical fiber so as to limit the area, and which is constituted by a metal film
that reflects the leaked light generated in the light leakage generation portion, in the
space between the light receiving element and the light leakage generation portion.
14. The hot line detection device according to Claim 12, further comprising:
a reflection portion which is disposed on an outer circumferential surface of
the other optical fiber so as to limit the area, and is constituted by a porous glass film
which totally reflects the leaked light generated in the light leakage generation portion,
in the space between the light receiving element and the light leakage generation
portion.
15. The hot line detection device according to Claim 13 or Claim 14, wherein

the reflection portion is formed so as to cover an outer circumference of the
clad of the other optical fiber, in a space between the transparent adhesive layer and
the light leakage generation portion.

A leaking generation portion (3) is formed at the connecting portion by connecting an optical fibers (1, 1). The
optical fibers (1, 1) are connected to differ a refractive index distribution at the connecting portion of the optical fibers from a refractive
index distribution at the other portions in the optical axis direction. A part of the light traveling in the core of one of the
fibers (1) (the optical fiber (1) on the right side in the shown example) is made to leak out to a clad (12) of the other fibers (1) (the
optical fiber (1) on the left side in the shown example). A light receiving element chip (5) is adhered to an outer circumferential
surface of the clad (12) of the other fibers (1) with a transparent adhesive to detect leaking light from the leaking light generation
portion (3).