DESCRIPTION
OPTICAL MULTIPLEXER AND FIBER LASER
TECHNICAL FIELD
[0001]
The present invention relates to an optical multiplexer
and a fiber laser, and especially relates to the optical
multiplexer and the fiber laser for providing a high-output
fiber laser with an excellent beam quality.
BACKGROUND ART
[0002]
Recently, a high-output of the fiber laser has been
developed and the fiber laser of which output is over 10 kW is
available commercially Such high-output fiber laser is
increasingly used industrially in various fields such as a
processor, a medical device and a measuring device, and
especially, in a field of material processing, since the fiber
laser may perform precision processing because this is more
excellent in a light collecting property than other lasers,
power density of which is high and this may obtain a small beam
spot, and since this performs non-contact processing and this
may also perform processing of a hard material, which may absorb
laser light, application thereof is rapidly enlarged.
[0003]
Such fiber laser over 10 kW is generally realized by
multiplexing output lights of a plurality of fiber lasers of

which outputs are few tens of W to few kW. A coherent beam system
or a wavelength beam system are used to multiplex the output
lights (for example, refer to the patent documents 1 to 3).
[0004]
The coherent beam system generates phase coupling to
multiplex by adjusting phases of a plurality of laser output
lights oscillated at the same wavelength (for example, refer
to the patent document 1) . According to this, high-output light
of the same wavelength is obtained.
[0005]
Herein, a method of generating the phase coupling without
performing phase control is suggested (for example, refer to
the patent document 2) . In this method, cores of two optical
fibers are moved closer to each other in a part of an oscillator,
light, which leaks from the core of one optical fiber, is
optically coupled with the core of the other optical fiber,
thereby performing injection locking. According to this, the
two fiber lasers automatically oscillate with the same phase
and it is possible to multiplex the laser output lights without
individually performing the phase control.
[0006]
On the other hand, in the wavelength beam system, a
plurality of laser outputs of different oscillation wavelengths
are allowed to enter a diffraction grating and the lights after
diffraction are spatially overlapped with each other by
utilizing difference in diffraction angles for each wavelength
(for example, refer to the patent document 3) . According to

this, the high-output light is obtained.
RELATED ART DOCUMENTS
PATENT DOCUMENTS
[0007]
Patent Document 1: US Patent Publication No. 20080085128
Patent Document 2: Japanese Patent Application Laid-Open
No. 10-118038
Patent Document 3: US Patent Publication No. 20070127123
DISCLOSURE OF INVENTION
PROBLEM TO BE SOLVED BY THE INVENTION
[0008]
In the coherent beam system, it is required to precisely
control such that the laser lights, which individually
oscillate, are in phase. The phase of the laser light easily
changes by disturbance, so that the control thereof is difficult,
and there has been a problem that a control system is extremely
complicated.
[0009]
Also, in a method of generating the phase coupling without
performing the phase control, a coupling unit is necessarily
present in the oscillator, so that it is difficult to make an
optical coupler, which may be used as the coupling unit, in a
case of the fiber laser of a clad pump type used in the
high-output fiber laser.
[0010]

In the wavelength beam system, the diffraction grating
is extremely expensive, and it is necessary to separate the
wavelengths of the fiber lasers to be multiplexed by
approλ1mately 1 ran in general. Therefore, when multiplexing
a great number of fiber lasers, a wavelength spectrum width of
the laser after the multiplexing becomes significantly large
and there has been a problem that an expensive optical component
should be used in order to remove chromatic aberration in actual
processing application, especially micro processing and the
like.
[0011]
Therefore, an object of the present invention is to
provide the optical multiplexer and the fiber laser for
obtaining the high-output light of the single wavelength.
MEANS FOR SOLVING THE PROBLEMS
[0012]
In order to solve the above-described problem, an optical
multiplexer according to the present invention is provided with
a wavelength multiplexing unit for wavelength-multiplexing
lights of a plurality of wavelengths input from input units
different for each wavelength to one multiplexed light; and a
multiplexed light converting unit for generating Raman light
with at least one wavelength out of the wavelengths included
in the multiplexed light from the wavelength multiplexing unit
and converting the multiplexed light from the wavelength
multiplexing unit to light of a single wavelength included in
a wavelength band of the Raman light.

[0013]
The wavelength multiplexing unit multiplexes the lights
of the different wavelengths, thereby generating high-output
multiplexed light including a plurality of wavelengths.
Herein, by wavelength-multiplexing, it is possible to multiplex
without a coupling loss. Futher, since the optical fiber in
which Raman scattering is generated is connected to a subsequent
stage of the wavelength multiplexing unit, the plurality of
wavelengths included in the multiplexed light may be converted
to the single wavelength. According to this, the high-output
light of the single wavelength may be generated. Also,
according to this configuration, the phase control is not
necessary and the light of the single wavelength may be
generated by a simple structure.
[0014]
In the optical multiplexer according to the present
invention, the single wavelength is preferably the same
wavelength as a longest wavelength out of the wavelengths
included in the multiplexed light from the wavelength
multiplexing unit.
The optical multiplexer directly outputs the light of the
longest wavelength input to the input unit. Therefore, it is
possible to output the high-output single wavelength light.
[0015]
In the optical multiplexer according to the present
invention, the single wavelength is preferably the wavelength
longer than a longest wavelength out of the wavelengths included

in the multiplexed light from the wavelength multiplexing unit.
There is a case in which the light output from the
multiplexed converting unit is reflected to enter a laser light
source connected to the input unit. Since the single wavelength
is outside a gain wavelength band of the laser light source,
damage of the laser light source may be prevented even when the
light of the single wavelength enters the laser light source.
[0016]
In the optical multiplexer according to the present
invention, it is preferable that the multiplexed light
converting unit transmits the wavelength not shorter than a
shortest wavelength and not longer than the single wavelength
out of the wavelengths included in the multiplexed light from
the wavelength multiplexing unit and blocks the wavelength
longer than the single wavelength.
In the multiplexed light converting unit, the multiplexed
light is converted to the light of a longer wavelength. At that
time, since the multiplexed light converting unit blocks the
wavelength longer than the single wavelength, the light of the
single wavelength may be efficiently generated.
[0017]
In the optical multiplexer according to the present
invention, it is preferable that the multiplexed light
converting unit is a fiber for continuously causing a loss in
a waveguide direction for N-th order Raman light out of N-th
order of the Raman light and inhibiting generation of N-th order
induced Raman scattering light.

A transmission wavelength band and a block wavelength
band of the fiber may be set by a structure thereof. According
to this, the light of the single wavelength may be efficiently
generated.
[0018]
In the optical multiplexer according to the present
invention, it is preferable that the fiber is a photonic bandgap
fiber (PBGF) in which an (N-1) -th order wavelength is set within
a bandgap wavelength band and a wavelength of the N-th order
Raman light is set outside the bandgap wavelength band.
By using the PBGF, the transmission wavelength band and
the block wavelength band of the fiber may be set.
[0019]
A fiber laser according to the present invention is
provided with the optical multiplexer according to the present
invention and a plurality of laser light sources of which output
wavelengths are different from each other, wherein the
plurality of laser light sources supply lights of the output
wavelengths to the different input units of the optical
multiplexer.
According to the fiber laser, the lights of a plurality
of wavelengths from the laser light sources are converted to
the light of the single wavelength, so that the high-output
light of the single wavelength may be generated. Since the
optical multiplexer wavelength-multiplexes, generation of the
coupling loss when multiplexing the output lights from a
plurality of laser light sources may be prevented from

generating.
[0020]
In the fiber laser according to the present invention,
it is preferable that at least one of the plurality of laser
light sources is provided with an output light converting unit
for generating Raman light by light allowed to enter and
converting to the light of the output wavelength to be supplied
to the optical multiplexer.
Even when the light generating units of a plurality of
laser light sources generate the lights of the same wavelength,
the lights of the different wavelengths maybe input to the input
units. According to this, the light generated by each laser
light source may be wavelength-multiplexed without a loss by
the wavelength multiplexing unit.
EFFECT OF THE INVENTION
[0021]
According to the present invention, the optical
multiplexer and the fiber laser for obtaining the high-output
light of the single wavelength may be provided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022]
FIG. 1 is a schematic configuration diagram of an optical
multiplexer according to a first embodiment.
FIG. 2 is an example of a spectrum of propagating light
in each part of a multiplexed light converting unit 15 in which
(a) illustrates an input light spectrum to the multiplexed light

converting unit and (b) illustrates an output light spectrum
from the multiplexed light converting unit.
FIG. 3 is an example of a PBGF in which (a) is a transverse
sectional view and (b) is a refractive index profile in a radial
direction on a straight line A.
FIG. 4 is a schematic configuration diagram of a fiber
laser according to a second embodiment.
FIG. 5 is a schematic configuration diagram of a fiber
laser according to a third embodiment.
FIG. 6 is a schematic configuration diagram of a fiber
laser according to a fourth embodiment.
FIG. 7 is a schematic configuration diagram of a fiber
laser according to a fifth embodiment.
FIG. 8 is a schematic configuration diagram of a fiber
laser according to a sixth embodiment.
BEST MODE(S) FOR CARRYING OUT THE INVENTION
[0023]
Embodiments of the present invention are described with
reference to the attached drawings. The embodiments described
hereinafter are examples of a configuration of the present
invention and the present invention is not limited to the
following embodiments.
[0024]
(First Embodiment)
FIG. 1 is a schematic configuration diagram of an optical
multiplexer according to this embodiment. An optical

multiplexer 10 according to this embodiment is provided with
input units 11 and 12, a wavelength multiplexing unit 14, a
multiplexed light converting unit 15 and an output unit 16.
Input ports of the wavelength multiplexing unit 14 are connected
to the input units 11 and 12 of the optical multiplexer 10,
respectively. An output port of the multiplexed light
converting unit 15 is connected to the output unit 16 of the
optical multiplexer 10.
[0025]
Lights of wavelengths λ1 and λ2 are input to the input units
11 and 12, respectively. The wavelengths λ1 and λ2 are different
from each other.
[0026]
The wavelength multiplexing unit 14
wavelength-multiplexes the lights of a plurality of wavelengths
λ1 and λ2 input from the input units 11 and 12 different for
each wavelength to one multiplexed light. By
wavelength-multiplexing, a plurality of input lights may be
multiplexed without a loss. A wavelength division multiplexer
(WDM) may be used as the wavelength multiplexing unit 14.
[0027]
The multiplexed light from the wavelength multiplexing
unit 14 is input to the multiplexed light converting unit 15.
The multiplexed light converting unit 15 converts the
multiplexed light of the wavelengths λ1 and λ2 from the
wavelength multiplexing unit 14 to light of a single wavelength
λm. For example, the multiplexed light converting unit 15 is

a fiber, which generates Raman light by the light of at least
one wavelength out of the wavelengths λ1 and λ2 included in the
multiplexed light from the wavelength multiplexing unit 14.
Then, the light of the single wavelength λm is output from the
output unit 16 of the optical multiplexer 10. For example, the
wavelengths λ1 and λ2 are set to 1040 nm, 1090 nm or 1140 nm.
[0028]
FIG. 2 is an example of a spectrum of propagating light
in each part of the multiplexed light converting unit 15 in which
(a) illustrates an input light spectrum to the multiplexed light
converting unit and (b) illustrates an output light spectrum
from the multiplexed light converting unit. Since each of the
light of the wavelength λ1 and the light of the wavelength λ2
is converted to the single wavelength λm optical intensity of
the single wavelength λm is a value closer to a sum of the optical
intensity of the wavelength λ1 and the optical intensity of the
wavelength λ2. In this manner, the optical multiplexer 10
illustrated in FIG. 1 may output the light of the single
wavelength λm with large optical intensity by including the
wavelength multiplexing unit 14 and the multiplexed light
converting unit 15. Although a case in which the number of the
input units is two is described in this embodiment, by
increasing the number of the input units to three, four, five,
etc., the optical intensity of the single wavelength λm from
the output unit 16 may be further increased.
[0029]
When the multiplexed light converting unit 15 performs

wavelength conversion using Raman scattering, the single
wavelength λm is included in a wavelength band of the Raman light
generated by the multiplexed light converting unit 15.
Therefore, the single wavelength λm is the same wavelength as
the longest wavelength λ2 out of the wavelengths λ1 and λ2
included in the multiplexed light from the wavelength
multiplexing unit 14 or the wavelength longer than the longest
wavelength λ2.
[0030]
Herein, it is preferable that the single wavelength λm
is the same wavelength as the longest wavelength λ2 out of the
wavelengths λ1 and λ2 included in the multiplexed light from
the wavelength multiplexing unit 14. In this case, in the
multiplexed light converting unit 15, the light of a short
wavelength (wavelength λ1) out of the input two lights of
different wavelengths is converted to the other light of the
wavelength λ2 to be output. Since the optical intensity of the
light of the wavelength λ2 is not decreased by the multiplexed
light converting unit 15, the optical intensity of the single
wavelength λm may be improved.
[0031]
Also, it is preferable that the single wavelength λm. is
the wavelength longer than the longest wavelength λ2 out of the
wavelengths λ1 and λ2 included in the multiplexed light from
the wavelength multiplexing unit 14. There is a case in which
the light output from the output unit 16 to outside is reflected
to enter laser light sources connected to the input units 11

and 12. For example, when the laser light source is a fiber
laser, by setting the single wavelength λm outside a gain
wavelength band of an amplifying fiber of the fiber laser, the
light of the single wavelength λm is not amplified even when
the light of the single wavelength λm enters the laser light
source. Therefore, the light with large power is not generated
in the laser light source, so that damage of the laser light
source may be prevented.
[0032]
In order to output the light of the single wavelength λm.
from the multiplexed light converting unit 15 illustrated in
FIG. 1, it is preferable that the multiplexed light converting
unit 15 transmits the wavelength not shorter than the shortest
wavelength λ1 and not longer than the single wavelength λm out
of the wavelengths λ1 and λ2 included in the multiplexed light
from the wavelength multiplexing unit 14 and blocks the
wavelength longer than the single wavelength λm. For example,
it is preferable that the multiplexed light converting unit 15
is the fiber, which continuously causes a loss in a waveguide
direction for N-th order Raman light out of the generated Raman
light, thereby inhibiting generation of N-th order induced
Raman scattering light. Especially, it is preferable that the
multiplexed light converting unit 15 is a PBGF, which causes
the loss distributed in the waveguide direction for high-order
Raman light, thereby inhibiting generation of high-order
induced Raman light. That is to say, it is preferable that a
bandgap wavelength band of the PBGF includes the shortest

wavelength λ1 and the single wavelength λm and does not include
a wavelength of a desired order, for example, a secondary Raman
light of the shortest wavelength λ1. According to this, the
continuous loss in the waveguide direction is generated for the
desired order (for example, secondary) Raman light and
generation of desired order (for example, secondary) Raman
scattering light may be inhibited. Further, by winding the PBGF
into a coil pattern, the bandgap wavelength band may be finely
adjusted.
[0033]
Herein, the order of the induced Raman light to be
inhibited is optional. For example, when the single wavelength
λm is set to the same wavelength as the wavelength λ2 and as
the wavelength of primary Raman scattering of the wavelength
λ1 the wavelength of the secondary Raman light of the wavelength
λ1 is inhibited. Also, when the single wavelength λm is set to
the same wavelength as the wavelength of secondary Raman
scattering of the wavelength λ1 and when the wavelength λ2 is
set to the same wavelength as the wavelength of the primary Raman
scattering of the wavelength X1 the wavelength of tertiary
Raman light of the wavelength λ1 is inhibited. In this manner,
the order of the induced Raman light to be inhibited is
preferably equal or larger than the number of the ports of the
input unit.
[0034]
FIG. 3 is an example of a structure of the PBGF in which
(a) is a transverse sectional view and (b) is a refractive index

profile in a radial direction on a straight line A. As
illustrated in FIG. 3(a) , a PBGF 500 has a low refractive index
area 501 formed of quartz without additive on center thereof,
and high refractive index areas 502 with Ge and the like added
are formed around the same. The high refractive index areas
502 are arranged in a periodic structure in a triangle grating
pattern. By forming refractive index distribution of the
low-refractive index area 501 and the high-refractive index
areas 502 as illustrated in FIG. 3(b), a bandgap for a specific
wavelength is formed. The bandgap may be formed in a desired
wavelength by adjusting a diameter and an interval of the
high-refractive index areas 502.
[0035]
When allowing the light of the wavelength band in which
the bandgap is formed to enter the PBGF 500, the light of the
wavelength band is guided in the PBGF 500 while being confined
in the low-reflective index area 501. On the other hand, when
allowing the light of the wavelength band outside the bandgap
to enter the PBGF 500, since the light of the wavelength band
cannot stay in the low-refractive index area 501, this spreads
to an entire PBGF 500 to be radiated. That is to say, in the
PBGF 500, the low-refractive index area 501 serves as a core
and the high-refractive index area 502 serves as a clad only
for the light of the wavelength band in which the bandgap is
formed.
[0036]
In this embodiment, the wavelength conversion is

performed by utilizing the Raman scattering generated in the
PBGF 500. In general, the light, which propagates in the
low-refractive index area 501, generates spontaneous Raman
scattering light on a longer wavelength side than the wavelength
of original light by the Raman scattering. Induced Raman
scattering in which the spontaneous Raman scattering light
induces further Raman scattering is generated from the light,
which propagates in the low-refractive index area 501, and the
Raman light is generated in large volume. In optical
communication and the like, it is suggested about a Raman
amplifier for allowing the light in the vicinity of 1450 nm to
enter the optical fiber and amplifying the light of 1550 nm being
a communication signal wavelength by an amplifying effect by
the induced Raman scattering of the light utilizing this
phenomenon.
[0037]
A signal used in the optical communication is of a few
hundred mW, and the light over several tens of W output by the
fiber laser is not supposed in the Raman amplifier. If the laser
of several tens of W is allowed to enter the optical fiber used
in the optical communication, the Raman light is generated by
the Raman scattering by only a few m, further, the secondary
Raman light is generated from the Raman light and the light of
a longer wavelength is generated one after another.
[0038]
The PBGF 500 may optionally set a transmission band and
a block band by the periodic structure and the like of the

high-refractive index areas 502. The transmission band is
intended to mean the band of the wavelength, which may be
propagated by being confined in the low-refractive index area
501. When the laser light of the wavelength in the transmission
band of the optical multiplexer according to this embodiment
is allowed to enter, if the wavelength band in which the
spontaneous Raman light is generated is within the bandgap
wavelength band of the PBGF 500, the wavelength conversion by
the induced Raman scattering occurs. The PBGF 500 has a
structure in which the wavelength of the secondary Raman light
of λ1 is out of the bandgap wavelength band. Therefore, although
primary induced Raman light of λ1 is generated, secondary or
higher-order induced Raman light of λ1 does not propagate. That
is to say, in the PBGF 500, since the high-order Raman light
of longer wavelength is not generated to be propagated one after
another unlike in the general optical fiber, a loss of power
of the converted wavelength light (wavelength λ1) may be
inhibited, thereby realizing high conversion efficiency.
[0039]
(Second Embodiment)
FIG. 4 is a schematic configuration diagram of a fiber
laser according to this embodiment. A fiber laser 100 according
to this embodiment is provided with the optical multiplexer 10
according to the first embodiment, a plurality of laser light
sources 101 and 102 of which output wavelengths are different
from each other and a laser output terminal 17.
[0040]

The plurality of laser light sources 101 and 102 supply
the lights of the different output wavelengths to the different
input units 11 and 12 of the optical multiplexer 10,
respectively. For example, the laser light source 101 supplies
the light of the wavelength λ1 to the input unit 11. The laser
light source 102 supplies the light of the wavelength λ2
different from the wavelength λ1 to the input unit 12. The
optical multiplexer 10 converts the lights df a plurality of
wavelengths λ1 and λ2 input to the input unitsj 11 and 12 to the
light of the single wavelength λm to output from the output unit
16. The laser output terminal 17 outputs the light of the single
wavelength λm The optical multiplexer 10 is as described in
the first embodiment.
[0041]
A specific example of the fiber laser 100 is described.
An Yb-doped optical fiber laser of which oscillation
wavelength λ1 is 1040 nm and of which output is 50 W is used
as the laser light source 101. The Yb-doped optical fiber laser
of which oscillation wavelength λ2 is 1090 nm and of which output
is 50 W is used as the laser light source 102. The wavelength
of the laser light source 102 is selected such that there is
the oscillation wavelength in the wavelength band in which the
Raman light is generated by propagation of the laser light of
the laser light source 101 through the fiber being the
multiplexed light converting unit 15. By such combination, it
becomes possible to make the induced Raman scattering of the
laser light of which wavelength is 1040 nm to easily occur in

the multiplexed light converting unit 15.
[0042]
As the multiplexed light converting unit 15, 50m of the
PBGF having the bandgap with the wavelength not shorter than
1030 nm and not longer than 1100 nm of which mode field diameter
is 10 µm is used. The laser light of which wavelength is 1040
nm generates the Raman light in the vicinity of 1090 nm by the
Raman scattering when propagating in the PBGF. At that time,
since the laser light of 1090 nm is simultaneously allowed to
enter the PBGF, the laser light of 1090 nm induces the induced
Raman scattering of the laser light of 1040 nm and the laser
light of which wavelength is 1040 nm is converted to the laser
light of which wavelength is 1090 nm at high efficiency. On
the other hand, although the band in which the Raman light of
the laser light of 1090 nm is generated is in the vicinity of
1140 nm, the vicinity of 1140 nm is outside the bandgap
wavelength band and the light of this wavelength cannot be
guided to the low-refractive index area (reference numeral 501
in FIG. 3), so that further conversion of the wavelength does
not occur. As a result, the laser light of which wavelength
is 1090 nm as the single wavelength λm is output from the laser
output terminal 17 as illustrated in FIG. 2. The output of the
output laser light is 8 4 W, and it is confirmed that the two
laser lights of different wavelengths are multiplexed at the
high efficiency to be output as the laser light of the single
wavelength.
[0043]

Also, when actually using the fiber laser 100 in
processing and the like, there is a case in which the laser light
reflected outside the laser output terminal 17 enters again the
fiber laser 100. The reflected light goes back in the optical
multiplexer 10 to reach the laser light sources 101 and 102.
At that time, when the wavelength of the laser output is within
the gain wavelength band of a gain medium used as the laser light
sources 101 and 102 connected to the input units 11 and 12 of
the optical multiplexer 10, there is a case in which the
reflected light is amplified by the gain medium to brake the
laser light sources 101 and 102. In order to prevent this, the
single wavelength λm output from the laser output terminal 17
is set outside the gain wavelength band of the gain medium used
as the laser light sources 101 and 102.
[0044]
In this embodiment, the Yb-doped optical fiber lasers are
connected to the input units 11 and 12 as the laser light sources
101 and 102 and the Yb-doped optical fiber has a large gain in
the wavelength band from the wavelength 1020 nm to the
wavelength approλ1mately 1100 nm. Therefore, by extending the
bandgap wavelength band of the PBGF used as the multiplexed
light converting unit 15 to approλ1mately 1150 nm, the
wavelength conversion to the wavelength 1140 nm inhibited in
the first embodiment occurs. In this manner, the output from
the laser output terminal 17 may be set outside the gain
wavelength band of the Yb-doped optical fiber and brake of the
laser light sources 101 and 102 may be prevented even when the

reflected light enters the laser light sources 101 and 102.
[0045]
(Third Embodiment)
FIG. 5 is a schematic configuration diagram of a fiber
laser according to this embodiment. A fiber laser 200 according
to this embodiment is provided with three laser light sources
101, 102 and 103, three input units 11, 12 and 13 and two
wavelength multiplexing units 14a and 14b.
[0046]
As compared to the above-described second embodiment, the
number of the wavelengths included in the multiplexed light
input to the multiplexed light converting unit 15 increases from
two to three, so that the optical intensity of the multiplexed
light input to the multiplexed light converting unit 15
increases. According to this, the optical intensity of the
single wavelength λm output from the output unit 16 may be
increased.
[0047]
A plurality of laser light sources 101, 102 and 103 are
connected to the input units 11, 12 and 13, respectively. The
wavelength multiplexing units 14a and 14b wavelength-multiplex
the lights of a plurality of wavelengths λ1, λ2 and λ3 input from
the input units 11, 12 and 13 different for each of the
wavelengths λ1 λ2 andλ3, respectively, to one multiplexed light.
Herein, the wavelengths λ1, λ2 and λ3 different from one another
are the wavelength 1040 nm, a wavelength of primary Raman light
1090 nm and the wavelength of the secondary Raman light 1140

nm, respectively, for example.
[0048]
The wavelength multiplexing units 14a and 14b are 2λ1 WDM
and the wavelength multiplexing units 14a and 14b are multistage
connected. In this case, the wavelength multiplexing unit 14a
wavelength-multiplexes the lights of the plurality of
wavelengths λ1 and λ2 input from the input units 11 and 12,
respectively, to one multiplexed light. The wavelength
multiplexing unit 14b wavelength-multiplexes the lights of the
wavelengths λ1 and λ2 input from the input units 11 and 12,
respectively, and the light of the wavelength λ3 input from the
input unit 13. The multiplexed light of the plurality of
wavelengths λ1, λ2 and λ3 is generated by the wavelength
multiplexing units 14a and 14b.
[0049]
Also, the wavelength multiplexing units 14a and 14b may
be made a common wavelength multiplexing unit. In this case,
the lights of the plurality of wavelengths λ1, λ2 and λ3 input
from the input units 11, 12 and 13 are wavelength-multiplexed
by one wavelength multiplexing unit. According to this, the
multiplexed light of the plurality of wavelengths λ1, λ2 and λ3
is generated. By wavelength-multiplexing the lights of a
plurality of wavelengths by one wavelength multiplexing unit,
the number of parts may be decreased.
[0050]
The multiplexed light converting unit 15 converts the
multiplexed light of a plurality of wavelengths from the

wavelength multiplexing unit 14 to the light of the single
wavelength λm. When the single wavelength λm is the same
wavelength as the longest wavelength λ3 out of the wavelengths
λ1 λ2 and λ3 included in the multiplexed light from the
wavelength multiplexing unit 14, the multiplexed light
converting unit 15 converts to the same wavelength 1140 nm as
the longest wavelength λ3. When the single wavelength λm is the
wavelength longer than the longest wavelength λ2, the
multiplexed light converting unit 15 converts to the wavelength
of the tertiary Raman light 1200 nm as the single wavelength
λm. Then, the output unit 16 and the laser output terminal 17
output the light of the single wavelength λm.
[0051]
(Fourth Embodiment)
FIG. 6 is a schematic configuration diagram of a fiber
laser according to this embodiment. A fiber laser 300 according
to this embodiment is provided with optical multiplexers 10a
and 10b and has a configuration in which the optical
multiplexers 10 described in the first embodiment are
multistage connected.
[0052]
A plurality of laser light sources 102 and 101 are
connected to the input units 11 and 12 of the optical multiplexer
10a and the lights of the wavelengths λ2 and λ1 are input,
respectively. Then, the light of the same wavelength as the
longest wavelength λ2 is output from the output unit 16 of the
optical multiplexer 10a as the single wavelength λm. For

example, when the wavelength λ1 is 1040 nm and the wavelength
λ2 is 1090 nm, the light of the same wavelength 1090 nm as the
longest wavelength λ2 is output from the output unit 16 of the
optical multiplexer 10b.
[0053]
The output unit 16 of the optical multiplexer 10a is
connected to the input unit 11 of the optical multiplexer 10b
and the light of the wavelength λ2 is input. On the other hand,
the laser light source 101 is connected to the input unit 12
of the optical multiplexer 10b and the light of the wavelength
λ1 is input. Then, the light of the same wavelength as the
longest wavelength λ2 is output from the output unit 16 of the
optical multiplexer 10a as the single wavelength λm. For
example, the light of the same wavelength 1090 nm as the longest
wavelength λ2 is output from the output unit 16 of the optical
multiplexer 10b.
[0054]
In this manner, by multistage connecting the optical
multiplexers 10a and 10b and connecting the laser light source
101 of the wavelength λ1 to the input unit 12 of the optical
multiplexers 10a and 10b, the optical intensity of the longest
wavelength λ2 may be increased according to the number of the
optical multiplexers 10a and 10b, which are multistage
connected.
[0055]
Although a case in which the two optical multiplexers are
multistage connected is described in this embodiment, by

increasing the number to three, four, five, etc., so as not to
be smaller than three, the optical intensity of the same
wavelength as the longest wavelength λ2 from the output unit
16 may be further increased.
[0056]
(Fifth Embodiment)
FIG. 7 is a schematic configuration diagram of a fiber
laser according to this embodiment. In a fiber laser 400
according to this embodiment, the laser light source 102
described in the second embodiment is provided with a light
generating unit 111 and an output light converting unit 112.
[0057]
The laser light sources of different wavelengths are
multiplexed in the second to fourth embodiments. Since the
wavelength multiplexing is used, the laser lights of the same
wavelength cannot be multiplexed. However, by allowing at
least one laser light source 102 out of a plurality of laser
light sources 101 and 102 to include the light generating unit
111 and the output light converting unit 112, the output light
wavelength of the laser light source 101 and the output light
wavelength of the light generating unit 111 may be made the same.
That is to say, even when the laser light source 101 and the
light generating unit 111 have the same configuration, the
single wavelength light with high intensity may be obtained by
the wavelength multiplexing.
[0058]
For example, the laser light source, which oscillates at

the wavelength λ1, is used as the laser light source 101 and
the light generating unit 111. The laser light of the
wavelength λ1 input from the input unit 11 is directly input
to the wavelength multiplexing unit 14.
[0059]
On the other hand, the laser light of the wavelength λ1
output from the light generating unit 111 is input to the output
light converting unit 112 and is converted to the light of the
wavelength λ2 by the Raman scattering to be output. The same
PBGF as that of the multiplexed light converting unit 15 may
be used as the output light converting unit 112 . Then, the laser
light source 102 inputs the light of the output wavelength λ2
to be supplied to the optical multiplexer 10 to the input unit
12.
[0060]
Meanwhile, although it is configured such that the laser
light source 102 is provided with the output light converting
unit 112 in this embodiment, the output light converting unit
112 may be provided between the input unit 12 and the wavelength
multiplexing unit 14. FIG. 8 is a schematic configuration
diagram of a fiber laser according to a sixth embodiment. In
a case of a fiber laser 600 illustrated in FIG. 8 also, the laser
lights of the wavelengths λ1 and λ2 different from each other
are input to the input ports of the wavelength multiplexing unit
14. Therefore, it is possible to multiplex without a loss by
the wavelength multiplexing unit 14. Then, the light
multiplexed by the wavelength multiplexing unit 14 is output

from the output unit 16 as the light of the wavelength λm after
a process similar to that of the first embodiment. An output
of the output laser light is 82 W, and it has been confirmed
that two fiber laser outputs of the same wavelength are
multiplexed to be output as the laser light of a single
wavelength component at efficiency substantially equivalent to
that of the second embodiment.
[0061]
With the configuration according to this embodiment, even
when the light of the same wavelength λ1 is input to the input
units 11 and 12, it is possible to convert the light of the
wavelength λ1 input from the input unit 12 to the wavelength
λ2 before inputting the same to the wavelength multiplexing unit
14. According to this, it is possible to wavelength-multiplex
by the wavelength multiplexing unit 14 without the loss.
[0062]
Although the PBGF is heretofore described as an example
of the configuration to generate the continuous loss in the
waveguide direction for the Raman light of a desired order of
the multiplexed light converting unit 15 in each described
embodiment, the multiplexed light converting unit 15 is not
limited to the PBGF as long as it is configured to transmit the
wavelength of the converted light and to generate the continuous
loss in the waveguide direction for the Raman light of the
desired order. In addition to" the PBGF, the fiber wound into
the coil pattern to generate a bending loss from the desired
wavelength may be used as the multiplexed light converting unit

15. Also, by using the fiber including dopant to absorb the
light of the wavelength band of which generation is desired to
be inhibited as the multiplexed light converting unit 15, an
effect to generate the continuous loss in the waveguide
direction for the Raman light of the desired order may be
obtained.
INDUSTRIAL APPLICABILITY
[0063]
Since the present invention may be utilized for a
processing fiber laser due to development of a high-output fiber
laser, this may be utilized for a broad range of industry such
as an electrical equipment industry and a general machinery
industry.
EXPLANATIONS OF REFERENCE NUMERALS
[0064]
10, 10a, 10b: optical multiplexer
11, 12, 13: input unit
14, 14a, 14b: wavelength multiplexing unit
15: multiplexed light converting unit
16: output unit
17: laser output terminal
100, 200, 300, 400, 600: fiber laser
101, 102, 103: laser light source
111: light generating unit
112: output light converting unit
500: PBGF
501: low-refractive index area

502: high-refractive index area

CLAIMS
1. An optical multiplexer, comprising:
a wavelength multiplexing unit for
wavelength-multiplexing lights of a plurality of wavelengths
input from input units different for each wavelength to one
multiplexed light; and
a multiplexed light converting unit for generating Raman
light with at least one wavelength out of the wavelengths
included in the multiplexed light from the wavelength
multiplexing unit and converting the multiplexed light from the
wavelength multiplexing unit to light of a single wavelength
included in a wavelength band of the Raman light.
2. The optical multiplexer according to claim 1, wherein
the single wavelength is the same wavelength as a longest
wavelength out of the wavelengths included in the multiplexed
light from the wavelength multiplexing unit.
3. The optical multiplexer according to claim 1, wherein
the single wavelength is the wavelength longer than a longest
wavelength out of the wavelengths included in the multiplexed
light from the wavelength multiplexing unit.
4. The optical multiplexer according to any one of claims
1 to 3, wherein the multiplexed light converting unit transmits
the wavelength not shorter than a shortest wavelength and not
longer than the single wavelength out of the wavelengths
included in the multiplexed light from the wavelength
multiplexing unit and blocks the wavelength longer than the
single wavelength.

5. The optical multiplexer according to claim 4, wherein
the multiplexed light converting unit is a fiber for
continuously causing a loss in a waveguide direction for N-th
order Raman light out of N-th order of the Raman light and
inhibiting generation of N-th order induced Raman scattering
light.
6. The optical multiplexer according to claim 5, wherein
the fiber is a photonic bandgap fiber (PBGF) in which an (N-l)-th
order wavelength is set within a bandgap wavelength band and
a wavelength of the N-th order Raman light is set outside the
bandgap wavelength band.
7. A fiber laser, comprising
the optical multiplexer according to any one of claims
1 to 6; and
a plurality of laser light sources of which output
wavelengths are different from each other, wherein the
plurality of laser light sources supply lights of the output
wavelengths to the different input units of the optical
multiplexer.
8. The fiber laser according to claim 7, wherein at least
one of the plurality of laser light sources is provided with
an output light converting unit for generating Raman light by
light allowed to enter and converting to the light of the output
wavelength to be supplied to the optical multiplexer.

An object of the present invention is to provide an optical
multiplexer and a fiber laser for obtaining high-output light
of a single wavelength. The optical multiplexer according to
the present invention is provided with input units 11 and 12,
a wavelength multiplexing unit 14, a multiplexed light
converting unit 15 and an output unit 16. Lights of a plurality
of wavelengths λ1 and λ2 are input to the input units 11 and
12, respectively. The wavelength multiplexing unit 14
wavelength-multiplexes the lights of the plurality of
wavelengths λ1 and λ2 input from the input units 11 and 12
different for each wavelength to one multiplexed light. By
wavelength-multiplexing, it is possible to multiplex without
a loss. The multiplexed light converting unit 15 generates
Raman light with at least one wavelength out of the wavelengths
λ1 and λ2 included in the multiplexed light from the wavelength
multiplexing unit 14 and converts the multiplexed light of the
wavelengths λ1 and λ2 from the wavelength multiplexing unit 14
to light of a single wavelength λm included in a wavelength band
of the Raman light.