FORM 2
The Patent Act 1970
(39 of 1970)
&
The Patent Rules, 2005

COMPLETE SPECIFICATION
(SEE SECTION 10 AND RULE 13)

TITLE OF THE INVENTION

“An optical fiber waveguide having reduced bend losses”

APPLICANTS:

Name: Sterlite Technologies Ltd.
Nationality: Indian
Address: Sterlite Technologies Ltd, E1/E2/E3, MIDC, Waluj, Aurangabad, 431136, India

The following specification particularly describes and ascertains the nature of this invention and the manner in which it is to be performed:-

This is a divisional application in furtherance to the first application number 312/MUM/2010 dated 06/02/2010.

FIELD OF INVENTION
Embodiments herein generally relate to an optical fiber waveguide, and more particularly but not exclusively, to an optical fiber waveguide which has reduced macro-bending loss and comply with G652 and G657B ITU-T standards.
BACKGROUND
Optical fiber waveguide plays an important role in the field of modern communications. A momentous increase in usage of optical fiber waveguide is being observed. It is expected that the use of optical fiber waveguide will continue to increase in order to deliver greater amount of information in the form of data, audio, and video signals to residential and commercial users.
A simple optical fiber waveguide has a core and a cladding surrounding the core. The refractive index of the core is higher as compared with the refractive index of the cladding in order to achieve light transmission inside the optical fiber waveguide, by a phenomenon known as total internal reflection.
An optical signal traveling through the optical fiber waveguide, apart from undergoing losses such as attenuation, dispersion and scattering, also suffers from other types of losses which are caused due to physical factors. One such loss is the macro-bending loss of the fiber, which is induced due to bending of the fiber due to improper handling or during installation.
Macro-bending loss of the fiber is particularly large when the fiber is laid with multiple bends or turns in its path. Additionally, due to harsh restrictions during installations at long distances, the optical fiber waveguide is always at the risk of being accidentally bent thereby inducing macro-bending losses, such macro-bending losses can be detrimental to good quality communication.
Since the optical fiber waveguides are fast replacing copper wires (even in short distance transmissions like in Local area networks, FTTX applications, etc.) situations of an optical fiber being laid with bends at corners, around the wall, corridors, etc. are becoming very common. An optical fiber waveguide which is not sufficiently immune to macro-bending losses may not perform satisfactorily under these conditions.
Ways and means have been devised to reduce the macro-bending loss of an optical fiber waveguide. A value called the MAC number, defined as the ratio of the mode field diameter (MFD) (measured in micrometer) of the optical fiber waveguide at 1310 nm to the effective cut-off wavelength, is of considerable significance in this regard. It is well known that the MAC number influences the macro-bending losses. Reducing the MAC number, either by reducing the MFD and/or by increasing the effective cut-off wavelength, can effectively reduce the macro-bending losses.
Optical fiber waveguides are generally divided into two classes, namely, single mode optical fiber (SMF) waveguide and multimode optical fiber (MMF) waveguide. In SMF waveguide, the core diameter is small (say, in the range of 8 µm to 10 µm) thereby allowing only a single mode to propagate, whereas in MMF waveguide the core diameter is large (say, in the range of 40 µm to 70 µm), thereby allowing multiple modes to propagate through the fiber. Generally, the overall diameter (sum of core and cladding) of both SMF and the MMF waveguides is about 125 µm. The SMF waveguide is widely used in transmission lines due to its high bandwidth and low attenuation.
The International Telecommunication Union (ITU) has laid down a standard known as ITU-T G652, wherein G652 is the standard that must be fulfilled by a Standard Single Mode Fiber (SMF). Details of specifications for various fiber parameters for a single mode optical fiber are listed in table 1 below.
TABLE 1
SR.NO. PARAMETERS VALUE
1 Mode field diameter (MFD) @ 1310 nm 8.6 to 9.5 µm
2 Cutoff wavelength [?CC] 1260 nm
3 Zero dispersion wavelength [?0] 1300 nm to 1324 nm
4 Chromatic dispersion slope = 0.093 ps/nm2-km

As mentioned above, in order to reduce the macro-bending losses in a SMF, if the MFD and MAC number are decreased, non-linear phenomenon such as four wave mixing would increase. Also, if the cut-off wavelength is increased then operating wavelength (that is the wavelength above which the optical fiber waveguide exhibits a single mode character) of the optical fiber waveguide gets shifted. These effects are undesirable.

Various types of optical fiber waveguides which are aimed at reducing macro-bending losses have been proposed. In order to have compatibility of standards among different manufacturers with respect to the macro-bending losses of optical fiber waveguide, the ITU-T has laid down G657B standard.
In accordance with the ITU-T G657B standard, at a wavelength of 1310 nm, the SMF waveguide should have a mode field diameter [MFD] in the range from about 6.3 to 9.5 µm; a fiber cutoff wavelength [?C] not more than 1260 nm; a zero dispersion wavelength [?0] in the range from 1300 nm to 1324 nm and a maximum chromatic dispersion slope of 0.093 ps/nm2-km. The macro-bending losses along with the optical parameters for said G657B fiber in accordance with ITU-T specifications are summarized in table 2 below.

TABLE 2
SR.NO. PARAMETER VALUE
1 Mode field diameter (MFD) @ 1310 nm 6.3 to 9.5 µm
2 Cutoff wavelength [?CC] = 1260 nm
3 Zero dispersion wavelength [?0] 1300 nm to 1324 nm
4 Chromatic dispersion slope = 0.093 ps/nm2-km
5 Macro-bending losses @ 1550 nm
15 mm radius mandrel & 10 turns 0.03 dB
10 mm radius mandrel & 1 turn 0.1 dB
7.5 mm radius mandrel & 1 turn 0.5 dB

To achieve the specifications of ITU-T G657B standard and reduce the macro-bending losses in the optical fiber waveguide, either the MFD of the optical fiber waveguide may be reduced and/or the cutoff wavelength of the optical fiber waveguide may be adjusted so that the MAC number gets reduced.. However, this method has a disadvantage, that is, if the MFD is reduced, the splicing of the optical fiber waveguide becomes difficult, whereas if cutoff wavelength is increased, the operating wavelength (that is the wavelength above which the optical waveguide fiber exhibits a single mode character) of the optical fiber waveguide gets shifted. This may render the optical fiber waveguide useless for any application.
Thus, there is a need for an optical fiber waveguide that would exhibit a reduced macro-bending loss even at bending radii of about 7.5 mm while adhering to the G652 standard. More particularly, there is a need for an optical fiber waveguide which would have a MFD and cut-off wavelength comparable to an optical fiber waveguide complying ITU-T G652 standard and at the same time should have reduced macro-bending losses even at bending radii of about 7.5 mm.
In other words, it is desirable to have an optical fiber waveguide which, apart from being compatible with the ITU-T G652 specifications (particularly the MFD and cutoff wavelength of the fiber must be as per ITU-T G652 specification), exhibits reduced bend sensitivity and macro-bend losses, meaning thereby, it is desired to have an optical fiber waveguide, which complies with both the ITU-T G652 and G657B standards.
OBJECTS OF THE INVENTION
An object of the invention is to provide an optical fiber waveguide having reduced macro-bending loss.
Another object is to provide an optical fiber waveguide with reduced macro-bending loss, which is compatible with both ITU-T G652 and G657B standards.
Yet another object is to provide an optical fiber waveguide with reduced macro-bending loss, wherein the optical waveguide fiber has desired values of the optical parameters, including the cutoff wavelength, zero dispersion wavelengths and the mode field diameter.
These and other objects and advantages of the present invention will be apparent from the following description when read in conjunction with the accompanying drawings which are incorporated for illustration of preferred embodiments of the present invention and are not intended to limit the scope thereof.
STATEMENT OF THE INVENTION
The present invention discloses an optical fiber waveguide which has reduced macro-bending losses and is compatible with both ITU-T G652 and G657B standards.
In accordance with embodiments of the present invention, the optical fiber waveguide has at least one layer of depressed refractive index (or a trench layer), provided around a core. Refractive index values and functions in the refractive index profile of the optical fiber waveguide are chosen so that a certain set of conditions are always complied with.
In accordance with one embodiment of the present invention, the optical fiber waveguide comprises of a core having refractive index n1 and radius a1. The optical fiber waveguide further has a first cladding layer surrounding the core, a second cladding layer surrounding the first cladding layer and a third cladding layer surrounding the second cladding layer. The first cladding layer has a refractive index n2 and a thickness a2. The second cladding layer has a refractive index n3 and a thickness a3. Further the third cladding layer has a refractive index n4 and a thickness a4. A particular set of values of n1, n2, n3, n4, a1, a2 and a3 for the optical fiber waveguide is selected from a group having a of plurality of sets of values for n1, n2, n3, n4, a1, a2 and a3. Within each set of values for n1, n2, n3, n4, a1, a2 and a3, n1 > n2 = n4 > n3, Further within the the group, the values of macro-bend loss and zero dispersion wavelength corresponding to various sets of values for n1, n2, n3, n4, a1, a2 and a3, vary inversely with a ratio R1, wherein R1 is ((n2 - n3) x (a1 + a2)) / ((n2 - n3) x (a3)), and within the group, the values of mode field diameter and fiber cutoff wavelength corresponding to various sets of values for n1, n2, n3, n4, a1, a2 and a3, vary proportionally with ratio R1 ((n2 - n3) x (a1 + a2)) / ((n2 - n3) x (a3)).
These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It is understood, however, that the following descriptions, while indicating preferred embodiments and numerous specific details thereof, are given by the way of illustration and not of limitation. Many changes and modifications may be made within the scope to the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications.

BRIEF DESCRIPTION OF THE DRAWINGS
The embodiments of the present invention is illustrated in the accompanying drawings, throughout which like reference letters indicate corresponding parts in the various figures. The embodiments herein will be better understood from the following description with reference to the drawings, in which:
FIG. 1 illustrates a cross-sectional view of a single trench layer optical fiber waveguide constructed in accordance with the embodiments as disclosed herein;
FIG. 2 illustrates the refractive index profile of an optical fiber waveguide constructed according to the first embodiment as disclosed herein;
FIG. 3 illustrates a cross-sectional view of a multiple trench layer optical fiber waveguide constructed in accordance with the embodiments as disclosed herein;
FIG. 4 illustrates the refractive index profile of an optical fiber waveguide constructed according to the second embodiment as disclosed herein;
FIG. 5 illustrates the refractive index profile of an optical fiber waveguide constructed according to the third embodiment as disclosed herein;
FIG. 6 illustrates the variation of zero dispersion wavelength with ratio R1 of the optical fiber waveguide in accordance with the first embodiment of the present invention;
FIG. 7 illustrates the variation of mode field diameter with ratio R1 of the optical fiber waveguide in accordance with the first embodiment of the present invention; and
FIG. 8 illustrates the variation of fiber cutoff wavelength with ratio R1 of the optical fiber waveguide in accordance with the first embodiment of the present invention.

Definitions as used herein:
Refractive index profile means a graph or a plot of variation of refractive indices of various regions of an optical fiber waveguide as a function of the radial distance from center of the optical fiber waveguide.

DETAILED DESCRIPTION OF THE PRESENT INVENTION
In accordance with the present invention, an optical fiber waveguide is disclosed wherein such optical fiber waveguide fabricated according to certain conditions, would not only have reduced macro-bending losses but would also be compatible with both ITU-T G652 and G657B standards.
In accordance with the embodiments of the present invention, the optical fiber waveguide has a core region, a cladding region surrounding the core region, at least one layer of depressed refractive index (or a trench layer) around the core embedded in the cladding region. Further among the multiple possible refractive index profiles of various regions of the waveguide, a refractive index profile is chosen such that the value of refractive index at any location of the core of the fiber is greater than the refractive index of any other location lying out of the core of the optical fiber waveguide, and the value of refractive index at any location in the trench layer(s) of the optical fiber waveguide is lesser than the value of refractive index at any location lying outside the trench layer(s) of the optical fiber waveguide. The macro-bend loss and the zero dispersion wavelength of the optical fiber waveguide vary inversely with ratio R1, and the mode field diameter and the optical fiber waveguide cutoff wavelength vary proportionally with ratio R1. In a graph of a refractive index profile of various regions of the optical fiber waveguide plotted against the radial distance from the center of the cross section of the waveguide, wherein ratio R1 is defined as the ratio of product of radius of the layer adjacent to the core and the difference of refractive index between the layer adjacent to the core and the first trench layer, ratio R1 may be represented as
((n2 - n3) x (a1 + a2)) / ((n2 - n3) x (a3))
wherein, n1, n2 and n3 are the refractive indices of the core region, the region adjacent to the core and that of the trench region respectively, and a1, a2 and a3 are the radius of the core region, thickness of the region adjacent to the core and thickness the first trench region respectively.
FIG. 1 illustrates a cross-sectional view of a single trench layer optical fiber waveguide constructed in accordance with the embodiments as disclosed herein. In accordance with the present invention the optical fiber waveguide has a core region 102 with a center depicted by point cc, said core region 102 is surrounded by three layers namely, a first layer 104, a second layer that is a trench layer 106 and a third layer 108. The refractive indices of all three layers 104, 106 and 108 is lesser than the refractive index of the core region 102, and the refractive index of the second layer that is the trench layer 106 is lower than the refractive index of the layers 104 and 108.
FIG. 2 illustrates the refractive index profile of an optical fiber waveguide constructed according to first embodiment as disclosed herein. In accordance with this embodiment the refractive index of each of the core region 102, the first layer 104, the second layer 106 and the third layer 108 in the optical fiber waveguide is substantially constant throughout its respective thickness. The refractive index and radius of the core 102 is n1 and r1 (r1= ab) respectively. The refractive index and radius of the first layer 104 is n2 and r2 - r1 (r2 - r1= cd) respectively. The refractive index and radius of the second layer 106 is n3 and r3 - r2 (r3 - r2= ef) respectively and refractive index and radius of the third layer 108 is n4 and r4 - r3 (r4 - r3= gh) respectively.
In accordance with the present invention, for this embodiment of the optical fiber waveguide to exhibit a reduced macro-bending loss, and be compatible with both ITU-T G652 and G657B standards, a set of values of the refractive indices and thickness of various regions of optical fiber waveguide are selected from a group having multiple such sets of values of the refractive indices and thickness of various regions of optical fiber waveguide, wherein

within each set of values, n1 > n2 = n4 > n3,

within the group, the values of macro-bend loss and zero dispersion wavelength corresponding to the sets vary inversely with ratio R1, and

within the group, the values of mode field diameter and fiber cutoff wavelength corresponding to the sets vary proportionally with ratio R1.

wherein ratio R1 is defined as:
Ratio R1 = (area of region pdeq)/(area of trench i.e. area of dgfe)
or more particularly,
Ratio R1 = [(n2 – n3) ´ (r2)] / [(n2 – n3) ´ (r3 - r2)]

Other possible embodiments which can be sourced form slight variation in the first embodiment of the invention as described above are also fully covered by the scope of the invention. One such variation in the first embodiment of the invention could be the change in the refractive index profile of the core. So far as the refractive index at any location of the core is kept higher than the refractive index of any location lying out of the core, the invention holds good for any type of refractive index profile of the core. As an example, in some embodiments, instead of keeping the refractive index of the core constant throughout, a variable refractive index profile can be provided, wherein the refractive index of the core varies as a mathematical function of ‘r’, say nc(r), ‘r’ being the radial distance of the optical fiber waveguide and nc(r) may represent a straight line or a curve of any shape.

The scope of the present invention also covers optical fiber waveguide types which have plurality of trench layers instead of a single trench layer. In particular, FIG. 3 illustrates a cross-sectional view of one such multiple trench layer optical fiber waveguide. As shown in the figure, the optical fiber waveguide comprises of three of trenches 206, 210 and 214 instead of a single trench layer or region.
In accordance with the present invention the optical fiber waveguide of FIG. 3 has a core region 202 having a center cc, which is surrounded by layers 204, 206, 208, 210, 212, 214 and 216 in said order, wherein 204, 208, 212, and 216 are cladding layers whereas 206, 210 and 214 are the trench layers.
FIG. 4 illustrates the refractive index profile of an optical fiber waveguide constructed according to the second embodiment of the present invention, wherein the refractive index profile of such an optical fiber waveguide has a core region 202, three trench regions 206, 210 and 214 separated by cladding regions or layers 204, 208, 212 and 216 respectively.
In accordance with this embodiment, the refractive index and radius of the core region 202 is n1 and r1 (r1= ab) respectively, the refractive index and thickness of region 204 are n2 and r2 -r1 (r2 -r1= cd) respectively, the refractive index and thickness of trench region 206 are n3 and r3 - r2 (r3 - r2= ef) respectively, the refractive index and thickness of region 208 are n4 and r4 - r3 (r4 - r3= gh) respectively, the refractive index and thickness of region 210 are n3 and r5 - r4 (r5 - r4= ij) respectively, the refractive index and thickness of region 212 are n4 and r6 - r5 (r6 - r5= kl) respectively, the refractive index and thickness of the region 214 are n3 and r7 - r6 (r7 - r6= m’n’) respectively, and that of region 216 are n4 and r8 - r7 (r8 - r7= p’q’) respectively.

In accordance with the present invention, for this embodiment of the optical fiber waveguide to exhibit a reduced macro-bending loss, and be compatible with both ITU-T G652 and G657B standards, a set of values of the refractive indices and thickness of various regions of optical fiber waveguide are selected from a group having multiple such sets of values of the refractive indices and thickness of various regions of optical fiber waveguide, wherein

within each set of values, n1 > n2 = n4 > n3,

within the group, the values of macro-bend loss and zero dispersion wavelength corresponding to the sets vary inversely with ratio R1, and

within the group, the values of mode field diameter and fiber cutoff wavelength corresponding to the sets vary proportionally with ratio R1.

wherein ratio R1 is defined as the ratio of [((n2 – n3) ´ r2), i.e. area of portion pdeq] and [(((n2 – n3) ´ (r3 - r2)) + ((n2 – n3) ´ (r5 – r4)) + ((n2 – n3) ´ (r7 – r6))), i.e the the sum of trench areas, i.e. area dgfe + area hkji + area lp’m’n’]
or more particularly,

FIG. 5 illustrates the refractive index profile of an optical fiber waveguide constructed according to the third embodiment of the present invention wherein the refractive index of core region 202 varies as a function of r, radially from the center cc of the optical fiber waveguide. In accordance with this embodiment the refractive index of the core region 202 is represented by nc(r) and the refractive indices of the trenches may not be same, that is, the trenches may have different refractive indices as indicated in FIG. 5 by regions 206, 210 and 214, wherein nt1, nt2 and nt3 are the refractive indices of the trench regions 206, 210 and 214 respectively.
In accordance with this embodiment the refractive index and radius of the core region 202 are nc(r) and r1 respectively, the refractive index and thickness of region 204 are n2 and (r2 - r1) respectively, the refractive index and thickness of the trench region 206 are nt1 and (r3 - r2) respectively, the refractive index and thickness of region 208 are n3 and (r4 - r3) respectively, the refractive index and thickness of the region 210 are nt2 and (r5 - r4) respectively, the refractive index and thickness of the region 212 are n3 and (r6 - r5) respectively, the refractive index and thickness of the region 214 are nt3 and (r7 - r6) respectively, whereas that of region 216 are n3 and r8 - r7 (r8 - r7=p’q’) respectively.
In accordance with this embodiment of the present invention, nc(r) may represent straight line or any other curve.
In accordance with the present invention, for this embodiment of the optical fiber waveguide to exhibit a reduced macro-bending loss, and be compatible with both ITU-T G652 and G657B standards, a set of profiles and values of the refractive indices and thickness of various regions of optical fiber waveguide are selected from a group having multiple such sets of profiles and values of the refractive indices and thickness of various regions of optical fiber waveguide, wherein

within each set of values, nc(r) > n2 = n3 > nt1,
nc(r) > n2 = n3 > nt2,
nc(r) > n2 = n3 > nt3,

within the group, the values of macro-bend loss and zero dispersion wavelength corresponding to the sets vary inversely with ratio R1, and

within the group, the values of mode field diameter and fiber cutoff wavelength corresponding to the sets vary proportionally with ratio R1.
wherein the ratio R1 is defined as,

Examples (present invention):
Few optical fiber waveguides were prepared in accordance with the first embodiment of the present invention, wherein the optical fiber waveguide comprised of a core having refractive index n1 and radius a1; a first cladding layer surrounding said core, said first cladding layer having a refractive index n2 and a thickness a2; a second cladding layer surrounding said first cladding layer, said second cladding layer having a refractive index n3 and a thickness a3; and a third cladding layer surrounding said second cladding layer, said a third cladding layer having refractive index n4 and a thickness a4, wherein a particular set of values of n1, n2, n3, n4, a1, a2 and a3 for the optical fiber waveguide were selected from a group comprising of plurality of sets of values for n1, n2, n3, n4, a1, a2 and a3, wherein within each set of values for n1, n2, n3, n4, a1, a2 and a3, n1 > n2 = n4 > n3 it was observed that the values of zero dispersion wavelength corresponding to various sets of values for n1, n2, n3, n4, a1, a2 and a3, vary inversely with ((n2 - n3) ´ (a1 + a2)) / ((n2 - n3) x (a3)), whereas within the group, the values of fiber cutoff wavelength and mode field diameter corresponding to various sets of values for n1, n2, n3, n4, a1, a2 and a3, vary proportionally with ((n2 - n3) ´ (a1 + a2)) / ((n2 - n3) ´ (a3)). The values of n1, n2, n3, n4, a1, a2 and a3 are listed in Table 3 below for various optical fiber waveguide samples.

These optical fiber waveguides were tested for various parameters including zero dispersion wavelength, cutoff wavelength, mode field diameter and macro-bending losses and are listed in table 4 below for said samples.

FIG. 9 illustrates a graph of zero dispersion wavelength versus ((n2 - n3) ´ (a1 + a2)) / ((n2 - n3) ´ (a3)) (or ratio R1). FIG. 10 is a graph of mode field diameter versus ((n2 - n3) ´ (a1 + a2)) / ((n2 - n3) ´ (a3)), whereas FIG. 11 is a graph of cutoff wavelength vs ((n2 - n3) ´ (a1 + a2)) / ((n2 - n3) ´ (a3)), which confirms the facts that zero dispersion wavelength varies inversely with ((n2 - n3) ´ (a1 + a2)) / ((n2 - n3) ´ (a3)), whereas mode field diameter and cutoff wavelength varies proportionally with ((n2 - n3) ´ (a1 + a2)) / ((n2 - n3) ´ (a3)).

TABLE 3

TABLE 3 (continued …)

TABLE 4

TABLE 4 (continued …)

It is to be noted that though the embodiments are explained with the help of the few exemplary refractive index profiles, additional ways for practicing the methods of the present invention will be evident to persons skilled in the art from the disclosure herein. Similar logic may be applied to any other optical fiber waveguides types and/or refractive index profiles. Such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments.
The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.

We Claim:

1. An optical fiber waveguide comprising:
a core having refractive index n1 and a radius a1;
a first cladding layer surrounding said core, said first cladding layer having a refractive index n2 and a thickness a2;
a second cladding layer surrounding said first cladding layer, said second cladding layer having a refractive index n3 and a thickness a3; and
a third cladding layer surrounding said second cladding layer, said a third cladding layer having refractive index n4;

wherein a particular set of values of n1, n2, n3, n4, a1, a2 and a3 for the optical fiber waveguide is selected from a group comprising of multiple such sets of values of n1, n2, n3, n4, a1, a2 and a3;

wherein, within said group, the values of macro-bend loss and zero dispersion wavelength corresponding to said sets vary inversely with a ratio R1, and

within said group, the values of mode field diameter and fiber cutoff wavelength corresponding to said sets vary proportionally with ratio R1,

wherein said ratio R1 is

R1 = ((n2 - n3) x (a1 + a2)) / ((n2 - n3) x (a3))

2. The optical fiber waveguide of claim 1 wherein within each of said set, n1 > n2 = n4 > n3.

3. The optical fiber waveguide of claim 1 wherein said ratio R1 varies in the range of 3.0 to 3.5.

4. The optical fiber waveguide of claim 1, wherein the values of n1, n2, n3, and n4, are constrained by the following inequalities:
1.440 = n1 = 1.470;
1.440 = n2 = 1.460;
1.440 = n3 = 1.455; and
1.440 = n4 = 1.460.

5. The optical fiber waveguide of claim 1, wherein the values of a1, a2 and a3 are constrained by the following inequalities:
6 µm = a1 = 10 µm;
2 µm = a2 = 15 µm; and
2 µm = a3 = 10 µm;

6. The optical fiber waveguide of claim 1, wherein said optical waveguide exhibits a bend loss of less than or equal to 0.03 dB with 10 turns on a mandrel of 15 mm radius.

7. The optical fiber waveguide of claim 1, wherein said optical waveguide exhibits a bend loss of less than or equal to 0.1 dB with 10 turns on a mandrel of 10 mm radius.

8. The optical fiber waveguide of claim 1, wherein said optical waveguide exhibits a bend loss of less than or equal to 0.5 dB with 10 turns on a mandrel of 7.5 mm radius.

9. An optical fiber waveguide comprising:
a core having refractive index nC and a radius a1; said core being surrounded by i layers, wherein i is an odd integer and is greater than 3,
wherein the refractive index of respective layers surrounding said core being ns1, ns2, ns3,… …..nsm…….nsi, wherein ns2, ns4, ns6… ns2m…….. ns(i-1) are trench layers,

ns1 > ns2 and ns2 < ns3, ns3 > ns4 and ns4 < ns5, ns5 > ns6 and ns6 < ns7,………. .……. ns s(i-2) > n s(i-1) and ns(i-1) < nsi,

each of ns1 , ns2 , ns3,………..nsm……...nsi being less than n1, and

the corresponding thickness of said layers being (rs1 max-a1), (rs2 max- rs1 max), (rs3 max- rs2 max),…… (rsm max-rs(m-1) max)…..…(rsi max-rs(i-1) max) respectively, wherein rsm max is the maximum radius of the mth layer;

wherein a particular set of values of nC, ns1 , ns2 , ns3,………..nsm……...nsi, a1, rs1 max, rs2 max, rs3 max, …… rsm max, …..…and rsi max for the optical fiber waveguide is selected from a group comprising of multiple sets of values of nC, ns1 , ns2 , ns3,………..nsm……...nsi, a1, rs1 max, rs2 max, rs3 max, …… rsm max, …..…and rsi max,

wherein, within said group, the values of macro-bend loss and zero dispersion wavelength corresponding to said sets vary inversely with ratio R1, and

within said group, the values of mode field diameter and fiber cutoff wavelength corresponding to said sets vary proportionally with ratio R1,

Wherein said ratio R1 is

10. The optical fiber waveguide of claim 9 wherein within each of said set, ns1 = ns3 = ns5 = … ns(2m+ 1)…….. = ns(i).

11. An optical fiber waveguide comprising:

a core having a radius rc and a refractive index profile nc(r), wherein nc(r) represents a mathematical function of r, r being the radial distance perpendicular to a longitudinal axis of the optical fiber waveguide;

a cladding layer surrounding said core, said cladding layer having a refractive index n2, wherein n2 is lower than the refractive index of any other location of the optical fiber waveguide outside said cladding layer;

said cladding layer further including a trench layer having a refractive index nt, wherein the thickness of said trench layer being (r3-r2), wherein r2 is the minimum radius of the trench layer and r3 is the maximum radius of the trench layer, and
nt is lower than the refractive index of any other location of the optical fiber waveguide lying outside said trench layer;

wherein a particular set of refractive index value of nt, r2, r3, and function type of nc(r) for the optical fiber waveguide is selected from a group comprising of multiple such sets of refractive index value of nt and function type of nc(r),

wherein, within said group, the values of macro-bend loss and zero dispersion wavelength corresponding to said sets vary inversely with a ratio R1, and

within said group, the values of mode field diameter and fiber cutoff wavelength corresponding to said sets vary proportionally with ratio R1,

Wherein said ratio R1 is

R1 = ((n2 – nt) x (r2)) / ((n2 - nt) x (r3 – r2))

12. An optical fiber waveguide comprising:

a core having a radius rc and a refractive index profile nc(r), wherein nc(r) represents a mathematical function of r, r being the radial distance perpendicular to a longitudinal axis of the optical fiber waveguide, said core being surrounded by i layers, wherein i is an odd integer and i>=3;

wherein the refractive index of respective layers surrounding said core being ns1, ns2, ns3,… …..nsm…….nsi,

wherein layers having refractive index profiles ns2, ns4, ns6……….. ns(i-1) are trench layers,
ns1 > ns2 and ns2 < ns3, ns3 > ns4 and ns4 < ns5, ns5 > ns6 and ns6 < ns7,………. .……. ns s(i-2) > n s(i-1) and ns(i-1) < nsi,
each of ns1 , ns2 , ns3,………..nsm……...nsi being less than n1, and
the corresponding thickness of said layers being (rs1 max-a1), (rs2 max- rs1 max), (rs3 max- rs2 max),…… (rsm max-rs(m-1) max)…..…(rsi max-rs(i-1) max) respectively, wherein rsm max is the maximum radius of the mth layer surrounding the core;

wherein a particular set of values of nC(r), ns1 , ns2 , ns3,………..nsm……...nsi, a1, rs1 max, rs2 max, rs3 max, …… rsm max, …..…and rsi max for the optical fiber waveguide is selected from a group comprising of multiple sets of values of nC(r), ns1 , ns2 , ns3,………..nsm……...nsi, a1, rs1 max, rs2 max, rs3 max, …… rsm max, …..…and rsi max,

wherein , within said group, the values of macro-bend loss and zero dispersion wavelength corresponding to said sets vary inversely with ratio R1, and

within said group, the values of mode field diameter and fiber cutoff wavelength corresponding to said sets vary proportionally with ratio R1,

Wherein said ratio R1 is

13. The optical fiber waveguide of claim 12 wherein within each of said set, ns1 = ns3 = ns5 = … ns(2m+ 1)…….. = ns(i).

14. An optical fiber waveguide comprising:

a core having refractive index n1 and a radius a1;

a first layer surrounding said core, said first layer having a refractive index n2; wherein n2 < n1;

said first layer further including i trench layers, wherein i is an integer and I is greater than or equal to 1,
wherein the refractive index of each of trench layers being nt, and
thickness of each trench layer being (r1 max-r1 min), (r2 max-r2 min), (r3 max-r3 min),…… (rm max-r m min)...…(ri max-ri min) respectively, wherein rm max is the maximum radius of the mth trench layer and rm min is the minimum radius of the mth trench layer respectively;

wherein a particular set of values of n1, n2, nt, a1, r1 min, r1 max, r2 min, r2 max, r3 min, r3 max, …… rm max, r m min, ……ri min, ri max for the optical fiber waveguide is selected from a group comprising of multiple sets of values of n1, n2, nt, a1, r1 min, r1 max, r2 min, r2 max, r3 min, r3 max …… rm max, r m min,….…ri min, ri max,

wherein within said group, the values of macro-bend loss and zero dispersion wavelength corresponding to said sets vary inversely with ratio R1, and

within said group, the values of mode field diameter and fiber cutoff wavelength corresponding to said sets vary proportionally with ratio R1.

Wherein said ratio R1 is

15. An optical fiber waveguide comprising:

a core having a radius rc and a refractive index profile nc(r), wherein nc(r) represents a mathematical function of r, r being the radial distance perpendicular to a longitudinal axis of the optical fiber waveguide;

a first layer surrounding said core, said first layer having a refractive index n2; wherein n2 is lower than the refractive index of any other location of the optical fiber waveguide outside said cladding layer;

said first layer further including i trench layers, i being an integer and i>=1,
wherein the refractive index of each of trench layers being nt,
thickness of each trench layer being (r1 max-r1 min), (r2 max-r2 min), (r3 max-r3 min),…… (rm max-r m min)...…(ri max-ri min) respectively, wherein rm max is the maximum radius of the mth trench layer and rm min is the minimum radius of the mth trench layer respectively;

wherein a particular set of values of nc(r), n2, nt, rc, r1 min, r1 max, r2 min, r2 max, r3 min, r3 max, …… rm max, r m min, ……ri min, ri max for the optical fiber waveguide is selected from a group comprising of multiple sets of values of n1, n2, nt, a1, r1 min, r1 max, r2 min, r2 max, r3 min, r3 max …… rm max, r m min,….…ri min, ri max,

wherein within said group, the values of macro-bend loss and zero dispersion wavelength corresponding to said sets vary inversely with ratio R1, and

within said group, the values of mode field diameter and fiber cutoff wavelength corresponding to said sets vary proportionally with ratio R1.

Wherein said ratio R1 is

Dated this 7th Feb 2011

Dr. Kalyan Chakravarthy
Patent Agent

ABSTRACT

An optical fiber waveguide has a core having refractive index n1 and radius a1, a first cladding layer surrounding the core, a second cladding layer surrounding the first layer and a third cladding layer surrounding the second layer. Refractive indices and thickness of first, second and third cladding layers are (n2, a2), (n3, a3) and (n4, a4) respectively. A particular set of values of n1 to n4, and a1to a3 for waveguide is selected from group having multiple sets of values for n1 to n4, and a1 to a3, with n1>n2=n4>n3. Within the group, the values of macro-bend loss and zero dispersion wavelength corresponding to various sets, vary inversely with ratio [((n2 - n3)x(a1 + a2))/((n2 - n3)x(a3))], and the values of macro-bend loss and zero dispersion wavelength corresponding to various sets, vary proportionally with the ratio. Fig 2