Few mode optical fiber

The present disclosure provides a few mode optical fiber (100). The few mode optical fiber (100) includes a core region (102). A core region (102) defined by a region around a central longitudinal axis (116) of the few mode optical fiber (100). In addition, the core region (102) has a first annular region (106) extended from central longitudinal axis (116) to radius r1, a second annular region (108) extended from radius r1 to radius r2, a third annular region (110) extended from radius r2 to radius r3, a fourth annular region (112) extended from radius r3 to radius r4 and a fifth annular region (114) extended from radius r4 to radius r5. Also, the few mode optical fiber (100) has a cladding defined by the sixth annular region (104) extended from radius r5 to radius r6.

TECHNICAL FIELD

The present disclosure relates to the field of optical fiber transmission. More particularly, the present disclosure relates to dispersion controlled few mode optical fiber with minimal spatial overlap between Lp01 and Lp11 guiding modes. The few mode optical fiber as described herein is suitable for space division multiplexing (SDM) applications.

BACKGROUND

Over the last few years, optical fibers are being widely used for communications. The present day coherent communication systems use the dense wavelength division multiplexing techniques to transfer the data. Several coherent modulation techniques such as OOK or QPSK with single mode fibers have been used to increase the data rate capacity of the communication system by taking almost all the freedoms available in modulation schemes. The telecommunication industry is continuously striving for the designs to meet the exponential increase in the data rate capacity demand. The ongoing research suggests that the few mode fiber which can allow the light to travel more than one mode with spatial division multiplexing schemes can be a potential solution to increase the data rate by allowing the signal to transmit in more than one mode. Typically, the performance of these optical fibers is determined based on dispersion, intermodal crosstalk occurring due to spatial overlap between guiding modes and bending losses over a broad range of wavelength. In general, the dispersion, spatial overlap and bending losses are optimized based on a refractive index profile. The refractive index profile defines the properties of a core section and a cladding section. Also, the refractive index profile illustrates a relationship between the refractive index of the optical fiber with a radius of the optical fiber. Further, this profile is determined based on a concentration of dopants and materials used during manufacturing. Furthermore, the dispersion, spatial overlap between modes and bending losses are controlled by varying the thickness of each region of the optical fiber.

Currently available profiles of few mode fibers are not optimized for dispersion and spatial overlap between the Lp01 mode and Lp11 mode to use in broad band SDM applications in S, C and L bands. This results in intermodal crosstalk between the guiding modes. In prior art U.S. Pat. No. 8,971,682 B2, a few mode optical fiber is disclosed which can be operated in two or more modes. The prior art provides a trench region after the central core and high index ring in the few mode optical fiber. However, the prior art does not optimize the dispersion properties and spatial mode overlap which in turn reduces the intermodal crosstalk. Low dispersion is necessary to use few mode optical fibers in space division multiplexing applications in the wavelength range from 1460 nm to 1625 nm.

In light of the above stated discussion, there is a dire need for a few mode optical fiber with dispersion control and minimized spatial overlap for low intermodal crosstalk between the modes while being suitable for SDM systems in long haul communications.

OBJECT OF THE DISCLOSURE

A primary object of the present disclosure is to provide a few mode optical fiber for increasing the data rate.

Another object of the present disclosure is to provide a few mode optical fiber for operating in Lp01 mode and Lp11 mode.

Yet another object of the present disclosure is to provide a few mode optical fiber with controlled dispersion in the wavelength range of 1460 nm to 1625 nm in both Lp01 mode and Lp11 mode.

Yet another object of the present disclosure is to provide an a few mode optical fiber which exhibit negligible spatial overlap between Lp01 mode and Lp11 mode.

Yet another object of the present disclosure is to provide a few mode optical fiber that is suitable for SDM applications.

SUMMARY

In an aspect of the present disclosure, the present disclosure provides a few mode optical fiber. The optical fiber includes a core region. A core region defined by a region around a central longitudinal axis of the few mode optical fiber. In addition, the core region has a first annular region. The first annular region is between the central longitudinal axis and a first radius r1from the central longitudinal axis of the few mode optical fiber. Moreover, the core region has a second annular region. The second annular region is between the first radius r1and a second radius r2from the central longitudinal axis of the few mode optical fiber. Further, the core has a third annular region. The third annular region is between the second radius r2to a third radius r3from the central longitudinal axis of the few mode optical fiber. Furthermore, the core has a fourth annular region. The fourth annular region is between the third radius r3and a fourth radius r4from the central longitudinal axis of the few mode optical fiber. Furthermore, the core has a fifth annular region. The fifth annular region is between the fourth radius r4and a fifth radius r5from the central longitudinal axis of the few mode optical fiber. The first annular region, the second annular region, the third annular region, the fourth annular region and the fifth annular region are concentrically arranged. In addition, the few mode optical fiber includes a cladding. The cladding is a sixth annular region. The optical fiber has a sixth annular region. The sixth annular region is between a fifth radius r5and a sixth radius r6from the central longitudinal axis of the few mode optical fiber. The sixth annular region is the cladding region. The sixth annular region has a sixth refractive index Δ6. The sixth annular region concentrically surrounds the fifth annular region. In addition, the first annular region has a first refractive index Δ1. Moreover, the second annular region has a second refractive index Δ2. Further, the third annular region has a third refractive index Δ3. Furthermore, the fourth annular region has a fourth refractive index Δ4. Furthermore, the fifth annular region has a fifth refractive index Δ5. The first radius r1is in the range of 3.8 microns to 4.2 microns. The first refractive index Δ1is in the range of 0.42 to 0.70. The second radius r2is in the range of 4.8 microns to 5.2 microns. The second refractive index Δ2is zero. The third radius r3is in the range of 8.2 microns to 8.7 microns. The third refractive index Δ3is in the range of 0.4 to 0.58. The fourth radius r4is in the range of 8.3 microns to 9.9 microns. The fourth refractive index Δ4is zero. The fifth radius r5is in the range of 10.9 microns to 12.6 microns. The fifth refractive index Δ5is in the range of 0.41 to 0.62. The sixth radius r6is 62.5 microns. The sixth refractive index Δ6is zero. The optical fiber is characterized by dispersion. The dispersion is in the range of 4 Ps/nm/km to 16 Ps/nm/km for Lp01 mode at a wavelength of 1460 nm. The dispersion is in the range of −0.3 ps/nm/km to 6 Ps/nm/km for Lp11 mode at a wavelength of 1460 nm. The dispersion is in the range of 4.1 Ps/nm/km to 21 Ps/nm/km for Lp01 mode at a wavelength of 1530 nm. The dispersion is in the range of 4.5 Ps/nm/km to 11 Ps/nm/km for Lp11 mode at a wavelength of 1530 nm. The dispersion is in the range of 4 Ps/nm/km to 22 Ps/nm/km for Lp01 mode at a wavelength of 1550 nm. The dispersion is in the range of 5.8 Ps/nm/km to 12 Ps/nm/km for Lp11 mode at a wavelength of 1550 nm. The dispersion is in the range of 4.5 Ps/nm/km to 23 Ps/nm/km for Lp01 mode at a wavelength of 1565 nm. The dispersion is in the range of 6.8 Ps/nm/km to 13 Ps/nm/km for Lp11 mode at a wavelength of 1565 nm. The dispersion is in the range of 3.9 Ps/nm/km to 26 Ps/nm/km for Lp01 mode at a wavelength of 1625 nm. The dispersion is in the range of 10. Ps/nm/km to 17 Ps/nm/km for Lp11 mode at a wavelength of 1625 nm. The optical fiber is characterized by a macrobending loss. The macrobending loss is less than 2.1 dB/turn for 16 mm bending radius at a wavelength of 1625 nm for Lp11 mode. The spatial overlap between the Lp01 mode and Lp11 mode is less than 10−5.

In an embodiment of the present disclosure, the first annular region is the central core region having an alpha profile wherein a peak shaping parameter alpha (a) is in the range of 2.7 to 10.

In an embodiment of the present disclosure, the second annular region of the few mode optical fiber is a buffer region.

In an embodiment of the present disclosure, the third annular region of the few mode optical fiber is a trench region.

In an embodiment of the present disclosure, the fourth annular region of the few mode optical fiber is a buffer region.

In an embodiment of the present disclosure, the thickness and refractive index of second annular region, third annular region and fourth annular region is optimized to minimize the spatial overlap between the Lp01 mode and Lp11 mode.

In an embodiment of the present disclosure, the fifth annular region of the few mode optical fiber is a high index ring region.

In an embodiment of the present disclosure, the few mode optical fiber is operated in the wavelength of 1460 nm to 1625 nm in Lp01 mode and Lp11 mode wherein the few mode optical fiber can be operated in six modes, wherein six modes includes two degenerate Lp01 mode and four degenerate Lp11 mode.

In an embodiment of the present disclosure, the few mode optical has a mode field diameter in the range of 7.4 μm to 8.4 μm for Lp01 mode at a wavelength of 1550 nm.

In an embodiment of the present disclosure, the few mode optical fiber has a effective area in the range of 40 μm2to 60 μm2for Lp01 mode at a wavelength of 1550 nm.

In an embodiment of the present disclosure, the few mode optical fiber has a effective area in the range of 360 μm2to 570 μm2for Lp11 mode at a wavelength of 1550 nm.

In an embodiment of the present disclosure, the theoretical cutoff wavelength for Lp11 mode is in the range of 2280 nm to 2810 nm.

In an embodiment of the present disclosure, the theoretical cutoff wavelength for Lp02 mode is less than 2500 nm.

In an embodiment of the present disclosure, the differential group delay between Lp01 mode and Lp11 mode is less than 0.2 ps/km at a wavelength of 1550 nm.

STATEMENT OF THE DISCLOSURE

In an aspect of the present disclosure, the present disclosure provides a few mode optical fiber. The optical fiber includes a core region. A core region defined by a region around a central longitudinal axis of the few mode optical fiber. In addition, the core region has a first annular region. The first annular region is between the central longitudinal axis and a first radius r1from the central longitudinal axis of the few mode optical fiber. Moreover, the core region has a second annular region. The second annular region is between the first radius r1and a second radius r2from the central longitudinal axis of the few mode optical fiber. Further, the core has a third annular region. The third annular region is between the second radius r2to a third radius r3from the central longitudinal axis of the few mode optical fiber. Furthermore, the core has a fourth annular region. The fourth annular region is between the third radius r3and a fourth radius r4from the central longitudinal axis of the few mode optical fiber. Furthermore, the core has a fifth annular region. The fifth annular region is between the fourth radius r4and a fifth radius r5from the central longitudinal axis of the few mode optical fiber. The first annular region, the second annular region, the third annular region, the fourth annular region and the fifth annular region are concentrically arranged. In addition, the few mode optical fiber includes a cladding. The cladding is a sixth annular region. The optical fiber has a sixth annular region. The sixth annular region is between a fifth radius r5and a sixth radius r6from the central longitudinal axis of the few mode optical fiber. The sixth annular region is the cladding region. The sixth annular region has a sixth refractive index Δ6. The sixth annular region concentrically surrounds the fifth annular region. In addition, the first annular region has a first refractive index Δ1. Moreover, the second annular region has a second refractive index Δ2. Further, the third annular region has a third refractive index Δ3. Furthermore, the fourth annular region has a fourth refractive index Δ4. Furthermore, the fifth annular region has a fifth refractive index Δ5. The first radius r1is in the range of 3.8 microns to 4.2 microns. The first refractive index Δ1is in the range of 0.42 to 0.70. The second radius r2is in the range of 4.8 microns to 5.2 microns. The second refractive index Δ2is zero. The third radius r3is in the range of 8.2 microns to 8.7 microns. The third refractive index Δ3is in the range of 0.4 to 0.58. The fourth radius r4is in the range of 8.3 microns to 9.9 microns. The fourth refractive index Δ4is zero. The fifth radius r5is in the range of 10.9 microns to 12.6 microns. The fifth refractive index Δ5is in the range of 0.41 to 0.62. The sixth radius r6is 62.5 microns. The sixth refractive index Δ6is zero. The optical fiber is characterized by dispersion. The dispersion is in the range of 4 Ps/nm/km to 16 Ps/nm/km for Lp01 mode at a wavelength of 1460 nm. The dispersion is in the range of −0.3 ps/nm/km to 6 Ps/nm/km for Lp11 mode at a wavelength of 1460 nm. The dispersion is in the range of 4.1 Ps/nm/km to 21 Ps/nm/km for Lp01 mode at a wavelength of 1530 nm. The dispersion is in the range of 4.5 Ps/nm/km to 11 Ps/nm/km for Lp11 mode at a wavelength of 1530 nm. The dispersion is in the range of 4 Ps/nm/km to 22 Ps/nm/km for Lp01 mode at a wavelength of 1550 nm. The dispersion is in the range of 5.8 Ps/nm/km to 12 Ps/nm/km for Lp11 mode at a wavelength of 1550 nm. The dispersion is in the range of 4.5 Ps/nm/km to 23 Ps/nm/km for Lp01 mode at a wavelength of 1565 nm. The dispersion is in the range of 6.8 Ps/nm/km to 13 Ps/nm/km for Lp11 mode at a wavelength of 1565 nm. The dispersion is in the range of 3.9 Ps/nm/km to 26 Ps/nm/km for Lp01 mode at a wavelength of 1625 nm. The dispersion is in the range of 10. Ps/nm/km to 17 Ps/nm/km for Lp11 mode at a wavelength of 1625 nm. The optical fiber is characterized by a macrobending loss. The macrobending loss is less than 2.1 dB/turn for 16 mm bending radius at a wavelength of 1625 nm for Lp11 mode. The spatial overlap between the Lp01 mode and Lp11 mode is less than 10−5.

It should be noted that the accompanying figures are intended to present illustrations of exemplary embodiments of the present disclosure. These figures are not intended to limit the scope of the present disclosure. It should also be noted that accompanying figures are not necessarily drawn to scale.

DETAILED DESCRIPTION

In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present technology. It will be apparent, however, to one skilled in the art that the present technology can be practiced without these specific details. In other instances, structures and devices are shown in block diagram form only in order to avoid obscuring the present technology.

Moreover, although the following description contains many specifications for the purposes of illustration, anyone skilled in the art will appreciate that many variations and/or alterations to said details are within the scope of the present technology. Similarly, although many of the features of the present technology are described in terms of each other, or in conjunction with each other, one skilled in the art will appreciate that many of these features can be provided independently of other features. Accordingly, this description of the present technology is set forth without any loss of generality to, and without imposing limitations upon, the present technology.

FIG. 1Aillustrates a cross-sectional view of a few mode optical fiber100, in accordance with various embodiments of the present disclosure. The few mode optical fiber100is a fiber used for transmitting information as light pulses from one end to another. In addition, the few mode optical fiber100is a thin strand of glass or plastic capable of transmitting optical signals. The few mode optical fiber100is configured to transmit large amount of information over long distances with relatively low attenuation. Moreover, the few mode optical fiber100can be utilized for Space Division Multiplexing Applications. Further, the few mode optical fiber100is operated in different modes including Lp01 mode and Lp11 mode. In another embodiment of the present disclosure, the few mode optical fiber100can be operated in six modes including two degenerate Lp01 modes and four degenerate Lp11 modes. In yet another embodiment of the present disclosure the few mode optical fiber is operated in broad range of wavelength between 1460 nm to 1625 nm for both Lp01 mode and Lp11 mode.

In yet another embodiment of the present disclosure, the few mode optical fiber is operated in broad range of wavelength in S, C and L bands. A few mode optical fiber is that in which fibers support only few guided modes. A two-mode optical fiber (with LP01 and LP11) exhibits 6 different modes considering the degeneracy's.

In an embodiment of the present disclosure, the few mode optical fiber100may be utilized for other applications. Going further, the few mode optical fiber100is dispersion optimized few mode optical fiber. The few mode optical fiber100allows the light to travel in more than one mode. The few mode dispersion optimized optical fiber is used for Space division multiplexing applications. In addition, the few mode optical fiber100has increased data rate by allowing the light to travel in more than one mode.

In an embodiment of the present disclosure, the type of the dispersion which occurs inside the few mode optical fiber is chromatic dispersion. The chromatic dispersion is the spreading of the optical signals which results from different speeds of light rays travelling inside the optical fiber100. Moreover, the chromatic dispersion occurs due to material dispersion and waveguide dispersion.

The material dispersion occurs due to a change in a refractive index of the optical fiber100with an optical frequency. Moreover, the waveguide dispersion occurs due to dependency of mode propagation on wavelength. In an embodiment of the present disclosure, the few mode optical fiber100has a pre-determined value of dispersion (provided below in the detailed description).

In an embodiment of the present disclosure, the dispersion optimized few mode optical fiber100enables controlled dispersion over a range of wavelength. In another embodiment of the present disclosure, the few mode optical fiber100exhibits low dispersion in Lp01 mode and Lp11 mode for wavelength range of 1460 nm-1625 nm. In addition, the dispersion optimized few mode fiber100enables minimization of spatial overlap between the Lp01 mode and Lp11 mode. In yet another embodiment of the present disclosure, the few mode optical fiber enables near zero spatial overlap between Lp01 mode and Lp11 mode throughout the range of wavelength. Further, the dispersion optimized few mode optical fiber100enables the dispersion optimization throughout the range of wavelength. The range of wavelength corresponds to a range in which the few mode optical fiber100is configured to operate. The range of wavelength for the present disclosure is 1460 nm-1625 nm. In yet another embodiment of the present disclosure, the few mode optical fiber100is used for space division multiplexing to increase the data capacity. In space division multiplexing the optical signals is transmitted in different guiding modes of the optical fiber100. Accordingly, the optical signals are separated at another end.

In an embodiment of the present disclosure, the dispersion optimized few mode optical fiber100is used for communication purpose. In another embodiment of the present disclosure, the dispersion optimized few mode optical fiber100is operated in S, C and L bands.

In an embodiment of the present disclosure, the mode field diameter defines a section or area of the few mode optical fiber100in which the optical signals travel. The theoretical cut-off wavelength is defined as the wavelength above which the given mode cannot propagate. In an embodiment of the present disclosure, each of the plurality of attributes has a specific value or a range of value. In an embodiment of the present disclosure, the few mode optical fiber100has a mode field diameter in the range of 7.4 μm to 8.4 μm for Lp01 mode at a wavelength of 1550 nm. The mode field diameter (MFD) is an expression of distribution of the optical power. It is measured using

Peterman⁢⁢II⁢⁢method⁢⁢where⁢⁢MFD=2[∫E2⁡(r)⁢dr∫[dE⁡(r)/dr]2⁢rdr]1/2
The integral limits being 0 to infinity. In another embodiment of the present disclosure, mode field diameter plays an important role in estimating macro bending losses.

In an embodiment of the present disclosure, the few mode optical fiber100exhibits bending losses. The bend losses correspond to the losses that the optical fiber exhibits when they are bent. The bending loss includes losses and micro bending losses. In an embodiment of the present disclosure, the few mode optical fiber100exhibits macrobending loss less than 2.1 dB/turn for 16 mm bending radius at a wavelength of 1625 nm for Lp11 mode.

In an embodiment of the present disclosure, the few mode optical fiber cable100has an effective area. Effective area determines how much energy the core can carry without causing non-linear type signal losses. The effective area of the fundamental mode is a measure of the area over which the energy in the electric field is distributed. In an embodiment of the present disclosure, the few mode optical fiber100has an effective area in the range of 40 μm2to 60 μm2for Lp01 mode at a wavelength of 1550 nm. In another embodiment of the present disclosure, the few mode optical fiber100has an effective area in the range of 360 μm2to 570 μm2for Lp11 mode at a wavelength of 1550 nm. The effective area is measured by using the expression:

In an embodiment of the present disclosure the few mode optical fiber100has a differential group delay between Lp01 mode and Lp11 mode. The differential group delay is the difference in propagation time between the two eigen modes. In an embodiment of the present disclosure, the differential group delay between Lp01 mode and Lp11 mode is less than 0.2 ps/km at a wavelength of 1550 nm.

In an embodiment of the present disclosure, there is spatial overlap between the Lp01 mode and Lp11 mode. The spatial overlap is defined as: Spatial Overlap—∫ I01I11drwherein, integral limits=−∞ to +∞‘r’: radial position from center;‘I01’: Normalised intensity profiles of Lp01 mode;‘I11’: Normalised intensity profile of Lp11 mode.

In an embodiment of the present disclosure, the spatial overlap between the Lp01 mode and Lp11 mode is less than 10−5.

In an embodiment of the present disclosure, the few mode optical fiber100has a theoretical cut-off wavelength. The theoretical cut-off wavelength refers to the wavelength above which the given mode cannot propagate. In an embodiment of the present disclosure, the theoretical cut-off wavelength for Lp11 mode is in the range of 2280 nm to 2810 nm. In another embodiment of the present disclosure, the theoretical cut-off wavelength for Lp02 mode less than 2500 nm.

Going further, the few mode optical fiber100includes a core region102and a cladding region. The core region102is an inner part of the few mode optical fiber100and the cladding section is an outer part of the few mode optical fiber100. Moreover, the core region102is defined by a region around a central longitudinal axis of the few mode optical fiber100(As shown in the perspective view of the few mode optical fiber inFIG. 1B). Moreover, the core region102is defined by a region around a central longitudinal axis of the few mode optical fiber100.

The refractive index profile determines a relationship between the refractive index of the few mode optical fiber100with a radius of the few mode optical fiber100. Also, the refractive index profile is maintained as per a desired level based on a concentration of chemicals used for the production of the few mode optical fiber100. In an embodiment of the present disclosure, the production of the few mode optical fiber100is carried out after construction of an optical fiber preform.

Moreover, the refractive index profile of the few mode optical fiber100is determined during the manufacturing of the few mode optical fiber preform. The refractive index profile is determined based on a concentration of chemicals used during the manufacturing of the few mode optical fiber preform. The chemicals used for the manufacturing of the few mode optical fiber100include one or more materials and one or more dopants. Moreover, the one or more materials and the one or more dopants are deposited over a surface of an initial material by performing flame hydrolysis. In an embodiment of the present disclosure, the initial material is a substrate rod or a tube. The deposition is done for achieving a pre-structure of the few mode optical fiber100.

Further, the few mode optical fiber100is manufactured by performing a specific chemical deposition technique of a plurality of chemical deposition techniques. Each of the plurality of chemical deposition techniques performs a chemical vapor deposition over a surface of the initial material by flame hydrolysis or inside the initial material. The plurality of chemical deposition techniques includes a modified chemical vapor deposition technique, an outside vapor deposition technique, an axial vapor deposition technique and the like. Each of the plurality of chemical deposition techniques ensures a specific refractive index required. Also, each of the plurality of chemical deposition techniques manufactures the core region102and the cladding region of the few mode optical fiber100.

In an embodiment of the present disclosure, the radius of the few mode optical fiber100is maintained under a pre-defined value set.

In an embodiment of the present disclosure, the Lp01 optical signals in the few mode optical fiber100will preferentially propagate in the first annular region106which is the central core region of the few mode optical fiber100. Further, the Lp11 signals in the few mode optical fiber100will preferentially propagate in the fifth annular region114which is the high index ring region of the few mode optical fiber100.

In an embodiment of the present disclosure, the cladding region is defined by a different refractive index profile. Moreover, the refractive index profile of the core region102and the cladding region is shown through a single graph (as shown in theFIG. 2). Going further, the few mode optical fiber100includes the core region102. The core region102has the refractive index profile (as shown in theFIG. 2). In addition, the few mode optical fiber100includes a plurality of regions in the core region102of the few mode optical fiber100. In an embodiment of the present disclosure, the core region102of the few mode optical fiber100is divided into the plurality of regions.

Each of the plurality of regions is defined by a corresponding refractive index and a corresponding radius. In an embodiment of the present disclosure, the refractive index of each of the plurality of regions of the core region102is different. In an embodiment of the present disclosure, the radius of each of the plurality of regions of the core region102is different.

Further, the refractive index profile of the core region102of the few mode optical fiber100changes from the center of the optical fiber100to the radius of the core. Moreover, the refractive index of each of the plurality of regions of the core region102has a pre-defined range of value (mentioned below in detail). In addition, the radius of each of the plurality of regions of the core region102has a pre-defined range of value (mentioned below in detail). In an embodiment of the present disclosure, the pre-defined range of value of the refractive index is set to obtain controlled dispersion, minimized spatial overlap and bending losses. In an embodiment of the present disclosure, the spatial overlap between the Lp01 mode and Lp11 mode is less than 10−5.

In an embodiment of the present disclosure, the pre-defined range of value of the refractive index of each of the plurality of regions is set to maintain the dispersion in pre-defined range or value. Further, the pre-defined range of the value of the core radius is optimized to enable the low bending losses. Furthermore, pre-defined range of the value of the core radius is optimized to enable the minimized spatial overlap between the Lp01 and Lp11 modes. In addition, each region of the plurality of regions has the corresponding refractive index value.

Further, in an embodiment of the present disclosure, the refractive index of each region of the plurality of regions is fixed over a cross-sectional area of each region. Going further, the core region102has a first annular region106, a second annular region108, a third annular region110, a fourth annular region112and a fifth annular region114. In an embodiment of the present disclosure, the plurality of regions includes the first annular region106, the second annular region108, and the third annular region110. In addition, the plurality of regions includes the fourth annular region112and the fifth annular region114. Moreover, the first annular region106, the second annular region108, the third annular region110, the fourth annular region112and the fifth annular region114are concentrically arranged.

Further, the second annular region108surrounds the first annular region106, the third annular region110surrounds the second annular region108and the fourth annular region112surrounds the third annular region110. Furthermore, the fifth annular region114surrounds the fourth annular region112. The first annular region106, the second annular region108, the third annular region110, the fourth annular region112and the fifth annular region114is associated with the corresponding refractive index and the corresponding radius. (Mentioned below in detail).

In an embodiment of the present disclosure, the first annular region106is the central core region. In an embodiment of the present disclosure, the peak shaping parameter alpha (α) of the central core region is in the range of 2.7 to 10. The expression used for the profile for central core region is as follows:

Further, the refractive index of the annular regions106,108,110,112and114is optimized to get different dispersion, minimized spatial overlap and low bending losses. In an embodiment of the present disclosure, the thickness and refractive index of annular regions106,108,110,112and114is optimized to minimize the spatial overlap between the Lp01 mode and Lp11 mode.

In an embodiment of the present disclosure, the refractive index and the radius are optimized based on a change in the concentration of a dopant used. In an embodiment of the present disclosure, the dopant includes germanium dioxide, phosphorous pentoxide, aluminium trioxide and the like.

Further, the radius of the first annular region106, the second annular region108, the third annular region110, the fourth annular region112and the fifth annular region114is optimized for the low bending loss. Furthermore, the radius of all the annular regions including106,108,110,112and114is optimized for minimized spatial overlap and low differential group delay between the modes.

Going further, the first annular region106is between the central longitudinal axis of the few mode optical fiber100and a first radius r1from the central longitudinal axis of the few mode optical fiber100. The first annular region106has a first refractive index Δ1. In addition, the second annular region108is between the first radius r1and a second radius r2from the central longitudinal axis of the few mode optical fiber100. The second annular region108has a second refractive index Δ2. Further, the third annular region110is between the second radius r2and a third radius r3from the central longitudinal axis of the few mode optical fiber100. The third annular region110has a third refractive index Δ3. Furthermore, the fourth annular region112is between the third radius r3and a fourth radius r4from the central longitudinal axis of the few mode optical fiber100. The fourth annular region112has a fourth refractive index Δ4. Furthermore, the fifth annular region114is between the fourth radius r4and a fifth radius r5from the central longitudinal axis of the few mode optical fiber100. The fifth annular region114has a fifth refractive index Δ5.

The expression used for calculating the refractive index is produced below:

wherein, nd: the average refractive index of the pure silica;ni: the refractive index of the layer;Δ%; the relative refractive index difference and given in percentage.

The first radius r1is in the range of 3.8 microns to 4.2 microns. The first refractive index Δ1is in the range of 0.42 to 0.70. The second radius r2is in the range of 4.8 microns to 5.2 microns. The second refractive index Δ2is zero. The third radius r3is in the range of 8.2 microns to 8.7 microns. The third refractive index Δ3is in the range of 0.4 to 0.58. The fourth radius r4is in the range of 8.3 microns to 9.9 microns. The fourth refractive index Δ4is zero. The fifth radius r5is in the range of 10.9 microns to 12.6 microns. The fifth refractive index Δ5is in the range of 0.41 to 0.62.

The first annular region106is the central core region, the second annular region108is the buffer region and the third annular region110is the trench region. The trench region is a downdopant region in the optical fiber100. Downdopant is a type of dopant which has the tendency to decrease the refractive index of glass with respect to pure. In addition, the fourth annular region112is the buffer region and the fifth annular region114is the high index ring region. The central core region and the high Index Ring region is an updopant region in the optical fiber cable100. Updopant is a type of dopant which has the tendency to increase the refractive index of glass with respect to pure. The buffer region is undopant region and consist pure silica.

Further, the few mode optical fiber100includes a cladding. The cladding surrounds the core region102. In addition, the cladding is concentrically arranged around the core region102. Moreover, the cladding covers the core region102. Further, the cladding is defined by a specific refractive index and a specific radius. In an embodiment of the present disclosure, the refractive index and the radius of the cladding is optimized for achieving the pre-defined value of the dispersion. The cladding is a sixth annular region104of the optical fiber100. The sixth annular region104is between the fifth radius r5and the sixth radius r6. The sixth annular region104concentrically surrounds the fifth annular region114. The sixth radius r6is 62.5 microns. The sixth refractive index Δ6is zero.

In an embodiment of the present disclosure, the value of the sixth refractive index Δ6is constant throughout a cross-sectional area of the sixth annular region104(as shown in theFIG. 2). In an embodiment of the present disclosure, the sixth radius r6of the sixth annular region110is fixed. Further, the value of the sixth refractive index Δ6of the sixth radius r6is optimized for achieving the pre-defined value of the dispersion, the intermodal crosstalk and the bending losses.

FIG. 2illustrates a refractive index profile200of the few mode optical fiber100, in accordance with various embodiments of the present disclosure. It may be noted that to explain a graphical appearance of the refractive index profile200, references will be made to the structural elements of the few mode optical fiber100. The refractive index profile200illustrates a relationship between the refractive index of the few mode optical fiber100and the radius of the few mode optical fiber100(as stated above in the detailed description of theFIG. 1A). In an embodiment of the present disclosure, the refractive index profile200shows the change in the refractive index of the few mode optical fiber100with the radius of the few mode optical fiber100.

Further, in an embodiment of the present disclosure, the first annular region106has high index region. The first annular region106is the central core region. The second annular region108is the buffer region. The third annular region110is the trench region. The fourth annular region112is the buffer region. The fifth annular region114is the high index ring region. The sixth annular region104is the cladding region. The first radius r1is in the range of 3.8 microns to 4.2 microns. The first refractive index Δ1is in the range of 0.42 to 0.70. The second radius r2is in the range of 4.8 microns to 5.2 microns. The second refractive index Δ2is zero. The third radius r3is in the range of 8.2 microns to 8.7 microns. The third refractive index Δ3is in the range of 0.4 to 0.58. The fourth radius r4is in the range of 8.3 microns to 9.9 microns. The fourth refractive index Δ4is zero. The fifth radius r5is in the range of 10.9 microns to 12.6 microns. The fifth refractive index Δ5is in the range of 0.41 to 0.62. The sixth radius r6is 62.5 microns. The sixth refractive index Δ6is zero. The peak shaping parameter alpha (α) of the central core region is in the range of 2.7 to 10.

In an embodiment of the present disclosure, the few mode optical fiber100is operated in the wavelength range of 1460 nm to 1625 nm in Lp01 mode and Lp11 mode. In addition, the few mode optical fiber is operated in six modes. The six modes include two degenerate Lp01 modes and four degenerate Lp11 modes.

FIG. 3illustrates an intensity-radial distance profile for Lp01 mode and Lp11 mode, in accordance with an embodiment of the present disclosure. The spatial overlap between the intensity profiles of Lp01 mode and Lp11 mode is less than 10−5. The marching line in the curve represents the Lp11 mode whereas the dark line in the curve represents the Lp01 mode.

The various embodiments of the present disclosure for the optimization of radius, refractive index, dispersion, macrobending losses, mode field diameter, spatial overlap, effective area, differential group delay and theoretical cut-off wavelength is described below. Note that the definitions of all the terms and parameters used to explain the below mentioned embodiments are already explained in detail above.

In an embodiment of the present disclosure, the radius r1of the first annular region106is 4.15 microns. The refractive index Δ1of the first annular region106is 0.54. The alpha (α) of the first annular region106which is the central core region is 2.7. The radius r2of the second annular region108is 5.15 microns. The refractive index Δ2of the second annular region108is zero. The radius r3of the third annular region110is 8.65 microns. The refractive index Δ3of the third annular region110is 0.41. The radius r4of the fourth annular region112is 8.85 microns. The refractive index Δ4of the fourth annular region112is zero. The radius r5of the fifth annular region114is 11.75 microns. The refractive index Δ5of the fifth annular region114is 0.6. The radius r6of the sixth annular region104is 62.5 microns. The refractive index Δ6of the sixth annular region104is zero. The dispersion is 4.94 Ps/nm/km for Lp01 mode at a wavelength of 1460 nm. The dispersion is 1.67 Ps/nm/km for Lp11 mode at a wavelength of 1460 nm. The dispersion is 4.95 Ps/nm/km for Lp01 mode at a wavelength of 1530 nm. The dispersion is 6.6 Ps/nm/km for Lp11 mode at a wavelength of 1530 nm. The dispersion is 4.78 Ps/nm/km for Lp01 mode at a wavelength of 1550 nm. The dispersion is 7.96 Ps/nm/km at Lp11 mode at a wavelength of 1550 nm. The dispersion is 4.55 Ps/nm/km for Lp01 mode at a wavelength of 1565 nm. The dispersion is 8.96 Ps·nm/km for Lp11 mode at a wavelength of 1565 nm. The dispersion is 3.95 Ps/nm/km for Lp01 mode at a wavelength of 1625 nm. The dispersion is 12.64 Ps/nm/km for Lp11 mode at a wavelength of 1625 nm. The mode field diameter of the optical fiber100for Lp01 mode is 8.2 μm at a wavelength of 1550 nm. The spatial overlap between Lp01 mode and Lp11 mode in the optical fiber100is less than 10−5. The macrobend loss for Lp11 mode in the optical fiber100is 1.492 dB/turn for 16 mm bending radius at a wavelength of 1625 nm. The effective area of the optical fiber100is 55 μm2for Lp01 mode at a wavelength of 1550 nm. The effective area of the optical fiber100is 390 μm2for Lp11 mode at a wavelength of 1550 nm. The theoretical cut-off wavelength for Lp11 mode is 2797 nm. The theoretical cut-off wavelength for Lp02 mode is 2165 nm. The differential group delay between Lp01 mode and Lp11 mode at a wavelength of 1550 nm is 0.004 ps/km.

In another embodiment of the present disclosure, the radius r1of the first annular region106is 4.15 microns. The refractive index Δ1of the first annular region106is 0.56. The alpha (α) of the first annular region106which is the central core region is 8. The radius r2of the second annular region108is 5.15 microns. The refractive index Δ2of the second annular region108is zero. The radius r3of the third annular region110is 8.65 microns. The refractive index Δ3of the third annular region110is 0.40. The radius r4of the fourth annular region112is 8.85 microns. The refractive index Δ4of the fourth annular region112is zero. The radius r5of the fifth annular region114is 11.75 microns. The refractive index Δ5of the fifth annular region114is 0.59. The radius r6of the sixth annular region104is 62.5 microns. The refractive index Δ6of the sixth annular region104is zero. The dispersion is 13.7 Ps/nm/km for Lp01 mode at a wavelength of 1460 nm. The dispersion is 1.62 Ps/nm/km for Lp11 mode at a wavelength of 1460 nm. The dispersion is 17.48 Ps/nm/km for Lp01 mode at a wavelength of 1530 nm. The dispersion is 6.58 Ps/nm/km for Lp11 mode at a wavelength of 1530 nm. The dispersion is 18.42 Ps/nm/km for Lp01 mode at a wavelength of 1550 nm. The dispersion is 7.98 Ps/nm/km at Lp11 mode at a wavelength of 1550 nm. The dispersion is 19.09 Ps/nm/km for Lp01 mode at a wavelength of 1565 nm. The dispersion is 8.98 Ps·nm/km for Lp11 mode at a wavelength of 1565 nm. The dispersion is 21.31 Ps/nm/km for Lp01 mode at a wavelength of 1625 nm. The dispersion is 12.95 Ps/nm/km for Lp11 mode at a wavelength of 1625 nm. The mode field diameter of the optical fiber100for Lp01 mode is 7.8 μm at a wavelength of 1550 nm. The spatial overlap between Lp01 mode and Lp11 mode in the optical fiber100is less than 10−5. The macrobend loss for Lp11 mode in the optical fiber100is 1.49 dB/turn for 16 mm bending radius at a wavelength of 1625 nm. The effective area of the optical fiber100is 49 μm2for Lp01 mode at a wavelength of 1550 nm. The effective area of the optical fiber100is 392 μm2for Lp11 mode at a wavelength of 1550 nm. The theoretical cut-off wavelength for Lp11 mode is 2738 nm. The theoretical cut-off wavelength for Lp02 mode is 2380 nm. The differential group delay between Lp01 mode and Lp11 mode at a wavelength of 1550 nm is 0.010 ps/km.

In yet another embodiment of the present disclosure, the radius r1of the first annular region106is 4.10 microns. The refractive index Δ1of the first annular region106is 0.49. The alpha (α) of the first annular region106which is the central core region is 10. The radius r2of the second annular region108is 4.9 microns. The refractive index Δ2of the second annular region108is zero. The radius r3of the third annular region110is 8.3 microns. The refractive index Δ3of the third annular region110is 0.52. The radius r4of the fourth annular region112is 8.3 microns. The refractive index Δ4of the fourth annular region112is zero. The radius r5of the fifth annular region114is 10.9 microns. The refractive index Δ5of the fifth annular region114is 0.62. The radius r6of the sixth annular region104is 62.5 microns. The refractive index Δ6of the sixth annular region104is zero. The dispersion is 12.69 Ps/nm/km for Lp01 mode at a wavelength of 1460 nm. The dispersion is 0.37 Ps/nm/km for Lp11 mode at a wavelength of 1460 nm. The dispersion is 15.35 Ps/nm/km for Lp01 mode at a wavelength of 1530 nm. The dispersion is 4.57 Ps/nm/km for Lp11 mode at a wavelength of 1530 nm. The dispersion is 16.1 Ps/nm/km for Lp01 mode at a wavelength of 1550 nm. The dispersion is 5.85 Ps/nm/km at Lp11 mode at a wavelength of 1550 nm. The dispersion is 16.3 Ps/nm/km for Lp01 mode at a wavelength of 1565 nm. The dispersion is 6.84 Ps·nm/km for Lp11 mode at a wavelength of 1565 nm. The dispersion is 18.1 Ps/nm/km for Lp01 mode at a wavelength of 1625 nm. The dispersion is 10.75 Ps/nm/km for Lp11 mode at a wavelength of 1625 nm. The mode field diameter of the optical fiber100for Lp01 mode is 8 μm at a wavelength of 1550 nm. The spatial overlap between Lp01 mode and Lp11 mode in the optical fiber100is less than 10−5. The macrobend loss for Lp11 mode in the optical fiber100is 1.47 dB/turn for 16 mm bending radius at a wavelength of 1625 nm. The effective area of the optical fiber100is 53 μm2for Lp01 mode at a wavelength of 1550 nm. The effective area of the optical fiber100is 368 μm2for Lp11 mode at a wavelength of 1550 nm. The theoretical cut-off wavelength for Lp11 mode is 2645 nm. The theoretical cut-off wavelength for Lp02 mode is 2241 nm. The differential group delay between Lp01 mode and Lp11 mode at a wavelength of 1550 nm is 0.005 ps/km.

In an embodiment of the present disclosure, the radius r1of the first annular region106is 3.8 microns. The refractive index Δ1of the first annular region106is 0.70. The alpha (α) of the first annular region106which is the central core region is 10. The radius r2of the second annular region108is 4.8 microns. The refractive index Δ2of the second annular region108is zero. The radius r3of the third annular region110is 8.4 microns. The refractive index Δ3of the third annular region110is 0.54. The radius r4of the fourth annular region112is 9.9 microns. The refractive index Δ4of the fourth annular region112is zero. The radius r5of the fifth annular region114is 12.6 microns. The refractive index Δ5of the fifth annular region114is 0.62. The radius r6of the sixth annular region104is 62.5 microns. The refractive index Δ6of the sixth annular region104is zero. The dispersion is 15.98 Ps/nm/km for Lp01 mode at a wavelength of 1460 nm. The dispersion is 3.64 Ps/nm/km for Lp11 mode at a wavelength of 1460 nm. The dispersion is 20.39 Ps/nm/km for Lp01 mode at a wavelength of 1530 nm. The dispersion is 8.63 Ps/nm/km for Lp11 mode at a wavelength of 1530 nm. The dispersion is 21.62 Ps/nm/km for Lp01 mode at a wavelength of 1550 nm. The dispersion is 10.01 Ps/nm/km at Lp11 mode at a wavelength of 1550 nm. The dispersion is 22.49 Ps/nm/km for Lp01 mode at a wavelength of 1565 nm. The dispersion is 11.03 Ps·nm/km for Lp11 mode at a wavelength of 1565 nm. The dispersion is 25.51 Ps/nm/km for Lp01 mode at a wavelength of 1625 nm. The dispersion is 14.75 Ps/nm/km for Lp11 mode at a wavelength of 1625 nm. The mode field diameter of the optical fiber100for Lp01 mode is 7.4 μm at a wavelength of 1550 nm. The spatial overlap between Lp01 mode and Lp11 mode in the optical fiber100is less than 10−5. The macrobend loss for Lp11 mode in the optical fiber100is 1.3 dB/turn for 16 mm bending radius at a wavelength of 1625 nm. The effective area of the optical fiber100is 43 μm2for Lp01 mode at a wavelength of 1550 nm. The effective area of the optical fiber100is 425 μm2for Lp11 mode at a wavelength of 1550 nm. The theoretical cut-off wavelength for Lp11 mode is 2810 nm. The theoretical cut-off wavelength for Lp02 mode is 2500 nm. The differential group delay between Lp01 mode and Lp11 mode at a wavelength of 1550 nm is 0.020 ps/km.

In an embodiment of the present disclosure, the radius r1of the first annular region106is 3.8 microns. The refractive index Δ1of the first annular region106is 0.42. The alpha (α) of the first annular region106which is the central core region is 10. The radius r2of the second annular region108is 5 microns. The refractive index Δ2of the second annular region108is zero. The radius r3of the third annular region110is 8.2 microns. The refractive index Δ3of the third annular region110is 0.58. The radius r4of the fourth annular region112is 9.7 microns. The refractive index Δ4of the fourth annular region112is zero. The radius r5of the fifth annular region114is 12.3 microns. The refractive index Δ5of the fifth annular region114is 0.41. The radius r6of the sixth annular region104is 62.5 microns. The refractive index Δ6of the sixth annular region104is zero. The dispersion is 12.3 Ps/nm/km for Lp01 mode at a wavelength of 1460 nm. The dispersion is 5.64 Ps/nm/km for Lp11 mode at a wavelength of 1460 nm. The dispersion is 13.9 Ps/nm/km for Lp01 mode at a wavelength of 1530 nm. The dispersion is 10.4 Ps/nm/km for Lp11 mode at a wavelength of 1530 nm. The dispersion is 13.84 Ps/nm/km for Lp01 mode at a wavelength of 1550 nm. The dispersion is 11.77 Ps/nm/km at Lp11 mode at a wavelength of 1550 nm. The dispersion is 13.6 Ps/nm/km for Lp01 mode at a wavelength of 1565 nm. The dispersion is 12.69 Ps·nm/km for Lp11 mode at a wavelength of 1565 nm. The dispersion is 10.86 Ps/nm/km for Lp01 mode at a wavelength of 1625 nm. The dispersion is 16.25 Ps/nm/km for Lp11 mode at a wavelength of 1625 nm. The mode field diameter of the optical fiber100for Lp01 mode is 8 μm at a wavelength of 1550 nm. The spatial overlap between Lp01 mode and Lp11 mode in the optical fiber100is less than 10−5. The macrobend loss for Lp11 mode in the optical fiber100is 2.1 dB/turn for 16 mm bending radius at a wavelength of 1625 nm. The effective area of the optical fiber100is 51 μm2for Lp01 mode at a wavelength of 1550 nm. The effective area of the optical fiber100is 570 μm2for Lp11 mode at a wavelength of 1550 nm. The theoretical cut-off wavelength for Lp11 mode is 2281 nm. The theoretical cut-off wavelength for Lp02 mode is 1950 nm. The differential group delay between Lp01 mode and Lp11 mode at a wavelength of 1550 nm is 0.012 ps/km.

Going further, the present disclosure provides numerous advantages over the prior art. The present disclosure provides the few mode optical fiber with controlled dispersion, minimized spatial overlap and low bending losses. In addition, the present disclosure, the few mode optical fiber is operated in Lp01 mode and Lp11 mode. In addition, the few mode optical fiber is operated in six modes including two degenerate Lp01 modes and four Lp11 modes. Further, the present disclosure provides spatial overlap less than 10−5between Lp01 mode and Lp11 mode throughout the range of wavelength between 1460 nm to 1625 nm.

While several possible embodiments of the disclosure have been described above and illustrated in some cases, it should be interpreted and understood as to have been presented only by way of illustration and example, but not by limitation. Thus, the breadth and scope of a preferred embodiment should not be limited by any of the above-described exemplary embodiments.