System and method for optically coupling single mode fiber to a multicore fiber

Abstract

Disclosed is a method of optically coupling Single Mode Fibers (SMFs) to a Multi Core Fiber (MCF). The method includes pre-tapering (102) a multi-hole capillary having one or more holes to predefined taper ratio. The method further includes etching (104) one or more SMFs to a predefined diameter to match a hole diameter of the one or more holes in a waist section of the pre-tapered multi-hole capillary. Further, the method includes inserting (106) the one or more etched SMFs into the one or more holes of the pre-tapered multi-hole capillary. Furthermore, the method includes tapering (108) the pre-tapered multi-hole capillary along with the one or more inserted SMFs to form a tapered-etched SMF bundle. Thereafter, the method includes aligning (110) and splicing (112) the tapered-etched SMF bundle to one or more cores of the MCF to match core positions of the tapered-etched SMF bundle and the MCF.

Description

SYSTEM AND METHOD FOR OPTICALLY COUPLING SINGLE MODE FIBER TO A MULTICORE FIBERTECHNICAL FIELD

[0001] The embodiments of the present disclosure generally relate to the field of fiber optics. More particularly, the present disclosure relates to a system and a method for optically coupling single mode fiber to a multicore fiber.BACKGROUND OF THE INVENTION

[0002] The subject matter disclosed in the background section should not be assumed or construed to be prior art merely because of its mention in the background section. Similarly, any problem statement mentioned in the background section or its association with the subject matter of the background section should not be assumed or construed to have been previously recognized in the prior art.

[0003] In recent years, there is growing demand for enhanced transmission capacity in optical fiber networks. Such a demand for transmission capacity has led to a growing interest in design and fabrication of multicore fibers. Multicore fibers with high density spatial multiplexing architecture provide an attractive avenue to address the ever-growing demand for enhanced transmission capacity of the optical fiber networks.

[0004] A key component for the multicore fiber based optical networks is a fan- in / fan-out device, which serves as an input / output device to couple light in and out of individual cores of the multicore fiber to standard single mode fibers.

[0005] In conventional multicore fiber based optical networks, the fan-in / fan-out devices are made using a bunch of single mode fibers bundled with the help of single-hole capillary that helps to maintain the relative position of multiple single mode fibers. The bundle of the single mode fibers, after tapering process is designed to match the core positions of individual fibers to the multicore fiber. However, during the tapering process, the core positions are not tightly controlled andencounter variations. This causes significant shift in the core positions and affects coupling with the multicore fiber leading to increased transmission loss and higher inter-core coupling, leading to undesirable levels of cross-talk.

[0006] Further, in the conventional multicore fiber based optical networks, during the tapering process of the bundle of single mode fibers bundle, the core diameter of individual single mode fibers in the bundle reduces. The reduction in the core diameter causes significant mismatch of Mode Field Diameter (MFD) between the single mode fibers and the multicore fiber.

[0007] In some other conventional multicore fiber based optical networks, the single mode fibers with specific refractive index profiles are used to compensate for the mode field diameter variation while tapering. However, usage of the single mode fibers with specific refractive index profiles increases the cost of the fan-in / fan-out device. Also, the usage of the single mode fibers with specific refractive index profiles do not completely address the possibility of shifting of the core positions while tapering.

[0008] Therefore, there lies a need for an improved fan-in / fan-out device that can overcome the above-mentioned shortcomings associated with the conventional multicore fiber based optical networks and provide improved optical coupling to multi core fiber.SUMMARY

[0009] The following embodiments present a simplified summary to provide a basic understanding of some aspects of the disclosed invention. This summary is not an extensive overview, and it is not intended to identify key / critical elements or to delineate the scope thereof. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is presented later.

[0010] In an embodiment of the present disclosure, a method of optically coupling light radiation from one or more Single Mode Fibers (SMFs) to a Multi Core Fiber(MCF) is disclosed. The method includes pre-tapering a multi-hole capillary having one or more holes to predefined taper ratio. The method further includes etching one or more SMFs to a predefined diameter to match a hole diameter of the one or more holes in a tapered section of the multi-hole capillary. Further, the method includes inserting the one or more etched SMFs into the one or more holes of the pre-tapered multi-hole capillary. Furthermore, the method includes tapering the pre-tapered multi -hole capillary along with the one or more inserted SMFs to form a tapered- etched SMF bundle. Thereafter, the method includes aligning the tapered-etched SMF bundle to one or more cores of the MCF to match core positions of the tapered- etched SMF bundle and the MCF. Further, the method includes splicing the tapered- etched SMF bundle to the one or more cores of the MCF to achieve optimum coupling of light from the tapered-etched SMF bundle into the MCF.

[0011] In some aspects of the present disclosure, the one or more SMFs are trench- assisted optical fibers for limiting mode field diameter of the light guided through the one or more SMFs.

[0012] In some aspects of the present disclosure, the multi-hole capillary is a monolithic multi -hole capillary and the one or more holes of the multi -hole capillary have equal diameter.

[0013] In some aspects of the present disclosure, the pre-tapered multi-hole capillary along with the one or more inserted SMFs is tapered to match an outer diameter of the pre-tapered multi-hole capillary with a clad diameter of the MCF.

[0014] In some aspects of the present disclosure, the multi-hole capillary and cladding of each of the one or more SMFs have same refractive index.

[0015] In some aspects of the present disclosure, the method includes measuring crosstalk in the SMFs by performing one or more steps. The method includes coupling a laser source into a core of a first SMF among a plurality of SMFs and measuring an output power at a cleaved end of the core of the first SMF. The method further includes coupling the laser source into a core of one of remaining SMFsamong the plurality of SMFs, measuring the output power at a cleaved end of the core of the one of remaining SMFs and measuring crosstalk as ratio of the output power at the core of the first SMF to the output power at the core of the one of remaining SMFs.

[0016] In some aspects of the present disclosure, the cleaved end of the core of the first SMF is coupled to a microscope objective to maximize the output power.

[0017] In another embodiment of the present disclosure, a capillary insertion system is disclosed, the system includes a capillary holder mounted on a four-axis alignment stage. The capillary holder is designed to hold a multi-hole capillary. The system further includes a multi fiber holder mounted on a two-axis alignment stage. The multi fiber holder is designed to hold one or more etched Single Mode Fibers (SMFs). Further, the system includes an imaging system mounted on two different axes. The imaging system is used to view and align the one or more etched SMFs inside the multi-hole capillary based on an angular rotational alignment using the capillary holder.

[0018] In some aspects of the present disclosure, the multi -fiber holder has a predefined groove width for holding the one or more etched SMFs in a specific geometry.

[0019] In some aspects of the present disclosure, the multi-hole capillary is pretapered to a predefined taper ratio and the multi -hole capillary has one or more holes with equal diameter.BRIEF DESCRIPTION OF DRAWINGS

[0020] Various embodiments disclosed herein will become better understood from the following detailed description when read with the accompanying drawings. The accompanying drawings constitute a part of the present disclosure and illustrate certain non-limiting embodiments of inventive concepts. Further, components and elements shown in the drawings are not necessarily to scale, emphasis instead beingplaced upon clearly illustrating the principles of the present disclosure. For consistency and ease of understanding, similar components and elements are annotated by reference numerals in the exemplary drawings.

[0021] FIG. 1 illustrates a flowchart of a method for optically coupling light radiation from one or more Single Mode Fibers (SMFs) to a Multi Core Fiber (MCF), in accordance with an embodiment of the present disclosure.

[0022] FIG. 2 illustrates a schematic diagram of a multi-hole capillary design for optically coupling light radiation from the one or more SMFs to the MCF, in accordance with an embodiment of the present disclosure.

[0023] FIG. 3 illustrates photographs of an insertion process of etched SMF into a pre-tapered multi-hole capillary, in accordance with an embodiment of the present disclosure.

[0024] FIG. 4 illustrates a schematic diagram of a capillary insertion system, in accordance with an embodiment of the present disclosure.

[0025] FIG. 5 illustrates a cross-sectional view of a multi -fiber holder apparatus, in accordance with an embodiment of the present disclosure.

[0026] FIG. 6 illustrates a schematic diagram of an exemplary fiber insertion apparatus, in accordance with an embodiment of the present disclosure.

[0027] FIG. 7 illustrates photographs of a multi fiber holder and the capillary insertion system, in accordance with an embodiment of the present disclosure.

[0028] FIG. 8 illustrates photographs of an exemplary Fan-in / Fan-out (FIFO) device and a cross-section of a taper end face of the waist region and a microscopic image of a splice point between the waist region and the MCF, in accordance with an embodiment of the present disclosure.

[0029] FIG. 9 illustrates a schematic diagram of the pre-tapered multi-hole capillary, in accordance with an embodiment of the present disclosure.

[0030] FIG. 10 illustrates a schematic diagram of a 40-micron etched SMF with taper profile for inserting into the pre-tapered multi-hole capillary, in accordance with an embodiment of the present disclosure.

[0031] FIG. 11 illustrates a schematic diagram of a tapered version of an etched SMF bundle 408 inserted inside the pre-tapered multi-hole capillary, in accordance with an embodiment of the present disclosure.

[0032] FIG. 12 illustrates a schematic diagram an exemplary FIFO device, in accordance with an embodiment of the present disclosure.

[0033] FIG. 13 illustrates a block diagram of crosstalk measurement of the FIFO device based on free space coupling scheme, in accordance with an embodiment of the present disclosure.

[0034] FIG. 14 illustrates graphs depicting simulation results of variation in insertion loss with taper ratio for different core radius, in accordance with an embodiment of the present disclosure.

[0035] FIG. 15 illustrates a graph depicting the simulation results of variation in the insertion loss with the taper ratio as well as the vertical shift in the core position, in accordance with an embodiment of the present disclosure.

[0036] FIG. 16 illustrates graphs depicting simulation results of variation in crosstalk with different core pitch at taper ratio 2 for different values of Numerical Aperture (NA), in accordance with an embodiment of the present disclosure.DETAILED DESCRIPTION

[0037] Inventive concepts of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, plots, and photographs in which examples of one or more embodiments of inventive concepts are shown. Inventive concepts may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Further, theone or more embodiments disclosed herein are provided to describe the inventive concept thoroughly and completely, and to fully convey the scope of each of the present inventive concepts to those skilled in the art. Furthermore, it should be noted that the embodiments disclosed herein are not mutually exclusive concepts. Accordingly, one or more components from one embodiment may be tacitly assumed to be present or used in any other embodiment.

[0038] The following description presents various embodiments of the present disclosure. The embodiments disclosed herein are presented as teaching examples and are not to be construed as limiting the scope of the present disclosure. The present disclosure should in no way be limited to the illustrative implementations, drawings, and techniques illustrated below, including the exemplary design and implementation illustrated and described herein, but may be modified, omitted, or expanded upon without departing from the scope of the present disclosure.

[0039] The following description contains specific information pertaining to embodiments in the present disclosure. The detailed description uses the phrases “in some embodiments” or “some implementations” which may each refer to one or more or all of the same or different embodiments or implementations. The term “some” as used herein is defined as “one, or more than one, or all.” Accordingly, the terms “one,” “more than one,” “more than one, but not all” or “all” would all fall under the definition of “some.” In view of the same, the terms, for example, “in an embodiment” or “in an implementation” refers to one embodiment or one implementation and the term, for example, “in one or more embodiments” refers to “at least one embodiment, or more than one embodiment, or all embodiments ”. Further, the term, for example, “in one or more implementations” refers to “at least one implementation, or more than one implementation, or all implementations.

[0040] The term “comprising,” when utilized, means “including, but not necessarily limited to;” it specifically indicates open-ended inclusion in the so-described one or more listed features, elements in a combination, unless otherwise stated with limiting language. Furthermore, to the extent that the terms “includes,” “has,”“have,” “contains,” and other similar words are used in either the detailed description, such terms are intended to be inclusive in a manner similar to the term“comprising.”

[0041] In the following description, for the purposes of explanation, various specific details are set forth in order to provide a thorough understanding of embodiments of the present disclosure. It will be apparent, however, that embodiments of the present disclosure may be practiced without these specific details. Several features described hereafter can each be used independently of one another or with any combination of other features.

[0042] The description provided herein discloses exemplary embodiments only and is not intended to limit the scope, applicability, or configuration of the present disclosure. Rather, the foregoing description of the exemplary embodiments will provide those skilled in the art with an enabling description for implementing any of the exemplary embodiments. Specific details are given in the following description to provide a thorough understanding of the embodiments. However, it may be understood by one of the ordinary skilled in the art that the embodiments disclosed herein may be practiced without these specific details.

[0043] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein the description, the singular forms "a", "an", and "the" include plural forms unless the context of the invention indicates otherwise.

[0044] The terminology and structure employed herein are for describing, teaching, and illuminating some embodiments and their specific features and elements and do not limit, restrict, or reduce the scope of the present disclosure. Accordingly, unless otherwise defined, all terms, and especially any technical and / or scientific terms, used herein may be taken to have the same meaning as commonly understood by one having ordinary skill in the art.

[0045] Embodiments of the present disclosure will be described below in detail with reference to the accompanying figures. FIG. 1 to FIG. 16, discussed below, and the one or more embodiments used to describe the principles of the present disclosure are by way of illustration only and should not be construed in any way to limit the scope of the present disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged system or device.

[0046] Further, a few of the figures in the accompanying drawings are represented in color for accurate illustration of results. The color drawings illustrate one or more results which cannot be adequately represented in black and white or gray scale. The color drawings are therefore necessary to ensure proper interpretation of the disclosed invention.

[0047] An aspect of the present disclosure is to provide a system and a method for optically coupling light radiation from one or more Single Mode Fibers (SMFs) to a Multi Core Fiber (MCF).

[0048] In another aspect of the present disclosure, the system and the method use a specially structured capillary to precisely hold relative positions of the one or more SMFs during tapering process to precisely match core positions with respect to cross-section of the MCF.

[0049] In another aspect of the present disclosure, the system and the method use the specially structured capillary to improve the repeatability in fabrication process of the system and to improve inter-core crosstalk.

[0050] In another aspect of the present disclosure, the system and the method use a pre-processed SMF in combination with the specially structured capillaries for better mode field control during the tapering process to match the SMF closely with the MCF to improve the loss performance of the system.

[0051] In another aspect of the present disclosure, the system and the method couple light from a tapered bundle of SMF to the MCF either through splicing or direct coupling for transmission with low loss and lower inter-core coupling.

[0052] In another aspect of the present disclosure, the method measures the crosstalk of the tapered bundle of SMF by selectively exciting one core using free space optics.

[0053] In one embodiment, the specially structured capillary may be utilized to hold individual SMF during the tapering process to keep the relative position of the SMF precise. The specially structured capillary may help to avoid any void space between the fibers during fusion and tapering process. The specially structured capillary may comprise multiple holes corresponding to number of cores in the MCF to which the light is to be coupled in and out. The diameter and the relative spacing of the holes may be designed to match with the MCF precisely after the tapering process. The specially structured capillary may be a multi-hole capillary.

[0054] FIG. 1 illustrates a flowchart of a method 100 for optically coupling light radiation from the one or more SMFs to the MCF, in accordance with an embodiment of the present disclosure. The method 100 comprises a series of operation steps indicated by blocks 102 through 112. The method 100 starts at block 102.

[0055] A multi-hole capillary and one or more SMFs may be prepared for optically coupling light from the one or more SMFs to into corresponding core regions of the MCF and for coupling light from the MCF into the one or more SMFs in the multi - hole capillary.

[0056] At block 102, a multi -hole capillary 202 (shown in FIG. 2) having one or more holes 204 (shown in FIG. 2) may be pre-tapered to predefined taper ratio.

[0057] In some aspects of the present disclosure, the multi-hole capillary may be a monolithic multi-hole capillary. The one or more holes of the multi-hole capillary may have equal diameter.

[0058] At block 104, one or more SMFs may be etched to a predefined diameter to match a hole diameter of the one or more holes in a tapered section of the multi - hole capillary.

[0059] At block 106, the one or more etched SMFs 408 (shown in FIG. 4) may be inserted into the one or more holes of the pre-tapered multi-hole capillary.

[0060] At block 108, the pre-tapered multi-hole capillary along with the one or more inserted SMFs may be tapered to form a tapered-etched SMF bundle.

[0061] In some aspects of the present disclosure, the pre-tapered multi-hole capillary along with the one or more inserted SMFs is tapered to match an outer diameter of the pre-tapered multi-hole capillary with a clad diameter of the MCF 1204 (shown in FIG. 12).

[0062] At block 110, the tapered-etched SMF bundle may be aligned to one or more cores of the MCF to match core positions of the tapered-etched SMF bundle and the MCF.

[0063] For coupling the tapered-etched SMF bundle to the one or more cores of the MCF, one end of the tapered-etched SMF bundle may be cleaved. The tapered- etched SMF bundle may be aligned to match the core positions of the one or more cores of the MCF with core position of each of the one or more SMFs in the tapered- etched SMF bundle. Based on the alignment, the cleaved end of the tapered-etched SMF bundle may be spliced inside the one or more cores of the MCF.

[0064] At block 112, the tapered-etched SMF bundle may be spliced to the one or more cores of the MCF to achieve optimum coupling of light from the tapered- etched SMF bundle into the MCF.

[0065] In some aspects of the present disclosure, the multi-hole capillary and cladding of each of the one or more SMFs have same refractive index. The one or more SMFs may be trench-assisted optical fibers for limiting mode field diameter of the light guided through the one or more SMFs. The trench-assisted optical fibers may use a low-refractive-index trench layer in cladding of the one or more SMFs to confine the light mode, thereby limiting the mode field diameter and reducing bending loss.

[0066] FIG. 2 illustrates a schematic diagram 200 of a multi-hole capillary design for optically coupling light radiation from the one or more SMFs to the MCF, in accordance with an embodiment of the present disclosure.

[0067] The multi-hole capillary may be used in a Fan-In / Fan-Out (FIFO) device. The FIFO device is an optical coupling component that connects multiple SMFs to a single MCF. The FIFO device may operate in two modes namely fan-in mode and fan-out mode. In the fan-in mode, the FIFO device may combines signals from several SMFs into multiple cores of the single MCF. In the fan-out mode, the FIFO device may split signals from the single MCF to separate SMFs.

[0068] The multi-hole capillary 202 may comprise a plurality of holes 204 (hereinafter may be referred to as “holes 204”), for instance, 4 holes. The multi -hole capillary 202 is adapted to be coupled with the MCF 1204 (shown in FIG. 12). The multi-hole capillary 202 may be a specially structured capillary and may comprise four holes. In a non-limiting example, the diameter of each hole of the holes 204 may be 125 microns and hole pitch of each hole may be 250 microns. In another non-limiting example, the tolerance of the holes 204 with the inner diameter and the pitch may be ±1 micron and ±5 micron respectively, resulting in a core pitch of 40 microns with 0.8-micron accuracy after the tapering process. In the multi-hole capillary 202, the core pitch of the inner diameter and the hole pitch matches with the core pitch of a commercial 4-core MCF. Further, a core position tolerance in the multi-hole capillary 202 may be at least 50dB. The material of a multi-hole capillarymay include fused quartz with melting point similar to a softening point of the SMF.In a non-limiting example, the melting point of the fused quartz may be 1630°C.

[0069] In one embodiment, a fabrication process may involve in making the FIFO device. The specially structured capillary may be pre-tapered with a particular taper ratio. The one or more SMFs may be etched to a diameter matching the hole diameter in a waist section of the pre-tapered multi-hole capillary. The one or more etched SMFs 408 (alternatively referred to as the etched SMF 408) (shown in FIG. 4) may be inserted into the individual holes of the pre-tapered capillary. The pretapered multi-hole capillary 202 (alternatively referred to as pre-tapered capillary 202) along with the etched SMF 408 may be tapered further until the relative core position of the etched SMF 408 may match with the core position of the MCF 1204. The pre-taper ratio and the fiber-etched diameters may be predefined in such a way that the mismatch of Mode Field Diameter (MFD) between the tapered fibers and the MCF 1204 is minimal and may lower the inter-core coupling.

[0070] In some embodiments, polymer coating of the SMF may be stripped / removed for a required length. For instance, the SMF may be a standard single mode silica fiber. The stripped region of the SMF may be etched to a predefined diameter or desired dimensions using a suitable glass etchant solution. The rate of etching may depend on the concentration of the etchant solution and the etching time may depend on the desired dimension of the etched SMF. The SMF may be etched to create an etched diameter within a tolerance < 1pm. The etched SMF may be made with a tapered profile at the etched end close to the coating stripped area of the SMF for better handling and strength.

[0071] FIG. 3 illustrates photographs 300 of an insertion process of etched SMF into a pre-tapered multi-hole capillary, in accordance with an embodiment of the present disclosure. FIG. 3 illustrates the process of inserting the etched SMF into the pre-tapered multi-hole capillary. In a non-limiting example, the pre-tapered multi-hole capillary may comprise four holes and four SMFs may be etched and inserted into the four holes of the pre-tapered multi -hole capillary. FIG. 3(a)illustrates the four holes of the pre-tapered multi -hole capillary. FIG. 3(b) and FIG. 3(c) illustrates the insertion of the etched SMFs into the four holes. FIG. 3(d) illustrates the four etched SMFs successfully inserted into the pre-tapered four-hole capillary.

[0072] FIG. 4 illustrates a schematic diagram 400 of a capillary insertion system, in accordance with an embodiment of the present disclosure. The capillary system may be a vertical capillary system. In the capillary insertion system 400, a capillary holder 402 may be mounted on a 4 axis (x, y, z, 0y) alignment stage and a multi fiber holder 404 may be mounted on a 2 axis (x, z) alignment stage. The etched SMF 408 may be viewed and precisely aligned to the pre-tapered capillary using an imaging system 406 mounted on two different axes. Initially, the etched SMF 408 and the pre-tapered capillary 202 may be aligned using x, y, z axis alignment. The imaging system 406 may be used to view and align the etched SMF 408 inside the multi-hole capillary 202 based on an angular (0y) rotational alignment using the capillary holder 402. The individual etched SMF 408 may be aligned to match the holes 204 of the pre-tapered capillary 202 using the 0yrotational alignment in the capillary holder 402 and the individual etched SMF 408 may be fully inserted into the individual holes 204 of the pre-tapered capillary 202.

[0073] FIG. 5 illustrates a cross-sectional view 500 of a multi-fiber holding apparatus, in accordance with an embodiment of the present disclosure. The multifiber holder 404 may include a predefined groove width for holding the one or more etched SMFs in a specific geometry. In a non-limiting example, the one or more SMFs may be held together using a special highly precise multi fiber holder 404 with a groove 602 (shown in FIG. 6) of width 500 microns for holding the SMF in a specific geometry. The etched SMF 408 may be inserted into individual holes of the pre-tapered capillary 202 using the capillary insertion system 400.

[0074] FIG. 6 illustrates a schematic diagram 600 of an exemplary fiber insertion apparatus, in accordance with an embodiment of the present disclosure. The one or more SMFs may be inserted into the pre-tapered capillary 202 based onappropriately spaced grooves. The multi fiber holder 404 may be designed as a holder with two grooves 602 of width 220-micron to hold the SMF, spaced 250 microns center-to-center. A two tapered etched SMF 408 may be placed on the holder 404. The holder 404 may be positioned in a loading fixture of a fiber processing system. The capillary 202 may be positioned on a block holder of the fiber processing system. The two tapered etched SMF 408 may be simultaneously inserted into the capillary 202, utilizing the fiber processing system and a high- quality magnifier for coarse alignment. In a non-limiting example, the fiber processing system may be a Vytran system.

[0075] FIG. 7 illustrates photographs 700 of a multi fiber holder 404 and the capillary insertion system 400, in accordance with an embodiment of the present disclosure.

[0076] FIG. 7(a) illustrates the process of inserting a fiber bundle of the etched SMFs 408 using the multi fiber holder 404. With the assistance of the multi fiber holder 404, the etched SMFs 408 may be inserted into the pre-tapered multi-hole capillary 202. FIG. 7(b) illustrates an exemplary capillary insertion system. In a nonlimiting example, the pre-tapered multi-hole capillary 202 may comprise four holes and four SMFs may be etched and inserted into the four holes of the pre-tapered multi-hole capillary.

[0077] In some embodiments, after inserting the etched SMFs 408 into the pretapered multi-hole capillary 202, a second stage of the tapering process may be carried out. During the second stage of tapering, the pre-tapered multi-hole capillary 202 along with the etched SMFs 408 may consist of three distinct regions, namely, a down-taper region, waist region, and an up-taper region. The pre-tapered multihole capillary 202 may be fused with the etched SMFs 408 in the capillary insertion system 400, for instance a glass processing system. The tapering process of the etched SMFs 408 positioned inside the pre-tapered multi -hole capillary 202 may be performed using the glass processing unit. Thereafter, the fused assembly may becleaved at the waist region to obtain the desired structural configuration, ensuring precise alignment.

[0078] FIG. 8 illustrates photographs 800 of an exemplary FIFO device and a crosssection of a taper end face of the waist region and a microscopic image of a splice point between the waist region and the MCF, in accordance with an embodiment of the present disclosure.

[0079] FIG. 8(a) illustrates the schematic of the FIFO device and the cross-section of the end face of the waist region. In a non-limiting example, the FIFO device may be made up of four SMFs, a pre-tapered four-hole capillary, the down-taper region, and the waist region. The four SMFs may be cleaved at the waist region and the four-core MCF may not yet be spliced. FIG. 8(a) also illustrates an end view of a Fan-In device (input side of the FIFO device) and the cross-sectional image of the cleaved taper end face of the waist region. The taper end face may be the end of the tapered etched SMF bundle. The taper end face displayed in the FIG. 8(a) is a square lattice structure with an approximate core pitch of 40 pm. The cleaved taper end face may be spliced with the four-core MCF.

[0080] FIG. 8(b) illustrates the microscopic image of the splice point between the waist region and the MCF. The microscopic image illustrates the splice point between the tapered end face and 4-core MCF. The angular alignment between the cores of the etched SMFs and the MCF may be manually adjusted during the splicing process using the glass processing system.

[0081] FIG. 9 illustrates a schematic diagram 900 of the pre-tapered multi -hole capillary 202, in accordance with an embodiment of the present disclosure. In a nonlimiting example, the pre-tapered multi-hole capillary 202 of the FIFO device for the four core MCF 1204 may have an outer diameter of 780 microns and the capillary may be pre-tapered to taper ratio 3.12. The inner hole diameter of the pretapered multi-hole capillary 202 may be 40 microns after the pre-tapering process.

[0082] FIG. 10 illustrates a schematic diagram 1000 of a 40-micron etched SMF with taper profile for inserting into the pre-tapered multi-hole capillary 202, in accordance with an embodiment of the present disclosure. The SMF may be precisely etched using a chemical etching method with explicit control over an etchant concertation and temperature. A tapered etched profile may be incorporated in order to keep the strength of the fiber while transitioning from 125 microns to 40 microns and to match the taper profile of the pre-tapered capillary. In a non-limiting example, an accuracy of etched diameter of the 40-micron SMF fiber profile may be 0.25 micron.

[0083] FIG. 11 illustrates a schematic diagram 1100 of a tapered version of an etched SMF bundle 408 inserted inside the pre-tapered multi-hole capillary 202, in accordance with an embodiment of the present disclosure. The one or more SMFs may be to the predefined diameter to match the hole diameter of the one or more holes 204 in the tapered section of the multi-hole capillary 202. In a non-limiting example, the pre-tapered capillary 202 along with the precisely etched SMF 408 may be tapered to ratio 2 such that the outer diameter of the tapered capillary 202 may match a clad diameter of the four core MCF 1204. The core positions of the etched SMF 408 may match the relative core positions of the four core MCF 1204. The tapered etched SMF bundle 408 may offer significant advantages over tapered normal SMF bundle by reducing the taper ratio necessary to reach the core pitch of the four core MCF 1204. The tapered etched SMF bundle 408 may decrease the MFD mismatch between the tapered etched SMF bundle 408 and the four core MCF 1204.

[0084] FIG. 12 illustrates a schematic diagram 1200 an exemplary FIFO device, in accordance with an embodiment of the present disclosure. The tapered etched SMF bundle 408 may be cleaved and spliced to the four core MCF 1204 by precisely aligning the respective cores of the tapered etched SMF bundle 408 and the four core MCF 1204 to make the FIFO device. The MCF 1204 may be spliced at a splicing point 1202 to the tapered version of the etched SMF bundle 408. The FIFO device may be suitably packaged to make the device environmentally robust.

[0085] In some aspects of the present disclosure, various simulation-based analysis may be performed to analyze insertion loss and the crosstalk. An optimal value of the pre-taper ratio and the fiber-etched diameters may be defined based on the simulation results of the insertion loss and the crosstalk. The analysis may consider mode coupling between a mode field at a taper length and an individual core of the MCF 1204 at the splice point 1202. The analysis may assume that the tapered fiber and the individual core of the MCF 1204 may align perfectly along their longitudinal and transverse axes. At the splice point 1202, the analysis may investigate the effects of different taper ratios on the interaction between a tapered standard SMF and a single core of the MCF.

[0086] FIG. 13 illustrates a block diagram 1300 of crosstalk measurement of the SMFs in Fan-in mode based on free space coupling scheme, in accordance with an embodiment of the present disclosure. The crosstalk may be considered as one of the key performance parameters of the FIFO device. The crosstalk of the FIFO device may include the crosstalk of a coupler device attached to the MCF 1204, due to which the actual crosstalk of the FIFO device may vary. To experimentally verify and measure the crosstalk of the FIFO device alone, the free space coupling scheme may be crafted. The free space coupling scheme may measure the crosstalk between ports of the FIFO device without connecting the FIFO device to the MCF 1204.

[0087] In some embodiments, the crosstalk may be measured in the Fan-in mode. In the Fan-in mode, the SMFs may be inserted inside one end of the multi -hole capillary 202 and may be cleaved at the other end of the multi-hole capillary 202. The crosstalk may be measured at the cleave end of the SMFs by measuring output power. A laser source (not shown) may be coupled to the core of SMFs and the cleaved end of the SMFs may be coupled to a suitable microscope objective 1302 to maximize the output power.

[0088] In some aspects of the present disclosure, the crosstalk in the Fan-in mode based on the free space coupling scheme may be measured using four steps.

[0089] At step 1, a light from the laser source may be coupled into a fiber core of a first SMF among a plurality of SMFs of the Fan-in (input side of the FIFO device). The output received from the core may be maximized at the cleaved end using the microscope objective 1302, for instance, 10 times the output. The output may be a power level of the fiber core at the cleaved end.

[0090] The output power at the cleaved end of the core of the first SMF may be measured. In a non-limiting example, an optical power meter may be coupled at the end of the microscope objective 1302 to measure the output power.

[0091] At step 2, the laser source may be coupled into cores of one of remaining SMFs among the plurality of SMFs. The output power at cleaved ends of the cores of the one of remaining SMFs may be measured. In a non-limiting example, the multi -hole capillary 202 may comprise four SMFs. The same laser source may be launched into a fiber core of a second SMF. The step 1 may be repeated without disturbing the setup to obtain the maximized output.

[0092] At step 3, the step 2 may be repeated for fiber cores of a third SMF and a fourth SMF. The crosstalk may be measured as ratio of the output power at the core of the first SMF to the output powers at the core of the one of remaining SMFs

[0093] At step 4, the crosstalk may be measured as a ratio of power levels measured in step 1 to power levels measured in steps 2 and 3.

[0094] FIG. 14 illustrates graphs 1400 depicting simulation results of variation in insertion loss with taper ratio for different core radius, in accordance with an embodiment of the present disclosure. In the graphs 1400, value of a Numerical Aperture (NA) is taken as 0.14, with the core radii of the SMF at 4.1 pm and 4.5 pm. The etched SMF 408 undergoes an adiabatic tapering process across different taper ratios before coupling to the individual core of the MCF 1204. The individual core of the MCF 1204 may be identical to the standard SMF and core radius of the individual core of the MCF 1204 may assumed to be 4.1 pm. As illustrated in FIG. 14, the insertion loss increases with an increase in the taper ratio.

[0095] FIG. 15 illustrates a graph 1500 depicting the simulation results of variation in the insertion loss with the taper ratio as well as the vertical shift in the core position, in accordance with an embodiment of the present disclosure. The graph 1500 depicts the insertion loss effects of the vertical shifts at the splice point between the adiabatically tapered fiber and the individual core of the MCF 1204. It is inferred from the graph of the variation of the insertion loss that a 1 pm transverse shift across different taper ratios may result in an insertion loss of about 0.1 dB. The above analysis may be utilized to obtain a taper ratio for an optimum design for minimizing the insertion loss. For example, the taper ratio 2 may be use for the optimum design.

[0096] FIG. 16 illustrates graphs 1600 depicting the simulation results of variation in crosstalk with different core pitch at taper ratio 2 for different values of Numerical Aperture (NA), in accordance with an embodiment of the present disclosure. The graphs 1600 depicts a crosstalk behaviour at a taper ratio of 2 at the splice point. As shown in the graphs 1600, a taper ratio of 2 may be an optimum best design choice to ensure that the crosstalk remains below a critical threshold of 20 dB at the core pitch 40pm.

[0097] In an exemplary embodiment, at the taper end face before splicing with MCF, an insertion loss for each port of the SMF was measured at 1550 nm. Table 1 summarizes the Insertion loss of the fabricated FIFO device (unit. dB). After the manual angular alignment in the glass processing unit, the taper end face was subsequently spliced to a 1 -meter length of 4-core MCF using the glass processing unit. The Insertion loss for each part summarized in Table 1.Table 1 : Insertion loss of the fabricated device

[0098] Table 2 illustrates Crosstalk (XT) measurements for the fabricated FIFO device with the with 1 meter long 4-core MCF.Table 2: Crosstalk (XT) measurements

[0099] Referring to the technical abilities and advantageous effect of the present disclosure, operational advantages that may be provided by above disclosed system and method may include utilization of the specially structured capillary to improve the repeatability in fabrication process of the FIFO device and to improve the intercore crosstalk. The present disclosure may use the etched SMF in combination with the specially structured (multi-hole) capillary for better mode field control during the tapering process to match the SMF closely with the MCF, thereby improving the loss performance of the device. The present disclosure may couple light from the tapered bundle of SMF to the MCF either through splicing or direct coupling for transmission with low loss and lower inter-core coupling.

[0100] Those skilled in the art will appreciate that the methodology described herein in the present disclosure may be carried out in other specific ways than those set forth herein in the above disclosed embodiments without departing from essential characteristics and features of the present invention. The above-described embodiments are therefore to be construed in all aspects as illustrative and not restrictive.

[0101] The drawings and the forgoing description give examples of embodiments. Those skilled in the art will appreciate that one or more of the described elements may well be combined into a single functional element. Alternatively, certain elements may be split into multiple functional elements. Elements from one embodiment may be added to another embodiment. For example, orders of processes described herein may be changed and are not limited to the manner described herein. Any combination of the above features and functionalities may be used in accordance with one or more embodiments.

[0102] In the present disclosure, each of the embodiments has been described with reference to numerous specific details which may vary from embodiment to embodiment. The foregoing description of the specific embodiments disclosed herein may reveal the general nature of the embodiments herein that others may, 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 are intended to be comprehended within the meaning of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and is not limited in scope.

Claims

1. I / We Claim:

1. A method (100) of optically coupling light radiation from one or more Single Mode Fibers (SMFs) into a Multi Core Fiber (MCF), the method (100) comprising: pre-tapering (102) a multi-hole capillary (202) having one or more holes (204) to a predefined taper ratio; etching (104) the one or more SMFs to a predefined diameter to match a hole diameter of the one or more holes (204) in a tapered section of the multi-hole capillary (202); inserting (106) the one or more etched SMFs (408) into the one or more holes (204) of the pre-tapered multi-hole capillary (202); tapering (108) the pre-tapered multi-hole capillary (202) along with the one or more inserted SMFs to form a tapered-etched SMF bundle; aligning (110) the tapered-etched SMF bundle to one or more cores of the MCF (1204) to match core positions of the tapered-etched SMF bundle and the MCF (1204); and splicing (112) the tapered-etched SMF bundle to the one or more cores of the MCF (1204) to achieve optimum coupling of light from the tapered-etched SMF bundle into the MCF (1204).

2. The method (100) as claimed in claim 1, wherein the one or more SMFs are trench-assisted optical fibers for limiting mode field diameter of the light guided through the one or more SMFs.

3. The method (100) as claimed in claim 1, wherein the multi -hole capillary (202) is a monolithic multi-hole capillary (202) and the one or more holes (204) of the multi-hole capillary (202) have equal diameter.

4. The method (100) as claimed in claim 1, wherein the pre-tapered multi-hole capillary (202) along with the one or more inserted SMFs is tapered to match anouter diameter of the pre-tapered multi-hole capillary (202) with a clad diameter of the MCF (1204).

5. The method (100) as claimed in claim 1, wherein the multi -hole capillary (202) and cladding of each of the one or more SMFs have same refractive index.

6. The method as claimed in claim 1, further comprising: measuring crosstalk in the SMFs by performing one or more steps: coupling a laser source into a core of a first SMF among a plurality of SMFs; measuring an output power at a cleaved end of the core of the first SMF; coupling the laser source into a core of one of remaining SMFs among the plurality of SMFs; measuring the output power at a cleaved end of the core of the one of remaining SMFs; and measuring crosstalk as ratio of the output power at the core of the first SMF to the output power at the core of the one of remaining SMFs.

7. The method as claimed in claim 6, wherein the cleaved end of the core of the first SMF is coupled to a microscope objective to maximize the output power.

8. A capillary insertion system (400) comprising: a capillary holder (402) mounted on a four-axis alignment stage, wherein the capillary holder (402) is designed to hold a multi-hole capillary (202); a multi fiber holder (404) mounted on a two-axis alignment stage, wherein the multi fiber holder (404) is designed to hold one or more etched Single Mode Fibers (SMFs); and an imaging system (406) mounted on two different axes, wherein the imaging system (406) is used to view and align the one or more etched SMFs (408)inside the multi-hole capillary (202) based on an angular rotational alignment using the capillary holder (402).

9. The system as claimed in claim 8, wherein the multi-fiber holder has a predefined groove width for holding the one or more etched SMF s (408) in a specific geometry.

10. The system as claimed in claim 8, wherein the multi -hole capillary (202) is pre-tapered to a predefined taper ratio and the multi-hole capillary (202) has one or more holes (204) with equal diameter.

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