Polarization-maintaining highly elliptical core fiber with stress-induced birefringence

Abstract

An optical fiber comprises a core with an elliptical cross section and a cladding with a circular cross section. The ellipticity of the core is between 2 and 40. The core and the cladding have a common central axis, wherein the core is enclosed by the cladding. The difference between the refractive index of the cladding and the refractive index of the core is within 1×10 –2 With 1.5×10 –1 The groove is located between the core and the cladding. The groove has a uniform width and surrounds the core. The refractive index of the groove is lower than the refractive index of the cladding.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to U.S. patent application serial number 16 / 943,713, filed on July 30, 2020, entitled “POLARIZATION-MAINTAINING HIGHLY ELLIPTICAL CORE FIBER WITH STRESS-INDUCED BIREFRINGENCE,” and U.S. patent application serial number 62 / 880,928, filed on July 31, 2019, entitled “POLARIZATION-MAINTAINING HIGHLY ELLIPTICAL CORE FIBER WITH STRESS-INDUCED BIREFRINGENCE,” both of which are incorporated herein by reference in their entirety. Technical Field

[0003] The invention relates to the field of optical fiber communication, and in particular to an elliptical core optical fiber. Background Art

[0004] The demand for network traffic and cloud computing places high demands on the current optical communication infrastructure. In particular, short-distance interconnections, such as those in data centers, require high-bandwidth links. Mode division multiplexing (MDM) over few-mode fiber (FMF) is a promising approach to meet these data traffic demands. In MDM systems, crosstalk between spatial modes is one of the most detrimental factors to signal quality.

[0005] In current MDM systems, compensating for channel crosstalk and receiving information data at the receiver side usually requires multiple-input multiple-output (MIMO) digital signal processing (DSP). One disadvantage of this full MIMO approach is its complexity. Although the complexity can be reduced to some extent by minimizing the differential modal group delay, this approach still consumes a lot of computing resources and power.

[0006] In order to reduce the complexity of DSP, various design strategies for FMF have been proposed. One approach is to increase the effective refractive index difference δn between spatial modes. eff , to reduce the complexity of the MIMO-DSP component.

[0007] Although partial MIMO-DSP approaches can reduce system complexity, a MIMO-free design is still desirable. To achieve this goal, some schemes have proposed polarization-maintaining (PM) FMF designs, in which the polarization degeneracy of spatial modes is reduced by using elliptical ring-core fiber (ERCF), PANDA ring-core fiber, or ERCF with internal air holes. These fiber designs aim to increase the effective refractive index difference between adjacent vector modes. However, the disadvantage of these schemes is that the number of modes is limited.

[0008]

[0006] Therefore, there is a need for optical fibers that do not suffer from one or more of the limitations of the prior art.

[0009] This background information is provided to reveal information believed by the applicant to be potentially relevant to the present invention. It is not necessarily intended, nor should it be construed, that any of the foregoing information constitutes prior art against the present invention. Summary of the invention

[0010] It is an object of embodiments of the present invention to provide an improved optical fiber for use in an MDM communication system.

[0011] One aspect of the present invention includes an optical fiber including a core having an elliptical cross-section and an ellipticity between 2 and 40. The optical fiber also includes a cladding having a circular cross-section, wherein the cladding encloses the core.

[0012] One aspect of the invention includes said core and said cladding having a common central axis.

[0013] One aspect of the present invention includes an optical fiber, wherein the difference between the refractive index of the cladding and the refractive index of the core is within 1×10 –2 With 1.5×10 –1 between.

[0014] One aspect of the present invention includes an optical fiber, wherein the ratio of the refractive index of the cladding to the refractive index of the core is within 1×10 –2 With 1.5×10 –1 between.

[0015] One aspect of the present invention includes an optical fiber, the optical fiber including a trench between the core and the cladding, the trench having a uniform width and surrounding the core, and a refractive index of the trench being lower than the refractive index of the cladding.

[0016] One aspect of the invention includes an optical fiber wherein the width of the core along the y-axis supports single-mode transmission.

[0017] One aspect of the invention includes an optical fiber wherein the width of the core along the x-axis supports transmission of multiple mode pairs.

[0018] One aspect of the invention includes an optical fiber wherein each mode pair of the plurality of mode pairs has two orthogonal linear polarizations.

[0019] One aspect of the present invention includes an optical fiber wherein the plurality of mode pairs have a relative spacing greater than 1×10 –4 The effective refractive index separation.

[0020] One aspect of the invention includes an optical fiber wherein the effective refractive index separation is caused by thermal stress induced during the manufacturing process of the optical fiber and the elliptical shape of the core.

[0021] One aspect of the present invention includes an optical fiber wherein the core is doped with rare earth ions.

[0022] One aspect of the present invention includes an optical fiber amplifier (OFA), which includes a first WDM coupler that receives an input signal and an output from a first pump light source. An optical fiber receives the output from the first WDM coupler. The optical fiber includes a core having an elliptical cross-section with an ellipticity between 2 and 40. The optical fiber also includes a cladding having a circular cross-section that encapsulates the core. The OFA also includes a second WDM coupler that receives the output of the optical fiber and the output of a second pump light source. The second WDM coupler outputs an amplified optical signal.

[0023] One aspect of the invention includes an OFA wherein the core and the cladding have a common central axis.

[0024] One aspect of the present invention includes an OFA wherein the core is doped with rare earth ions.

[0025] One aspect of the present invention includes an OFA, wherein the optical fiber includes a trench between the core and the cladding. The trench has a uniform width and surrounds the core. The refractive index of the trench is lower than the refractive index of the cladding.

[0026] One aspect of the present invention includes an OFA wherein the width of the core along the y-axis supports single mode transmission and the width of the core along the x-axis supports transmission of multiple mode pairs.

[0027] One aspect of the present invention includes a method for manufacturing an optical fiber. The method includes preparing a cylindrical preform having a cross-section including an inner core and an outer cladding. The inner core has a circular profile. Two opposing sides of the cylindrical preform are cut along the length of the cylindrical preform to produce the cut preform having relatively parallel surfaces along the longitudinal axis of the cut preform. The cut preform is heated until the cut preform has a circular profile and the inner core of the cut preform has an elliptical profile. The cut preform is stretched to form the optical fiber, which includes a core having an elliptical profile. The core has an ellipticity between 2 and 40, and the cladding has a circular cross-section, wherein the core is enclosed by the cladding.

[0028] One aspect of the present invention includes: the core and the cladding have a common central axis.

[0029] One aspect of the present invention includes a trench portion located between the core and the cladding. The trench portion exists in the optical fiber and separates the core from the cladding.

[0030] One aspect of the present invention includes a cylindrical preform that is manufactured using a modified chemical vapor deposition (MCVD) process.

[0031] In another aspect of the present invention, the preform further comprises a groove portion between the core and the cladding. The groove portion exists in the optical fiber and separates the core from the cladding.

[0032] In another aspect of the invention, the elliptical profile is formed due to surface tension and material flow during heating.

[0033] Embodiments are described above in conjunction with various aspects of the present invention, and these embodiments can be implemented based on these aspects. It will be appreciated by those skilled in the art that embodiments can be implemented in conjunction with the aspects describing these embodiments, but can also be implemented together with other embodiments of this aspect. When the embodiments are mutually exclusive or incompatible with each other, it will be apparent to those skilled in the art. Some embodiments can be described in conjunction with an aspect, but can also be applied to other aspects, which will be apparent to those skilled in the art. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Further features and advantages of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:

[0035] Figure 1A cross-sectional view of an optical fiber provided by one embodiment is shown;

[0036] Figure 2 shows a refractive index profile along the x-axis of an optical fiber provided by one embodiment;

[0037] Figure 3 shows a cross-sectional view of an optical fiber and the compressive thermal stress induced into the core along the normal direction of the core / cladding boundary during the fiber drawing process;

[0038] Figure 4 shows a cross-sectional view of an optical fiber provided by another embodiment;

[0039] Figure 5 shows a refractive index profile along the x-axis of an optical fiber provided by one embodiment;

[0040] Figure 6 An optical communication system combining WDM and MDM is shown;

[0041] Figure 7 The invention shows the mode multiplexing of data on optical fiber provided by one embodiment;

[0042] Figure 8 The present invention shows the mode demultiplexing of data on optical fiber provided by one embodiment;

[0043] Fig. 9 An optical fiber amplifier using an optical fiber provided by one embodiment is shown;

[0044] Fig.10 An optical fiber sensing device using an optical fiber provided by an embodiment is shown;

[0045] Fig.11 An MDM transmitter using optical fiber provided by one embodiment is shown;

[0046] Fig.12 An MDM receiver using optical fiber provided by one embodiment is shown;

[0047] Fig.13 An MDM transceiver using optical fiber provided by one embodiment is shown;

[0048] Fig.14 A method for manufacturing a HECF provided by an embodiment is shown;

[0049] Fig.15 The present invention is a flowchart of a method for manufacturing a HECF provided by an embodiment.

[0050] It should be noted that throughout the drawings, like features are identified by like reference numerals. DETAILED DESCRIPTION

[0051] Embodiments of the present invention include a polarization-maintaining highly elliptical core fiber (HECF). By combining a highly elliptical core shape and thermal stress induced during the fiber manufacturing process, the birefringence value is increased to greater than 1×10 –4 , which reduces mode coupling and makes the fiber suitable for MIMO-free MDM transmission systems.

[0052] Figure 1 A cross-sectional view of a highly elliptical core fiber (HECF) 100 provided by a first embodiment of the present invention is shown. The fiber includes a cladding 102, which is generally an industry standard and has a diameter of 125 μm. The center of the fiber is a solid core 104 surrounded by a groove 106. Although Figure 1 Not shown, but in most embodiments, the cladding is also surrounded by a buffer layer, which in turn is covered by a sheath as is known in the art.

[0053] The cross-sectional profile of the core 104 is elliptical. The cross-section of the core 104 has an x-axis 110 and a y-axis 108. In one embodiment, the approximate cross-sectional dimensions of the core 104 are: 38.5 μm 202 along the x-axis 110 and 6.1 μm along the y-axis 108. The dimension along the short y-axis 108 is selected to support single-mode operation, for TE m,n / TM m,n mode, n=1. The size of the x-axis 110 is selected to support multiple spatial modes distributed in a one-dimensional array in the x-axis 110. In other embodiments, the ellipticity η of the core is defined as the ratio of the cross-sectional length in the x-direction to the cross-sectional length in the y-direction, between 2 and 40. Those skilled in the art will understand that the x-axis 110 can also be referred to as the major axis of the elliptical core, and the y-axis 108 can be referred to as the minor axis of the elliptical core. Rotation of the optical fiber so that the main axis is no longer horizontal should not be considered to change the alignment of the x-axis and the y-axis. Those skilled in the art will also understand that the ellipticity η can also be considered as the ratio of the width of the core along the x-axis 110 to the width of the core along the y-axis 108.

[0054] The core 104 can be considered as an elliptical cylinder such that the length of the x-axis 110 is greater than the length of the y-axis, and thus, the x-axis 110 forms the major axis of the ellipse and the y-axis 108 forms the minor axis of the ellipse. The x-axis 110 and the y-axis 108 intersect at right angles, and the intersection of the x-axis 110 and the y-axis 108 defines the center of the elliptical cross section. The core 104 is shaped as an elliptical cylinder, and its central axis, also referred to as the longitudinal axis, passes through the center of each elliptical cross section of the core 104. The cladding 102 can be considered to have a circular cross section with a center, and has a cylindrical shape, and its central axis passes through the center of each circular cross section of the cladding 102. The core 104 and the cladding 102 have a common central axis, such that the core 104 is located at the center within the cladding 102. Therefore, the HECF is formed such that the cladding 102 and the core 104 share a common central axis.

[0055] The optical fiber is made of a silica glass material mainly composed of SiO2, and the cladding 102 is composed of a substantially pure silica glass material. The core 104 is made by doping the SiO2 material with GeO2. In some embodiments, the core 104 is composed of SiO2 doped with 7.3 mol% GeO2.

[0056] The trench 106 surrounds the core 104 and is approximately 4.7 μm wide 206 in some embodiments. The trench is made of SiO2 doped with fluorine (F). In some embodiments, the trench is doped with 2 mol% F. The bending losses experienced by HECFs increase with increasing ellipticity, but the trench is used to reduce the bending losses of higher order modes in the fiber.

[0057] Figure 2 The refractive index profile of the optical fiber 100 along the x-axis 110 is shown. The core 104, the trench 106, and the cladding 102 have different refractive indices determined by their respective materials. In one embodiment, the difference in refractive index Δn 204 between the core 104 and the cladding 102 is approximately 1.1×10 –2 In an embodiment, the refractive index difference between the core 104 and the cladding 102 is 1×10 –2 ≤Δn≤1.5×10 –1 In one embodiment, the refractive index difference between the trench 106 and the cladding 102 is -Δn trench 208 is approximately 5.7×10 –3 .

[0058] The geometry of the highly elliptical core leads to geometrically enhanced birefringence in the optical fiber. The source of this birefringence is related to the core geometry, where the higher the core ellipticity, the greater the birefringence value.

[0059] refer to Figure 3During the manufacturing process of the optical fiber, a non-constant compressive thermal stress 302 is induced into the core 104 mainly along the y-axis 108 direction. During the fiber drawing and annealing process, the fiber becomes stressed due to the different thermal expansion coefficients of the core 104 and the cladding 102. Due to the asymmetric core structure of the optical fiber, different amounts of stress are applied along the major x-axis 110 and the minor y-axis 108. As this stress increases, the isotropic glass begins to become anisotropic and subsequently the refractive index changes along the principal x and y stress directions. Thermal stress has the effect of increasing the effective refractive index difference (δn) between the two polarizations of the same spatial mode. eff )’s role.

[0060] The optical fiber provided by the embodiment of the present invention can transmit data on five spatial mode groups with dual polarization degeneracy to obtain 10 MDM channels. The supported modes are marked as TE 1n and TM 1n , depending on the polarization state (along the x-axis or y-axis, respectively). Specifically, the subscript "1" indicates single-mode operation along the minor axis (y-axis), while "n" is an integer representing the number of dark lines of the mode distribution along the major axis (x-axis).

[0061] The elliptical shape of the core combined with the thermal stresses induced during the manufacturing process produces a relatively large birefringence, resulting in a mode effective refractive index separation of δn eff Greater than 1×10 –4 This reduces mode coupling inside the HECF, allowing fiber modes to propagate without significant crosstalk, up to fiber lengths of approximately 1 km. This supports the design of transmission systems that do not require a MIMO DSP.

[0062] In some embodiments, the core may be doped with rare earth ions (eg, erbium and / or ytterbium) to produce an optically active optical fiber.

[0063] Figure 4 Another embodiment of the present invention provides an optical fiber 400 having an alternative structure. Figure 1 Compared to the embodiment depicted in FIG. 1 , this embodiment includes a cladding 102 and a core 104, but lacks a trench 106 between the core and the cladding. The trench 106 helps reduce bending losses of higher-order modes in the optical fiber. However, in some embodiments, the bending losses can also be reduced by increasing the refractive index difference 204Δn to about 1.5×10 –1 to reduce.

[0064] Figure 5 The refractive index profile of the optical fiber 400 along the x-axis 110 is shown. The core 104 and the cladding 102 have different refractive indices determined by their respective materials. In one embodiment, the difference in refractive index Δn204 between the core 104 and the cladding 102 is approximately 1.1×10 –2 .

[0065] Figure 6 A system incorporating an embodiment of the present invention is shown. The present invention can be used for a non-MIMO mode division multiplexing system. The output of a WDM transmitter 602 is input to a WDM coupler 604 and multiplexed into a single output optical fiber. Then, each output of the WDM coupler 604 is multiplexed by a mode multiplexer 606 and converted to a corresponding mode in a HECF 608. After transmission through the HECF 608, the optical fiber mode is received and separated by a mode demultiplexer 610 and subsequent multiple WDM couplers 612 to separate wavelength channels and ultimately detected by a receiver 614. Since the crosstalk between the modes within the optical fiber is low, a MIMO-DSP is not required.

[0066] Figure 7 An embodiment of a mode division multiplexer using HECF 702 is shown. Different Modes TE 11 TE 12 ……TE 1n The optical input can be multiplexed onto HECF 702 using fused fiber mode coupler 704.

[0067] Figure 8 An embodiment of a mode demultiplexer using HECF 802 is shown. A fused fiber mode coupler 804 delivers light of a predetermined mode to an output fiber 806 for receiving light from a TE 11 TE 12 ……TE 1n signal.

[0068] Fig. 9 An optical fiber amplifier (OFA) 900 including a HECF 902 is shown in one embodiment. The HECF 902 has a core doped with rare earth ions (e.g., erbium) and is connected to two WDM couplers 904. Each WDM coupler receives the output of a pump diode 908. The optical power of the input 906 is amplified by the OFA and output on an optical fiber 910.

[0069] Fig.10 A sensing system 1000 is shown in another embodiment. HECF 1002 passes through a sensing element 1004. A signal source and a data acquisition module are co-located in a device 1006. In some embodiments, the sensing element 1004 is a fiber Bragg grating (FBG). When light from an optical signal source 1006 passes through the sensing element 1004, light of a predetermined fiber mode is reflected back to the source and received by the data acquisition module 1006.

[0070] Fig.11An optical transmitter 1100 with an integrated mode division multiplexing module is shown. The transmitter is typically contained in a housing, enabling it to be easily integrated into optical transmission equipment. The transmitter 1100 can be packaged separately or integrated with a receiver to form a transceiver. In some embodiments, the light source 1102 can be a diode or a laser, outputting at a continuous wavelength or mode. Data is applied to the light source 1102 by a modulator 1104, and then the data is multiplexed with other modulated light sources to be transmitted on the HECF 1108. In some embodiments, the light source and modulator can be integrated together.

[0071] Fig.12 An optical receiver 1200 with an integrated mode division multiplexing module is shown. The receiver is typically contained in a housing, enabling it to be easily integrated into optical transmission equipment. The receiver 1100 can be packaged separately or integrated with the transmitter 1100 to form a transceiver. The mode multiplexed data is received from the HECF 1108 and divided into modes in the mode demultiplexer 1206. The light of each mode is then received by the optical detector 1202, which can be a PIN diode or APD.

[0072] Fig.13 An optical transceiver 1300 with an integrated mode division multiplexer / demultiplexer module is shown. The transceiver is typically contained in a housing, enabling it to be easily integrated into optical transmission equipment. The transceiver 1300 combines the functions of a transmitter 1100 and a receiver 1200. In some embodiments, the light source 1102 may be a diode or a laser, outputting at a continuous wavelength or mode. Data is applied to the light source 1102 by a modulator 1104, which is passed through a circulator 1312 and then multiplexed with other modulated light sources to be transmitted on the HECF 1108. In some embodiments, the light source and the modulator may be integrated together. The received light passes through the mode MUX / DeMUX 1310 and enters the circulator 1312, which sends the demultiplexed received light to a light detector 1202 to receive the data, which may be a PIN diode or an APD.

[0073] like Fig.14As shown, HECF 1400 can be manufactured using a preform that is manufactured using a modified chemical vapor deposition (MCVD) process. The preform has a cylindrical shape and includes a coaxial inner core 104 and an outer cladding 102. The inner core 104 has a circular cross-section. Opposite longitudinal sides 1402, 1404 are cut from the preform to produce two opposite flat, parallel sides 1406, 1408. The cut preform is then heated so that the flat surface disappears due to surface tension and material flow. Therefore, the circular core 104 becomes elliptical during the heating process. The cut preform with an elliptical core is stretched to form an optical fiber. The resulting optical fiber includes a core 104 and a cladding 102, wherein the core 104 has an elliptical cross-section with an ellipticity between 2 and 40, and the cladding 102 has a circular cross-section. The core 104 and the cladding 102 have a common central axis, and the core 104 is enclosed by the cladding 102. Since the preform is manufactured by MCVD, it can include a groove 106 surrounding the core.

[0074] Those skilled in the art will appreciate that multiple cuts may be made that are not necessarily aligned with one another (eg, do not produce longitudinal sides) but that as a whole produce the above-described elliptical core after heat-induced reshaping.

[0075] Fig.15 It is shown as Fig.14 Flow chart of a method 1500 for manufacturing a HECF shown in FIG. 1. In step 1502, a cylindrical preform having an inner core 104 and an outer cladding 102 is formed. The inner core 104 has a circular cross-sectional profile. The cylindrical preform can be formed using an MCVD process. In step 1504, two opposing sides 1402, 1404 of the cylindrical preform are cut along the length of the cylindrical preform to produce a cut preform having relatively parallel surfaces 1406, 1408 along the longitudinal axis of the cylindrical preform. In various embodiments, the cut preform is cut in a manner to avoid cutting the inner core 104. In step 1506, the cut preform is heated. The surface tension of the outer surface of the cut preform is subjected to softening caused by heating, causing the cut preform to deform until the outer part of the preform becomes circular again. The surface tension causes the entire preform to deform, so that when the cut preform has an outer circular profile, the inner core 104 has been deformed and an elliptical profile of the core 104 is produced. As described above, the ellipticity of such a generally elliptical core is between 2 and 40. The outer cladding has a generally circular cross-section after encapsulating (or surrounding) the elliptical core. In step 1508, the cut and heated preform is stretched to form an optical fiber. In some embodiments, the core 104 and the cladding 102 are generally coaxial, having a common central axis.

[0076] One aspect of the present invention includes an optical fiber including a core having an elliptical cross-section and an ellipticity between 2 and 40. The optical fiber also includes a cladding having a circular cross-section enclosing the core.

[0077] One aspect of the present invention includes: the core and the cladding have a common central axis.

[0078] One aspect of the present invention includes an optical fiber, wherein the difference between the refractive index of the cladding and the refractive index of the core is within 1×10 –2 With 1.5×10 –1 between.

[0079] One aspect of the present invention includes an optical fiber, wherein the ratio of the refractive index of the cladding to the refractive index of the core is within 1×10 –2 With 1.5×10 –1 between.

[0080] One aspect of the present invention includes an optical fiber, the optical fiber including a trench between the core and the cladding, the trench having a uniform width and surrounding the core, and a refractive index of the trench being lower than the refractive index of the cladding.

[0081] One aspect of the invention includes an optical fiber wherein the width of the core along the y-axis supports single-mode transmission.

[0082] One aspect of the invention includes an optical fiber wherein the width of the core along the x-axis supports transmission of multiple mode pairs.

[0083] One aspect of the invention includes an optical fiber wherein each mode pair of the plurality of mode pairs has two orthogonal linear polarizations.

[0084] One aspect of the present invention includes an optical fiber wherein the plurality of mode pairs have a relative spacing greater than 1×10 –4 The effective refractive index separation.

[0085] One aspect of the invention includes an optical fiber wherein the effective refractive index separation is caused by thermal stress induced during the manufacturing process of the optical fiber and the elliptical shape of the core.

[0086] One aspect of the present invention includes an optical fiber wherein the core is doped with rare earth ions.

[0087] One aspect of the present invention includes an optical fiber amplifier (OFA), which includes a first WDM coupler that receives an input signal and an output from a first pump light source. An optical fiber receives the output from the first WDM coupler. The optical fiber includes a core having an elliptical cross-section with an ellipticity between 2 and 40. The optical fiber also includes a cladding having a circular cross-section that encapsulates the core. The OFA also includes a second WDM coupler that receives the output of the optical fiber and the output of a second pump light source. The second WDM coupler outputs an amplified optical signal.

[0088] One aspect of the invention includes an OFA wherein the core and the cladding have a common central axis.

[0089] One aspect of the present invention includes an OFA wherein the core is doped with rare earth ions.

[0090] One aspect of the present invention includes an OFA, wherein the optical fiber includes a trench between the core and the cladding. The trench has a uniform width and surrounds the core. The refractive index of the trench is lower than the refractive index of the cladding.

[0091] One aspect of the present invention includes an OFA wherein the width of the core along the y-axis supports single mode transmission and the width of the core along the x-axis supports transmission of multiple mode pairs.

[0092] One aspect of the present invention includes an optical sensor for detecting light transmission of light patterns. The optical sensor includes a plurality of sensing elements arranged along an optical fiber. The optical fiber includes a core having an elliptical cross-section and an ellipticity between 2 and 40. The optical fiber includes a cladding having a circular cross-section. The core is enclosed by the cladding. The optical fiber receives an input signal including a plurality of vector patterns. Each sensing element of the plurality of sensing elements reflects one of the plurality of vector patterns. A data acquisition module receives one of the plurality of vector patterns reflected by one of the plurality of sensing elements. In some embodiments, the core and the cladding have a common central axis.

[0093] One aspect of the present invention includes an optical transmitter module. The module includes a plurality of light sources. Each of the plurality of light sources outputs a constant optical signal in one of a plurality of vector modes. A plurality of optical modulators receive one of the constant optical signals and output a modulated optical signal. A mode multiplexer receives each modulated optical signal to generate a mode multiplexed optical output. An optical fiber receives the mode multiplexed optical output. The optical fiber includes a core having an elliptical cross-section with an ellipticity between 2 and 40. The optical fiber also includes a cladding having a circular cross-section, wherein the core is enclosed by the cladding. In some embodiments, the core and the cladding have a common central axis.

[0094] One aspect of the present invention includes an optical receiver module, which includes an optical fiber. The optical fiber receives a mode-multiplexed optical signal. The optical fiber includes a core, and the core has an elliptical cross-section with an ellipticity between 2 and 40. The optical fiber also includes a cladding. The core is encapsulated by the cladding. The optical receiver module also includes a mode demultiplexer, which receives the mode-multiplexed optical signal from the optical fiber and outputs a plurality of modulated optical signals. Each of the plurality of modulated optical signals includes light in one of a plurality of vector modes. A plurality of optical detectors each receives a modulated optical signal in the plurality of modulated optical signals. In some embodiments, the core and the cladding have a common central axis.

[0095] One aspect of the present invention includes an optical transceiver, which includes a transmission path and a receiving path. The transmission path includes a plurality of light sources, which output a constant optical signal in one of a plurality of vector modes. A plurality of optical modulators receive one of the constant optical signals and output a modulated optical signal. A plurality of circulators receive one of the modulated optical signals and output one of the modulated optical signals. A mode multiplexer receives each modulated optical signal from the plurality of circulators to generate a mode multiplexed optical output. An optical fiber receives the mode multiplexed optical output. The optical fiber includes a core having an elliptical cross-section and an ellipticity between 2 and 40. The optical fiber also includes a cladding having a circular cross-section, wherein the core is encapsulated by the cladding. In some embodiments, the core and the cladding have a common central axis.

[0096] The receiving path includes a mode demultiplexer that receives a mode-multiplexed optical signal from an optical fiber and outputs a plurality of received modulated optical signals. Each of the plurality of received modulated optical signals includes light in one of a plurality of vector modes. Each of the plurality of optical detectors receives one of the plurality of received modulated optical signals through a plurality of circulators.

[0097] One aspect of the present invention includes a method for manufacturing an optical fiber. The method includes preparing a cylindrical preform having a cross-section including an inner core and an outer cladding. The inner core has a circular profile. Two opposing sides of the cylindrical preform are cut along the length of the cylindrical preform to produce the cut preform having relatively parallel surfaces along the longitudinal axis of the cut preform. The cut preform is heated until the cut preform has a circular profile and the inner core of the cut preform has an elliptical profile. The cut preform is stretched to form the optical fiber, which includes a core having an elliptical profile. The ellipticity of the core is between 2 and 40, and the cladding has a circular cross-section. The core is enclosed by the cladding. In some embodiments, the core and the cladding have a common central axis.

[0098] One aspect of the present invention includes a trench portion located between the core and the cladding. The trench portion exists in the optical fiber and separates the core from the cladding.

[0099] One aspect of the present invention includes a cylindrical preform that is manufactured using a modified chemical vapor deposition (MCVD) process.

[0100] In another aspect of the present invention, the preform further comprises a groove portion between the core and the cladding. The groove portion exists in the optical fiber and separates the core from the cladding.

[0101] In another aspect of the invention, the elliptical profile is formed due to surface tension and material flow during heating.

[0102] Unless defined otherwise, all technical and / or scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art.

[0103] Although the present invention has been described with reference to specific features and embodiments of the present invention, it is apparent that various modifications and combinations of the present invention may be made without departing from the present invention. Therefore, the specification and drawings are only regarded as an explanation of the present invention as defined by the appended claims, and are intended to cover any and all modifications, variations, combinations or equivalents falling within the scope of the present invention.

Claims

1. An optical fiber, characterized in that: include: A core having an elliptical cross-section, the ellipticity of the core being between 2 and 40; A cladding having a circular cross-section, encapsulating the core; The width of the fiber core along the x-axis supports the transmission of multiple mode pairs; Each mode pair of the plurality of mode pairs consists of two orthogonal linear polarizations; The distance between the vector patterns in each pattern pair is greater than 1×10 – 4 The effective refractive index separation of The effective refractive index separation is caused by thermal stresses induced during the manufacturing process of the optical fiber and the elliptical shape of the core.

2. The optical fiber according to claim 1, characterized in that The core and the cladding have a common central axis.

3. The optical fiber according to claim 1, characterized in that The difference between the refractive index of the cladding and the refractive index of the core is within 1×10 – 2 With 1.5×10 – 1 between.

4. The optical fiber according to claim 1, characterized in that The invention also includes a trench located between the core and the cladding, wherein the trench has a uniform width and surrounds the core, and a refractive index of the trench is lower than that of the cladding.

5. The optical fiber according to claim 1, characterized in that The width of the core along the y-axis supports single-mode transmission.

6. The optical fiber according to any one of claims 1 to 5, characterized in that The fiber core is doped with rare earth ions.

7. An optical fiber amplifier, characterized in that: include: a first WDM coupler receiving an input signal and an output from a first pump light source; An optical fiber receiving the output from the first WDM coupler, the optical fiber comprising a core having an elliptical cross-section and a cladding having a circular cross-section, the ellipticity of the core being between 2 and 40, and the cladding encapsulating the core; The width of the fiber core along the x-axis supports the transmission of multiple mode pairs; Each mode pair of the plurality of mode pairs consists of two orthogonal linear polarizations; The distance between the vector patterns in each pattern pair is greater than 1×10 – 4 The effective refractive index separation of The effective refractive index separation is caused by thermal stress induced during the manufacturing process of the optical fiber and the elliptical shape of the core; The second WDM coupler receives the output of the optical fiber and the output of the second pump light source, and the second WDM coupler outputs the amplified optical signal.

8. The optical fiber amplifier according to claim 7, characterized in that: The core and the cladding have a common central axis.

9. The optical fiber amplifier according to claim 7, characterized in that: The core is doped with rare earth ions.

10. The optical fiber amplifier according to claim 7, characterized in that: The optical fiber further includes a trench located between the core and the cladding, wherein the trench has a uniform width and surrounds the core, and a refractive index of the trench is lower than a refractive index of the cladding.

11. The optical fiber amplifier according to any one of claims 7, 8, 9 or 10, characterized in that: The width of the core along the y-axis supports single-mode transmission, and the width of the core along the x-axis supports transmission of multiple mode pairs.

12. A method for manufacturing an optical fiber, characterized in that: The method comprises: preparing a cylindrical preform having a cross-section including an inner core and an outer cladding, the inner core having a circular profile; cutting two opposing sides of the cylindrical preform along the length of the cylindrical preform to produce the cut preform having opposing parallel surfaces along a longitudinal axis of the cut preform; heating the cut preform until the cut preform has a circular profile and an inner core of the cut preform has an oval profile; stretching the cut preform to form the optical fiber, the optical fiber comprising a core having an elliptical profile and a cladding having a circular cross-section, the ellipticity of the core being between 2 and 40, the core being enclosed by the cladding; The width of the fiber core along the x-axis supports the transmission of multiple mode pairs; Each mode pair of the plurality of mode pairs consists of two orthogonal linear polarizations; The distance between the vector patterns in each pattern pair is greater than 1×10 – 4 The effective refractive index separation of The effective refractive index separation is caused by thermal stresses induced during the manufacturing process of the optical fiber and the elliptical shape of the core.

13. The method according to claim 12, characterized in that The cylindrical preform further includes a trench portion located between the core and the cladding, the trench portion existing in the optical fiber and separating the core from the cladding.

14. The method according to claim 12, characterized in that The cylindrical preform is manufactured using a modified chemical vapor deposition (MCVD) process.

15. The method according to claim 12, characterized in that The elliptical profile is formed due to surface tension and material flow during heating.

16. The method according to any one of claims 12, 13, 14 or 15, characterized in that The core and the cladding have a common central axis.

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