Optical fiber mode rotating device

Abstract

The invention discloses an optical fiber mode rotating device which comprises a few-mode magneto-optic optical fiber, a matching optical fiber, a solenoid and an electromagnetic driving module. The different few-mode magneto-optical fibers are connected through the matching fibers, the few-mode magneto-optical fibers are arranged in the solenoids, the solenoids are connected with the electromagnetic driving module, and the electromagnetic driving module controls the current of the solenoids to be large, so that mode fields of non-circular symmetric fiber modes passing through the few-mode magneto-optical fibers can rotate at different angles.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical communication, and more specifically, relates to an optical fiber mode rotation device. Background Art

[0002] In the field of optical fiber communication, people have an increasing demand for the transmission capacity of optical fiber. The existing single-mode optical fiber has become unable to meet the requirements of higher information rate transmission in the future. The number of modes supported by few-mode optical fiber is between that of single-mode optical fiber and multi-mode optical fiber. It can not only realize the parallel transmission of dozens of mode channels in the same optical fiber, but also its mode demultiplexing process is easier to achieve than that of multi-mode optical fiber. Therefore, the mode multiplexing technology based on few-mode optical fiber has attracted much attention.

[0003] Few-mode optical fiber supports the transmission of multiple spatial modes at the same time. The optical fiber LP mode can use LP ln It means that when l = 0, the mode field intensity has a circularly symmetric distribution; when the integer l ≥ 1, the mode field intensity is non-circularly symmetric. When demultiplexing, the light field orientations of each mode reaching the mode demultiplexer will be different, affecting the mode crosstalk and polarization-dependent loss performance of the mode division multiplexing system. At this time, a mode rotator is needed to control the mode spot azimuth. Currently, the mode rotators that can partially support related functions mainly include: (1) universal few-mode fiber polarization controller (FMPC), which is an all-fiber device formed by winding several few-mode fiber (FMF) rings on each paddle; (2) adding a graphene coating to the outside of the FMF, and controlling the chemical potential and magnetic field of the graphene layer by doping or gate voltage to achieve control of the multimode fiber mode spot; (3) placing the multimode fiber on a support plate. When the support plate is rotated or tilted, the spot pattern of the output light spot will rotate accordingly, and the rotation angle of the speckle pattern can be semi-automatically detected from the image data. The existing mode rotators have the following shortcomings: (1) they cannot control all mode light fields separately at the same time; (2) their controllability and repeatability cannot meet practical needs. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art and provide an optical fiber mode rotation device, which uses few-mode magneto-optical optical fiber as a medium and adopts electromagnetic control to realize arbitrary rotation of the non-circularly symmetric optical fiber linear polarization (LP) mode pattern. It has the advantages of flexible controllability, good repeatability, and no need to reprocess the transmission optical fiber. It is particularly suitable for mode division multiplexing optical fiber transmission system and multi-dimensional optical switching node construction.

[0005] To achieve the above-mentioned purpose of the invention, the present invention provides an optical fiber mode rotation device, characterized in that it comprises: different types of few-mode magneto-optical optical fibers, matching optical fibers, a solenoid and an electromagnetic drive module;

[0006] The few-mode magneto-optical optical fibers are connected by matching optical fibers, and each section of the few-mode magneto-optical optical fiber is placed in a solenoid, which is then connected to an electromagnetic drive module;

[0007] The electromagnetic driving module controls the current size of the solenoid, so that the mode field of the non-circularly symmetric optical fiber mode passing through the few-mode magneto-optical optical fiber rotates at different angles.

[0008] The object of the invention of the present invention is achieved in this way:

[0009] The present invention discloses an optical fiber mode rotation device, comprising: a few-mode magneto-optical optical fiber, a matching optical fiber, a solenoid, and an electromagnetic driving module; different few-mode magneto-optical optical fibers are connected by matching optical fibers, the few-mode magneto-optical optical fibers are placed in the solenoid, and the solenoid is connected to the electromagnetic driving module. The electromagnetic driving module controls the current of the solenoid, so that the mode field of the non-circularly symmetric optical fiber mode passing through the few-mode magneto-optical optical fiber can rotate at different angles.

[0010] At the same time, the optical fiber mode rotation device of the present invention also has the following beneficial effects:

[0011] (1) Matching optical fiber as the transition zone of mode evolution is used to reduce the connection loss between optical fibers and improve the transmission efficiency of optical fiber modes.

[0012] (2) According to the characteristics of the few-mode magneto-optical fiber used, the fiber length and tapered curvature are optimized and designed to match, so that the insertion loss between the two sections of few-mode magneto-optical fiber and even the entire fiber mode rotation device can be minimized.

[0013] (3) The electromagnetic driving module adjusts the mode spot rotation angle of the linear polarization (LP) mode in each segment of the few-mode magneto-optical fiber by changing the solenoid driving current around each segment of the few-mode magneto-optical fiber according to different mode rotation angle requirements, thereby realizing arbitrary rotation of the non-circularly symmetric LP mode mode spot.

[0014] (4) The device of the present invention has the advantages of flexibility, controllability, good repeatability, and no need to reprocess the transmission optical fiber. It is particularly suitable for the construction of mode division multiplexing optical fiber transmission systems and multi-dimensional optical switching nodes. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a schematic diagram of a specific implementation of an optical fiber mode rotation device of the present invention;

[0016] Figure 2 Support LP 11 and LP 21 Mode fiber mode rotation device diagram;

[0017] Figure 3 It is the LP in two sections of few-mode magneto-optical fiber 11 and LP 21Curve of the rotation angle of the mode changing with the magnetic field strength; where (a) is the first section of the few-mode magneto-optical fiber; (b) is the second section of the few-mode magneto-optical fiber;

[0018] Figure 4 It is the size diagram of the matching optical fiber;

[0019] Figure 5 This device is used to control the relative rotation angle between modes; wherein, (a) is the application scenario diagram; (b) is the mode input to the few-mode transmission fiber; (c) is the mode after transmission through the few-mode fiber; (d) is the mode after passing through this device. DETAILED DESCRIPTION

[0020] The specific implementation of the present invention is described below in conjunction with the accompanying drawings so that those skilled in the art can better understand the present invention. It should be noted that in the following description, when the detailed description of known functions and designs may dilute the main content of the present invention, these descriptions will be omitted here.

[0021] Example

[0022] Figure 1 It is a structural diagram of a specific implementation of an optical fiber mode rotation device of the present invention.

[0023] In this embodiment, if Figure 1 As shown, the optical fiber mode rotation device of the present invention comprises: different types of few-mode magneto-optical optical fibers, matching optical fibers, a solenoid, and an electromagnetic drive module;

[0024] In this embodiment, the electromagnetic driving module is mainly composed of FPGA and driving circuit, different few-mode magneto-optical fiber segments are connected by matching optical fibers, the few-mode magneto-optical fiber is placed in a solenoid, and the solenoid is connected to the electromagnetic driving module.

[0025] The current of the solenoid is controlled by the electromagnetic drive module, which can make the mode field of the non-circularly symmetric optical fiber linear polarization (LP) mode passing through the few-mode magneto-optical fiber rotate at different angles. The matching optical fiber connected to the few-mode magneto-optical fiber is used as a transition zone for mode evolution to reduce the connection loss between optical fibers and improve the transmission efficiency of the optical fiber mode.

[0026] The matching fiber can be a few-mode magneto-optical fiber or other types of few-mode fibers, which are often designed to be tapered in geometry. The matching of the mode fields of adjacent few-mode magneto-optical fibers is achieved by optimizing the matching fiber structure, length, and refractive index distribution. According to the characteristics of the few-mode magneto-optical fiber used, the matching fiber length and tapered curvature are optimized and designed to minimize the insertion loss between the two sections of the few-mode magneto-optical fiber and even the entire fiber mode rotation device.

[0027] Each section of the few-mode magneto-optical fiber is made of magneto-optical materials such as yttrium iron garnet (YIG); each section of the few-mode magneto-optical fiber supports N types of non-circularly symmetric fiber mode transmission. In order to enable each non-circularly symmetric fiber mode to rotate at any angle, the fiber mode rotation device requires at least N different types of few-mode magneto-optical fibers to be connected.

[0028] Assume that each section of few-mode magneto-optical fiber has different non-circularly symmetric fiber modes LP ln There are different magnetic susceptibility coefficients The corresponding rotation angle is Where M j and L j are the axial magnetization intensity and corresponding fiber length of the jth few-mode magneto-optical fiber segment, and the magnetic susceptibility coefficient It is closely related to the few-mode magneto-optical fiber materials and their refractive index distribution.

[0029] The electromagnetic drive module can calculate the axial magnetization intensity M of each section of the few-mode magneto-optical fiber using the magnetic susceptibility coefficient transfer matrix method according to the requirements of different mode rotation angles. j , and then determine the driving current I applied to the solenoid j , M j with I j The proportional coefficient is related to the magneto-optical fiber material, i.e. the solenoid structure. For any set mode rotation angle θ ln (l≥1), the magnetic field M to be applied to each section of the few-mode magneto-optical fiber can be calculated by the following formula: j ,Right now:

[0030]

[0031] According to the magnetization intensity M j and drive current I j The proportional relationship between the drive current and the solenoid is determined by I j ;

[0032]

[0033] in, is the number of turns per unit length of the solenoid, χ m is the magnetic susceptibility of the magnetic medium.

[0034] Example Simulation

[0035] In this embodiment, the core material of each section of the few-mode magneto-optical fiber is yttrium iron garnet and the cladding material is quartz, and the few-mode magneto-optical fiber is manufactured; the design supports the arbitrary rotation function of the non-circularly symmetric LP mode spot. Therefore, the optical fiber mode rotation device needs to be composed of two sections of few-mode magneto-optical fibers with different characteristics (N=2), whose lengths are L1 and L2 respectively, and there is a matching fiber between them, such as Figure 2 The driving currents applied to the two sections of few-mode magneto-optical fibers are I1 and I2 respectively; the two non-circularly symmetric modes LP 11 and LP 21 The magnetic susceptibility coefficient in two sections of few-mode magneto-optical fiber is and

[0036] Combine the following Figure 2 The device structure shown in the figure describes the scheme of the present invention in detail:

[0037] The core radius of the two sections of few-mode magneto-optical fibers is 8μm, the cladding radius is 20μm and 30μm respectively, the refractive index difference between the core and the cladding is 0.022, and the length of the two sections of few-mode magneto-optical fibers is 3m. 11 and LP 21 The rotation angle of the pattern and With the magnetization intensity M i (i=1,2) The change curve is as follows Figure 3 As shown. Figure 3 It can be seen that LP 11 Mode changes with M1 or M2 and It is not a straight line, and the corresponding magnetic sensitivity coefficient depends on the specific value of M1 or M2. 11 and LP 21 The rotation angle of the pattern is θ 11 and θ 21 , then the corresponding values ​​of M1 and M2 can be determined by the following equation, that is

[0038]

[0039] The cladding sizes of the two sections of few-mode magneto-optical fibers are different. In order to reduce the transmission loss between them, a suitable matching fiber needs to be set to achieve the minimum energy attenuation. The matching section is set to a cone, and the upper and lower base radii are matched with the two sections of few-mode magneto-optical fibers respectively, and the length is set to 50mm. COMSOL simulation shows that the matching loss is less than -30dB, such as Figure 4 shown.

[0040] The following is combined with Figure 5The few-mode fiber transmission scenario shown in (a) illustrates the application value of the device in flexibly compensating for mode spot rotation. At the beginning, the mode LP input to the few-mode transmission fiber 11 and LP 21 The azimuth of the pattern is consistent, such as Figure 5 (b) shows that when Z = 0, Δθ = θ 11 -θ 21 = 0. During the transmission process through the few-mode fiber with a length of L0, due to fiber bending, twisting, etc., different modes will cause relative rotation Δθ = 18° at the output end of the few-mode fiber, such as Figure 5 (c) At this time, the device can be connected to the output end Z = L0 of the few-mode transmission fiber to compensate for the mode spot rotation caused by it. Use this device to control LP 11 and LP 21 The pattern rotates when θ 11 =θ 21 -Δθ, the two output mode spots can be made parallel to each other, such as Figure 5 (d). According to the above formula and Figure 3 It can be known that M1=36.89 (KA / m), M1=40.98 (KA / m), based on which the current of the corresponding solenoid can be further determined.

[0041] Although the above describes the illustrative specific embodiments of the present invention to facilitate those skilled in the art to understand the present invention, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations using the concept of the present invention are protected.

Claims

1. An optical fiber mode rotation device, characterized in that: include: Different types of few-mode magneto-optical fibers, matching fibers, solenoids, and electromagnetic drive modules; The few-mode magneto-optical optical fibers are connected by matching optical fibers, and each section of the few-mode magneto-optical optical fiber is placed in a solenoid, which is then connected to an electromagnetic drive module; The electromagnetic driving module controls the current size of the solenoid, so that the mode field of the non-circularly symmetric optical fiber mode passing through the few-mode magneto-optical optical fiber rotates at different angles.

2. The optical fiber mode rotation device according to claim 1, characterized in that: The optical fiber mode rotation device comprises at least N sections of different types of few-mode magneto-optical optical fibers connected together; the material of each section of the few-mode magneto-optical optical fiber is preferably yttrium iron garnet, and each section of the few-mode magneto-optical optical fiber supports N types of non-circularly symmetric optical fiber mode transmission.

3. The optical fiber mode rotation device according to claim 1, characterized in that: Each section of the few-mode magneto-optical fiber is for each non-circularly symmetric fiber mode LP ln The rotation angle is: in, For each section of few-mode magneto-optical fiber, different LP ln The modes have different magnetic susceptibility coefficients j = 1, 2, ..., N, where the subscripts l and n are the azimuthal index and radial distribution index of the weakly guiding fiber LP mode, respectively; M j is the axial magnetization intensity of the jth few-mode magneto-optical fiber; L j is the fiber length of the jth section of few-mode magneto-optical fiber.

4. The optical fiber mode rotation device according to claim 1, characterized in that: The electromagnetic drive module is mainly composed of FPGA and drive circuit; FPGA is based on the few-mode magneto-optical fiber to different LP ln The rotation angle in the mode controls the drive circuit to change the current size of the solenoid so that the optical fiber mode rotates according to the rotation angle.

5. The optical fiber mode rotation device according to claim 1, characterized in that: The method for the electromagnetic drive module to control the current of the solenoid is: (5.1) Record the different LPs of each section of few-mode magneto-optical fiber ln The rotation angle in mode is (5.2) Calculate the axial magnetization intensity M of each section of the few-mode magneto-optical fiber j ; ( 5.3) According to the magnetization intensity M j and drive current I j The relationship between the drive current I applied to the solenoid is determined by j ; in, is the number of turns per unit length of the solenoid, χ m is the magnetic susceptibility of the magnetic medium.

6. The optical fiber mode rotation device according to claim 1, characterized in that: The matching optical fiber is a few-mode magneto-optical optical fiber or other types of few-mode optical fibers; the geometric shape of the matching optical fiber is designed to be conical, and the matching of the mode fields of adjacent few-mode magneto-optical optical fibers is achieved by optimizing the matching optical fiber structure, length and refractive index distribution.

Images