A fiber mode rotating device

Abstract

The application discloses a kind of optical fiber mode rotating device, comprising: few-mode magneto-optical fiber, matching optical fiber, solenoid, electromagnetic drive module;Different few-mode magneto-optical fiber is connected by matching optical fiber, few-mode magneto-optical fiber is placed in solenoid, solenoid is connected with electromagnetic drive module, the current of solenoid can be controlled by electromagnetic drive module, and the mode field of non-circular symmetry optical fiber mode through few-mode magneto-optical fiber can be rotated at different angles.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of optical communication, and more particularly relates to a fiber mode rotating device. BACKGROUND

[0002] In the field of optical fiber communication, the demand for transmission capacity of optical fiber is getting higher and higher, and the existing single-mode optical fiber is already insufficient, and it is difficult to meet the requirements of higher information rate transmission in the future. The number of modes supported by few-mode optical fiber is between single-mode optical fiber and multi-mode optical fiber, which not only can realize the parallel transmission of dozens of mode channels in the same optical fiber, but also is easier to realize mode demultiplexing than multi-mode optical fiber. Therefore, the mode multiplexing technology based on few-mode optical fiber is highly concerned.

[0003] The transmission of multiple spatial modes in few-mode optical fiber simultaneously supports multiple spatial modes, and the fiber LP mode can be represented by LP ln When l=0, the mode field intensity has circular symmetry distribution; when the integer l is greater than or equal to 1, the mode field intensity is non-circular symmetry distribution. When demultiplexing, the light field azimuth of each mode reaching the mode demultiplexer will be different, which will affect 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 spot azimuth angle. At present, the mode rotators that can partially support related functions mainly include: (1) a general few-mode fiber polarization controller (FMPC), which is a kind of all-fiber device formed by winding several few-mode fiber (FMF) rings on each paddle; (2) adding a graphene coating outside the FMF, and controlling the chemical potential and magnetic field of the graphene layer by doping or gate voltage to control the mode spot of the multi-mode fiber; (3) placing the multi-mode fiber on a support plate, and rotating or tilting the support plate, the spot pattern of the output light spot will rotate accordingly, and the rotation angle of the speckle pattern is semi-automatically detected from the image data. The existing mode rotators have the following disadvantages: (1) cannot control all mode light fields simultaneously; (2) controllability and repeatability are difficult to meet the actual needs. SUMMARY

[0004] The present application aims to overcome the shortcomings of the prior art, and provides a fiber mode rotating device, which uses few-mode magneto-optical fiber as a medium and realizes the arbitrary rotation of non-circular symmetric fiber linear polarization (LP) mode spots by using electromagnetic control method, has the advantages of flexible controllability, good repeatability, no need for reprocessing of transmission optical fiber, and is particularly suitable for mode division multiplexing optical fiber transmission system and multi-dimensional optical switching node construction.

[0005] In order to achieve the above-mentioned application purposes, the fiber mode rotating device of the present application comprises: few-mode magneto-optical fibers of different types, matching optical fibers, solenoids and electromagnetic driving modules.

[0006] The few-mode magneto-optical fiber is connected by a matching fiber, each few-mode magneto-optical fiber is placed in a solenoid, and the solenoid is connected with an electromagnetic drive module.

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

[0008] The application aims to achieve the following purposes:

[0009] The application is a fiber mode rotating device, comprising: few-mode magneto-optical fibers, matching fibers, solenoids, and an electromagnetic drive module; the few-mode magneto-optical fibers are connected by the matching fibers, the few-mode magneto-optical fibers are placed in the solenoids, the solenoids are connected with the electromagnetic drive module, the current size of the solenoids is controlled by the electromagnetic drive module, and the mode field of the non-circular symmetric fiber mode passing through the few-mode magneto-optical fiber is rotated at different angles.

[0010] Meanwhile, the application also has the following advantages:

[0011] (1) The matching fiber is used as a transition zone for mode evolution, so as to reduce the connection loss between the fibers and improve the fiber mode transmission efficiency.

[0012] (2) According to the characteristics of the few-mode magneto-optical fibers, the length and taper curvature of the matching fiber are optimized, so that the insertion loss between the two few-mode magneto-optical fibers or the entire fiber mode rotating device is minimized.

[0013] (3) The electromagnetic drive module changes the driving current size of the solenoids around the few-mode magneto-optical fibers according to different mode rotation angle requirements, so as to adjust the mode spot rotation angle of the linear polarization (LP) mode in each few-mode magneto-optical fiber, thereby realizing the arbitrary rotation of the LP mode spot.

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

[0015] Figure 1 is a specific embodiment architecture diagram of the fiber mode rotating device of the application;

[0016] Figure 2 is a fiber mode rotating device supporting LP 11 and LP 21 modes;

[0017] Figure 3 is the LP 11 and LP 21The curve of the rotation angle of the mode with the change of the magnetic field intensity; wherein (a) is a first section of the few-mode magneto-optical fiber; and (b) is a second section of the few-mode magneto-optical fiber.

[0018] Figure 4 is a size matching fiber;

[0019] Figure 5 is a device for controlling the relative rotation angle between modes; wherein (a) is an application scenario diagram; (b) is a mode input into the few-mode transmission fiber; (c) is a mode after transmission through the few-mode fiber; and (d) is a mode after passing through the device. DETAILED DESCRIPTION

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

[0021] EMBODIMENT

[0022] Figure 1 is a specific embodiment architecture diagram of the optical fiber mode rotating device of the present application.

[0023] In this embodiment, as shown in Figure 1 , the optical fiber mode rotating device of the present application comprises: different types of few-mode magneto-optical fibers, a matching fiber, a solenoid, and an electromagnetic driving module.

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

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

[0026] The matching fiber can be a few-mode magneto-optical fiber or other types of few-mode fiber, which is often designed as a taper in geometry. By optimizing the structure, length and refractive index distribution of the matching fiber, the matching of the mode field of the adjacent few-mode magneto-optical fiber can be achieved. According to the characteristics of the used few-mode magneto-optical fiber, the matching fiber length and taper curvature are optimized and designed, so that the insertion loss between the two sections of the few-mode magneto-optical fiber and even the entire optical fiber mode rotating device can be minimized.

[0027] Each segment of the few-mode magneto-optical fiber is made of magneto-optical material such as yttrium iron garnet (YIG); each segment of the few-mode magneto-optical fiber supports N non-circularly symmetric fiber mode transmissions. In order to enable each non-circularly symmetric fiber mode to rotate by an arbitrary angle, the fiber mode rotating device needs to be connected by at least N few-mode magneto-optical fibers of different types.

[0028] Suppose that each segment of the few-mode magneto-optical fiber has different non-circularly symmetric fiber modes LP ln with different magnetic susceptibilities The corresponding rotation angle is wherein M j and L j are the axial magnetization intensity and the corresponding fiber length of the jth segment of the few-mode magneto-optical fiber, respectively, and the magnetic susceptibility is closely related to the magneto-optical fiber material and its refractive index distribution, etc.

[0029] The electromagnetic drive module can calculate the axial magnetization intensity M j of each segment of the few-mode magneto-optical fiber according to the requirement of different mode rotation angles by using the magnetic susceptibility transfer matrix method, and then determine the drive current size I j applied to the solenoid, wherein M j is proportional to I j , and 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 j that should be applied to each segment of the few-mode magneto-optical fiber can be calculated by the following formula, i.e.:

[0030]

[0031] According to the proportional relationship between the magnetization intensity M j and the drive current I j , the drive current size I j applied to the solenoid is determined.

[0032]

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

[0034] Example simulation

[0035] In this embodiment, each segment of few-mode magneto-optical fiber has a core material of yttrium iron garnet and a cladding material of quartz to fabricate the few-mode magneto-optical fiber; the design supports arbitrary rotation of non-circular symmetric LP mode spots. Therefore, this fiber mode rotation device needs to consist of two segments of few-mode magneto-optical fibers with different characteristics (N=2), with lengths L1 and L2 respectively, and a matching fiber between them, such as... Figure 2 As shown. The driving currents applied to the two segments of few-mode magneto-optical fiber are I1 and I2, respectively; the two non-circular symmetric modes LP 11 and LP 21 The magnetic susceptibility coefficient in the two segments of few-mode magneto-optical fiber is and

[0036] The following is combined Figure 2 The device structure shown below provides a detailed description of the present invention:

[0037] Both few-mode magneto-optical fiber segments have a core radius of 8 μm and cladding radii of 20 μm and 30 μm, respectively. The refractive index difference between the core and cladding is 0.022, and both segments are 3 m long. The two few-mode magneto-optical fiber segments are paired with LP... 11 and LP 21 Rotation angle of the pattern and With magnetization M i The variation curve for (i = 1, 2) is as follows: Figure 3 As shown. By Figure 3 It can be seen that LP 11 Pattern variation curves with M1 or M2 and It's not a straight line; the corresponding magnetic sensitivity coefficient depends on the specific values ​​of M1 or M2. If LP is set in this case... 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, namely

[0038]

[0039] The two few-mode magneto-optical fiber segments have different cladding dimensions. To reduce transmission loss between them, a suitable matching fiber is needed to achieve minimal energy attenuation. The matching segment is tapered, with its top and bottom radii matching the two few-mode magneto-optical fiber segments respectively, and its length is set to 50 mm. COMSOL simulations show that the matching loss is below -30 dB. Figure 4 As shown.

[0040] The following is combined with, for example Figure 5(a) the transmission scenario of the few-mode fiber, which shows the application value of the device in the flexible compensation of the mode spot rotation. At the beginning, the mode LP 11 and LP 21 have the same azimuth angle, i.e. Figure 5 (b) shown in the figure, i.e. when Z = 0, Δθ = θ 11 - θ 21 = 0. During the transmission in the few-mode fiber with a length of L0, the relative rotation Δθ = 18° of different modes at the output end of the few-mode fiber will be caused by the fiber bending, twisting and other factors, as shown in 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 thereby. The device is used to control the mode spot rotation of LP 11 and LP 21 , and when θ 11 = θ 21 - Δθ, the two output mode spots can be parallel to each other, as shown in Figure 5 (d). According to the above formula and Figure 3 , it can be known that M1 = 36.89 (KA / m) and M1 = 40.98 (KA / m), and accordingly the current of the corresponding solenoid can be further determined.

[0041] Although the above describes the specific embodiments of the present application in a demonstrative manner, so as to facilitate the understanding of the present application by the person skilled in the art, it should be clear that the present application is not limited to the scope of the specific embodiments, and for the person skilled in the art, all the changes which are obvious and within the spirit and scope of the present application defined and determined by the appended claims are all included in the protection of the present application.

Claims

1. An optical fiber mode rotator device, comprising: The application relates to a fiber mode rotating device. The different types of few-mode magneto-optical fibers are connected by matching fibers, each few-mode magneto-optical fiber is arranged in a solenoid, and the solenoid is connected with an electromagnetic driving module. The electromagnetic driving module controls the current size of the solenoid, so that the mode field of the non-circular symmetric fiber mode passing through the few-mode magneto-optical fiber is rotated at different angles. The fiber mode rotating device comprises at least N different types of few-mode magneto-optical fibers connected in series; the material of each few-mode magneto-optical fiber is yttrium iron garnet, and each few-mode magneto-optical fiber supports N non-circular symmetric fiber mode transmission.

2. A device for rotating the modes of an optical fiber as recited in claim 1, wherein The method for controlling the current size of the solenoid of the electromagnetic driving module is as follows:

3. A device for rotating the modes of an optical fiber as recited in claim 1, wherein The rotation angle of each segment of few-mode magneto-optical fiber for each non-circularly symmetric optical fiber mode is: ; wherein, is different for different modes , the subscripts and are the azimuthal and radial distribution indices of the LP mode of the weakly guiding fiber, respectively; is the axial magnetization of the few-mode magneto-optical fiber; is the fiber length of the few-mode magneto-optical fiber.

4. A device for rotating the modes of an optical fiber as recited in claim 1, wherein The electromagnetic drive module mainly consists of FPGA and drive circuit; FPGA controls the drive circuit to change the current size of the solenoid according to the rotation angle of the different modes of the few-mode magnetic optical fiber, so that the fiber mode rotates according to the rotation angle. mode.

5. A device for rotating the modes of an optical fiber as recited in claim 1, wherein The matching fiber is a few-mode magneto-optical fiber or other types of few-mode fiber; the geometric shape of the matching fiber is designed as a taper, and the matching of the mode field of adjacent few-mode magneto-optical fibers is realized by optimizing the structure, length and refractive index distribution of the matching fiber. (5.1), record each segment of few-mode magneto-optical fiber for different rotational angle as ; (5.2) calculating the axial magnetization of each segment of the few-mode magneto-optical fiber ; (5.3) Based on magnetization intensity and drive current The relationship determines the magnitude of the drive current applied to the solenoid. ; ; wherein N is the number of turns per unit length of the solenoid, χ is the magnetic susceptibility of the magnetic medium.

6. A device for rotating modes of a fiber according to claim 1, wherein ​

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