Self-calibrating multimode dynamic polarization fiber-waveguide coupler and method of calibration thereof

Abstract

The application discloses a self-calibration multimode dynamic polarization fiber-waveguide coupler and a calibration method thereof. The application comprises a multimode optical fiber, a multimode end face coupler, a main waveguide and a plurality of self-calibration modules. Light emitted from the multimode optical fiber is incident on the main waveguide through the multimode end face coupler. The plurality of self-calibration modules are arranged along the transmission direction of the main waveguide in sequence and are coupled with the main waveguide. Each self-calibration module comprises a power sensor, a control circuit and a 2*2 Mach-Zehnder interferometer. The 2*2 Mach-Zehnder interferometer comprises two phase shifters. The power sensor is used to detect the optical power of one port of the 2*2 Mach-Zehnder interferometer. The control circuit and the two phase shifters are used to adjust the phase of the light wave in the optical waveguide so that the optical power detected by the power sensor is zero, thereby realizing the self-calibration of the coupler. The application can efficiently realize the dynamic polarization self-adjusting coupling output between the multimode optical fiber and the waveguide.

Description

TECHNICAL FIELD

[0001] The present application relates to a multimode dynamic polarization fiber-waveguide coupler, in particular to a dynamic polarization fiber-waveguide coupler based on a self-feedback control circuit and an integrated optical structure and a calibration method thereof. BACKGROUND

[0002] Integrated optoelectronic chips realize complex functions such as communication, sensing and computing through large-scale on-chip integrated optoelectronic devices. With the rapid development of integrated optics, the coupling between integrated optical waveguides and external optical signals has become one of the main problems to be solved. At present, one of the mainstream coupling methods is to use end-face coupling to couple light in the optical fiber into the waveguide, but in general, the polarization in the optical fiber will dynamically change with the change of the environment, and the integrated optical waveguide shows strong polarization dependence due to its asymmetric structure, which greatly affects the signal transmission between the optical fiber and the waveguide. In addition, in order to improve the signal transmission capacity between the optical fiber and the waveguide, it is also very important to realize dynamic polarization coupling of multiple modes. Therefore, it is of great practical significance to develop a multimode fiber-waveguide coupler for dynamic polarization. SUMMARY

[0003] In order to solve the problems and needs in the background art, the present application aims to realize a multimode fiber-waveguide coupler for dynamic polarization controlled by a self-calibration control system circuit. The present application additionally provides a power sensor in the integrated optical path structure for detecting the optical power of the corresponding optical path, the control circuit connects the interference arms of the Mach-Zehnder interferometer and the sensor, and according to the results of the detector, the circuit is used for real-time optical phase regulation of the front optical path, finally the output optical power of the device is controlled, thereby meeting the coupling of various dynamic polarizations, and being suitable for large-capacity optical fiber communication and other fields.

[0004] The technical scheme of the present application is as follows:

[0005] One, a self-calibration multimode dynamic polarization fiber-waveguide coupler

[0006] The multimode dynamic polarization fiber-waveguide coupler comprises a multimode optical fiber, a multimode end-face coupler, a main waveguide and a plurality of self-calibration modules, light emitted from the multimode optical fiber enters the main waveguide through the multimode end-face coupler, the plurality of self-calibration modules are arranged at intervals, and the plurality of self-calibration modules are coupled with the main waveguide.

[0007] The plurality of self-calibration modules are identical in structure and comprise a power sensor, a control circuit and a 2x2 Mach-Zehnder interferometer.

[0008] The two input ports of the 2*2 Mach-Zehnder interferometer are arranged in sequence along the transmission direction of the main waveguide, the two input ports of the 2*2 Mach-Zehnder interferometer are used as the two inputs of the self-calibration module, the two input ports of the 2*2 Mach-Zehnder interferometer are coupled with the main waveguide respectively, the control circuit is electrically connected with the 2*2 Mach-Zehnder interferometer, one of the output ports of the 2*2 Mach-Zehnder interferometer is connected with the power sensor, and the other output port of the 2*2 Mach-Zehnder interferometer is used as the output of the self-calibration module.

[0009] The modes of the optical signals in the two input ports of each 2*2 Mach-Zehnder interferometer are the same.

[0010] The multiple self-calibration modules are arranged in sequence along the transmission direction of the main waveguide.

[0011] The multimode end face coupler is a multimode polarization-insensitive coupler.

[0012] Two, a calibration method of a self-calibrated multimode dynamic polarization fiber-waveguide coupler

[0013] The light emitted from the multimode optical fiber is incident on the main waveguide through the multimode end face coupler, the light in the main waveguide is coupled to the self-calibration module, in each self-calibration module, when the power sensor detects that the optical power in the output port of the 2*2 Mach-Zehnder interferometer is not zero, the power sensor sends an electrical signal to the control circuit according to the detected optical power, the control circuit controls and adjusts the phase of the light wave in the interference arm of the 2*2 Mach-Zehnder interferometer according to the received electrical signal, until the optical power detected by the power sensor is zero, so that all the optical signals coupled into the 2*2 Mach-Zehnder interferometer are output from the other output port of the 2*2 Mach-Zehnder interferometer, thereby realizing self-calibration.

[0014] The beneficial effects of the present application are as follows:

[0015] 1. The present application adopts polarization-insensitive coupling and polarization regulation means based on polarization beam splitting rotation and Mach-Zehnder interferometer combination, supplemented by self-feedback calibration circuit and algorithm, to realize dynamic polarization coupling and solve the polarization problem of fiber and waveguide coupling.

[0016] 2. The present application adopts on-chip multimode coupling and multi-dimensional multiplexing structure to realize high-order mode and waveguide coupling and improve the data capacity between the fiber and the waveguide. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 A plan view of an arbitrary polarization fiber-waveguide coupler based on self-calibration designed for the present application;

[0018] In the figure: 1. Multimode fiber, 2. Multimode end face coupler, 3. Mode demultiplexer, 4. Phase shifter, 5. Control circuit, 6. Power sensor, 7. Output waveguide, 8. Main waveguide, 9. 2×2 Mach-Zehnder interferometer. Detailed Implementation

[0019] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the scope of the disclosure.

[0020] Example 1

[0021] like Figure 1 As shown in the figure, solid lines represent optical paths, and dashed lines represent circuits. The multimode dynamic polarization fiber-waveguide coupler of this invention includes a multimode fiber 1, a multimode end-face coupler 2, a main waveguide 8, and multiple self-calibration modules. Light emitted from the multimode fiber 1 is incident on the main waveguide 8 through the multimode end-face coupler 2. The multiple self-calibration modules are arranged sequentially at intervals along the transmission direction of the main waveguide 8. All self-calibration modules are coupled to the main waveguide 8. The multimode end-face coupler 2 is a multimode polarization-insensitive coupler.

[0022] The multiple self-calibration modules have the same structure, including a power sensor 6, a control circuit 5, and a 2×2 Mach-Zehnder interferometer 9;

[0023] The two input ports of the 2×2 Mach-Zehnder interferometer 9 are arranged sequentially at intervals along the transmission direction of the main waveguide 8. The two input ports of the 2×2 Mach-Zehnder interferometer 9 serve as the two inputs of the self-calibration module. The two input ports of the 2×2 Mach-Zehnder interferometer 9 (i.e., the first input waveguide and the fourth input waveguide) are coupled to the main waveguide 8 respectively. The control circuit 5 is electrically connected to the two phase shifters 4 of the 2×2 Mach-Zehnder interferometer 9. One of the output ports of the 2×2 Mach-Zehnder interferometer 9 is connected to the power sensor 6. The other output port of the 2×2 Mach-Zehnder interferometer 9 outputs optical power and serves as the output of the self-calibration module.

[0024] Each 2×2 Mach-Zehnder interferometer can demultiplex optical signals of the same mode. Optical signals of the same mode but different polarizations are coupled into the two input ports of the 2×2 Mach-Zehnder interferometer. The optical signals in the two input ports of each 2×2 Mach-Zehnder interferometer 9 have the same mode and either the same or different polarizations.

[0025] 2x2 Mach-Zehnder interferometer 9 includes 2 phase shifters 4, 4 input waveguides, an output waveguide 7, 1 interference waveguide and 2 output control waveguides; the first input waveguide is coupled with the main waveguide 8, the first input waveguide is connected with the power sensor 6 in turn through the first output control waveguide, the second input waveguide, the second output control waveguide and the third input waveguide, the power sensor 6 is electrically connected with the control circuit 5, the control circuit 5 is electrically connected with the two phase shifters 4 respectively, the first phase shifter is coupled with the first output control waveguide, and the second phase shifter is coupled with the second output control waveguide; the fourth input waveguide is connected with the output waveguide 7 in turn through the fifth input waveguide and the first interference waveguide, the fourth input waveguide is coupled with the main waveguide 8, the first input waveguide and the fourth input waveguide are arranged in sequence along the transmission direction of the main waveguide 8, the second input waveguide is coupled with the fifth input waveguide, the second output control waveguide and the first interference waveguide serve as two interference arms of the Mach-Zehnder interferometer, and the third input waveguide is coupled with the output waveguide 7.

[0026] The first input waveguide, the first output control waveguide, the second input waveguide, the second output control waveguide and the third input waveguide constitute a first integrated optical waveguide, and the first integrated optical waveguide adopts a strip waveguide.

[0027] The self-calibration control system is composed of the 2x2 Mach-Zehnder interferometer 9, the control circuit 5 and the power sensor 6.

[0028] Different modes and different polarizations in the main waveguide 8 are coupled to different channels through the mode demultiplexer 3. Polarization control is realized by controlling the phase of the Mach-Zehnder interferometer interference arm. The phase shifter and the power sensor 6 are controlled by the control circuit 5.

[0029] The calibration method comprises the following steps:

[0030] The light emitted from the multimode optical fiber 1 enters the main waveguide 8 through the multimode end face coupler 2, and the light in the main waveguide 8 is coupled into the self-calibration module. In each self-calibration module, when the power sensor 6 detects that the light power in the output port of the 2x2 Mach-Zehnder interferometer 9 is not zero, the power sensor 6 sends an electrical signal to the control circuit 5 according to the detected light power, the control circuit 5 controls the first phase shifter and the second phase shifter of the 2x2 Mach-Zehnder interferometer 9 to modulate the corresponding output control waveguide according to the received electrical signal, so as to adjust the phase of the light wave in the interference arm of the 2x2 Mach-Zehnder interferometer 9, until the light power detected by the power sensor 6 is zero, so that all the light signals coupled into the 2x2 Mach-Zehnder interferometer 9 are output from the other output port (i.e. the output waveguide 7) of the 2x2 Mach-Zehnder interferometer 9, thereby realizing self-calibration.

[0031] The end face coupling is composed of a multimode optical fiber and an integrated optical waveguide, light in the multimode optical fiber is coupled into the integrated optical waveguide through the end face coupling, as a structural input light source, the coupling efficiency can be improved by improving the waveguide outer coating polymer type, cantilever beam type coupler subwavelength grating type, double-layer taper, multi-layer SiN and other structures. After the light is coupled from the multimode optical fiber into the waveguide, the light of different modes and different polarizations is coupled into different channels through a mode demultiplexer, and two beams of light belonging to the same mode but different polarizations are coherently superimposed through a self-calibrating Mach-Zehnder interferometer.

[0032] The multimode fiber (MMF) is an optical fiber with multiple transmission modes, mainly used for short-distance optical fiber communication. In general, the core diameter of the optical fiber is larger than the cross section of the integrated optical waveguide, and the cladding diameter is larger by an order of magnitude, so that the mode mismatch problem occurs. The influence of mode mismatch can be reduced by some structural design. The integrated optical waveguide adopts a strip waveguide. Taking silicon material as an example, a 220nm full-silicon waveguide is generally used. By designing the width of the silicon waveguide and the upper cladding structure, the mode spot size of the multimode fiber can be close to that of the silicon waveguide, the mode mismatch can be reduced, and the end face coupling efficiency can be improved.

[0033] After the light of different modes and different polarizations is coupled into the waveguide, it is coupled into different channels through a mode demultiplexer 3 with the same mode. The light of different polarizations belonging to the same mode will be interfered and controlled by a Mach-Zehnder interferometer, and finally coherently superimposed and output. Taking an integrated silicon photon chip as an example, since the thermal-optic coefficient of silicon material is large, the phase control can be realized by thermal-optic tuning. Since the polarization in the optical fiber changes over time, the interference of the Mach-Zehnder interferometer will change over time, and the coherent superposition output cannot be maintained in real time. The output of the Mach-Zehnder interferometer is monitored in real time by using a power sensor, and a self-feedback circuit is used to adjust the phase on the interference arm of the Mach-Zehnder interferometer in real time until the power measured by the power sensor is 0, and the coherent superposition output is realized again, and the self-calibration is completed.

[0034] The above embodiments are the preferred embodiments of the present application, but the embodiments of the present application are not limited to the above embodiments, and any changes, modifications, substitutions, combinations and simplifications made without departing from the spirit and principles of the present application shall be equivalent replacement modes and shall be included in the protection scope of the present application.

Claims

1. A self-calibrating multimode dynamic polarization fiber-waveguide coupler, characterized in that, It includes a multimode fiber (1), a multimode end-face coupler (2), a main waveguide (8) and multiple self-calibration modules. The light emitted from the multimode fiber (1) is incident on the main waveguide (8) through the multimode end-face coupler (2). The multiple self-calibration modules are arranged at intervals and are all coupled to the main waveguide (8). The multiple self-calibration modules have the same structure, including a power sensor (6), a control circuit (5), and a 2×2 Mach-Zehnder interferometer (9). The two input ports of the 2×2 Mach-Zehnder interferometer (9) are arranged sequentially at intervals along the transmission direction of the main waveguide (8). The two input ports of the 2×2 Mach-Zehnder interferometer (9) serve as the two inputs of the self-calibration module. The two input ports of the 2×2 Mach-Zehnder interferometer (9) are coupled to the main waveguide (8) respectively. The control circuit (5) is electrically connected to the 2×2 Mach-Zehnder interferometer (9). One of the output ports of the 2×2 Mach-Zehnder interferometer (9) is connected to the power sensor (6). The other output port of the 2×2 Mach-Zehnder interferometer (9) serves as the output of the self-calibration module.

2. The self-calibrating multimode dynamic polarization fiber-waveguide coupler according to claim 1, characterized in that, The optical signals in the two input ports of each of the 2×2 Mach-Zehnder interferometers (9) have the same pattern.

3. The self-calibrating multimode dynamic polarization fiber-waveguide coupler according to claim 1, characterized in that, The multiple self-calibration modules are arranged sequentially at intervals along the transmission direction of the main waveguide (8).

4. A self-calibrating multimode dynamic polarization fiber-waveguide coupler according to claim 1, characterized in that, The multimode end-face coupler (2) is a multimode polarization-insensitive coupler.

5. A calibration method for a self-calibrating multimode dynamic polarization fiber-waveguide coupler according to any one of claims 1-4, characterized in that, Includes the following steps: The light emitted from the multimode fiber (1) is incident on the main waveguide (8) through the multimode end-face coupler (2). The light in the main waveguide (8) is coupled to the self-calibration module. In each self-calibration module, when the power sensor (6) detects that the optical power in the output port of the 2×2 Mach-Zehnder interferometer (9) is not zero, the power sensor (6) sends an electrical signal to the control circuit (5) according to the detected optical power. The control circuit (5) controls and adjusts the phase of the light wave in the interference arm of the 2×2 Mach-Zehnder interferometer (9) according to the received electrical signal until the optical power detected by the power sensor (6) is zero, so that all the optical signals coupled into the 2×2 Mach-Zehnder interferometer (9) are output from the other output port of the 2×2 Mach-Zehnder interferometer (9), thereby realizing self-calibration.

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