A monolithically integrated polarization switch, control method and system

Abstract

The application provides a monolithic integrated polarization switch, a control method and a system. The polarization switch comprises: an input monitoring module for receiving an input optical signal, monitoring the power of the input optical signal, and dividing the input optical signal into a first optical path signal and a second optical path signal; a phase modulation feedback module for phase modulating the first optical path signal and the second optical path signal to obtain a first modulation signal, a second modulation signal, and a phase difference between the first modulation signal and the second modulation signal; and a polarization synthesis output module for beam combining the first modulation signal and the second modulation signal to obtain an output optical signal. The phase difference is used to determine whether the polarization state of the output optical signal is a preset value. In the case of a non-pre-set value, the driving voltage applied to the phase modulation feedback module is adjusted until the polarization state of the output optical signal is the preset value. Real-time monitoring and automatic compensation of the output optical signal are achieved, so that the output optical signal is always stable at the preset polarization state.

Description

Technical Field

[0001] This application relates to the field of optical device technology, and in particular to a monolithically integrated polarization switch, control method and system. Background Technology

[0002] In fiber optic sensing systems, especially in interferometric fiber optic hydrophones, the polarization state of light has a significant impact on detection accuracy and stability. Due to environmental factors (such as temperature and pressure), the transmitted light in the fiber is prone to polarization drift, leading to unstable or even failed interference signals, i.e., polarization fading.

[0003] In related technologies, to address the polarization instability problem, discrete optical elements (such as waveplates and polarization beam splitters) or electro-optic modulation devices based on lithium niobate materials are often used to achieve polarization switching functions. Although these solutions have a certain degree of adjustment capability, they suffer from problems such as large size, high power consumption, high driving voltage, and difficulty in compatibility with optoelectronic integrated platforms, which limits their application in miniaturized hydrophone probes.

[0004] While current silicon-based photonics technology can achieve highly integrated polarization control chips, the significant thermo-optical effects of silicon cause phase modulators to easily experience phase drift under temperature fluctuations, thus affecting the stability of the output polarization state. Without an effective feedback mechanism, it will be difficult to maintain the required polarization output state in complex environments.

[0005] Therefore, there is an urgent need for a polarization switch design that is both chip-based and integrates on-chip real-time monitoring and closed-loop feedback functions to achieve a high-performance, highly integrated, and environmentally adaptable polarization control solution. Summary of the Invention

[0006] This application provides a monolithically integrated polarization switch, control method, and system, which enables real-time monitoring and automatic compensation of the output optical signal, thereby ensuring that the output optical signal remains stable in a preset polarization state. The technical solution of this application is implemented as follows: In a first aspect, embodiments of this application provide a monolithically integrated polarization switch, the polarization switch comprising: The input monitoring module is used to receive the input optical signal, monitor the power of the input optical signal, and divide the input optical signal into a first optical path signal and a second optical path signal. The phase modulation feedback module is used to perform phase modulation on the first optical path signal and the second optical path signal to obtain the first modulated signal, the second modulated signal, and the phase difference between the first modulated signal and the second modulated signal. The polarization combining output module is used to combine the first modulation signal and the second modulation signal to obtain the output optical signal; The output optical signal is an orthogonally polarized optical signal; the phase difference is used to determine whether the polarization state of the output optical signal is a preset value. If it is not a preset value, the driving voltage applied to the phase modulation feedback module is adjusted until the polarization state of the output optical signal is a preset value.

[0007] In some embodiments, the input monitoring module includes at least a first directional coupler, a first detector, and an input beam splitter; the first directional coupler is used to receive an input optical signal, perform asymmetric beam splitting on the input optical signal to obtain a first detection signal and a main optical path signal, send the first detection signal to the first detector through a first directional output terminal, and send the main optical path signal to the input beam splitter through a second directional output terminal; the first detector is used to monitor the power of the input optical signal based on the detection signal; the input beam splitter is used to split the main optical path signal to obtain a first optical path signal and a second optical path signal; wherein the power and phase of the first optical path signal and the second optical path signal are equal.

[0008] In some embodiments, the phase modulation feedback module includes at least a first optical path, a second optical path, a monitoring end beam splitter, and a second detector; the first optical path is used to modulate and split the first optical path signal to obtain a second detection signal and a first modulation signal; the second optical path is used to modulate and split the second optical path signal to obtain a third detection signal and a second modulation signal; the monitoring end beam splitter is used to combine the second detection signal and the third detection signal to obtain a combined detection signal; the second detector is used to detect the combined detection signal to obtain the phase difference between the first modulation signal and the second modulation signal.

[0009] In some embodiments, the first optical path includes at least a first phase modulator and a second directional coupler connected in sequence, and the second optical path includes at least a second phase modulator and a third directional coupler connected in sequence; the first phase modulator is used to modulate the first optical path signal to obtain a first signal; the second directional coupler is used to split the first signal based on a preset splitting ratio to obtain a second detection signal and a first modulation signal; the second phase modulator is used to modulate the second optical path signal to obtain a second signal; and the third directional coupler is used to split the second signal based on a preset splitting ratio to obtain a third detection signal and a second modulation signal.

[0010] In some embodiments, the polarization combining output module includes at least a polarization beam combiner and a third detector; the polarization beam combiner is used to perform polarization state conversion and beam combining of the first modulation signal and the second modulation signal to obtain an output optical signal; the third detector is used to detect the output optical signal to obtain a detection result.

[0011] Secondly, embodiments of this application provide a control method for a polarization switch, applied to a control circuit in a control system. The control system further includes the aforementioned polarization switch connected to the control circuit. The control method includes: applying a driving voltage to a phase modulator in the polarization switch to obtain a first voltage of a first detector and a second voltage of a second detector in the polarization switch at the current moment; determining a current monitoring signal based on the first and second voltages; wherein the current monitoring signal has a cosine mapping relationship with the phase difference between the first modulation signal and the second modulation signal output by the phase modulation feedback module in the polarization switch; the phase modulation feedback module includes at least a phase modulator; determining the output state of the output optical signal of the polarization switch based on the current monitoring signal; adjusting the driving voltage applied to the phase modulator in response to the output state being a non-target state until the output state reaches the target state; the phase modulator includes at least one of a first phase modulator and a phase modulator; the target state characterizes the polarization state of the output optical signal as a preset value.

[0012] In some embodiments, determining the output state of the output optical signal of the polarization switch based on the current monitoring signal includes: acquiring the previous monitoring signal at the previous moment; comparing the previous monitoring signal with the current monitoring signal to obtain a comparison result; the comparison result includes whether the current monitoring signal is an extreme value or a non-extreme value; and determining the output state based on the comparison result.

[0013] In some embodiments, when the preset value is 45 degrees of linear polarization, the current monitoring signal should be a maximum value; when the preset value is 135 degrees of linear polarization, the current monitoring signal should be a minimum value. Correspondingly, based on the comparison result, the output state is determined, including: when the preset value is 45 degrees of linear polarization, if the comparison result indicates one of the following: the current monitoring signal is less than the previous monitoring signal; or when the current monitoring signal is greater than or equal to the previous monitoring signal, the difference between the current monitoring signal and the target maximum value is greater than a preset threshold, the output state is determined to be a non-target state; when the preset value is 135 degrees of linear polarization, if the comparison result indicates one of the following: the current monitoring signal is greater than the previous monitoring signal; or when the current monitoring signal is less than or equal to the previous monitoring signal, the difference between the current monitoring signal and the target minimum value is greater than a preset threshold, the output state is determined to be a non-target state.

[0014] In some embodiments, adjusting the driving voltage applied to the phase modulator until the output state reaches a target state includes: adjusting the driving voltage in a target direction to obtain an adjustment monitoring signal; the target direction includes increasing or decreasing the adjustment; if the adjustment monitoring signal is greater than the current monitoring signal when the preset value is 45 degrees of linear polarization, adjusting based on the target direction until the adjustment monitoring signal is less than or equal to the current monitoring signal; if the adjustment monitoring signal is less than the current monitoring signal when the preset value is 135 degrees of linear polarization, adjusting based on the target direction until the adjustment monitoring signal is greater than or equal to the current monitoring signal.

[0015] Thirdly, embodiments of this application provide a control system, characterized in that the control system includes at least the aforementioned polarization switch and control circuit; the control circuit, connected to the polarization switch, is used to apply a driving voltage to the phase modulator in the polarization switch to obtain a first voltage of the first detector and a second voltage of the second detector in the polarization switch at the current moment; based on the first voltage and the second voltage, a current monitoring signal is determined; wherein the current monitoring signal has a cosine mapping relationship with the phase difference between the first modulation signal and the second modulation signal output by the phase modulation feedback module in the polarization switch; the phase modulation feedback module includes at least a phase modulator; based on the current monitoring signal, the output state of the output optical signal of the polarization switch is determined; in response to the output state being a non-target state, the driving voltage applied to the phase modulator is adjusted until the output state reaches the target state; the phase modulator includes at least one of a first phase modulator and a phase modulator; the target state characterizes the polarization state of the output optical signal as a preset value. Attached Figure Description

[0016] Figure 1 A schematic diagram of an optional structure of the polarization switch provided in the embodiments of this application. Figure 1 ; Figure 2 This is a schematic diagram illustrating the principle of the relationship between polarization synthesis and phase difference provided in the embodiments of this application; Figure 3 A schematic diagram of an optional structure of the polarization switch provided in the embodiments of this application. Figure 2 ; Figure 4 A schematic diagram of an optional structure of the polarization switch provided in the embodiments of this application. Figure 3 ; Figure 5 A schematic diagram of an optional structure of the polarization switch provided in the embodiments of this application. Figure 4 ; Figure 6 A schematic diagram of an optional structure of the polarization switch provided in the embodiments of this application. Figure 5 ; Figure 7An optional flowchart illustrating the control method provided in an embodiment of this application; Figure 8 An optional structural schematic diagram of the control system provided in an embodiment of this application; Figure 9 This is an optional flowchart of the closed-loop feedback control method provided in the embodiments of this application.

[0017] It should be noted that the terms "first" and "second" mentioned above are only used to distinguish between different options and do not represent the degree of superiority or inferiority of the options or their priority in the implementation process. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described in detail below with reference to the accompanying drawings. The described embodiments should not be regarded as limitations on this application. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0019] It should be understood that the following description of the embodiments is intended to explain and illustrate the overall concept of the embodiments of this application, and should not be construed as limiting the embodiments of this application. In the specification and drawings, the same or similar reference numerals refer to the same or similar parts or components. For clarity, the drawings are not necessarily drawn to scale, and some well-known parts and structures may be omitted in the drawings.

[0020] In some embodiments, unless otherwise defined, the technical or scientific terms used in the embodiments of this application should have the meaning understood by a person skilled in the art to which the embodiments of this application pertain. The terms "first," "second," and similar terms used in the embodiments of this application do not indicate any order, quantity, or importance, but are merely used to distinguish different components. The word "a" or "an" does not exclude multiple components. The terms "comprising" or similar terms mean that the element or object preceding the word covers the elements or objects listed after the word and their equivalents, without excluding other elements or objects. The terms "connected" or similar terms are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. "Above," "below," "left," "right," "top," or "bottom," etc., are used only to indicate relative positional relationships, and these relative positional relationships may change accordingly when the absolute position of the described object changes. When an element such as a layer, film, region, or substrate is referred to as being "above" or "below" another element, the element may be "directly" located "above" or "below" the other element, or there may be intermediate elements present.

[0021] Fiber optic hydrophones, as a novel type of underwater acoustic sensor, have been widely used in marine resource exploration, underwater security, and environmental monitoring due to their advantages such as high sensitivity, resistance to electromagnetic interference, large dynamic range, and ease of multiplexing into arrays. In interferometric fiber optic hydrophone systems, the stability of the polarization state of light directly affects the system's detection accuracy and signal-to-noise ratio. Because the birefringence effect in optical fibers is affected by environmental pressure, temperature, and bending, the polarization state of the transmitted light undergoes random drift, leading to polarization fading in the interference signal, and in severe cases, even complete signal loss.

[0022] To address the polarization fading problem, related technologies employ polarization diversity detection or polarization switching techniques. Polarization switching technology, in particular, requires the ability to quickly and accurately switch between orthogonal or specific polarization states (such as 45-degree linear polarization and 135-degree linear polarization). Traditional polarization control devices often utilize lithium niobate crystals or discrete optical waveplate assemblies, which suffer from drawbacks such as large size, high driving voltage, and difficulty in integration with other optoelectronic devices, hindering the miniaturization and lightweight design of hydrophone probes.

[0023] In contrast, silicon photonics technology, manufactured using CMOS processes, offers extremely high integration and waveguide-based high confinement of the light field, making it an ideal solution to the aforementioned problems. Polarization switch chips implemented using silicon photonics technology can be scaled down to millimeters or even micrometers, reducing volume and weight by more than two orders of magnitude compared to traditional bulk lithium niobate modules. Furthermore, silicon photonic chips can utilize mature thermo-optical effects or carrier dispersion effects to achieve low-power modulation and possess the ability to be monolithically integrated with other passive / active devices, significantly improving the overall reliability of hydrophone front-end systems and reducing manufacturing costs.

[0024] However, silicon has a high thermo-optic coefficient, making silicon-based waveguide-based phase modulators extremely sensitive to changes in ambient temperature. In practical applications, even small fluctuations in ambient temperature can cause phase shifts between interferometer arms, resulting in the output polarization state deviating from the design value (e.g., the originally designed linearly polarized light becomes elliptically polarized light), leading to increased demodulation errors in the hydrophone system. If open-loop control is used directly, silicon photonic chips cannot maintain a stable polarization output state for extended periods in underwater variable-temperature environments.

[0025] Therefore, in order to fully leverage the significant advantages of silicon photonics technology in terms of power consumption, size, weight, and integration, and to enable it to truly replace traditional bulk lithium niobate devices in practical environments, there is an urgent need for a polarization switch design that combines the characteristics of silicon photonics chip-based design with on-chip real-time monitoring and closed-loop feedback functions, in order to achieve a high-performance, highly integrated, and environmentally adaptable polarization control solution.

[0026] To address the problems existing in related technologies, this application provides a monolithically integrated polarization switch, control method, and system. The input monitoring module, phase modulation feedback module, and polarization synthesis output module are integrated onto the same chip, and a closed-loop feedback control mechanism is introduced to achieve real-time monitoring and automatic compensation of phase difference. This ensures that the output optical signal remains stable in a preset polarization state (such as 45 degrees or 135 degrees linear polarization), significantly improving the system's stability, reliability, and environmental adaptability.

[0027] The technical solution of this application will now be described in detail with reference to the accompanying drawings.

[0028] Figure 1 This is a schematic diagram of an optional structure of the polarization switch provided in an embodiment of this application. Figure 1 ,like Figure 1 As shown, the polarization switch 10 provided in this application embodiment may include an input monitoring module 100, a phase modulation feedback module 200, and a polarization synthesis output module 300.

[0029] The input monitoring module 100 is used to receive the input optical signal, monitor the power of the input optical signal, and divide the input optical signal into a first optical path signal and a second optical path signal. The input optical signal can come from a narrow linewidth laser source, such as a laser operating in the 1550nm band.

[0030] Here, the power of the input optical signal can be detected by a high-precision photodetector (such as a germanium-silicon photodiode). The power stability of the input optical signal is crucial to the performance of the polarization switch. Real-time monitoring of the input optical power helps the switch maintain stable operation under environmental fluctuations.

[0031] Optical signals can be split into two paths by a beam splitter, which divides the input optical signal into two paths: the first optical path signal and the second optical path signal. This ensures that the amplitudes of the two optical signals are equal, thus providing a basis for subsequent polarization synthesis.

[0032] In some embodiments, the phase modulation feedback module 200 is used to perform phase modulation on the first optical path signal and the second optical path signal to obtain a first modulation signal, a second modulation signal, and a phase difference between the first modulation signal and the second modulation signal.

[0033] Here, the phase modulation feedback module 200 may include two parallel optical waveguide branches, each of which may be equipped with a phase modulator. The function of this modulator is to introduce a controllable phase difference by changing the refractive index of the waveguide, thereby obtaining a modulation signal, namely a first modulation signal and a second modulation signal. To achieve closed-loop control, this application may include a directional coupler after each phase modulator. The directional coupler extracts a small amount of monitoring optical signal from the main optical path. This monitoring optical signal is transmitted to a beam splitter at the monitoring end for interference superposition, forming an interference intensity signal. This interference intensity signal is detected by a detector and used to determine the current phase difference between the first and second modulation signals.

[0034] Phase difference is a key parameter determining the polarization state of the output optical signal. When the phase difference between the first and second modulation signals is 0 or π, it corresponds to linear polarization of 45 degrees or 135 degrees, respectively. By precisely controlling the phase difference, polarization state switching and locking can be achieved. The design of the phase modulation feedback module enables the polarization switch to have self-sensing and self-calibration capabilities, thereby overcoming the polarization instability problem caused by temperature drift in traditional silicon photonic devices.

[0035] The phase modulation feedback module 200, by introducing a closed-loop feedback mechanism, can monitor and compensate for phase drift caused by the environment in real time, thereby ensuring the stability of the polarization state of the output optical signal and improving the long-term reliability and adaptability of the polarization switch.

[0036] In some embodiments, the polarization combining output module 300 is used to combine a first modulation signal and a second modulation signal to obtain an output optical signal. The beam combining can be performed using a polarization beam combiner, which can converge the first and second modulation signals into the same output waveguide, forming an orthogonally polarized optical signal containing horizontal and vertical components through vector superposition.

[0037] The preset value can refer to the target polarization state set by the user, such as 45-degree linear polarization or 135-degree linear polarization. The preset value determines the final polarization direction of the polarization switch output and is the basis for closed-loop adjustment of the phase difference. For example, if the user wants to output 45° linearly polarized light, the phase difference between the first modulation signal and the second modulation signal is adjusted to 0 through the feedback mechanism, thereby achieving the desired polarization direction.

[0038] In this embodiment, when the polarization state of the output optical signal is detected to deviate from the preset value, the driving voltage applied to the phase modulator can be dynamically adjusted based on the phase difference, so that the phase difference between the first modulation signal and the second modulation signal is restored to near the target value, ensuring that the output optical signal is always kept within the set polarization state range.

[0039] Figure 2 This is a schematic diagram illustrating the principle of polarization combining and phase difference relationship provided in the embodiments of this application, such as... Figure 2 As shown, the optical field Eout in the output waveguide is the horizontal polarization component E from the upper arm 201. TE and the vertical polarization component E from the lower arm 202 TM The vector superposition. Since the beam splitter in the input monitoring module 100 ensures equal amplitude, the output polarization state of the output optical signal depends only on the phase difference between the two.

[0040] When 45-degree linearly polarized light needs to be output, such as Figure 2 As shown in (A), the control circuit adjusts the phase modulator in the phase modulation feedback module 200 to make the phase difference between the two arms... At this point, the TE component and the TM component vibrate in phase, and the resultant vector points to the 45-degree direction in the first quadrant.

[0041] When it is necessary to output 135-degree linearly polarized light, such as Figure 2 As shown in (B), the control circuit adjusts the phase modulator so that the phase difference between the two arms is... At this point, the TE component and the TM component vibrate in opposite phases, and the combined vector points to the 135-degree direction in the second quadrant.

[0042] Here, the polarization synthesis output module 300 not only realizes the synthesis output of polarization state, but also adjusts the output state of the output optical signal in real time through a closed-loop feedback mechanism, thereby ensuring that the optical sensing system can still provide high-precision and stable polarization control capability in complex environments, meeting the needs of high-performance optical sensing systems.

[0043] This embodiment of the application realizes beam splitting and power monitoring of the input optical signal, phase modulation and phase difference extraction of the two optical signals, and polarization state beam combining of the output optical signal through an input monitoring module, a phase modulation feedback module, and a polarization combining output optical signal. Using the phase difference as a judgment criterion, the driving voltage is dynamically adjusted to keep the polarization state of the output optical signal stable at a preset value. Through the feedback control structure, the thermal drift problem of silicon waveguide caused by changes in ambient temperature can be compensated, thereby ensuring high accuracy and stability of the output polarization state and improving the reliability and adaptability of the polarization switch. At the same time, the monolithically integrated polarization switch will turn discrete polarization devices into on-chip waveguide networks. The devices are integrated into the chip, reducing peripheral devices, increasing integration, and significantly reducing the size of the polarization switch.

[0044] Figure 3 This is a schematic diagram of an optional structure of the polarization switch provided in an embodiment of this application. Figure 2 ,like Figure 3 As shown, the input monitoring module 100 includes at least a first directional coupler 110, a first detector 120, and an input beam splitter 130.

[0045] In some embodiments, the first directional coupler 110 is used to receive the input optical signal, perform asymmetric beam splitting on the input optical signal to obtain a first detection signal and a main optical path signal, send the first detection signal to the first detector 102 through the first directional output terminal of the first directional coupler 110, and send the main optical path signal to the input beam splitter 130 through the second directional output terminal of the first directional coupler 110.

[0046] Here, asymmetric beam splitting can refer to the first directional coupler 110 splitting the input optical signal into two output signals according to different proportions, which can be divided into a first detection signal with a small proportion (e.g., 1% to 5%) and a main optical path signal with a large proportion.

[0047] The primary function of the first detection signal is to power the first detector 120 for real-time monitoring of the power level of the input optical signal. Since the first detection signal constitutes only a small portion of the total input light, it does not significantly affect the strength and quality of the main optical path signal.

[0048] The main optical path signal is the part of the input optical signal that has not been extracted. The main optical path signal enters the input beam splitter 130 through the second directional output terminal as the basis for subsequent processing.

[0049] In some embodiments, the first detector 120 monitors the power of the input optical signal based on the first detection signal; the input beam splitter 130 splits the main optical path signal to obtain a first optical path signal and a second optical path signal, and the power and phase of the first optical path signal and the second optical path signal are equal.

[0050] Here, the first detector 120 can be a germanium-silicon photodiode integrated on a chip, used to monitor fluctuations in input optical power in real time and provide normalized reference data for subsequent closed-loop feedback control.

[0051] The input beam splitter 130 is used to split the main optical path signal into two paths, namely the first optical path signal and the second optical path signal. These two signals are not only equal in power, but also in phase. Only when the power and phase of the two signals are perfectly matched can the accuracy of the polarization synthesis output be ensured.

[0052] In some embodiments, the input beam splitter 130 may employ a 1x2 multimode interference coupler (MMI) to split the optical signal into two beams with equal power and phase.

[0053] In this embodiment, the first directional coupler in the input monitoring module adopts an asymmetric beam splitting method, extracting only a small amount of optical signal for the first detector to monitor the input optical power, without affecting the signal strength of the main optical path; the input beam splitter divides the main optical path signal into two paths, ensuring amplitude balance in the subsequent phase modulation process, and realizing high-quality linear polarization state switching and stable output.

[0054] Figure 4 This is a schematic diagram of an optional structure of the polarization switch provided in an embodiment of this application. Figure 3 ,like Figure 4 As shown, the phase modulation feedback module 200 includes at least a first optical path 210, a second optical path 220, a monitoring end beam splitter 230, and a second detector 240.

[0055] In some embodiments, the first optical path 210 is used to modulate and split the signal of the first optical path 210 to obtain a second detection signal and a first modulation signal.

[0056] The first optical path 210 can refer to an optical path used to transmit the first optical path signal. The first optical path 210 can be composed of a waveguide, and a phase modulator and a directional coupler can be integrated on the first optical path 210.

[0057] Modulation can refer to changing the refractive index of a waveguide by applying voltage or other means, thereby altering the phase of the optical signal. This can be achieved using a phase modulator to obtain the first modulated signal, which is then used for the final synthesized output. Beam splitting can refer to extracting a portion of the optical signal (i.e., the second detection signal) from the main optical path using a directional coupler as a detection signal for interferometric monitoring.

[0058] In the first optical path 210, the modulation and beam splitting operations work together to enable the main optical signal to be effectively modulated by the first phase modulator and to retain a portion of the optical signal for phase difference detection.

[0059] In some embodiments, the second optical path 220 is used to modulate and split the second optical path signal to obtain a third detection signal and a second modulation signal. The second optical path 220 is similar to the first optical path 210 and will not be described again here. The first modulation signal and the second modulation signal enter the polarization combining output module 300.

[0060] In some embodiments, the monitoring-end beam splitter 230 is used to combine the second detection signal and the third detection signal to obtain a combined detection signal. The monitoring-end beam splitter 230 can be an interferometric device, such as a 2x1 MMI or a Y-branch beam combiner. The monitoring-end beam splitter 230 interferometrically superimposes the detection signals from the two optical paths to form a combined detection signal.

[0061] In some embodiments, the second detector 240 is used to detect the beam combining detection signal to obtain the phase difference between the first modulation signal and the second modulation signal. Here, the light intensity I detected by the second detector 240 is... mon There is a direct mapping relationship (usually a cosine function relationship) between the phase difference between the first and second modulated signals. Therefore, by reading I... mon The value can be used to obtain the current phase state of the two optical paths.

[0062] In this embodiment, the phase modulation feedback module performs phase modulation through two parallel optical paths and extracts a portion of the signal from each optical path for interference monitoring. The detected light intensity has a cosine mapping relationship with the phase difference between the two main optical signals, realizing lossless and real-time phase state monitoring and providing accurate feedback signals for subsequent closed-loop control.

[0063] Figure 5 A schematic diagram of an optional structure of the polarization switch provided in the embodiments of this application. Figure 4 ,like Figure 5 As shown, the first optical path 210 includes at least a first phase modulator 211 and a second directional coupler 212 connected in sequence, and the second optical path 220 includes at least a second phase modulator 221 and a third directional coupler 222 connected in sequence.

[0064] In some embodiments, the first phase modulator 211 and the second phase modulator 221 may be a thermo-optical phase modulator or a carrier dispersion effect phase modulator. By adjusting the voltage applied to the first phase modulator 211 and / or the second phase modulator 221, the propagation phase of the optical signal in the waveguide can be precisely controlled, thereby affecting the polarization state of the final output optical signal.

[0065] In some embodiments, a first phase modulator 211 is used to modulate a first optical path signal to obtain a first signal. The first phase modulator 211 can achieve phase modulation of the first optical path signal by changing the refractive index of the silicon waveguide. The phase modulation achieved by the first phase modulator 211 can be continuous or discrete, depending on the driving signal provided by the external control circuit. By modulating the first optical path signal, the phase difference between the first optical path signal and the second optical path signal can be dynamically adjusted, thereby affecting the polarization state of the output light.

[0066] In some embodiments, the second directional coupler 212 is used to split the first signal based on a preset splitting ratio to obtain a second detection signal and a first modulation signal.

[0067] The second directional coupler 212 can divide the first signal into two parts according to a preset splitting ratio (such as 1%). One part is used as the second detection signal for the interference measurement of the second detector 240; the other part is used as the first modulation signal and is transmitted to the polarization synthesis output module 300.

[0068] In some embodiments, the second phase modulator 221 is used to modulate the second optical path signal to obtain a second signal. The second phase modulator 221 is the same as the first phase modulator 211, both of which achieve phase modulation of the optical signal by applying heat or current to the silicon waveguide to change the refractive index of the silicon waveguide.

[0069] In some embodiments, the third directional coupler 222 is used to split the second signal based on a preset splitting ratio to obtain a third detection signal and a second modulation signal. The third directional coupler 222 is the same as the second directional coupler 212. The third directional coupler 222 also splits the second signal into two parts according to the preset splitting ratio. One part is used as the third detection signal for interferometric measurement by the second detector 240; the other part is used as the second modulation signal and is further transmitted to the polarization synthesis output module 300.

[0070] The embodiments of this application can obtain accurate phase difference information without interfering with the main optical path, and provide a basis for closed-loop control based on this information to achieve stable control of the polarization state of the output light, thereby significantly improving the detection accuracy and signal-to-noise ratio of the fiber optic hydrophone system.

[0071] In some embodiments, Figure 6 A schematic diagram of an optional structure of the polarization switch provided in the embodiments of this application. Figure 5 ,like Figure 6 As shown, the polarization combining output module 300 includes at least a polarization combiner 310 and a third detector 320.

[0072] In some embodiments, the polarization combiner 310 is used to perform polarization state conversion and beam combining of the first modulation signal and the second modulation signal to obtain an output optical signal.

[0073] Here, the polarization combiner 310 can be an optical device capable of combining two optical signals with different polarization directions (such as TE mode and TM mode) into a single output waveguide. The polarization combiner 310 can employ a polarization splitting rotator (PSR) structure, achieving the synthesis of orthogonally polarized light through reverse operating modes. For example, in a silicon photonic chip, the PSR has two input ports, allowing the TE mode to pass directly through and rotating the TM mode by 90 degrees before outputting it to the same output waveguide. The two optical signals coexist spatially in a single waveguide, forming the synthesized polarization state.

[0074] The first and second modulated signals originate from two branches of the phase modulation feedback module 200, respectively, and carry specific phase information after phase modulation. The polarization directions of the first and second modulated signals are adjusted to be orthogonal for synthesis in the polarization combiner 310. For example, if the first modulated signal is horizontally polarized (TE mode) and the second modulated signal is vertically polarized (TM mode), the polarization combiner 310 will vector-superimpose the first and second modulated signals to form the final linearly polarized output.

[0075] The output optical signal is formed after processing by the polarization combiner 310. The polarization state of the output optical signal is determined by the phase difference between the two modulation signals. When the phase difference between the two modulation signals is 0, 45-degree linearly polarized light is output; when the phase difference between the two modulation signals is π, 135-degree linearly polarized light is output. Through the above output method, the polarization switch can flexibly switch between different polarization states, thereby meeting the needs of different application scenarios.

[0076] In some embodiments, the third detector 320 is used to detect the output optical signal and obtain a detection result.

[0077] Here, the third detector 320 can be a device integrated on a silicon photonic chip, used to monitor the status of the output optical signal in real time. The third detector 320 can be coupled to the end of the output waveguide via an optical beam splitter structure to collect the power and on / off status of the output optical signal, thereby providing a self-test function and enabling fault diagnosis across the entire chain. For example, in underwater applications, if the output optical signal is interrupted or its power decreases, the third detector 320 can immediately report the abnormal information, facilitating timely fault diagnosis.

[0078] The detection result refers to the measurement data of the output optical signal by the third detector 320. This data can be output as an electrical signal for external control circuitry to read and use to determine whether the system is operating normally. The detection result is not only used to evaluate the stability of the output optical signal but also for the calibration and compensation of the closed-loop feedback system. For example, when changes in ambient temperature cause phase drift, the change in the detection result value can trigger a feedback mechanism that automatically adjusts the drive voltage of the phase modulator, thereby ensuring the stability of the output polarization state.

[0079] The embodiments of this application can effectively improve the output accuracy and stability of the polarization switch by performing polarization state conversion and beam combining of the modulation signal and real-time detection of the output optical signal, thereby addressing the thermal drift problem in complex environments and ensuring the high signal-to-noise ratio and long-term reliability of the fiber optic hydrophone system.

[0080] Based on the polarization switch provided in the foregoing embodiments, this application further provides a control method for the polarization switch to eliminate phase drift caused by ambient temperature. The executing entity is a control circuit connected to the polarization switch. The control circuit can be integrated on the silicon photonics chip where the polarization switch is located, or it can be an external control circuit. The control circuit can be a microcontroller unit (MCU), a field-programmable gate array (FPGA), or an analog proportional-integral-derivative controller (PID), etc., and is not limited thereto.

[0081] Figure 7 An optional flowchart illustrating the control method provided in an embodiment of this application is shown below. Figure 7 As shown, the control method can be implemented through steps S701 to S704: S701, apply a driving voltage to the phase modulator in the polarization switch to obtain the first voltage of the first detector and the second voltage of the second detector in the polarization switch at the current moment.

[0082] In some embodiments, in a polarization switch-locked fiber optic hydrophone system or other system, after the system is powered on, a target operating mode can be set (e.g., requesting the output of 45-degree linearly polarized light). Then, a driving voltage is applied to the phase modulator in the polarization switch to adjust the phase difference between the corresponding signals of the two waveguides, so that the output optical signal of the polarization switch is 45-degree linearly polarized light.

[0083] In some embodiments, the phase modulator includes at least one of a first phase modulator and a second phase modulator in a polarization switch, and the application of the driving voltage is to achieve precise control of the phase modulator, thereby adjusting the phase difference between the two optical signals.

[0084] The first and second detectors can be photodetectors integrated on a silicon photonic chip, used to collect light intensity information before and after phase modulation by a phase modulator, respectively, to assist in the subsequent feedback control process.

[0085] Here, the magnitude of the driving voltage determines the phase difference introduced by the phase modulator. By applying different driving voltages to the phase modulator, the phase relationship between the two optical paths can be changed, thereby affecting the polarization state of the output optical signal and realizing different operating modes of the polarization switch.

[0086] S702, based on the first voltage and the second voltage, determine the current monitoring signal; wherein, the current monitoring signal has a cosine mapping relationship with the phase difference between the first modulation signal and the second modulation signal output by the phase modulation feedback module in the polarization switch; the phase modulation feedback module includes at least a phase modulator.

[0087] Here, the current monitoring signal is obtained by monitoring the first voltage. V ref Second voltage V mon The calculated current monitoring signal S reflects the change in phase difference between the two arms in the main optical path. The current monitoring signal S can be obtained by formula (1): (1); Due to the interference characteristics of the beam splitter at the monitoring end, the phase difference between the current monitoring signal and the optical signals of the two arms has a cosine function relationship, that is... When the phase difference between the two arms is 0 or π, the current monitoring signal reaches its maximum or minimum value, respectively. This cosine function relationship is the key foundation for achieving polarization state locking.

[0088] By analyzing the current monitoring signal, it can be determined whether the current phase difference deviates from the preset target value, and then it can be determined whether the driving voltage needs to be adjusted to compensate for the phase deviation.

[0089] S703 determines the output state of the polarization switch's output optical signal based on the current monitoring signal.

[0090] The output state of the output optical signal can refer to whether the polarization state currently output by the polarization switch is the target state (e.g., 45-degree linear polarization or 135-degree linear polarization). The target state indicates that the polarization state of the output optical signal has stabilized in the specific direction set by the user, while the non-target state indicates that the polarization state has not yet stabilized or has drifted due to environmental disturbances.

[0091] By comparing the current monitoring signal with the characteristic value (such as the maximum or minimum value) corresponding to the target state, it can be determined whether the current output state meets the requirements. When the current monitoring signal is close to the target value, it is determined that the polarization switch is in the target state; otherwise, it will enter the adjustment stage.

[0092] S704, in response to the output state being a non-target state, adjusts the driving voltage applied to the phase modulator until the output state reaches the target state; the phase modulator includes at least one of a first phase modulator and a phase modulator; the target state characterizes the polarization state of the output optical signal as a preset value.

[0093] The target state is a preset value used to characterize the polarization state of the output optical signal. This preset value can be either 45-degree linear polarization or 135-degree linear polarization. When the current output state is detected to be non-target state, the control circuit can dynamically adjust the driving voltage applied to the phase modulator, thereby returning the polarization switch to the target state.

[0094] In some embodiments, the adjustment process can be optimized using a closed-loop control algorithm (such as PID control or hill-climbing algorithm) to ensure that the target state can be restored in the shortest possible time. Simultaneously, the driving voltage adjustment process exhibits good anti-interference capability; even under the influence of external factors such as ambient temperature fluctuations, the polarization state of the output optical signal can be kept stable near the target value.

[0095] In this embodiment, when the output state of the polarization switch's output optical signal is not in the target state, the driving voltage is adjusted to prevent the output state from returning to the target state, thus achieving stable polarization state locking. On one hand, the complex phase difference is converted into an easily processed voltage signal using a cosine mapping relationship, simplifying the control logic; on the other hand, a closed-loop feedback mechanism is used to compensate for phase deviations caused by environmental temperature drift in real time, achieving high-precision, real-time control of the polarization switch's output optical signal and ensuring stable operation of the polarization switch's output optical signal under various environments.

[0096] In some embodiments, step S703 can be implemented by steps S7031 to S7033: S7031, acquire the previous monitoring signal from the previous moment.

[0097] Here, the previous monitoring signal can refer to the most recently acquired monitoring signal data before the current moment. This data is used to compare with the current monitoring signal to determine the signal change trend. For example, in a silicon photonic polarization switch, the previous monitoring signal could be detected by the second detector in the previous sampling period. By recording and storing this historical data, dynamic analysis over time series can be achieved, thereby improving the sensitivity to phase drift and response speed.

[0098] The interval between the previous moment and the current moment is the sampling period or control period Δt of the control closed loop, which is determined by the control circuit and can be constrained by the ADC sampling rate, algorithm calculation time, and phase modulator response time.

[0099] When the current monitoring signal is detected, the latest previous monitoring signal can be used as a reference point. By comparing the previous monitoring signal with the current monitoring signal, the misjudgment problem that may be caused by using outdated data can be avoided, and the stability of the closed-loop feedback can be improved.

[0100] S7032 compares the previous monitoring signal with the current monitoring signal to obtain the comparison result; the comparison result includes whether the current monitoring signal is an extreme value or a non-extreme value.

[0101] The comparison result can be a conclusion drawn by comparing the current monitoring signal with the previous monitoring signal. It can indicate that the current monitoring signal is an extreme value (maximum or minimum) or a non-extreme value. An extreme value represents the peak or valley of the interference light intensity, corresponding to a phase difference of 0 or π between the two optical signals, meaning the polarization switch is in an ideal polarization state. A non-extreme value indicates that the output optical signal has not reached the target state and further phase difference adjustment is needed.

[0102] In 45-degree linear polarization output mode, the current monitoring signal should be in a constructive interference (maximum value) state. If the current monitoring signal is higher than the monitoring signal at the previous moment, it may indicate that it is approaching the target state; if the current monitoring signal is lower than the monitoring signal at the previous moment, it may indicate that it is moving away from the target state. By continuously tracking the trend of the current monitoring signal's extreme value, the optimal operating point can be quickly identified.

[0103] Here, the comparison process can be optimized using various strategies such as digital PID algorithm, perturbation and observation (P&O) method or hill climbing algorithm. The core of all these strategies is to compare the numerical difference between the current monitoring signal and the previous monitoring signal in real time, determine whether the target extreme value has been reached or deviated from, and adjust the driving voltage of the phase modulator according to the judgment result.

[0104] S7033 determines the output status based on the comparison results.

[0105] The output state can be the polarization state of the current output of the polarization switch, determined based on the comparison results. Specifically, it refers to whether the polarization direction of the output optical signal is stable at a preset target value (such as 45 degrees or 135 degrees of linear polarization). If the current monitored signal is determined to be an extreme value, then the output state is the target state; if the current monitored signal is not an extreme value, it indicates that the polarization switch has a phase drift, which is a non-target state. The controller can adjust the driving voltage of the phase modulator to bring the output back to the target state.

[0106] This application embodiment introduces the previous monitoring signal and compares it with the current monitoring signal, and activates a closed-loop feedback mechanism, which can effectively suppress phase drift caused by ambient temperature fluctuations, thereby ensuring the long-term stable operation of the polarization switch and significantly improving the overall performance and reliability of the hydrophone system.

[0107] In some embodiments, when the preset value is 45 degrees of linear polarization, the current monitoring signal should be a maximum value; when the preset value is 135 degrees of linear polarization, the current monitoring signal should be a minimum value.

[0108] Correspondingly, step S7033 can be achieved through steps S1 to S2: S1, with a preset value of 45 degrees of linear polarization, if the comparison result indicates one of the following: the current monitoring signal is less than the previous monitoring signal, or the difference between the current monitoring signal and the target maximum value is greater than the preset threshold when the current monitoring signal is greater than or equal to the previous monitoring signal, the output state is determined to be a non-target state.

[0109] When the target output polarization state is set to 45 degrees linear polarization, it means that the phase difference between the two optical paths should be controlled near 0 (or an integer multiple of 2π) so that the interference signal reaches its maximum value.

[0110] In some embodiments, if the current monitoring signal is less than the previous monitoring signal, it indicates that the current monitoring signal is not a maximum value, and the output state is determined to be a non-target state.

[0111] In some embodiments, the target maximum can be the maximum possible value of the monitoring light intensity signal detected by the second detector, typically corresponding to the case where the two arm light signals are completely in phase. In this case, the two signals undergo constructive interference at the beam combiner at the monitoring end, producing the strongest interference light intensity. The target maximum serves as a reference point to determine whether the current phase difference is within the desired range.

[0112] The preset threshold can be a pre-defined numerical range used to determine whether the current monitored signal deviates from the target maximum value. When the difference between the current monitored signal and the target maximum value exceeds the preset threshold, it can be determined that the phase difference has exceeded the acceptable range, and the output state is determined to be a non-target state. At this time, an adjustment operation needs to be performed to bring the phase difference back to the acceptable range, thereby restoring the target state.

[0113] When the output state is not the target state, the polarization state of the output light may change to elliptic polarization or other non-orthogonal polarization states. This change will affect the measurement accuracy and stability of the system. Therefore, it is necessary to adjust the phase difference in a timely manner through closed-loop feedback to bring the system back to the target state.

[0114] S2, with a preset value of 135 degrees of linear polarization, if the comparison result indicates one of the following: the current monitoring signal is greater than the previous monitoring signal, or the difference between the current monitoring signal and the target minimum value is greater than the preset threshold when the current monitoring signal is less than or equal to the previous monitoring signal, the output state is determined to be a non-target state.

[0115] In this embodiment of the application, when the target output polarization state is set to 135 degrees linear polarization, it indicates that the phase difference between the two optical path branches should be controlled to be near π radians (or an odd multiple of (2k+1)π) so that the obtained interference signal reaches the minimum value.

[0116] The target minimum can be used as a reference point to determine whether the current phase difference is within the expected range. Here, if the current monitoring signal is greater than the previous monitoring signal, or if the current monitoring signal is less than or equal to the previous monitoring signal, and the difference between the current monitoring signal and the target minimum is greater than a preset threshold, it indicates that the current monitoring signal is not a minimum, and the output state is determined to be a non-target state.

[0117] Here, when the system switches operating modes, for example from 45-degree linear polarization to 135-degree linear polarization, the target of the feedback control also switches accordingly from locking the maximum value to locking the minimum value. The control circuit achieves the above process by dynamically adjusting the driving voltage applied to the phase modulator, ensuring that the output polarization state remains stable near the preset value regardless of environmental changes.

[0118] The embodiments of this application can dynamically adjust the judgment logic according to different target states, thereby improving the flexibility and accuracy of control. At the same time, the introduction of a preset threshold to determine whether the target range has been deviated from helps to prevent misjudgment of the state due to noise interference and enhances the robustness of the system.

[0119] In some embodiments, step S704 can be implemented by steps S7041 to S7043: S7041 adjusts the drive voltage in the target direction to obtain an adjustment monitoring signal; the target direction includes increasing or decreasing.

[0120] Here, the driving voltage is an electrical signal used to control the operating state of the silicon photonic phase modulator (e.g., a thermo-optical phase modulator). The target direction can refer to increasing or decreasing the driving voltage. The adjustment monitoring signal is a current monitoring signal acquired in real time during the adjustment process. This signal is typically obtained by normalizing the interference light intensity detected by the second detector. The adjustment monitoring signal reflects the phase difference state between the two arms of the main optical path and serves as the input to the closed-loop feedback algorithm.

[0121] When the output polarization state is detected to deviate from the preset value, a target direction is determined based on the deviation trend (e.g., adjusting the drive voltage up or down), and the result after adjustment is continuously monitored to determine whether to continue adjusting along the target direction.

[0122] S7042, with a preset value of 45 degrees of linear polarization, if the adjusted monitoring signal is greater than the current monitoring signal, it continues to adjust based on the target direction until the adjusted monitoring signal is less than or equal to the current monitoring signal.

[0123] In 45-degree linear polarization mode, the ideal monitoring signal corresponds to the maximum value of constructive interference. Therefore, when the adjusted monitoring signal is greater than the original monitoring signal, it indicates that the adjustment direction is helping to approach the maximum value of constructive interference. Adjustment should continue along the target direction until the adjusted monitoring signal no longer increases or decreases slightly, thus locking the signal near its maximum value. This effectively eliminates phase deviations caused by factors such as temperature drift, maintains the long-term stability of the output polarization state, and meets the stringent requirements for polarization stability in complex underwater environments.

[0124] S7043, with a preset value of 135 degrees of linear polarization, if the adjusted monitoring signal is less than the current monitoring signal, it continues to adjust based on the target direction until the adjusted monitoring signal is greater than or equal to the current monitoring signal.

[0125] In 135-degree linear polarization mode, ideally the monitoring signal should be at the minimum value of destructive interference. Therefore, when the adjusted monitoring signal value is less than the current monitoring signal value, it indicates that the current adjustment direction helps to bring the monitoring signal closer to the minimum value. Adjustment should continue along the target direction until the monitoring signal value no longer decreases or increases slightly. At this point, the monitoring signal has been locked near the minimum value.

[0126] This application embodiment achieves precise control of the phase difference by employing targeted adjustment strategies under different preset polarization states. This effectively addresses the temperature sensitivity of silicon photonic devices, thereby improving the long-term operational stability of the polarization switch and significantly enhancing the signal-to-noise ratio and detection accuracy of the fiber optic hydrophone system.

[0127] This application embodiment provides another control system. Figure 8 An optional structural schematic diagram of the control system provided in the embodiments of this application is shown below. Figure 8 As shown, the control system 80 includes at least a polarization switch 10 and a control circuit 20.

[0128] The polarization switch 10 can be an optical device used to regulate the polarization state of an optical signal. It modulates the phase of two optical branches separately and combines the two beams to output an orthogonal polarization state, thereby meeting the requirement for stable polarization output in applications such as fiber optic hydrophones. The polarization switch is designed based on silicon-based integrated optoelectronic technology, which has the advantages of small size, low power consumption, and easy integration with other optoelectronic devices.

[0129] The control circuit 20 is an electronic device connected to the polarization switch 10. It executes closed-loop feedback control logic to maintain the stable polarization state of the output light from the polarization switch. The control circuit calculates the phase difference in the current optical path by reading the voltage signal from the detector inside the polarization switch, and dynamically adjusts the driving voltage applied to the phase modulator according to a preset target (such as 45-degree or 135-degree linear polarization). The control circuit compensates for phase drift caused by changes in ambient temperature in real time through closed-loop feedback control logic, ensuring that the polarization switch always outputs a polarization state that meets the design requirements.

[0130] This embodiment combines the polarization switch 10 with the control circuit 20 to form a closed-loop feedback system. This not only improves the adaptability of the underwater acoustic detection system containing the polarization switch 10, but also significantly enhances the stability of the polarization output. The closed-loop feedback system formed by combining the polarization switch with the control circuit enables the polarization switch to maintain high-performance operation for a long time in complex environments, making it suitable for high-precision, long-term underwater acoustic detection systems.

[0131] It should be noted that the description of the system embodiments in this application is similar to the description of the method embodiments described above, and has similar beneficial effects as the method embodiments; therefore, it will not be repeated. For technical details not disclosed in the system embodiments, please refer to the description of the method embodiments in this application for understanding.

[0132] The following will describe an exemplary application of the embodiments of this application in a real-world application scenario.

[0133] To address the problems existing in related technologies, this application provides a monolithically integrated closed-loop feedback silicon optical polarization switch. Through chip-level architecture design, it achieves extreme miniaturization, low power consumption, and monolithic integration of the device, while using an on-chip closed-loop feedback mechanism to solve the thermal drift problem, thereby providing a polarization control solution that combines high performance and high environmental adaptability.

[0134] The miniaturization is achieved through monolithic silicon photonics integration, which reduces system size. In this embodiment, discrete polarization devices (e.g., bulk lithium niobate / discrete waveplate + coupling) are transformed into on-chip waveguide networks. Secondly, although monitoring taps and detectors are added, they are integrated within the chip, preventing an increase in system size. Simultaneously, reliance on external polarization monitors, manual parameter tuning, and temperature control equipment is reduced, resulting in a smaller and simpler design.

[0135] The monolithically integrated closed-loop feedback silicon optical polarization switch provided in this application embodiment can be manufactured based on a silicon-on-insulator photonic integration platform (SOI) to achieve monolithic integration. The optical path structure of the polarization switch consists of three parts connected in sequence: an input monitoring module 100, a phase modulation feedback module 200, and a polarization synthesis output module 300.

[0136] The optical signal (e.g., from a narrow-linewidth laser source in the 1550nm band) first enters the input monitoring module 100. The input waveguide is connected to the first directional coupler 110, which is designed as an asymmetric beam splitter, coupling approximately 1% to 5% of the optical power to the first detector 120 (e.g., a germanium-silicon photodiode integrated on a chip). The first detector is used to monitor fluctuations in the input optical power in real time, providing a normalized reference for subsequent feedback control; the remaining main optical path signal enters the input beam splitter 130.

[0137] In this embodiment, the input beam splitter 130 can be a 1x2 multimode interference coupler (MMI). The input beam splitter divides the optical signal into two beams with equal power and phase. These two beams (i.e., the first optical path signal and the second optical path signal) are respectively sent to the upper and lower branches of the phase modulation feedback module 200 (i.e., the first optical path and the second optical path in the aforementioned embodiment).

[0138] In this embodiment, the input monitoring module 100 serves as a signal input for receiving optical signals from an external light source. The input monitoring module includes a first directional coupler, a first detector, and an input beam splitter. The first directional coupler is configured with an asymmetric beam splitting structure to couple a small portion of the optical power in the main input optical path (e.g., 1% to 5%, i.e., the first detection signal) to the first detector to monitor fluctuations in the input optical power in real time, providing normalized reference data for subsequent feedback control. The input beam splitter (e.g., a 1x2 MMI or Y-branch waveguide) is connected after the first directional coupler to divide the power-monitored optical signal into two equally powerful signals (i.e., the first optical path signal and the second optical path signal), laying the foundation for amplitude balance in generating 45-degree or 135-degree linearly polarized light.

[0139] The upper branch (i.e., the first optical path) and the lower branch (i.e., the second optical path) integrate a first phase modulator 211 and a second phase modulator 221, respectively. The phase modulator can be a miniature metal thermo-optical phase shifter, which changes the local temperature of the silicon waveguide by applying voltage and changes the refractive index of the waveguide by utilizing the thermo-optical effect of silicon material, thereby achieving precise phase control.

[0140] To achieve on-chip closed-loop monitoring, a second directional coupler 212 and a third directional coupler 222 are respectively placed on the waveguide path after each modulator. Both the second directional coupler 212 and the third directional coupler 222 can be designed with extremely low splitting ratios (e.g., 1%), extracting only a very small amount of optical signal from the main optical path as monitoring light. The two monitoring beams extracted by the second directional coupler 212 and the third directional coupler 222 are transmitted through the waveguide to the monitoring end beamsplitter 230 (e.g., a 2x1 MMI or a Y-branch beam combiner) for interference. The interfered optical signal is received by the second detector 240.

[0141] At this point, the light intensity Imon detected by the second detector 240 has a direct mapping relationship (usually a cosine function relationship) with the phase difference between the upper and lower main optical signals. Therefore, by reading the value of Imon, the current phase state of the main optical path can be determined. The two main optical signals (i.e., the first modulation signal and the second modulation signal) after phase modulation enter the polarization synthesis output module 300.

[0142] In this embodiment, the phase modulation feedback module 200 is the core control area, used to introduce a controllable phase difference between two optical signals. This module includes two parallel optical waveguide branches, each equipped with a first phase modulator and a second phase modulator. The phase modulators can employ thermo-optic modulation (e.g., thermo-optic effect or carrier dispersion) to achieve phase shift by changing the waveguide refractive index. To achieve closed-loop control, this embodiment cascades a second directional coupler and a third directional coupler after each phase modulator. These two couplers serve as signal sampling points, extracting minute amounts of optical signal from each of the two branches and transmitting these sampled signals to a monitoring beamsplitter. The monitoring beamsplitter (e.g., a 2x1 beam combiner) coherently superimposes the two sampled signals to form an interference signal, which is then coupled to a second detector. Therefore, the light intensity detected by the second detector reflects the phase difference between the two branches of the main optical path. When the phase difference is 0 or π, the interference light intensity exhibits its maximum or minimum value respectively (depending on the specific phase relationship of the beam combiner), thereby realizing real-time, non-destructive monitoring of the phase state of the main optical path.

[0143] The core component of the polarization combining output module 300 is the polarization beam combiner 310, which can operate in reverse mode as a polarization rotating beam splitter (PSR). The optical signal from the upper branch, as the TE mode (horizontally polarized), directly enters the output waveguide through the PSR. The optical signal from the lower branch is rotated 90 degrees in the PSR to convert it into the TM mode (vertically polarized) before entering the same output waveguide. The output port ultimately outputs a beam of combined light (i.e., the output optical signal). The polarization state of the combined light is obtained by the vector superposition of the TE and TM components, and the combined light ultimately exhibits a linear or elliptical polarization state.

[0144] At the final output of the chip, a beam splitter structure can be used to couple the third detector 320 to the chip. The third detector 320 is used to monitor the on / off state of the switch and the total power, and to perform fault diagnosis of the entire optical link by collecting this data.

[0145] In this embodiment, the polarization combining output module 300 is used to convert two phase-controlled optical signals into a specific polarization state output. The core device of the polarization combining output module is a polarization beam combiner, which can be a polarization rotating beam splitter (PSR) used in reverse. The polarization rotating beam splitter has two input ports: the upper input port allows TE mode optical signals to pass directly; the lower input port rotates the input TE mode optical signal by 90 degrees to convert it into a TM mode optical signal. The TE mode optical signal input from the upper input port and the TM mode optical signal input from the lower input port and rotated are finally converged in the same output waveguide, forming polarized light containing horizontal and vertical components through vector superposition. In addition, a third detector is integrated at the end of the output waveguide, coupled to the optical beam splitter structure. The third detector is used to monitor the final light transmission state and output power stability of the device, facilitating system fault self-diagnosis.

[0146] Based on the aforementioned hardware structure, the polarization switch, in conjunction with the external control circuit, operates in a closed-loop feedback mode. The control circuit acquires the output voltage of the second detector and uses the extreme point (maximum or minimum value) of the second detector's output voltage as the locking target. The control circuit dynamically adjusts the driving voltage applied to the first or second phase modulator. Regardless of changes in ambient temperature, once phase drift occurs, the intensity of the interfering light will deviate from the extreme value, and the feedback circuit will immediately compensate, thereby locking the polarization state of the output light at a preset 45-degree or 135-degree linear polarization state.

[0147] This embodiment employs a closed-loop feedback control method to eliminate phase drift caused by ambient temperature. Figure 9 This is an optional flowchart illustrating the closed-loop feedback control method provided in an embodiment of this application, such as... Figure 9 As shown, the closed-loop feedback control method can be implemented through steps S901 to S907: S901, System Initialization.

[0148] S902, set the target polarization state.

[0149] In some embodiments, the system is powered on and a target operating mode is set, such as requesting the output of 45-degree linearly polarized light.

[0150] S903, acquires monitoring signals (Vmon) from the second detector.

[0151] The control circuit simultaneously reads the voltage signal Vref from the first detector 120 (as an input power reference) and the voltage signal Vmon from the second detector 240 (as a phase monitoring signal). To eliminate the influence of light source power fluctuations, the normalized monitoring value S = Vmon / Vref is calculated. S (i.e., the current monitoring signal) is a normalized monitoring intensity value, dimensionless. The normalized monitoring intensity value is not the phase difference itself, but it is mapped one-to-one with the phase difference Δφ (e.g., a typical cosine relationship): S∝1+cos(Δφ+φ0).

[0152] S904, the current state is not the preset target state.

[0153] The target state is essentially the output polarization state reaching the preset value (45° / 135° linear polarization), which is equivalent to Δφ being locked at 0 or π (mod 2π). In the structure, this is manifested as follows: when the output polarization state is 45°, the monitoring interference is at the constructive interference maximum; when the output polarization state is 135°, the monitoring interference is at the destructive interference minimum.

[0154] To determine whether the current state is the preset target state, it is only necessary to check whether S has reached and stabilized near the target extreme value (maximum / minimum).

[0155] S905 searches for the maximum value of the interference signal when the target polarization state is 45°.

[0156] If the target is set to 45-degree linear polarization (corresponding to a phase difference of 0), according to the interference characteristics of the beam splitter at the monitoring end, the monitoring end should be in a constructive interference (maximum value) state when the target is set to 45-degree linear polarization (corresponding to a phase difference of 0). The control algorithm (e.g., π-D control algorithm or hill-climbing algorithm) compares the current S value (i.e., the current monitoring signal) with the value at the previous moment (i.e., the previous monitoring signal) and fine-tunes the driving voltage applied to the first phase modulator to search for and lock the maximum point of S.

[0157] S906 searches for the minimum value of the interference signal when the target polarization state is 135°.

[0158] If the target is set to 135 degrees linear polarization (corresponding to a phase difference of π), the monitoring end should be in a state of destructive interference (minimum value). The control algorithm adjusts the driving voltage to search for and lock the minimum point of S.

[0159] S907 uses PID control to regulate or adjust the phase modulator voltage.

[0160] When changes in ambient temperature cause a shift in the refractive index of the silicon waveguide, resulting in a deviation of the actual phase difference from 0 or π, the monitored value S will immediately deviate from its extreme point. Upon detecting this deviation, the feedback loop automatically adjusts the voltage of the phase modulator, forcing the system back to its extreme point, thereby ensuring that the output polarization state remains stably locked at a preset 45 degrees or 135 degrees.

[0161] Feedback adjustment can be achieved by applying an initial voltage V (i.e., the drive voltage) to the phase modulator, measuring and recording the current S(k). A step ΔV (positive or negative) is applied to obtain a new signal value S(k+1). If S(k+1) is closer to the target (increasing the value to lock the maximum and decreasing the value to lock the minimum), the current adjustment direction is maintained; otherwise, the adjustment is reversed. This iteration is repeated until the change in parameter S falls within a set threshold range, indicating that parameter S has stabilized near its extreme value. When changes in ambient temperature cause the S parameter to deviate from the preset value, the above iterative process continues to achieve real-time compensation for the deviation.

[0162] In this embodiment, the control circuit acts as the execution entity for comparison, judgment, and adjustment of the drive voltage, and is responsible for completing the relevant operations. The control circuit can be an MCU, an FPGA, or an analog PID.

[0163] The connection between the control circuit and the chip can be achieved by leading heating electrodes, PN junction electrodes, and detector electrodes from the electrode pads on the chip, and then connecting these electrodes to the package substrate or printed circuit board (PCB) using gold wire bonding or flip-chip bonding processes. The control circuit does not need to be integrated on the silicon photonics chip; it can also be integrated with the polarization switch in the same package.

[0164] This application embodiment utilizes silicon-based photonic integration technology to shrink the traditional centimeter-sized bulk lithium niobate polarization module to millimeter- or even micrometer-sized chips. While maintaining the same functionality, this application embodiment reduces volume and weight by more than 95%. The polarization switch implemented using silicon-based photonic integration technology can be easily embedded into the internal space of a thin-diameter fiber optic hydrophone towed array, thereby significantly reducing the array's fluid resistance noise and deployment difficulty.

[0165] This application's embodiments achieve monolithic integration of optical devices, thereby significantly improving system reliability. It utilizes mature complementary metal-oxide-semiconductor (CMOS) technology to fabricate multiple optical components, such as beam splitters, modulators, couplers, and detectors, on a single silicon wafer in a single step (i.e., monolithic integration). Compared to the traditional approach of splicing multiple discrete devices together using fiber optic pigtails, this application's embodiments eliminate numerous fiber optic splices and adhesive points, thus greatly improving the mechanical stability and long-term reliability of devices used in deep-sea environments with high water pressure and strong vibrations.

[0166] The embodiments of this application significantly reduce power consumption and extend the operating time of underwater equipment. By employing the high light confinement capability of silicon waveguides and miniaturized heating electrode design, the required phase modulation power consumption is much lower than that of traditional devices, and high-speed, low-power modulation can be achieved through carrier effects. When applied to underwater detection systems that rely on batteries or remote power, this technical solution can significantly reduce the system's total energy consumption and extend its continuous operating time.

[0167] This application overcomes the challenge of poor thermal stability in silicon photonics devices, achieving environmental adaptability. It innovatively constructs a phase monitoring loop based on the interference principle within the chip (reading Vref and Vmon → normalizing to obtain S → optimizing and locking the extreme value (maximum / minimum) → real-time compensation for temperature drift). This on-chip self-monitoring structure transforms the chip from an open-loop device sensitive to ambient temperature into an intelligent device with self-sensing and self-calibration capabilities. This on-chip self-monitoring structure can offset thermal drift using a simple closed-loop algorithm without relying on external large-scale temperature control equipment, ensuring high precision and high stability of polarization state control.

[0168] This application provides end-to-end status monitoring capabilities, reducing array maintenance costs. It integrates monitoring points across three dimensions: input, intermediate modulation, and output. When constructing large-scale hydrophone arrays, this end-to-end status monitoring capability allows engineers to quickly determine the signal continuity, modulation status, and coupling efficiency of any node, greatly simplifying the array troubleshooting process. This end-to-end status monitoring capability reduces the operation and maintenance costs of the hydrophone array throughout its entire lifecycle.

[0169] It should be understood that the phrase "one embodiment" or "an embodiment" throughout the specification means that a specific feature, structure, or characteristic related to the embodiment is included in at least one embodiment of this application. Therefore, "in one embodiment" or "in an embodiment" appearing throughout the specification does not necessarily refer to the same embodiment. Furthermore, these specific features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. It should be understood that in the various embodiments of this application, the sequence numbers of the above-described processes do not imply a sequential order of execution; the execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application. The sequence numbers of the above-described embodiments are merely descriptive and do not represent the superiority or inferiority of the embodiments.

[0170] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover a non-exclusive inclusion, such that a process, method, or apparatus that includes a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element. In the several embodiments provided in this application, it should be understood that the disclosed devices and methods can be implemented in other ways. The device embodiments described above are merely illustrative; for example, the division of units is only a logical functional division, and in actual implementation, there may be other division methods, such as: multiple units or components may be combined, or integrated into another system, or some features may be ignored or not performed.

[0171] The above are merely embodiments of this application and are not intended to limit the scope of protection of this application. Any modifications, equivalent substitutions, and improvements made within the spirit and scope of this application are included within the scope of protection of this application.

Claims

1. A monolithically integrated polarization switch, characterized in that, The polarization switch includes at least: An input monitoring module is used to receive input optical signals, monitor the power of the input optical signals, and divide the input optical signals into a first optical path signal and a second optical path signal. A phase modulation feedback module is used to perform phase modulation on the first optical path signal and the second optical path signal to obtain a first modulated signal, a second modulated signal, and a phase difference between the first modulated signal and the second modulated signal; A polarization combining output module is used to combine the first modulation signal and the second modulation signal to obtain an output optical signal; The output optical signal is an orthogonally polarized optical signal; the phase difference is used to determine whether the polarization state of the output optical signal is a preset value. If it is not a preset value, the driving voltage applied to the phase modulation feedback module is adjusted until the polarization state of the output optical signal is the preset value.

2. The polarization switch according to claim 1, characterized in that, The input monitoring module includes at least a first directional coupler, a first detector, and an input beam splitter; The first directional coupler is used to receive the input optical signal, perform asymmetric beam splitting on the input optical signal to obtain a first detection signal and a main optical path signal, send the first detection signal to the first detector through the first directional output terminal, and send the main optical path signal to the input beam splitter through the second directional output terminal; The first detector is used to monitor the power of the input optical signal based on the detection signal; The input beam splitter is used to split the main optical path signal to obtain the first optical path signal and the second optical path signal; wherein the power and phase of the first optical path signal and the second optical path signal are equal.

3. The polarization switch according to claim 1, characterized in that, The phase modulation feedback module includes at least a first optical path, a second optical path, a monitoring end beam splitter, and a second detector; The first optical path is used to modulate and split the first optical path signal to obtain a second detection signal and a first modulation signal; The second optical path is used to modulate and split the signal of the second optical path to obtain a third detection signal and a second modulation signal; The monitoring terminal beam splitter is used to combine the second detection signal and the third detection signal to obtain a combined detection signal. The second detector is used to detect the beam combining detection signal to obtain the phase difference between the first modulation signal and the second modulation signal.

4. The polarization switch according to claim 1, characterized in that, The first optical path includes at least a first phase modulator and a second directional coupler connected in sequence, and the second optical path includes at least a second phase modulator and a third directional coupler connected in sequence; The first phase modulator is used to modulate the first optical path signal to obtain a first signal; The second directional coupler is used to split the first signal based on a preset splitting ratio to obtain a second detection signal and the first modulation signal; The second phase modulator is used to modulate the second optical path signal to obtain a second signal; The third directional coupler is used to split the second signal based on a preset splitting ratio to obtain a third detection signal and a second modulation signal.

5. The polarization switch according to claim 1, characterized in that, The polarization combining output module includes at least a polarization beam combiner and a third detector; The polarization combiner is used to perform polarization state conversion and combine the first modulation signal and the second modulation signal to obtain the output optical signal; The third detector is used to detect the output optical signal and obtain the detection result.

6. A control method for a polarization switch, characterized in that, A control circuit applied in a control system, the control system further comprising a polarization switch as described in any one of claims 1 to 5 connected to the control circuit; the control method comprising: By applying a driving voltage to the phase modulator in the polarization switch, the first voltage of the first detector and the second voltage of the second detector in the polarization switch at the current moment are obtained. Based on the first voltage and the second voltage, a current monitoring signal is determined; wherein, the current monitoring signal has a cosine mapping relationship with the phase difference between the first modulation signal and the second modulation signal output by the phase modulation feedback module in the polarization switch; the phase modulation feedback module includes at least the phase modulator; Based on the current monitoring signal, determine the output state of the output optical signal of the polarization switch; In response to the output state being a non-target state, the driving voltage applied to the phase modulator is adjusted until the output state reaches the target state; the phase modulator includes at least one of a first phase modulator and a phase modulator; the target state characterizes the polarization state of the output optical signal as a preset value.

7. The control method according to claim 6, characterized in that, Determining the output state of the polarization switch's output optical signal based on the current monitoring signal includes: Obtain the previous monitoring signal from the previous moment; The previous monitoring signal is compared with the current monitoring signal to obtain a comparison result; the comparison result includes whether the current monitoring signal is an extreme value or a non-extreme value. Based on the comparison results, the output state is determined.

8. The control method according to claim 7, characterized in that, When the preset value is 45 degrees of linear polarization, the current monitoring signal should be at its maximum value; when the preset value is 135 degrees of linear polarization, the current monitoring signal should be at its minimum value. Correspondingly, determining the output state based on the comparison result includes: When the preset value is 45 degrees of linear polarization, if the comparison result indicates one of the following: the current monitoring signal is less than the previous monitoring signal, or the current monitoring signal is greater than or equal to the previous monitoring signal, and the difference between the current monitoring signal and the target maximum value is greater than a preset threshold, then the output state is determined to be the non-target state. When the preset value is 135 degrees of linear polarization, if the comparison result indicates one of the following: the current monitoring signal is greater than the previous monitoring signal, or the current monitoring signal is less than or equal to the previous monitoring signal, and the difference between the current monitoring signal and the target minimum value is greater than a preset threshold, then the output state is determined to be the non-target state.

9. The control method according to any one of claims 6 to 8, characterized in that, Adjusting the driving voltage applied to the phase modulator until the output state reaches the target state includes: The driving voltage is adjusted in a target direction to obtain an adjustment monitoring signal; the target direction includes increasing or decreasing the voltage. If the preset value is 45 degrees of linear polarization, and the adjusted monitoring signal is greater than the current monitoring signal, the adjustment continues based on the target direction until the adjusted monitoring signal is less than or equal to the current monitoring signal. If the preset value is 135 degrees of linear polarization, and the adjustment monitoring signal is less than the current monitoring signal, the adjustment continues based on the target direction until the adjustment monitoring signal is greater than or equal to the current monitoring signal.

10. A control system, characterized in that, The control system includes at least the polarization switch and control circuit as described in any one of claims 1 to 5; The control circuit, connected to the polarization switch, applies a driving voltage to the phase modulator in the polarization switch to obtain a first voltage of the first detector and a second voltage of the second detector in the polarization switch at the current moment; based on the first voltage and the second voltage, it determines the current monitoring signal; wherein the current monitoring signal has a cosine mapping relationship with the phase difference between the first modulation signal and the second modulation signal output by the phase modulation feedback module in the polarization switch; the phase modulation feedback module includes at least the phase modulator; based on the current monitoring signal, it determines the output state of the output optical signal of the polarization switch; in response to the output state being a non-target state, it adjusts the driving voltage applied to the phase modulator until the output state reaches the target state; the phase modulator includes at least one of a first phase modulator and a phase modulator; the target state characterizes the polarization state of the output optical signal as a preset value.

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