Fiber polarization control system based on electro-optic phase modulation

Abstract

The application discloses an optical fiber polarization control system based on electro-optic phase modulation, wherein an arbitrary waveform generator provides a first driving signal and a second driving signal to a first electro-optic phase modulator and a second electro-optic phase modulator in an MZI interferometer respectively; a polarization beam splitter divides a received laser signal into two paths, and the two paths of laser signals are transmitted to the MZI interferometer through a first transmission path and a second transmission path; the MZI interferometer regulates the relative amplitude of the two paths of laser signals according to the first driving signal; the second electro-optic phase modulator regulates the relative phase of the two paths of laser signals according to the second driving signal; and the polarization beam combiner combines and outputs the two paths of laser signals which have completed the regulation of the relative amplitude and phase, thereby forming a laser signal with a corresponding polarization state. The application can realize high-speed regulation of an arbitrary polarization state of an arbitrary waveband laser signal, and has a simple structure.

Description

Technical Field

[0001] This invention belongs to the field of laser polarization control, specifically relating to a fiber polarization control system based on electro-optic phase modulation. Background Technology

[0002] In recent decades, with the increase in transmission rates of fiber optic communication systems, polarization control technology has received widespread attention. In the 1064 nm band, due to the widespread application of Nd:YAG lasers and ytterbium-doped fiber lasers, this band has become the core operating wavelength for laser processing, high-power laser coherent combining, spectral combining, and nonlinear frequency conversion systems. In these applications, the laser polarization state directly affects the system performance. For example, in high-power laser coherent combining, the consistency of the polarization states of multiple lasers is crucial for achieving high-efficiency, high-beam-quality combining; in spectral combining, efficient matching of the polarization state of each wavelength channel with the combining grating is essential; in nonlinear frequency conversion, the polarization state is a core element of the phase-matching condition, directly determining the energy conversion efficiency. Therefore, precise and stable polarization control of 1064 nm lasers is not only a guarantee for the efficient and stable operation of the aforementioned systems, but also a key technology for improving overall system performance and promoting the development of related technologies to a higher level. Polarization control is also of critical importance in the 1550 nm band. This wavelength band is the mainstream operating wavelength for fiber optic communication, lidar, quantum communication, and optical sensing. The polarization state of the laser directly affects the core performance of the system. For example, in high-speed coherent optical communication, the polarization state of the signal directly carries information, and precise polarization control and tracking are fundamental to overcoming channel polarization disturbances, achieving high-sensitivity coherent demodulation, and maintaining ultra-low bit error rates. In high-precision sensing or quantum key distribution systems based on fiber optic interferometers, polarization drift directly introduces noise or bit errors, requiring rapid and stable compensation and control. Therefore, achieving precise and dynamic polarization control of 1550 nm lasers is a core technological prerequisite for ensuring the high-performance and high-reliability operation of the aforementioned systems.

[0003] Existing fiber polarization control technologies mainly include fiber squeeze polarization controllers based on mechanical perturbations and free-space polarization modulators based on waveplates or liquid crystals. These solutions typically rely on mechanical adjustment or slow electronic control response of the fiber or optical components, resulting in limited modulation bandwidth, large system size, insufficient long-term stability, and difficulty in integration with all-fiber systems. Especially in high-power or high-speed applications, these methods struggle to simultaneously meet the requirements of fast response, long-term stability, and fiber compatibility.

[0004] On the other hand, phase modulators based on the electro-optic effect have been widely used in high-speed optical communication and laser modulation, offering advantages such as fast response speed, high modulation accuracy, and ease of fiber integration. However, existing polarization control schemes based on electro-optic modulators rely on a combination of commercially available low-speed electrically controlled polarization controllers and phase modulators, resulting in complex system structures and an applicable wavelength range of 1550 nm.

[0005] Therefore, researching high-speed fiber polarization control structures that can be applied in multiple wavelength bands, while maintaining the advantages of high-speed electro-optic modulation and possessing the characteristics of simple structure, is a technical challenge that needs to be overcome in this field. Summary of the Invention

[0006] This invention provides an optical fiber polarization control system based on electro-optic phase modulation to solve the problems of slow polarization state modulation speed, complex structure, narrow coverage band, and inability to achieve arbitrary polarization state modulation.

[0007] According to a first aspect of the present invention, an optical fiber polarization control system based on electro-optic phase modulation is provided, comprising a polarization beam splitter, a Mach-Zehnder MZI interferometer, a second electro-optic phase modulator, an arbitrary waveform generator, and a polarization beam combiner, wherein the arbitrary waveform generator provides a first driving signal and a second driving signal to the first electro-optic phase modulator and the second electro-optic phase modulator in the MZI interferometer, respectively. The polarization beam splitter splits the received laser signal into two paths, and the two laser signals are transmitted to the MZI interferometer after passing through the first transmission path and the second transmission path, respectively. The MZI interferometer modulates and outputs the relative amplitude of the two laser signals according to the first driving signal; one of the two output laser signals is transmitted to the polarization beam combiner through the first electro-optic phase modulator, and the other is transmitted to the polarization beam combiner through the third transmission path. The second electro-optic phase modulator adjusts the relative phase of the two laser signals transmitted to the polarization combiner according to the second driving signal; This polarization beam combiner combines two laser signals with relative amplitude and phase modulation to form a laser signal with a corresponding polarization state.

[0008] Optionally, the input end of the polarization beam splitter is used to input laser signals, and the two output ends are connected to the input end of the MZI interferometer through the first transmission path and the second transmission path, respectively. One output end of the MZI interferometer is connected to the first input end of the polarization beam combiner through the second electro-optic phase modulator, and the other output end is connected to the second input end of the polarization beam combiner through the third transmission path. The laser signal received by the polarization beam splitter is a laser signal of arbitrary wavelength, and the two laser signals it splits into have the same polarization state and are mutually irrational.

[0009] Optionally, the MZI interferometer includes a first coupler, a first electro-optic phase modulator, a fourth transmission path, and a second coupler. The two outputs of the polarization beam splitter are connected to the two inputs of the first coupler through the first transmission path and the second transmission path, respectively. The two outputs of the first coupler are connected to the two inputs of the second coupler through the first electro-optic phase modulator and the fourth transmission path, respectively. The two outputs of the second coupler are connected to the two inputs of the polarization beam combiner through the second electro-optic phase modulator and the third transmission path, respectively.

[0010] Optionally, all devices in the system are polarization-maintaining devices and maintain slow-axis alignment, wherein the polarization beam splitter is a polarization-maintaining fiber polarization beam splitter; the first coupler and the second coupler are both polarization-maintaining fiber couplers; the first to fourth transmission paths are polarization-maintaining fibers; and the two laser signals transmitted in the system are both two orthogonal polarization components.

[0011] Optionally, both the first and second electro-optic phase modulators are lithium niobate electro-optic phase modulators.

[0012] Optionally, the third and fourth transmission paths introduce the same optical path.

[0013] Optionally, the Stokes parameter used to represent the polarization state is related to the first driving voltage in the first driving signal. The second driving voltage in the second driving signal The relationship between them is represented as follows: in , and There are three Stokes parameters. The phase introduced for the first electro-optic phase modulator, The phase introduced for the second electro-optic phase modulator, The half-wave voltage of the first electro-optic phase modulator, The half-wave voltage of the second electro-optic phase modulator; When controlling the polarization state, the Stokes parameter corresponding to the required polarization state of the output laser signal and the relationship between the Stokes parameter and the first driving voltage are used. Second driving voltage The relationship between the two is used to determine the first driving voltage and the second driving voltage that the arbitrary waveform generator should provide to the first electro-optic phase modulator and the second electro-optic phase modulator, respectively.

[0014] Optionally, the phase introduced by the first electro-optic phase modulator The relative amplitude distribution of the two laser signals is determined, which in turn determines the latitudinal position of the polarization state on the Poincaré sphere; the phase introduced by the second electro-optic phase modulator... It determines the azimuth angle of the polarization state in the equatorial plane; The phase introduced by the first electro-optic phase modulator i Represented as: i = ,in The first driving voltage in the first driving signal. The half-wave voltage of the first electro-optic phase modulator; The relative phase φ introduced by the second electro-optic phase modulator is expressed as: φ= ,in The second driving voltage in the second driving signal. The half-wave voltage of the second electro-optic phase modulator; When modulating the polarization state, the latitudinal position of the polarization state on the Poincaré sphere and the azimuth angle of the polarization state in the equatorial plane are determined according to the required polarization state of the output laser signal. Based on the determined latitudinal position, the phase to be introduced by the first electro-optic phase modulator is determined. Based on the determined azimuth angle, the phase introduced by the second electro-optic phase modulator is determined. According to phase Determine the first driving voltage in the first driving signal; based on the phase Determine the second driving voltage in the second driving signal.

[0015] Optionally, it also includes a controller connected to the arbitrary waveform generator, which locally stores Stokes parameters and a first drive voltage. Second driving voltage The relationship between these parameters is based on the Stokes parameters corresponding to the desired polarization state and the relationship between the Stokes parameters and the first driving voltage. Second driving voltage The relationship between the two is used to determine the first driving voltage and the second driving voltage that the arbitrary waveform generator should provide to the first electro-optic phase modulator and the second electro-optic phase modulator, respectively, and to send control commands including the first driving voltage and the second driving voltage to the arbitrary waveform generator.

[0016] Optionally, the device also includes a controller connected to the arbitrary waveform generator, which locally stores the latitudinal positions of different polarization states on the Poincaré sphere, as well as the azimuth angle of the polarization states in the equatorial plane, the latitudinal positions, and the phase introduced by the first electro-optic phase modulator. The relationship between the azimuth angle and the phase introduced by the second electro-optic phase modulator Relationships and phases Relationship with the first driving voltage and phase The relationship between the input polarization state and the second driving voltage is determined based on the latitude of the desired polarization state on the Poincaré sphere, the azimuth angle of the polarization state in the equatorial plane, and the above correspondence. The arbitrary waveform generator should provide the first driving voltage and the second driving voltage to the first electro-optic phase modulator and the second electro-optic phase modulator respectively, and the control command including the first driving voltage and the second driving voltage is sent to the arbitrary waveform generator.

[0017] The beneficial effects of this invention are: 1. This invention represents the polarization state of a laser signal as the superposition of complex amplitudes of two orthogonal polarization components. Their relative amplitude and phase determine the polarization state of the output laser signal. That is, the polarization state control of the laser signal is divided into amplitude control and phase control. An MZI interferometer is used to control the relative amplitude of the two transmitted laser signals in the system, and a second electro-optic phase modulator is used to control the relative phase of the two transmitted laser signals in the system. This allows for high-speed adjustment of the arbitrary polarization state of laser signals in any wavelength band. When controlling the relative amplitude and phase, an arbitrary waveform generator controls the first and second electro-optic phase modulators in the MZI interferometer. This requires no mechanical or spatial optical components, has a compact structure, is easy to integrate, and enables high-speed dynamic polarization control. Programming the arbitrary waveform generator allows for programmable control of the arbitrary polarization state, i.e., controlling the polarization change trajectory and speed. Furthermore, by applying a high-speed signal to the phase modulator, it can be used as a high-speed polarization scrambler. 2. All devices in the system of this invention are polarization-maintaining devices and maintain slow-axis alignment, which can ensure that the polarization reference of the two laser signals remains stable throughout the entire transmission process, with only the phase changing; 3. This invention uses a lithium niobate electro-optic phase modulator for phase modulation, which has a fast response speed and supports high-speed dynamic polarization control; 4. The third and fourth transmission paths of this invention introduce the same optical path, thereby ensuring that the optical path difference between the two laser signals is only introduced by the first electro-optic phase modulator and the second electro-optic phase modulator, which facilitates subsequent control. 5. This invention uses Stokes parameters to represent different polarization states, based on the Stokes parameters and the first driving voltage. Second driving voltage The relationship between polarization states is used to control polarization state, which is a more common method. Different points on the Poincaré sphere are used to represent different polarization states, and then polarization state control is performed. The output laser signal can achieve full polarization state adjustment covering the entire Poincaré sphere, and the control logic is clear and the control process is intuitive. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of an embodiment of the fiber polarization control system based on electro-optic phase modulation of the present invention. Detailed Implementation

[0019] To enable those skilled in the art to better understand the technical solutions in the embodiments of the present invention, and to make the above-mentioned objectives, features and advantages of the embodiments of the present invention more apparent and understandable, the technical solutions in the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0020] In the description of this invention, unless otherwise specified and limited, it should be noted that the term "connection" should be interpreted broadly. For example, it can be a mechanical connection or an electrical connection, or it can be a connection between two internal components. It can be a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above term according to the specific circumstances.

[0021] See Figure 1 This is a schematic diagram of an embodiment of the fiber polarization control system based on electro-optic phase modulation of the present invention. The fiber polarization control system based on electro-optic phase modulation may include a polarization beamsplitter (PBS), a Mach-Zehnder (MZI) interferometer, a second electro-optic phase modulator (PM2), an arbitrary waveform generator (AWG), and a polarization beam combiner (PBC). The AWG provides a first driving signal and a second driving signal to the first electro-optic phase modulator (PM1) and the second electro-optic phase modulator (PM2) in the MZI interferometer, respectively. The polarization beamsplitter (PBS) splits the received laser signal into two paths, which are then transmitted to the MZI interferometer via a first transmission path (P1) and a second transmission path (P2), respectively. The MZI interferometer modulates and outputs the relative amplitudes of the two laser signals according to the first driving signal. One of the two output laser signals is transmitted to the polarization combiner PBC through the first electro-optic phase modulator PM1, and the other is transmitted to the polarization combiner PBC through the third transmission path P3. The second electro-optic phase modulator PM2 modulates the relative phases of the two laser signals transmitted to the polarization combiner PBC according to the second driving signal. The polarization combiner PBC combines the two laser signals with relative amplitude and phase modulation to form a laser signal with a corresponding polarization state.

[0022] In this embodiment, the laser signal received by the polarization beamsplitter (PBS) can be a laser signal of any wavelength, and the two laser signals it splits into have the same polarization state and are mutually coherent, thus facilitating the provision of a unified polarization reference for the subsequent MZI interferometer. The input terminal of the polarization beamsplitter (PBS) is used to input the laser signal, and its two output terminals are connected to the input terminal of the MZI interferometer through the first transmission path P1 and the second transmission path P2, respectively. One output terminal of the MZI interferometer is connected to the first input terminal of the polarization beam combiner (PBC) through the second electro-optic phase modulator (PM2), and the other output terminal is connected to the second input terminal of the polarization beam combiner (PBC) through the third transmission path P3.

[0023] The MZI interferometer may include a first coupler OC1, a first electro-optic phase modulator PM1, a fourth transmission path P4, and a second coupler OC2. The two outputs of the polarization beam splitter PBS are connected to the two inputs of the first coupler OC1 via the first transmission path P1 and the second transmission path P2, respectively. The two outputs of the first coupler OC1 are connected to the two inputs of the second coupler OC2 via the first electro-optic phase modulator PM1 and the fourth transmission path P4, respectively. The two outputs of the second coupler OC2 are connected to the two inputs of the polarization beam combiner PBC via the second electro-optic phase modulator PM2 and the third transmission path P3, respectively.

[0024] In this invention, all devices in the system are polarization-maintaining devices and maintain slow-axis alignment to ensure that the polarization reference of the two laser signals remains stable throughout the transmission process, with only the phase changing. The polarization beamsplitter can be a polarization-maintaining fiber polarization beamsplitter; the first and second couplers can both be polarization-maintaining fiber couplers; the first to fourth transmission paths can be polarization-maintaining fibers; and the first and second electro-optic phase modulators can both be lithium niobate electro-optic phase modulators. This invention uses lithium niobate electro-optic phase modulators for phase modulation, resulting in fast response and support for high-speed dynamic polarization control.

[0025] In this embodiment, the polarization beam splitter PBS splits the received laser signal into two laser signals with the same polarization state and mutual interference. The two laser signals are then transmitted to the first coupler OC1 through the first transmission path P1 and the second transmission path P2, respectively. At the first coupler OC1, the two laser signals interfere, and the interfered laser signal is split into two paths by the first coupler OC1 (under the premise that the polarization beam splitter, the first transmission path and the second transmission path remain unchanged, the power distribution constant of the two laser signals split by the first coupler OC1 is usually fixed). The two laser signals are then transmitted to the second coupler OC2 through the first electro-optic phase modulator PM1 and the fourth transmission path P4, respectively. Interference occurs at the second coupler OC2, and the interfered laser signal is split into two paths by the second coupler OC2 (the power distribution constant of the two laser signals split by the second coupler OC2 is determined by the phase change introduced by the first electro-optic phase modulator). The two laser signals are then transmitted to the polarization beam combiner PBC through the second electro-optic phase modulator PM2 and the third transmission path, respectively.

[0026] This invention introduces a first transmission path and a second transmission path between the polarization beamsplitter and the MZI interferometer. This is to enable the polarization beamsplitter, the first transmission path, the second transmission path, and the first coupler to jointly construct a structurally symmetrical, phase-sensitive interference unit. In this way, the phase change introduced by the first electro-optic phase modulator in the MZI interferometer can be converted into a power redistribution of the two laser signals. That is, only with the introduction of the first and second transmission paths can the MZI interferometer modulate the relative amplitude of the two laser signals through the interference of the first and second couplers and the phase change introduced by the first electro-optic phase modulator. If the two laser signals output from the polarization beamsplitter are directly transmitted to the first electro-optic phase modulator and the fourth transmission path respectively, without passing through this structurally symmetrical, phase-sensitive interference unit, then the phase change introduced by the first electro-optic phase modulator will only manifest as an optical path delay and will not be able to affect the amplitude distribution of the two laser signals through interference.

[0027] It is important to note that the third transmission path P3 and the fourth transmission path P4 introduce the same optical path length, thus ensuring that the optical path difference between the two laser signals is introduced only by the first and second electro-optic phase modulators, facilitating subsequent control. At this point, the phase introduced by the first electro-optic phase modulator located between the first and second couplers will be coherently superimposed at the second coupler and converted into a power distribution of the two laser signals, achieving a phase-to-amplitude mapping. The second electro-optic phase modulator located after the second coupler introduces a controllable relative phase difference between the two laser signals without altering their amplitude distribution. In this invention, the two transmitted laser signals can each be two orthogonal polarization components.

[0028] As can be seen from the above embodiments, the present invention represents the polarization state of a laser signal as the superposition of complex amplitudes of two orthogonal polarization components. Their relative amplitude and phase determine the polarization state of the output laser signal. That is, the polarization state control of the laser signal is divided into amplitude control and phase control. The relative amplitude of the two laser signals transmitted in the system is controlled by an MZI interferometer, and the relative phase of the two laser signals transmitted in the system is controlled by a second electro-optic phase modulator. This enables high-speed adjustment of arbitrary polarization state of laser signals in any band. When controlling the relative amplitude and phase, the arbitrary waveform generator controls the first and second electro-optic phase modulators in the MZI interferometer. This requires no mechanical or spatial optical components, has a compact structure, is easy to integrate, and can achieve high-speed dynamic polarization control. By programming the arbitrary waveform generator, programmable control of arbitrary polarization state can be achieved, that is, controlling the polarization change trajectory and speed. At the same time, a high-speed signal can be applied to the phase modulator to use it as a high-speed polarization scrambler.

[0029] When adjusting the polarization state, the first and second drive signals output by the arbitrary waveform generator can be controlled in the following two ways according to the desired polarization state: First, establish the Stokes parameters representing the polarization state and the first driving voltage in the first driving signal. The second driving voltage in the second driving signal The relationship between the Stokes parameter used to represent the polarization state and the first driving voltage in the first driving signal. The second driving voltage in the second driving signal The relationship between them is represented as follows:

[0030] in , and There are three Stokes parameters. The phase introduced for the first electro-optic phase modulator, The phase introduced for the second electro-optic phase modulator, The half-wave voltage of the first electro-optic phase modulator, The half-wave voltage of the second electro-optic phase modulator; When controlling the polarization state, the Stokes parameter corresponding to the required polarization state of the output laser signal and the relationship between the Stokes parameter and the first driving voltage are used. Second driving voltage The relationship between the two is used to determine the first driving voltage and the second driving voltage that the arbitrary waveform generator should provide to the first electro-optic phase modulator and the second electro-optic phase modulator, respectively.

[0031] Second, different polarization states are considered as corresponding points on a Poincaré sphere, and the polarization state is equivalently represented as the superposition of complex amplitudes of two orthogonal polarization components. Their relative amplitudes and phases determine the polarization state of the output laser signal. The phase introduced by this first electro-optic phase modulator... The relative amplitude distribution of the two laser signals is determined, which in turn determines the latitudinal position of the polarization state on the Poincaré sphere; the phase introduced by the second electro-optic phase modulator... This determines the azimuth angle of the polarization state in the equatorial plane. The phase introduced by this first electro-optic phase modulator... i Represented as:

[0032] i = ,in The first driving voltage in the first driving signal. The half-wave voltage of the first electro-optic phase modulator; The relative phase φ introduced by the second electro-optic phase modulator is expressed as: φ= ,in The second driving voltage in the second driving signal. The half-wave voltage of the second electro-optic phase modulator; When modulating the polarization state, the latitudinal position of the polarization state on the Poincaré sphere and the azimuth angle of the polarization state in the equatorial plane are determined according to the required polarization state of the output laser signal. Based on the determined latitudinal position, the phase to be introduced by the first electro-optic phase modulator is determined. Based on the determined azimuth angle, the phase introduced by the second electro-optic phase modulator is determined. According to phase Determine the first driving voltage in the first driving signal; based on the phase The second driving voltage in the second driving signal is determined. This invention uses Stokes parameters to represent different polarization states, based on the Stokes parameters and the first driving voltage. Second driving voltage The relationship between polarization states is used to control polarization state, which is a more common method. Different points on the Poincaré sphere are used to represent different polarization states, and then polarization state control is performed. The output laser signal can achieve full polarization state adjustment covering the entire Poincaré sphere, and the control logic is clear and the control process is intuitive.

[0033] Additionally, the present invention may also include a controller connected to the arbitrary waveform generator, the controller being able to locally store Stokes parameters and a first drive voltage. Second driving voltage The relationship between these parameters can be determined based on the Stokes parameters corresponding to the desired polarization state and the relationship between the Stokes parameters and the first driving voltage. Second driving voltage The relationship between the two parameters determines the first driving voltage and the second driving voltage that the arbitrary waveform generator should provide to the first electro-optic phase modulator and the second electro-optic phase modulator, respectively, and sends a control command including the first driving voltage and the second driving voltage to the arbitrary waveform generator; and / or, The controller can locally store the latitudinal positions of different polarization states on the Poincaré sphere, as well as the azimuth angle and latitudinal position of the polarization states in the equatorial plane, and the phase introduced by the first electro-optic phase modulator. The relationship between the azimuth angle and the phase introduced by the second electro-optic phase modulator Relationships and phases Relationship with the first driving voltage and phase The relationship between the first and second driving voltages can be determined based on the latitude of the desired polarization state on the Poincaré sphere, the azimuth of the polarization state on the equatorial plane, and the aforementioned correspondence. This allows the arbitrary waveform generator to determine the first and second driving voltages that it should provide to the first and second electro-optic phase modulators, respectively, and to send control commands including the first and second driving voltages to the arbitrary waveform generator.

[0034] This invention achieves this by independently adjusting the drive voltages of two phase modulators. V 1 , V 2 This allows for continuous and controllable trajectory scanning on the surface of the Poincaré sphere, thereby generating arbitrary polarization states. Both PM1 and PM2 can be simultaneously subjected to DC bias and AC modulation signals. The DC bias is used to set the system's operating point, i.e., to determine the reference position of the current polarization state on the Poincaré sphere; the AC signal can be used to achieve dynamic polarization control and polarization perturbation. For example, when the DC bias of PM2 is set to 0, and an AC modulation signal (such as a sine wave or triangular wave) with a voltage 1.5 times the half-wave voltage is applied to PM1, the output polarization can continuously rotate along the equator of the Poincaré sphere.

[0035] The response speed of polarization control is crucial in polarization disturbances, and its speed is limited only by the bandwidth of the two phase modulators and the arbitrary waveform generator. The speed can be controlled by the frequencies of the two channels of the AWG. The polarization control rate can be calculated using the following formula:

[0036] in i range and f range These represent the phase shift ranges applied to PM1 and PM2, respectively. f θ and f φ These represent the signal frequencies applied to PM1 and PM2, respectively. Therefore, it can be seen that this structure can achieve rapid polarization control and scrambling when high-speed signals are applied to the two phase modulators.

[0037] Other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein.

[0038] It should be understood that the present invention is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is defined solely by the appended claims.

Claims

1. A fiber optic polarization control system based on electro-optic phase modulation, characterized in that, It includes a polarization beam splitter, a Mach-Zehnder MZI interferometer, a second electro-optic phase modulator, an arbitrary waveform generator, and a polarization beam combiner. The arbitrary waveform generator provides a first driving signal and a second driving signal to the first electro-optic phase modulator and the second electro-optic phase modulator in the MZI interferometer, respectively. The polarization beam splitter splits the received laser signal into two paths, and the two laser signals are transmitted to the MZI interferometer after passing through the first transmission path and the second transmission path, respectively. The MZI interferometer modulates and outputs the relative amplitude of the two laser signals according to the first driving signal; one of the two output laser signals is transmitted to the polarization beam combiner through the first electro-optic phase modulator, and the other is transmitted to the polarization beam combiner through the third transmission path. The second electro-optic phase modulator adjusts the relative phase of the two laser signals transmitted to the polarization combiner according to the second driving signal; This polarization beam combiner combines two laser signals with relative amplitude and phase modulation to form a laser signal with a corresponding polarization state.

2. The fiber polarization control system based on electro-optic phase modulation according to claim 1, characterized in that, The input end of the polarization beam splitter is used to input laser signals, and the two output ends are connected to the input end of the MZI interferometer through the first transmission path and the second transmission path, respectively. One output end of the MZI interferometer is connected to the first input end of the polarization beam combiner through the second electro-optic phase modulator, and the other output end is connected to the second input end of the polarization beam combiner through the third transmission path. The laser signal received by the polarization beam splitter is a laser signal of arbitrary wavelength, and the two laser signals it splits into have the same polarization state and are mutually irrational.

3. The fiber polarization control system based on electro-optic phase modulation according to claim 1 or 2, characterized in that, The MZI interferometer includes a first coupler, a first electro-optic phase modulator, a fourth transmission path, and a second coupler. The two outputs of the polarization beam splitter are connected to the two inputs of the first coupler through the first transmission path and the second transmission path, respectively. The two outputs of the first coupler are connected to the two inputs of the second coupler through the first electro-optic phase modulator and the fourth transmission path, respectively. The two outputs of the second coupler are connected to the two inputs of the polarization beam combiner through the second electro-optic phase modulator and the third transmission path, respectively.

4. The fiber polarization control system based on electro-optic phase modulation according to claim 3, characterized in that, All devices in this system are polarization-maintaining devices and maintain slow-axis alignment. The polarization beam splitter is a polarization-maintaining fiber polarization beam splitter. The first and second couplers are both polarization-maintaining fiber couplers. The first to fourth transmission paths are polarization-maintaining fibers. The two laser signals transmitted in the system are both two orthogonal polarization components.

5. The fiber polarization control system based on electro-optic phase modulation according to claim 3, characterized in that, Both the first and second electro-optic phase modulators are lithium niobate electro-optic phase modulators.

6. The fiber polarization control system based on electro-optic phase modulation according to claim 3, characterized in that, The third and fourth transmission paths introduce the same optical path.

7. The fiber polarization control system based on electro-optic phase modulation according to claim 1, characterized in that, The Stokes parameters used to represent the polarization state and the first driving voltage in the first driving signal. The second driving voltage in the second driving signal The relationship between them is represented as follows: in , and There are three Stokes parameters. The phase introduced for the first electro-optic phase modulator, The phase introduced for the second electro-optic phase modulator, The half-wave voltage of the first electro-optic phase modulator, The half-wave voltage of the second electro-optic phase modulator; When controlling the polarization state, the Stokes parameter corresponding to the required polarization state of the output laser signal and the relationship between the Stokes parameter and the first driving voltage are used. Second driving voltage The relationship between the two is used to determine the first driving voltage and the second driving voltage that the arbitrary waveform generator should provide to the first electro-optic phase modulator and the second electro-optic phase modulator, respectively.

8. The fiber polarization control system based on electro-optic phase modulation according to claim 1 or 7, characterized in that, The phase introduced by the first electro-optic phase modulator The relative amplitude distribution of the two laser signals is determined, which in turn determines the latitudinal position of the polarization state on the Poincaré sphere; the phase introduced by the second electro-optic phase modulator... It determines the azimuth angle of the polarization state in the equatorial plane; The phase introduced by the first electro-optic phase modulator θ Represented as: θ = ,in The first driving voltage in the first driving signal. The half-wave voltage of the first electro-optic phase modulator; The relative phase φ introduced by the second electro-optic phase modulator is expressed as: φ= ,in The second driving voltage in the second driving signal. The half-wave voltage of the second electro-optic phase modulator; When modulating the polarization state, the latitudinal position of the polarization state on the Poincaré sphere and the azimuth angle of the polarization state in the equatorial plane are determined according to the required polarization state of the output laser signal. Based on the determined latitudinal position, the phase to be introduced by the first electro-optic phase modulator is determined. Based on the determined azimuth angle, the phase introduced by the second electro-optic phase modulator is determined. According to phase Determine the first driving voltage in the first driving signal; based on the phase Determine the second driving voltage in the second driving signal.

9. The fiber polarization control system based on electro-optic phase modulation according to claim 7, characterized in that, It also includes a controller connected to the arbitrary waveform generator, which locally stores Stokes parameters and a first drive voltage. Second driving voltage The relationship between these parameters is based on the Stokes parameters corresponding to the desired polarization state and the relationship between the Stokes parameters and the first driving voltage. Second driving voltage The relationship between the two is used to determine the first driving voltage and the second driving voltage that the arbitrary waveform generator should provide to the first electro-optic phase modulator and the second electro-optic phase modulator, respectively, and to send control commands including the first driving voltage and the second driving voltage to the arbitrary waveform generator.

10. The fiber polarization control system based on electro-optic phase modulation according to claim 8, characterized in that, It also includes a controller connected to the arbitrary waveform generator, which locally stores the latitudinal positions of different polarization states on the Poincaré sphere, as well as the azimuth angle, latitudinal position, and phase introduced by the first electro-optic phase modulator in the equatorial plane. The relationship between the azimuth angle and the phase introduced by the second electro-optic phase modulator Relationships and phases Relationship with the first driving voltage and phase The relationship between the input polarization state and the second driving voltage is determined based on the latitude of the desired polarization state on the Poincaré sphere, the azimuth angle of the polarization state in the equatorial plane, and the above correspondence. The arbitrary waveform generator should provide the first driving voltage and the second driving voltage to the first electro-optic phase modulator and the second electro-optic phase modulator respectively, and the control command including the first driving voltage and the second driving voltage is sent to the arbitrary waveform generator.

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