Mode-locked laser based on cross-polarization feedback injection and control method thereof

Abstract

The invention discloses a mode-locked laser based on cross-polarization feedback injection and a control method thereof, and belongs to the technical field of lasers, a light beam emitted by a VCSEL laser is divided into two beams through an optical splitter, the first beam is divided into a first TM mode light beam and a first TE mode light beam through a first polarization-maintaining beam splitter, the two beams form an annular loop on a light path, and the first TM mode light beam and the first TE mode light beam form an annular loop on the light path; and a half-wave plate is arranged on the loop. And the two beams of light are respectively and oppositely propagated along the annular loop, return to the VCSEL laser after being subjected to polarization state conversion by the half-wave plate, are reflected by a resonant cavity of the VCSEL laser again, are coupled into the resonant cavity after being subjected to secondary polarization state conversion by the half-wave plate, and finally finish the output of the mode-locked laser. The laser reaches a mode-locked state by adjusting the angle of the half-wave plate. The laser uses an orthogonal polarization feedback injection mechanism, does not need to use a saturable absorber and a polarization inverter, is simple in structure and easy to implement, greatly reduces the cost and complexity of a system, and meets the requirements of different application scenes.

Description

Technical Field

[0001] The invention belongs to the technical field of lasers and relates to a mode-locked laser based on orthogonal polarization feedback injection and a control method thereof. Background Art

[0002] At a time when optoelectronics technology is booming, ultrashort pulse light sources, with their unique properties, occupy an irreplaceable position in cutting-edge research fields such as high-speed optical communications, microwave photonics, biomedical imaging, nonlinear optics, and precision optical sensing. They are core devices that promote technological innovation and development in various fields. Currently, traditional titanium sapphire solid-state lasers, as the mainstream ultrashort pulse source, have played an important role in the past, but they face significant technical bottlenecks. Their large system size, requiring several cubic meters of space and the high cost of a single system exceeding one million US dollars, significantly restrict their large-scale application and promotion. The complex pulse repetition frequency control and electronic synchronization mechanisms not only increase the difficulty of operation, but also place extremely high demands on the professional skills of operators.

[0003] In this context, mode-locked lasers have become a research hotspot for the next generation of ultrashort pulse sources due to their advantages in miniaturized integration, high electro-optical conversion efficiency, and wavelength tuning flexibility. This device works based on a passive mode-locking mechanism. The saturable absorber integrated in the cavity serves as a nonlinear control unit, which can exhibit significant nonlinear response characteristics according to changes in light intensity, thereby achieving intracavity pulse mode selection and compression. However, the existing technology system still faces many challenges. The carrier dynamics process is complex, requiring fine control to maintain the inversion distribution of the population; the design of the optical resonant cavity requires a balance between precise parameters such as cavity length, refractive index, and reflectivity; in terms of polarization characteristic control, the light propagation characteristics under different polarization states vary greatly, and accurate control is required to achieve the ideal mode-locking effect. In addition, traditional passive mode-locked lasers rely on saturated absorbers or nonlinear polarization rotation, with complex structures and low tuning flexibility. Summary of the Invention

[0004] The purpose of the present invention is to solve the technical problems in the prior art that the mode-locked laser has a complex structure and is difficult to implement, and to provide a mode-locked laser based on orthogonal polarization feedback injection and a control method thereof.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions: A first aspect of the present invention provides a mode-locked laser based on orthogonal polarization feedback injection, comprising a VCSEL laser, a first polarization-maintaining beam splitter, a beam splitter, a reflector, and a half-wave plate; The light beam emitted by the VCSEL laser is split into a first beam and a second beam by a beam splitter; the first beam is used to generate a mode-locked laser, and the second beam is used to monitor the mode-locked laser; The first light beam is split into a first TM mode light beam and a first TE mode light beam by a first polarization-maintaining beam splitter; a plurality of reflectors are provided on the propagation paths of the first TM mode light beam and the first TE mode light beam, so that the first TM mode light beam and the first TE mode light beam form a ring loop on the optical path; a half-wave plate is provided on the ring loop; The first TM mode beam and the first TE mode beam propagate in opposite directions along the ring loop, undergo the first polarization state conversion through the half-wave plate, and then continue to propagate along the ring loop. They return to the VCSEL laser through the first polarization-maintaining beam splitter and the optical splitter, forming orthogonal feedback with the initial polarization state in the VCSEL laser resonator. After the orthogonal feedback, the light beam is reflected by the VCSEL laser resonant cavity, passes through the beam splitter and the first polarization-maintaining beam splitter in sequence, propagates along a ring loop, undergoes a second polarization state conversion by a half-wave plate, and is coupled into the VCSEL laser resonant cavity to complete the output of the mode-locked laser. The mode-locked laser reaches the mode-locked state by adjusting the angle of the half-wave plate to adjust the nonlinear coupling strength and phase between the orthogonal polarization modes.

[0006] Furthermore, the annular loop is a square loop with four vertical corners.

[0007] Furthermore, the beam splitting ratio of the optical splitter is 50:50.

[0008] Furthermore, a collimating lens is provided between the VCSEL laser and the beam splitter.

[0009] Furthermore, it also includes a second polarization-maintaining beam splitter; the second beam of light is split into a second TM mode beam and a second TE mode beam by the second polarization-maintaining beam splitter.

[0010] Furthermore, photodetectors are provided on the propagation paths of the second TM mode light beam and the second TE mode light beam.

[0011] Furthermore, optical isolators are provided on the propagation paths of the second TM mode light beam and the second TE mode light beam; the optical isolators are provided between the second polarization-maintaining beam splitter and the photodetector.

[0012] A second aspect of the present invention provides a method for controlling a mode-locked laser based on orthogonal polarization feedback injection, comprising: Splitting the light beam emitted by the VCSEL laser to obtain a first beam of light and a second beam of light; the first beam of light is used to generate a mode-locked laser, and the second beam of light is used to monitor the mode-locked laser; Polarization splitting is performed on the first light beam to obtain a first TM mode beam and a first TE mode beam. The first TM mode beam and the first TE mode beam propagate in opposite directions along a ring loop. During the propagation process, the first TM mode beam and the first TE mode beam undergo a first polarization state conversion via a half-wave plate and enter the VCSEL laser, forming orthogonal feedback with the initial polarization state in the VCSEL laser resonator. After being reflected by the VCSEL laser, the first TM mode light beam and the first TE mode light beam continue to propagate in opposite directions along the ring loop after undergoing beam splitting and polarization splitting in sequence, undergo a second polarization state conversion through a half-wave plate, and are coupled into the VCSEL laser resonant cavity; By adjusting the angle of the half-wave plate, the nonlinear coupling strength and phase between the orthogonal polarization modes are adjusted to achieve a mode-locked state and realize mode-locked laser output.

[0013] Furthermore, during the second polarization state conversion, both the first TM mode light beam and the first TE mode light beam are restored to their initial polarization states. Furthermore, by adjusting the pump current of the VCSEL laser, both the TE mode and the TM mode of the light beam operate above the threshold current of the TE mode and the TM mode.

[0014] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses a mode-locked laser based on orthogonal polarization feedback injection. This design utilizes a VCSEL laser, a first polarization-maintaining beam splitter, a reflector, and a half-wave plate to split the optical beam into a first TM mode beam and a first TE mode beam. A circular loop is constructed using the reflector, allowing the two modes to undergo mode conversion via the half-wave plate and then be coupled back into the VCSEL laser with a time delay. This design provides an efficient path for achieving mode-locked laser output. Compared to traditional mode-locked lasers, this structure enables more precise control of the beam mode conversion and feedback process, reducing energy loss and improving mode-locking efficiency, thereby achieving stable, high-quality mode-locked laser output. Mode-locked laser output can be achieved by adjusting the angle of the half-wave plate. This flexible control method can meet the diverse requirements of different application scenarios for parameters such as laser pulse width and repetition rate, greatly expanding the application range of this mode-locked laser. The orthogonal polarization feedback injection mechanism creates a stable optical feedback loop within the laser, reducing the interference of external environmental factors (such as temperature and vibration) on the laser output performance, thereby improving the stability and reliability of the laser operation. This invention achieves complex mode-locking with a relatively small number of optical components (VCSEL laser, first polarization-maintaining beam splitter, reflector, and half-wave plate). Compared to other mode-locked laser systems that rely on a large number of stacked optical components, this effectively simplifies the overall structure. This not only reduces system cost but also reduces the complexity of optical path debugging, improving laser assembly efficiency and practicality.

[0015] Furthermore, the present invention provides a method for controlling a mode-locked laser based on orthogonal polarization feedback injection. This method polarizes and splits the light beam emitted by a VCSEL laser to produce a first TM mode beam and a first TE mode beam. These two mode beams propagate in opposite directions along a circular loop and are coupled back into the VCSEL laser after mode conversion using a half-wave plate. This series of operations forms a closed-loop feedback mechanism that enables efficient and precise mode locking. Compared to traditional methods, this control method avoids unnecessary energy loss and mode interference, significantly improves mode locking efficiency, and can quickly and stably output high-quality mode-locked laser light. The present invention achieves mode locking by adjusting the angle of the half-wave plate, adapting to the needs of different application scenarios such as optical communications, laser processing, and scientific research experiments, greatly enhancing the adaptability and versatility of the mode-locked laser in practical applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0017] Figure 1 This is a structural diagram of a mode-locked laser based on orthogonal polarization feedback injection according to an embodiment of the present invention; Figure 2 TE mode time domain output at different half-wave plate angles according to the embodiment of the present invention, where the horizontal axis represents time and the vertical axis represents feedback light intensity. Figure 3 TE mode frequency domain output at different half-wave plate angles according to the embodiment of the present invention, where the horizontal axis represents frequency and the vertical axis represents feedback light intensity. Figure 4 This is a flowchart of a method for controlling a mode-locked laser based on orthogonal polarization feedback injection according to an embodiment of the present invention.

[0018] Among them, M is a reflector; PBS1 is a first polarization-maintaining beam splitter; PBS2 is a second polarization-maintaining beam splitter; BS is a beam splitter; L is a collimating lens; VCSEL is a VCSEL laser; PD is a photodetector; ISO is an optical isolator; and Osc. is an oscilloscope. DETAILED DESCRIPTION

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Generally, the components of the embodiments of the present invention described and marked in the drawings herein can be arranged and designed in various different configurations.

[0020] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are intended to fall within the scope of protection of the present invention.

[0021] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings.

[0022] In the description of the embodiments of the present invention, it should be noted that the terms "first", "second", etc. are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0023] Explanation of terms: VCSEL: The full name of English is Vertical-Cavity Surface-Emitting Laser, and the full name of Chinese is Vertical Cavity Surface Emitting Laser; TM: Transverse Magnetic Mode in English and transverse magnetic mode in Chinese. TE: Transverse Electric Mode in English and Transverse Electric Mode in Chinese. BS: Beam Splitter in English and Beam Splitter in Chinese. M: The full name in English is Mirror, and the full name in Chinese is Reflector; L: The full name in English is Collimating Lens, and the full name in Chinese is Collimating Lens; PBS: The full name of English is Polarization-Maintaining Beam Splitter, and the full name of Chinese is Polarization-Maintaining Beam Splitter; ISO: The full English name is Optical Isolator, and the full Chinese name is optical isolator; PD: The full name in English is Photodetector, and the full name in Chinese is photoelectric detector; Sco.: The full English name is Oscilloscope, and the full Chinese name is oscilloscope.

[0024] The present invention is described in further detail below with reference to the accompanying drawings: See also Figure 1 The present invention provides a mode-locked laser based on orthogonal polarization feedback injection, comprising a VCSEL laser, a beam splitter BS, a first polarization-maintaining beam splitter PBS1, a reflector M, and a half-wave plate. The light emitted by the VCSEL laser passes through a collimating lens L and is then split by the beam splitter BS into a first beam and a second beam. In this embodiment, the beam splitter BS employs a beam splitting prism with a 50:50 splitting ratio. The first beam is used to generate the mode-locked laser, and the second beam is used to monitor the generated laser.

[0025] The first light beam is divided into a first TM mode light beam and a first TE mode light beam through the first polarization-maintaining beam splitter PBS1; the first TM mode light beam and the first TE mode light beam propagate in opposite directions, and a plurality of reflectors M are provided on the propagation paths of the first TM mode light beam and the first TE mode light beam, so that the first TM mode light beam and the first TE mode light beam form a ring loop on the optical path; in this embodiment, the ring loop is a square loop with four vertical corners; a half-wave plate is provided on the ring loop; the first TM mode light beam and the first TE mode light beam undergo a first polarization state conversion through the half-wave plate, that is, the TE mode and the TM ... After rotating 90 degrees, the TE mode becomes the TM mode, and the TM mode becomes the TE mode. After polarization conversion, the first TM mode beam and the first TE mode beam continue to propagate along the ring loop and return to the VCSEL laser, forming orthogonal feedback with the initial polarization state in the VCSEL laser. The beam returned to the VCSEL laser is reflected by the VCSEL laser, split by the first polarization-maintaining beam splitter PBS1, and then continues to propagate in the opposite direction of the ring loop. After a second polarization state conversion through a half-wave plate, it is coupled into the VCSEL laser resonant cavity to achieve mode-locked laser output. In this embodiment, the ring loop is 1.8m. During the second polarization state conversion, both the TM mode and the TE mode are restored to their original polarization state and then coupled into the VCSEL laser resonant cavity. At the same time, the mode-locked laser of the present invention adjusts the nonlinear coupling strength between the orthogonal polarization modes and the phase between the modes by adjusting the angle of the half-wave plate, so that the beam reaches a mode-locked state.

[0026] After passing through the second polarization-maintaining beam splitter PBS2, the second light beam is divided into a second TM mode light beam and a second TE mode light beam; an optical isolator ISO and a photodetector PD are provided on the propagation paths of the second TM mode light beam and the second TE mode light beam, and the second TM mode light beam and the second TE mode light beam both pass through the optical isolator ISO on their respective propagation paths and enter the photodetector PD on their respective propagation paths; in this embodiment, the photodetector PD adopts a 10 GHz bandwidth, and the photodetector PD is connected to an oscilloscope Sco. for optical signal acquisition.

[0027] The present invention designs a ring loop based on a mode-locked laser with orthogonal polarization feedback injection, so that the first TM mode light beam and the first TE mode light beam can propagate in opposite directions on the ring loop. During the propagation process, the mutual conversion between the TM mode and the TE mode is achieved through a half-wave plate. By precisely controlling the length of the ring loop, the feedback timing of the two modes can be precisely regulated, thereby optimizing the mode coupling efficiency. By adjusting the pump current of the VCSEL laser, it is ensured that both the TE and TM modes operate above their respective threshold currents. By embedding a half-wave plate in the external ring cavity, the feedback intensity and phase relationship of the TE and TM modes are further regulated. No additional saturated absorber is required to achieve mode-locked operation of the TE mode and output an ultrashort pulse sequence. The experimental optical path design is simple and the cost is much lower than that of existing technologies.

[0028] See also Figure 4 One embodiment of the present invention provides a method for controlling a mode-locked laser based on orthogonal polarization feedback injection, comprising the following steps: S1, splitting the light beam emitted by the VCSEL laser to obtain a first beam of light and a second beam of light; the first beam of light is used to generate a mode-locked laser, and the second beam of light is used to monitor the mode-locked laser; S2, performing polarization splitting on the first light beam to obtain a first TM mode light beam and a first TE mode light beam; S3, propagating the TM mode beam and the TE mode beam in opposite directions along the ring loop. During the propagation process, the first TM mode beam and the first TE mode beam undergo a first polarization state conversion via a half-wave plate and enter the VCSEL laser, forming orthogonal feedback with the initial polarization state in the VCSEL laser resonator, thus completing the first polarization feedback. S4, after being reflected by the VCSEL laser, the first TM mode light beam and the first TE mode light beam after polarization splitting continue to propagate in opposite directions along the ring loop, undergo a second polarization state conversion by the half-wave plate, and are coupled into the VCSEL laser resonant cavity; S5, by adjusting the angle of the half-wave plate, the nonlinear coupling strength and phase between the orthogonal polarization modes are adjusted to achieve the mode-locked state and realize mode-locked laser output.

[0029] One embodiment of the present invention provides a method for controlling a mode-locked laser based on orthogonal polarization feedback injection, comprising the following steps: S1, the light beam emitted by the VCSEL laser passes through the collimating lens L to obtain collimated laser light; the collimated laser light is divided into a first beam and a second beam after passing through the beam splitter BS; the VCSEL laser of this embodiment uses the 850nm band, and the VCSEL laser has an excellent temperature control and power supply control system and has good stability.

[0030] The first beam of light is used to generate a mode-locked laser. The first beam of light enters the first polarization-maintaining beam splitter PBS1 for polarization splitting to obtain a first TM mode beam and a first TE mode beam. The second beam of light is used to monitor the generated mode-locked laser. The second beam of light enters the second polarization-maintaining beam splitter PBS2 for polarization splitting to obtain a second TM mode light beam and a second TE mode light beam. An optical isolator ISO and a photodetector PD are provided on the propagation paths of the second TM mode light beam and the second TE mode light beam. The second TM mode light beam and the second TE mode light beam respectively enter the optical isolator ISO on their respective propagation paths, and then enter the photodetector PD on their respective propagation paths. The photodetector PD is connected to an oscilloscope Osc., and the output optical signal is monitored and collected through the oscilloscope Osc.

[0031] S2, the first TM mode light beam and the first TE mode light beam are propagated in opposite directions along the ring loop respectively. During the propagation process, the first TM mode light beam and the first TE mode light beam undergo the first polarization conversion through the half-wave plate; during the first polarization conversion, the TM mode is converted into the TE mode, and the TE mode is converted into the TM mode; after the first polarization conversion is completed, the first TM mode light beam and the first TE mode light beam continue to propagate along the ring loop into the VCSEL laser, forming orthogonal feedback with the initial polarization state in the VCSEL laser; then reflected by the VCSEL laser, split by the beam splitter BS and the first polarization-maintaining beam splitter PBS1 in sequence, and continue to propagate along the ring loop, undergo the second polarization state conversion through the half-wave plate, and then couple into the VCSEL laser resonant cavity; in this embodiment, the ring loop is 1.8m, and two separated linear polarization modes are passed through the ring loop and then injected into the laser resonant cavity again to achieve gain modulation.

[0032] S3, adjust the pump current of the VCSEL laser so that both linear polarization modes (TE and TM modes) operate above the threshold current of the TE and TM modes; rotate the angle of the half-wave plate to dynamically adjust the feedback intensity and phase difference of the TE and TM modes, optimize the mode coupling efficiency, and finally achieve the mode locking condition, thereby realizing mode-locked laser output; the rotation angle of the half-wave plate Range is 0 ° ≤ ≤180° .

[0033] In order to illustrate the advantages of the present invention, an embodiment of the present invention uses an oscilloscope Osc. to monitor and collect time domain signals, such as Figure 2 As shown in Figure 1, the data monitoring window of the oscilloscope Osc. is 20μs. Then the collected time domain signal is Fourier transformed to perform frequency domain characterization, as shown in Figure 1. Figure 3 shown.

[0034] Figure 2 (a) shows the TE mode time domain output of the VCSEL laser when the pump current is 5.38 mA and the half-wave plate angle is 102°. It can be seen that two pulses are locked within the delayed feedback cycle. Figure 2 (b) is the TE mode time domain output of the VCSEL laser when the pump current is 5.38 mA and the half-wave plate angle is 144°. It can be seen from the figure that a pulse locking is achieved within the delayed feedback cycle.

[0035] Figure 3 yes Figure 2 The corresponding spectrum characterization shows that the TE mode is at a pump current of 5.38 mA and a half-wave plate angle of 102° (e.g. Figure 3 (a)) and the pump current is 5.38 mA, the half-wave plate angle is 144° (as Figure 3 (b) The two conditions show a locked mode state with a mode spacing of 80 MHz.

[0036] The present invention ensures that both the TE and TM modes operate above their respective threshold currents by adjusting the pump current of the VCSEL laser, which is a key prerequisite for achieving mode-locked laser output. The rotating half-wave plate can dynamically adjust the feedback intensity and phase relationship of the TE and TM modes. By fine-tuning the angle of the half-wave plate, the interaction between the two modes can be precisely controlled, making it easier to achieve mode-locked conditions. The present invention not only achieves stable locked output of a single pulse, but also achieves a breakthrough in synchronous locking and stable output of a dual-pulse sequence, significantly expanding the application scenarios of mode-locked lasers. This technological innovation successfully achieves precise control of the dual-pulse interval while maintaining the performance indicators of a single pulse through the optimized design of the intracavity nonlinear control mechanism, providing a new light source solution for cutting-edge fields such as time-division multiplexing optical communications and two-photon excitation microscopy.

[0037] While maintaining the advantages of device miniaturization, this invention expands the application of traditional single-pulse lasers to scenarios requiring multi-pulse sequences. Experimental data demonstrates good pulse energy consistency in dual-pulse output at 850 nm. Furthermore, this method demonstrates excellent technical compatibility, laying a foundation for the development of multi-wavelength integrated optoelectronic systems.

[0038] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A mode-locked laser based on orthogonal polarization feedback injection, characterized in that: It includes a VCSEL laser, a first polarization-maintaining beam splitter, a beam splitter, a reflector and a half-wave plate; The light beam emitted by the VCSEL laser is split into a first beam and a second beam by a beam splitter; the first beam is used to generate a mode-locked laser, and the second beam is used to monitor the mode-locked laser; The first light beam is split into a first TM mode light beam and a first TE mode light beam by a first polarization-maintaining beam splitter; a plurality of reflectors are provided on the propagation paths of the first TM mode light beam and the first TE mode light beam, so that the first TM mode light beam and the first TE mode light beam form a ring loop on the optical path; a half-wave plate is provided on the ring loop; The first TM mode beam and the first TE mode beam propagate in opposite directions along the ring loop, undergo the first polarization state conversion through the half-wave plate, and then continue to propagate along the ring loop. They return to the VCSEL laser through the first polarization-maintaining beam splitter and the optical splitter, forming orthogonal feedback with the initial polarization state in the VCSEL laser resonator. After the orthogonal feedback, the light beam is reflected by the VCSEL laser resonant cavity, passes through the beam splitter and the first polarization-maintaining beam splitter in sequence, propagates along a ring loop, undergoes a second polarization state conversion by a half-wave plate, and is coupled into the VCSEL laser resonant cavity to complete the output of the mode-locked laser. The mode-locked laser reaches the mode-locked state by adjusting the angle of the half-wave plate to adjust the nonlinear coupling strength and phase between the orthogonal polarization modes.

2. The mode-locked laser based on orthogonal polarization feedback injection according to claim 1, characterized in that: The annular loop is a square loop with four vertical corners.

3. The mode-locked laser based on orthogonal polarization feedback injection according to claim 1, characterized in that: The beam splitting ratio of the optical splitter is 50:

50.

4. The mode-locked laser based on orthogonal polarization feedback injection according to claim 1, characterized in that: A collimating lens is provided between the VCSEL laser and the beam splitter.

5. The mode-locked laser based on orthogonal polarization feedback injection according to claim 1, characterized in that: It also includes a second polarization-maintaining beam splitter; the second beam of light is split into a second TM mode beam and a second TE mode beam by the second polarization-maintaining beam splitter.

6. The mode-locked laser based on orthogonal polarization feedback injection according to claim 5, characterized in that: Photodetectors are provided on the propagation paths of the second TM mode light beam and the second TE mode light beam.

7. The mode-locked laser based on orthogonal polarization feedback injection according to claim 6, characterized in that: Optical isolators are provided on the propagation paths of the second TM mode light beam and the second TE mode light beam; the optical isolators are provided between the second polarization-maintaining beam splitter and the photodetector.

8. A control method for a mode-locked laser based on orthogonal polarization feedback injection, based on the mode-locked laser based on orthogonal polarization feedback injection according to any one of claims 1 to 7, characterized in that: include: Splitting the light beam emitted by the VCSEL laser to obtain a first beam of light and a second beam of light; the first beam of light is used to generate a mode-locked laser, and the second beam of light is used to monitor the mode-locked laser; Polarization splitting is performed on the first light beam to obtain a first TM mode beam and a first TE mode beam. The first TM mode beam and the first TE mode beam propagate in opposite directions along a ring loop. During the propagation process, the first TM mode beam and the first TE mode beam undergo a first polarization state conversion via a half-wave plate and enter the VCSEL laser, forming orthogonal feedback with the initial polarization state in the VCSEL laser resonator. After being reflected by the VCSEL laser, the first TM mode light beam and the first TE mode light beam continue to propagate in opposite directions along the ring loop after undergoing beam splitting and polarization splitting in sequence, undergo a second polarization state conversion through a half-wave plate, and are coupled into the VCSEL laser resonant cavity; By adjusting the angle of the half-wave plate, the nonlinear coupling strength and phase between the orthogonal polarization modes are adjusted to achieve a mode-locked state and realize mode-locked laser output.

9. The method for controlling a mode-locked laser based on orthogonal polarization feedback injection according to claim 8, characterized in that: During the second polarization state conversion, both the first TM mode light beam and the first TE mode light beam are restored to their initial polarization states.

10. The method for controlling a mode-locked laser based on orthogonal polarization feedback injection according to claim 8, characterized in that: By adjusting the pump current of the VCSEL laser, the TE mode and TM mode of the light beam are both operated above the threshold current of the TE mode and the TM mode.

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