Self-oscillation light source and microwave source based on hybrid integration and photoelectric feedback and working method of self-oscillation light source and microwave source

Abstract

The invention discloses a self-oscillation light source and microwave source based on hybrid integration and photoelectric feedback and a working method of the self-oscillation light source and microwave source. According to the device, an erbium-doped silicon nitride gain waveguide and a lithium tantalate electrooptical modulator are heterogeneously integrated on the same chip, and a high-Q-value optical resonant cavity is formed by the device, a single-mode polarization maintaining optical fiber and a reflector of the single-mode polarization maintaining optical fiber through end face coupling; the microwave feedback loop comprises a photoelectric detector, a narrowband frequency-selecting filter, a phase shifter and a microwave amplifier, and the microwave feedback loop and the optical resonant cavity form a photoelectric interlocking closed oscillation ring through a modulator and a detector. During working, the frequency-selecting filter selects a target microwave frequency, the phase shifter is adjusted to enable feedback microwaves to be synchronous with optical pulses in the cavity, and the system realizes self-sustaining oscillation without an external microwave source and outputs optical pulses with stable repetition frequency and microwave signals with low phase noise at the same time. The invention has the advantages of compact structure, high stability and low noise.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of integrated laser and microwave technology, and in particular to a pulsed light source based on a thin film erbium-doped silicon nitride / lithium tantalate chip and a fiber hybrid structure, as well as a working method and a preparation method thereof. The device provides gain through erbium-doped silicon nitride, modulation through lithium tantalate electro-optic, and high-Q resonant cavity through fiber cavity, and combines a microwave feedback loop to realize a self-oscillating pulsed light source and microwave source without external microwave source, which can be used as a low-noise source to provide a reference clock for measurement, synchronization and other applications. BACKGROUND

[0002] Low-noise pulsed light source and microwave source have important applications in the fields of measurement, synchronization, etc. Traditional pulsed light sources and light-generated microwave sources include active mode-locked lasers, optoelectronic oscillators, and optical frequency comb frequency division methods. These methods either require an additional microwave source for driving, or have poor stability, or have a complex system, which limits their practical application.

[0003] In recent years, the development of integrated photonics technology has provided a new way for the miniaturization of high-performance light sources and microwave sources. For example, erbium ions can be doped into silicon nitride waveguides to achieve low-noise and high-gain optical amplification; and lithium tantalate, lithium niobate and other electro-optic materials can be heterogeneously integrated with silicon-based optical circuits through microtransfer printing technology, thereby achieving efficient electro-optic modulation on the chip. On the other hand, optical fibers have ultra-low loss characteristics and can build high-Q resonant cavities, significantly improving the frequency stability and phase noise performance of the system. If the compactness and scalability of integrated photonics chips and the high-Q characteristics of fiber cavities can be combined, it is expected to realize a pulsed light source and microwave source with small size, low noise, and high stability, and to promote the practical application of such devices.

[0004] However, the efficient cooperation of integrated optical circuits and fiber cavities has not been fully realized in the prior art, especially in the self-oscillating, external microwave source-free optoelectronic coupling oscillation structure, there is still a lack of mature solutions. Therefore, there is an urgent need for a hybrid integrated device that can combine thin film erbium-doped gain, high-speed electro-optic modulation, fiber high-Q cavity and microwave feedback loop to solve the problems of system complexity, insufficient stability, dependence on external sources and other problems in the prior art. SUMMARY

[0005] In view of the problems of system complexity, dependence on external microwave source, insufficient stability, and large size in the prior art of pulsed light source and microwave generation, the present application provides a design, preparation method and working method of a pulsed light source and light-generated microwave source based on a thin film silicon nitride / lithium tantalate chip and a fiber hybrid structure. The present application has a simple structure and wide application prospects.

[0006] The technical solution of the present application is as follows: In one aspect, the present application provides a self-oscillating light source and microwave source based on hybrid integration and optoelectronic feedback, characterized in that it comprises: a silicon nitride / lithium tantalate chip, on the substrate of which an erbium-doped silicon nitride waveguide and a lithium tantalate electro-optic modulator are integrated, the erbium-doped silicon nitride waveguide being optically coupled to the electro-optic modulator through an on-chip mode converter; a fiber device composed of a single-mode polarization-maintaining optical fiber coupled to the end face of the silicon nitride / lithium tantalate chip and a fiber mirror at the end of the fiber; the silicon nitride / lithium tantalate chip and the fiber device together form a linear Fabry-Perot optical resonator; a microwave feedback loop for converting part of the optical signal output by the optical resonator into an electrical signal, processing it, and then feeding it back to drive the electro-optic modulator in the silicon nitride / lithium tantalate chip, thus forming an optoelectronic-coupled self-oscillating system; the microwave feedback loop comprises, in sequence, a photodetector, a frequency selection filter, a phase shifter, a microwave amplifier, and a microwave beam splitter, wherein the input end of the photodetector is optically connected to part of the optical signal coupled out of the optical resonator; the first output end of the microwave beam splitter is electrically connected to the microwave driving electrode of the lithium tantalate electro-optic modulator; the frequency selection filter is used to select a target microwave frequency from the optoelectronic conversion signal f R , and the target microwave frequency f R matches the free spectral range of the optical resonator; the phase shifter is used to adjust the phase of the feedback microwave signal, so that when the optical pulse circulates in the optical resonator to the electro-optic modulator, the microwave modulation applied by the electro-optic modulator is at a phase that minimizes the transmission loss of the optical pulse, thus achieving self-sustained oscillation, and simultaneously outputting pulsed light with a repetition frequency of f R from the optical output port of the silicon nitride / lithium tantalate chip, and a microwave signal with a frequency of f R from the second output port of the microwave beam splitter.

[0007] Further, the silicon nitride / lithium tantalate chip is characterized in that: in the direction of the optical signal, an optical beam splitter, a mirror, a wavelength division multiplexer, an erbium-doped waveguide, a first mode converter, a lithium tantalate electro-optic modulator, a second mode converter, and an end face coupler are prepared.

[0008] The optical beam splitter is a silicon nitride device, and its function is to divide the optical signal into two parts, with one part being directly output as a pulsed light source, and the other part being converted into a microwave signal by the photodetector in the microwave feedback loop for subsequent processing. The optical beam splitter can be a multimode interferometer, a directional coupler, or other structures with beam splitting function.

[0009] The mirror is a silicon nitride device, and functions as an end mirror on the side of the optical chip in the optical resonant cavity, and simultaneously couples part of the optical signal in the resonant cavity to the optical beam splitter. The mirror can be a loop mirror, a Bragg grating, or other structures with partial reflection function.

[0010] The wavelength division multiplexer is a silicon nitride device, and functions to combine and split the pump light and signal light of the erbium-doped waveguide. The wavelength division multiplexer is a three-port device, the signal port corresponds to the signal light, the pump port corresponds to the pump light, and the combining port combines the signal light and the pump light. The wavelength of the pump light is the typical erbium-doped amplifier pump wavelength of 980 nm or 1480 nm, and the wavelength of the signal light is the 1550 nm band. The signal port is connected to the input port of the mirror, the pump port is connected to the external pump light source, and the combining port is connected to the erbium-doped waveguide. The wavelength division multiplexer can be a non-equal arm Mach-Zehnder interferometer or other structures with wavelength division multiplexing function.

[0011] The erbium-doped waveguide is an erbium-doped silicon nitride device, and functions to amplify the signal in the optical resonant cavity. One end of the erbium-doped waveguide is connected to the combining port of the wavelength division multiplexer, and the other end is connected to the first mode converter. The erbium-doped waveguide is obtained by selective injection of erbium ions into a section of silicon nitride waveguide.

[0012] The function of the lithium tantalate electro-optic modulator is to realize electro-optic modulation of the microwave signal to the optical signal. The optical signal in the silicon nitride device is coupled to the lithium tantalate electro-optic modulator through the first mode converter to realize electro-optic modulation, and then the optical signal is coupled back to the silicon nitride device through the second mode converter.

[0013] The function of the end face coupler is to amplify the optical field mode spot in the silicon nitride waveguide, so that it matches the optical field mode spot in the optical fiber, and reduces the coupling loss. The end face coupler can be a reverse taper structure or other structures with mode spot adjustment function.

[0014] The optical fiber device is a single-mode polarization maintaining optical fiber and an optical fiber mirror coupled to the end face of the silicon nitride / lithium tantalate chip. One axis of the single-mode polarization maintaining optical fiber is consistent with the output light deflection of the silicon nitride / lithium tantalate chip, ensuring the polarization maintaining transmission of the optical signal in the optical fiber. The other end of the optical fiber device has an optical fiber mirror, which together with the silicon nitride / lithium tantalate chip forms an optical resonant cavity. The optical fiber mirror can be a loop mirror, a grating, an end face coating, or other structures with full reflection function.

[0015] The microwave feedback loop is characterized in that: In the signal direction, it includes a photodetector, a frequency selection filter, a phase shifter, a microwave amplifier, and a microwave beam splitter.

[0016] The photoelectric detector is used for converting the optical signal (pulsed light source) output from the silicon nitride / lithium tantalate chip into an electrical signal, and the bandwidth should cover the frequency of the required generated microwave signal.

[0017] The frequency selective filter is a narrowband filter, and functions to filter the noise of the microwave signal generated in the photoelectric detector. In the starting stage of the optical resonant cavity, the frequency selective filter also functions as a microwave frequency selector. The frequency selective filter can be a YIG filter, a cavity filter, or other narrowband filter devices.

[0018] The phase shifter is used for phase shifting the microwave signal. Since the optical resonant cavity and the microwave feedback loop are coupled with each other in the application, it is necessary to ensure the synchronization between the microwave signal fed back to the lithium tantalate electro-optical modulator and the optical signal modulated in the optical resonant cavity.

[0019] The microwave amplifier is used for amplifying the microwave signal, and the output enters the microwave beam splitter, which is then divided into two parts, one part is used for feeding back to drive the lithium tantalate electro-optical modulator, and the other part is used as a low-noise microwave source output.

[0020] The lithium tantalate electro-optical modulator is prepared by preparing microwave electrodes on both sides of the lithium tantalate waveguide. When the electric field between the electrodes is along the lithium tantalate crystal axis (z-axis), the optical signal propagates along the y-axis, realizing high-efficiency electro-optical modulation.

[0021] The optical field mode spot in the lithium tantalate electro-optical modulator can be all in the lithium tantalate waveguide, or partially in the lithium tantalate waveguide and partially in the lower silicon nitride waveguide. The latter is realized by the lithium tantalate waveguide and the silicon nitride waveguide to jointly constrain the optical field.

[0022] Preferably, the pump light wavelength used by the wavelength division multiplexer is 1480 nm, so as to ensure that the silicon nitride waveguide is single-mode or few-mode to the pump light, and to reduce the possible mode disturbance.

[0023] Preferably, the thickness of the silicon nitride of all the silicon nitride devices is 100-300 nm, so as to ensure the coupling efficiency between the silicon nitride waveguide and the lithium tantalate waveguide.

[0024] Preferably, the length of the polarization maintaining optical fiber in the optical fiber device is 0.1-10 km, so as to ensure that the optical resonant cavity has a relatively high Q value.

[0025] Preferably, the passband bandwidth of the frequency selective filter should be less than 100 MHz, so as to suppress the generation of supermode noise in the optical resonant cavity.

[0026] In another aspect, the application also provides a working method based on the above-mentioned self-oscillating light source and microwave source, and the method comprises the following steps: Pump light is injected into the erbium-doped silicon nitride waveguide to start the optical resonant cavity; starting the microwave feedback loop; selecting a target frequency from the electrical signal outputted from the photodetector through the frequency selective filter f R ; adjusting the phase shifter to change the phase of the microwave signal fed back to the electro-optical modulator until the optical signal outputted from the optical resonator stabilizes into a pulse train with repetition frequency equal to f R and the microwave signal outputted from the microwave feedback loop stabilizes into a single frequency signal with frequency equal to f R , at which the system enters a self-sustained oscillation state.

[0027] Further, the selection of the target frequency f R is independent of the exact length of the optical resonator, which is achieved by replacing or tuning the center frequency of the frequency selective filter.

[0028] The working method of the present application is as follows: energize the erbium-doped waveguide in the silicon nitride / lithium tantalate chip by a pump light source to make it produce gain to the 1550 nm band light; turn on the microwave amplifier to make the microwave feedback loop form a photoelectric coupling resonator; adjust the phase shifter to make the microwave signal generated by the microwave feedback loop synchronized with the optical signal in the optical resonator, at which the silicon nitride / lithium tantalate chip outputs a frequency-stable pulsed light source and the microwave feedback loop outputs a low-noise microwave source The preparation method of the present application is as follows: The preparation method of the silicon nitride / lithium tantalate chip: 1) prepare a silicon oxide layer on a silicon-based wafer by thermal oxidation; 2) prepare a silicon nitride layer by a method such as low-pressure chemical vapor deposition (LPCVD); 3) etch the silicon nitride layer to device structure by dry etching; 4) make a mask to expose only the silicon nitride waveguide area that needs to be implanted with erbium ions; 5) implant erbium ions and anneal to prepare an erbium-doped silicon nitride waveguide; 6) deposit a silicon oxide cladding layer and ensure the surface flatness and the distance from the silicon nitride to the surface of the cladding layer by chemical mechanical polishing; 7) on another lithium tantalate wafer (containing a silicon oxide lower cladding layer and a silicon substrate), make the waveguide part of the lithium tantalate electro-optical modulator, the mode converter part for coupling with the silicon nitride waveguide, and the tether structure for micro-transfer printing; 8) The silicon oxide under cladding of the lithium tantalate device is etched and removed by a wet process, and the lithium tantalate film is transferred to the area where the electro-optical modulator is to be made by a micro transfer process, ensuring that the mode converter part on the lithium tantalate film is aligned with the mode converter part in the silicon nitride waveguide; 9) The microwave electrode is prepared on the lithium tantalate film transferred to the silicon nitride chip by a stripping process; 10) The silicon oxide over cladding is deposited, and the window is opened in the pad area of the microwave electrode to provide the interface of the external microwave signal with the lithium tantalate electro-optical modulator.

[0029] The working principle and process of the present application are as follows: First, the silicon nitride / lithium tantalate chip and the optical fiber form a linear optical resonant cavity. When no external microwave signal is applied, the laser frequency can resonate at all frequencies that satisfy the resonant condition in the cavity, i.e. the cavity length corresponds to an integer multiple of the free spectral range FSR.

[0030] Then, the frequency selection filter of the microwave selects the optical signal with the required oscillation repetition frequency f R (microwave frequency, such as 10 GHz) from all the free-running modes of the optical resonant cavity, and drives the electro-optical modulator after phase shifting and amplification. At this time, when the microwave feedback loop after adjusting the phase shifter is synchronized with the corresponding mode in the optical resonant cavity, i.e. the optical pulse reaches the electro-optical modulator, it corresponds to the peak of the microwave modulation, realizing the lowest loss transmission, and the optical-electric coupling efficiency reaches the highest, realizing stable oscillation. At this time, the silicon nitride / lithium tantalate chip outputs optical pulses with a repetition frequency of f R , and the microwave feedback loop outputs a single-frequency microwave signal with a frequency of f R .

[0031] The present application also provides a communication or measurement system, characterized in that it comprises the self-oscillating light source and the microwave source described above, the pulsed light output is used for optical communication or optical sampling, and the microwave signal output is used as the local clock reference of the system.

[0032] Compared with the prior art, the present application has the following advantages: 1) Compared with the traditional opto-electric coupling oscillator (including active mode-locked laser and opto-electric oscillator OEO) scheme, the present application takes into account the advantages of integrated photonics and optical fiber. Integrated photonics ensures the miniaturization of the system, and optical fiber ensures the high Q value of the resonant cavity by using its ultra-low loss, so the system is compact, has higher stability, and has lower supermode noise.

[0033] 2) Compared with the optical frequency comb frequency division scheme, the application adopts no complex locking and external microwave source, and the required microwave oscillation frequency can be obtained through photoelectric coupling resonance and microwave frequency selection filtering without external microwave source. Moreover, the optical part of the scheme has compact structure, only including a photonic integrated chip and an optical fiber, compared with the complex and huge system of the optical frequency comb frequency division scheme, the scheme has important practical prospect. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 is a schematic diagram of a photonic integrated chip and optical fiber hybrid structure of the light source and microwave source of the application. In the figure: 1 - silicon nitride / lithium tantalate chip, 2 - optical beam splitter, 3 - mirror, 4 - wavelength division multiplexer, 5 - erbium-doped silicon nitride waveguide, 6 - first mode converter, 7 - lithium tantalate electro-optic modulator, 8 - second mode converter, 9 - end face coupler, 10 - pump light source, 11 - optical fiber device, 12 - single-mode polarization maintaining optical fiber, 13 - optical fiber mirror, 14 - photodetector, 15 - frequency selection filter, 16 - phase shifter, 17 - microwave amplifier, 18 - microwave beam splitter.

[0035] Figure 2 is a typical coupling structure of lithium tantalate electro-optic modulator and silicon nitride waveguide, and the silicon nitride and lithium tantalate are surrounded by silicon oxide cladding (not shown in the figure). DETAILED DESCRIPTION

[0036] The application will be further described below in combination with the drawings and examples, but the protection scope of the application should not be limited thereby. The embodiments of the application include but are not limited to the following examples.

[0037] Please refer to Figure 1 , the embodiment provides a pulsed light source and light generated microwave source based on a thin film silicon nitride / lithium tantalate chip and optical fiber hybrid structure, and the overall structure includes three core parts: a silicon nitride / lithium tantalate integrated chip 1, an optical fiber device 11 and a microwave feedback loop. The three together constitute a self-sustaining oscillation system of optical and electrical interlocking.

[0038] 1. The silicon nitride / lithium tantalate integrated chip 1 is a multi-layer heterogeneous integrated structure. From bottom to top, it includes: a silicon substrate, a silicon oxide lower cladding, and a device layer located thereon. The device layer is a key functional area, which integrates passive and active optical paths composed of undoped silicon nitride and erbium-doped silicon nitride, and a lithium tantalate electro-optic modulation unit. The flow direction of optical signals in the chip and the functional devices are as follows: An optical beam splitter 2 is used to divide the optical signal in the resonant cavity into two paths, one of which is used as a pulsed light output, and the other of which is sent into a microwave feedback loop.

[0039] The mirror 3, which is a ring mirror or a Bragg grating, is used as an end mirror on the chip side of the optical resonant cavity to achieve partial reflection to maintain resonance and guide light to the beam splitter.

[0040] The wavelength division multiplexer 4, which is a non-equal arm Mach-Zehnder interferometer, is used to combine and separate 980 nm or 1480 nm pump light and 1550 nm signal light to provide energy for the gain medium.

[0041] The erbium-doped silicon nitride waveguide 5, which is prepared by selective erbium ion implantation and annealing process, is used as a gain medium to provide optical amplification for 1550 nm signal light.

[0042] The first mode converter 6 and the second mode converter 8 achieve efficient mode conversion and coupling between the silicon nitride waveguide and the lithium tantalate waveguide.

[0043] The lithium tantalate electro-optical modulator 7, which has microwave electrodes along the crystal axis (z-axis) prepared on both sides of the lithium tantalate waveguide, realizes electro-optical intensity or phase modulation of the y-axis propagating light signal. The waveguide structure can be a pure lithium tantalate waveguide or a lithium tantalate-silicon nitride hybrid waveguide to optimize the light field confinement and modulation efficiency.

[0044] The end face coupler 9, which uses a reverse tapered structure, expands the mode field of the silicon nitride waveguide to achieve low-loss coupling with external optical fibers.

[0045] 2. The fiber device 11 is composed of a section of single-mode polarization maintaining optical fiber 12 and a fiber mirror 13 welded at one end of the optical fiber. The other end of the optical fiber is connected to the silicon nitride / lithium tantalate integrated chip 1 through an end face coupler to form a linear Fabry-Perot optical resonant cavity together. The polarization maintaining optical fiber ensures the stability of the light polarization state, and its length (preferably 0.1-10 km) determines the free spectral range and high Q value of the resonant cavity.

[0046] 3. The microwave feedback loop converts optical pulses into microwaves and feeds back to drive the closed circuit of the modulator, which includes in turn: The photodetector 14 converts the optical pulses output by the optical beam splitter 12 into electrical signals. The frequency selective filter 15, which uses a YIG or cavity narrowband filter, filters out noise from the photoelectric conversion signal and selects the target oscillation microwave frequency. The phase shifter 16 adjusts the phase of the microwave signal to ensure that the microwave modulation peak fed back to the electro-optical modulator is precisely synchronized with the optical pulse reaching the modulator, achieving the minimum loss condition.

[0047] The microwave amplifier 17 amplifies the power of the filtered and phase-shifted microwave signal. The amplified microwave signal is split into two by the microwave beam splitter 18, one of which is fed back to drive the lithium tantalate electro-optic modulator on the chip to form a closed oscillation loop, and the other is directly output as a low-noise microwave source.

[0048] The workflow of the embodiment is as follows: The erbium-doped silicon nitride waveguide in the silicon nitride / lithium tantalate chip is energized by an external pump light source to produce gain for the 1550 nm band light; The microwave amplifier is turned on to form an optoelectronic coupling resonant cavity for the microwave feedback loop. Part of the light in the resonant cavity is converted into an electrical signal after being split and detected. The frequency selection filter accurately selects the microwave component of the target frequency (corresponding to the pulse repetition frequency determined by the optical cavity length) from the electrical signal.

[0049] The phase shifter is adjusted so that the microwave signal generated by the microwave feedback loop is synchronized with the optical signal in the optical resonant cavity. At this time, the silicon nitride / lithium tantalate chip outputs a frequency-stable pulsed light source, and the microwave feedback loop outputs a low-noise microwave source.

[0050] Extension of different microwave frequencies: If different microwave frequencies f R , such as 20 GHz or 40 GHz, are needed, the optical resonant cavity length (fiber length) does not need to be changed. The main adjustments are as follows: Replace the frequency selection filter 15 in the microwave feedback loop so that its center frequency becomes the target f R frequency (e.g., 20 GHz).

[0051] Ensure that the bandwidth of the photodetector 14 and the microwave amplifier 17 covers the new f R .

[0052] Accordingly, the electrode design (such as length and impedance) of the lithium tantalate electro-optic modulator 7 can be optimized so that it has higher modulation efficiency and bandwidth near the target frequency.

[0053] Through the above adjustments, the system will automatically select the mode with the closest longitudinal mode spacing to the target f R frequency in the optical resonant cavity for oscillation, thereby realizing the output of different frequency microwave signals and corresponding repetition frequency optical pulses. This reflects the flexibility and scalability of the present scheme.

[0054] Method for preparing a silicon nitride / lithium tantalate chip: 1) Prepare a silicon oxide layer on a silicon-based wafer by thermal oxidation; 2) Prepare a silicon nitride layer by low-pressure chemical vapor deposition (LPCVD) or other methods; 3) Etch the silicon nitride layer to form a device structure using dry etching. 4) Fabricate a mask to expose only the region of the silicon nitride waveguide where erbium ion implantation is needed; 5) Erbium ion implantation and annealing to fabricate erbium-doped silicon nitride waveguide; 6) Deposit silicon oxide cladding layer and ensure the flatness of the surface and the distance between the silicon nitride and the surface of the cladding layer by chemical mechanical polishing; 7) On another lithium tantalate wafer (containing silicon oxide under cladding layer and silicon substrate), fabricate the waveguide part of the lithium tantalate electro-optical modulator, the mode converter part for coupling with the silicon nitride waveguide, and the tether structure for micro-transfer printing; 8) Use wet etching process to remove the silicon oxide under cladding layer under the lithium tantalate device, and use micro-transfer printing process to transfer the lithium tantalate film to the region where the electro-optical modulator is to be fabricated, to ensure that the mode converter part on the lithium tantalate film is aligned with the mode converter part in the silicon nitride waveguide; 9) Use a lift-off process to fabricate microwave electrodes on the lithium tantalate film transferred to the silicon nitride chip; 10) Deposit silicon oxide over cladding layer and open a window in the pad area of the microwave electrode to provide an interface for external microwave signal to the lithium tantalate electro-optical modulator.

[0055] The above describes specific embodiments of the present application. It should be understood that the present application is not limited to the specific embodiments described above, and various modifications or variations can be made by those skilled in the art within the scope of the claims, without affecting the essential content of the present application. The above embodiments and features in the embodiments can be combined with each other without conflict, provided that they do not conflict.

Claims

1. A self-oscillating light source and microwave source based on hybrid integration and photoelectric feedback, characterized in that, include: A silicon nitride / lithium tantalate chip (1) has an erbium-doped silicon nitride waveguide (5) and a lithium tantalate electro-optic modulator (7) integrated on its substrate. The erbium-doped silicon nitride waveguide (5) and the electro-optic modulator (7) are optically coupled through an on-chip mode converter. The fiber optic device (11) consists of a single-mode polarization-maintaining fiber (12) coupled to the end face of the silicon nitride / lithium tantalate chip (1) and a fiber optic mirror (13) at its end; the silicon nitride / lithium tantalate chip (1) and the fiber optic device (11) together form a linear Fabry-Perot optical resonator. A microwave feedback loop is used to convert a portion of the optical signal output from the optical resonant cavity into an electrical signal and process it, then feed it back to drive the electro-optic modulator in the silicon nitride / lithium tantalate chip (1), thereby forming a photoelectric coupling self-oscillating system; the microwave feedback loop includes a photodetector (14), a frequency-selective filter (15), a phase shifter (16), a microwave amplifier (17), and a microwave beam splitter (18) connected in sequence, wherein the input end of the photodetector (14) is optically connected to a portion of the optical signal coupled out from the optical resonant cavity; the first output end of the microwave beam splitter (18) is electrically connected to the microwave driving electrode of the lithium tantalate electro-optic modulator (7); the frequency-selective filter (15) is used to select a target microwave frequency from the photoelectric conversion signal. f R And the target microwave frequency f R Matching the free spectral range of the optical resonant cavity; the phase shifter (16) is used to adjust the phase of the feedback microwave signal so that when the light pulse circulates within the optical resonant cavity to the electro-optic modulator (7), the microwave modulation applied by the electro-optic modulator (7) is in the phase that minimizes the transmission loss of the light pulse, thereby achieving self-sustaining oscillation, and simultaneously outputting a repetition frequency of [value missing] from the optical output port of the silicon nitride / lithium tantalate chip (1). f R The pulsed light, and the output frequency from the second output port of the microwave beam splitter (18) is... f R microwave signals.

2. The self-oscillating light source and microwave source based on hybrid integration and photoelectric feedback according to claim 1, characterized in that, The silicon nitride / lithium tantalate chip (1) also integrates the following in the light propagation path: The optical beam splitter (2) receives optical signals from the optical resonant cavity at its input end, its first output end serves as the optical output port, and its second output end is connected to the input end of the photodetector (14). A reflector (3) is disposed in the input optical path of the optical beam splitter (2) as a cavity mirror of the optical resonant cavity on the chip side; The wavelength division multiplexer (4) has its signal end connected between the reflector (3) and the optical beam splitter (2), its beam combining end connected to the input end of the erbium-doped silicon nitride waveguide (5), and its pump end used to connect to an external pump light source (10).

3. The self-oscillating light source and microwave source based on hybrid integration and photoelectric feedback according to claim 1, characterized in that, The lithium tantalate electro-optic modulator (7) uses thin-film lithium tantalate material, and its waveguide structure covers the silicon nitride waveguide layer, with the two separated by a silicon oxide layer; the optical field is coupled between the silicon nitride waveguide layer and the thin-film lithium tantalate waveguide through the on-chip mode converter, so that in the region of the lithium tantalate electro-optic modulator (7), the optical field is constrained by the thin-film lithium tantalate waveguide and the underlying silicon nitride waveguide or by the thin-film lithium tantalate waveguide alone.

4. The self-oscillating light source and microwave source based on hybrid integration and photoelectric feedback according to claim 1, characterized in that, The lithium tantalate electro-optic modulator (7) couples the optical signal in the silicon nitride waveguide into the lithium tantalate electro-optic modulator through the first on-chip mode converter (6) to achieve electro-optic modulation, and then couples the optical signal back into the silicon nitride waveguide through the second mode converter (8).

5. The self-oscillating light source and microwave source based on hybrid integration and photoelectric feedback according to claim 1, characterized in that, The frequency-selective filter (15) is a narrowband filter with a passband bandwidth of less than 100 MHz, and its center frequency is... f R Adjustable in the range of 1 GHz to 40 GHz.

6. The self-oscillating light source and microwave source based on hybrid integration and photoelectric feedback according to claim 1, characterized in that, The length of the single-mode polarization-maintaining fiber (12) is from 0.1 km to 10 km.

7. The self-oscillating light source and microwave source based on hybrid integration and photoelectric feedback according to claim 1, characterized in that, The distance between the reflector of the silicon nitride / lithium tantalate chip (1) and the fiber optic reflector (13) determines the fundamental frequency of the optical resonant cavity. f 0, and satisfy the relation f R ≈ N× f 0, where N is a positive integer.

8. A method for operating a self-oscillating light source and a microwave source according to any one of claims 1 to 6, characterized in that, Includes the following steps: Pump light is injected into the erbium-doped silicon nitride waveguide (5) to cause the optical resonant cavity to oscillate. Start the microwave feedback loop; The target frequency is selected from the electrical signal output by the photodetector (14) by the frequency selective filter (15). f R ; Adjusting the phase shifter (16) changes the phase of the microwave signal fed back to the electro-optic modulator (7) until the optical signal output from the optical resonant cavity stabilizes at a repetition frequency equal to f R The pulse sequence, and the microwave signal output by the microwave feedback loop is stabilized at a frequency equal to... f R The system enters a self-sustaining oscillation state when a single-frequency signal is received.

9. The working method of the self-oscillating light source and microwave source according to claim 7, characterized in that, The target frequency f R The selection is independent of the precise length of the optical resonator and is achieved by changing or tuning the center frequency of the frequency-selective filter (15).

10. A method for fabricating a heterogeneous integrated functional chip for the self-oscillating light source and microwave source as described in claim 1, characterized in that, Includes the following steps: S1: A silicon oxide undercoat is formed on a silicon substrate, and a silicon nitride thin film is deposited; S2: Pattern the silicon nitride thin film to form a silicon nitride waveguide structure including a wavelength division multiplexer (4), an optical beam splitter (2), a partial mirror (3), a mode converter region, and an end coupler (9); S3: Selective erbium ion implantation and annealing are performed on the silicon nitride waveguide in the predetermined region to form the erbium-doped silicon nitride waveguide (5). S4: Deposit a silicon oxide intermediate cladding layer and perform chemical mechanical polishing; S5: Provide a thin-film lithium tantalate donor wafer, which includes a silicon oxide sacrificial layer and a thin-film lithium tantalate layer; S6: An electro-optic modulator waveguide and a coupling structure aligned with the mode converter region are patterned on the thin-film lithium tantalate layer. S7: Selectively etch the silicon oxide sacrificial layer to form a micro-transfer cord; S8: The patterned thin-film lithium tantalate structure is transferred and bonded to a predetermined position on the chip surface after polishing in step S4 using micro-transfer technology. S9: Fabrication of microwave-driven electrodes on the transferred thin-film lithium tantalate structure; S10: Deposit silicon oxide cladding and open electrode contact windows.

11. A communication or measurement system, characterized in that, The system comprises a self-oscillating light source and a microwave source as described in any one of claims 1 to 6, wherein the pulsed light output is used for optical communication or optical sampling, and the microwave signal output is used as a local clock reference for the system.

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