A microwave generating device for a temperature-controlled Brillouin laser Kerr optical frequency comb

Abstract

The present invention discloses a microwave generating device for a temperature-controlled Brillouin laser Kerr optical frequency comb, comprising: a control module; a tunable wavelength laser; an optical amplifier; an optical circulator, the first port of which receives the amplified pump laser; a silicon nitride microring cavity that generates Brillouin laser inside the cavity and outputs the mixed laser together with the reflected pump laser to the second port of the optical circulator through the optical input end; an optical polarization beam splitter; a photon filtering module that receives the Brillouin laser from the optical polarization beam splitter, selects the corresponding frequency interval and then outputs the filtered photon signal; a first optical detector; the silicon nitride microring cavity realizes the second pumping of the Brillouin laser to form a Kerr optical frequency comb by tuning the tunable wavelength laser through the control module. The present invention generates an orthogonally polarized mode stimulated Brillouin laser for second pumping to form a Kerr optical frequency comb, filters the optical waves with a specific comb tooth interval of the optical frequency comb, and performs beat frequency on the filtered optical wave signal to obtain the required microwave signal output.

Description

Technical Field

[0001] The present invention relates to the field of microwaves, and in particular, to a microwave generating device for a temperature-controlled Brillouin laser Kerr optical frequency comb. Background Art

[0002] Modern radars and microwave communication systems both need to transmit and receive microwave signals. Microwave local oscillator signal sources are used in both transmitters and receivers. In the transmitting channel direction, generally, the transmitted signal is mixed with the local oscillator signal and then power-amplified before being transmitted. In the receiving channel, generally, the received signal is mixed with the local oscillator signal to obtain an intermediate-frequency signal and then subjected to detection processing to extract the required information. Therefore, microwave local oscillator signal sources are essential in modern radars and microwave communication systems. Generating local oscillator signals with high spectral purity and low phase noise has always been a pursuit goal of modern radars and communication systems.

[0003] Generally speaking, the quality of the microwave signal generated by a microwave oscillator depends on the energy storage performance of the oscillation cavity. To generate high-quality microwave signals, a high-Q and low-loss energy storage unit is required. Current microwave oscillators mostly rely on electronic (such as dielectric oscillators) and acoustic (such as crystal oscillators) energy storage elements. When these elements operate at frequencies above GHz, their energy storage characteristics will decline significantly, and the phase noise and spectral purity of the generated high-frequency microwaves will also deteriorate.

[0004] To meet the requirements for the generation, transmission, and processing of high-frequency and ultra-wideband signals in the microwave field, microwave photonics utilizes the advantages of large bandwidth and electromagnetic interference resistance of photon technology to generate and process microwave radio frequency signals. It can generate high-frequency spectral purity and low-phase noise signals of several GHz or even hundreds of GHz, showing unique technical advantages in the microwave / millimeter-wave frequency band and having excellent phase noise performance.

[0005] Optical microcavities, such as traditional Fabry-Perot (F-P) cavities and all-solid-state dielectric whispering gallery mode microcavities, have stable high-Q resonance modes. By combining a continuous-wave pump laser with a high-Q microcavity, this new type of photonic microwave technology can be used to generate high-quality microwave signals. Currently, companies such as OEwaves in the United States have combined a DFB laser with a narrow linewidth output and a magnesium fluoride crystal whispering gallery mode resonator to achieve an OEO optoelectronic oscillator product with a Ka-band 35 GHz frequency output. They have also released a product that uses the Kerr nonlinear effect of a magnesium fluoride crystal whispering gallery mode resonator, pumps and excites it with a DFB laser, generates a Kerr optical frequency comb through the optical frequency comb signal, and obtains an ultra-low phase noise 10 GHz microwave signal output through beat frequency of the optical frequency comb signal.

[0006] In the current photonic microwave scheme for generating microwave signals using such optical microcavities, the main problems are that optical microcavities such as F-P cavities are relatively large in size and not easy to integrate. The cavity mirrors with high reflectivity are costly and have high assembly requirements. For whispering gallery mode resonators made of dielectric materials such as magnesium fluoride and silicon-based materials, there are also problems such as difficult processing and extremely high precision requirements for processing equipment. In addition, there are difficulties in optical assembly and debugging, and complex production processes. For this type of photonic microwave technology to generate high-quality microwave signal output, in order to improve the stability of the system, it is necessary to perform reverse self-injection locking on the DFB laser, which requires the reflected light of the resonator to have a special optical mode field and phase matching, resulting in complex debugging and assembly processes. All these seriously increase the difficulty of large-scale application of this type of technical solution.

[0007] With the development of silicon-based integrated photonics in recent years, the design of micro-ring cavities based on silicon nitride waveguides has attracted more and more attention. Considerable research has also been carried out on the Kerr nonlinear effect of straight-through ring waveguide micro-ring cavities based on silicon nitride. There are also related schemes for generating 10 GHz microwave signals after beat frequency by exciting Kerr optical frequency combs with silicon nitride micro-ring cavities, but there are still relatively large technical problems. For example, it requires high-power laser signal pumping excitation in the communication band, while high-power DFB lasers have poor noise performance, and the output optical noise performance of the pumping laser will directly affect the final beat frequency microwave signal, making it difficult for the system to obtain microwave signal output with good phase noise performance. Moreover, during the output process of Kerr effect solitons based on silicon nitride micro-ring cavities, the pumping laser needs to be detuned. When the pumping light is red-detuned and excited in the single soliton state of the Kerr optical frequency comb, the micro-ring cavity is actually in a thermally unstable state, and the system cannot obtain a relatively stable long-term working state.

[0008] Therefore, some have proposed a scheme of using laser-assisted heating. In addition to the pumping laser that generates Kerr optical frequency combs, an auxiliary laser is added and injected into the micro-ring cavity in the direction opposite to the transmission direction of the pumping laser injected into the micro-ring cavity. By precisely controlling the red-detuned wavelength position of the pumping laser and the blue-detuned wavelength position of the auxiliary laser, the control and adjustment of thermal equilibrium of the micro-ring cavity in the single soliton state of the Kerr optical frequency comb are realized, avoiding thermal instability in the single soliton state of the Kerr optical frequency comb, so as to achieve stable long-term operation of the silicon nitride micro-ring cavity in the single soliton state of the Kerr optical frequency comb. However, after adding an auxiliary laser to inject laser into the micro-ring cavity for heating, the system needs to have two lasers for real-time control simultaneously, increasing the control difficulty and system complexity of the system. Therefore, there is currently no report on the actual application of this scheme.

[0009] According to the latest research report, based on an optical fiber microcavity, Brillouin laser is generated by pumping laser injection excitation. The Brillouin laser has an ultra-narrow linewidth and very low noise. Using this Brillouin laser as the pump light to excite the microcavity to generate Kerr optical frequency comb, the advantage of this scheme is to use the Brillouin laser to pump and excite the Kerr optical frequency comb, thus avoiding the influence of the high noise level brought by the initial high-power laser pump injection. It is a great progress for photon microwave technology. However, the fiber F-P microcavity technology used in this scheme adjusts the stress inside the fiber material by applying pressure to the outside of the fiber F-P microcavity to achieve the adjustment of the microcavity resonance frequency parameters. The fiber microcavity of this scheme is sensitive to external stress, the system stability is not high, and the parameter adjustment process is complex. Summary of the Invention

[0010] The object of the present invention is to overcome the deficiencies of the prior art and provide a temperature-controlled microwave generating device for Brillouin laser Kerr optical frequency comb.

[0011] The object of the present invention is achieved by the following technical solutions:

[0012] In the first aspect of the present invention, there is provided a temperature-controlled microwave generating device for Brillouin laser Kerr optical frequency comb, including:

[0013] A control module;

[0014] An adjustable wavelength laser, which receives the command of the control module and outputs pump laser with corresponding wavelength and power;

[0015] An optical amplifier for amplifying the pump laser;

[0016] An optical circulator, the first port of which is used to receive the amplified pump laser;

[0017] A silicon nitride micro-ring cavity, the optical input end of which receives the pump laser through the second port of the optical circulator, generates Brillouin laser inside the cavity, and outputs the mixed laser together with the reflected pump laser to the second port of the optical circulator through the optical input end;

[0018] An optical polarization beam splitter, which receives the mixed laser output from the third port of the optical circulator, filters the pump laser in the mixed laser, and outputs the split Brillouin laser;

[0019] A photon filtering module, which receives the Brillouin laser from the optical polarization beam splitter, selects the corresponding frequency interval, and outputs the filtered photon signal;

[0020] A first optical detector, which receives the photon signal, performs beat frequency, and outputs a microwave signal;

[0021] The silicon nitride micro-ring cavity generates resonant light under the coupled input pump laser and excites orthogonally polarized Brillouin lasers in the micro-ring cavity as secondary pump lasers to form a Kerr optical frequency comb.

[0022] Further, the Brillouin laser and the pump laser are two orthogonally polarized laser signals; wherein the Brillouin laser is in the TM mode and the pump laser is in the TE mode, or the Brillouin laser is in the TE mode and the pump laser is in the TM mode.

[0023] Further, the control of the tunable wavelength laser by the control module includes:

[0024] Initially set the input pump laser wavelength at the blue detuning of the resonant peak wavelength corresponding to the TE mode polarized photons of the silicon nitride micro-ring cavity, gradually increase the wavelength blue shift so that the pump laser approaches the resonant peak, the input pump laser is coupled into the silicon nitride micro-ring cavity for resonance, the resonant power gradually increases, and the orthogonally polarized TM mode Brillouin laser excited by the resonant light in the silicon nitride micro-ring cavity;

[0025] The control module further adjusts the blue shift speed and optical power of the pump laser wavelength until the Kerr optical frequency comb state appears, and continues to blue shift and finely adjust the input pump laser. The stimulated Brillouin laser of the secondary pump laser will redshift from the red detuning position of the TM mode resonant peak wavelength and gradually move away from the resonant peak of the silicon nitride micro-ring cavity. The power of the Kerr optical frequency comb excited in the silicon nitride micro-ring cavity will decrease in a step-like manner until the required soliton state optical frequency comb output is obtained, and the optical comb tooth interval is stabilized.

[0026] Further, the microwave generating device further includes one or more of the following optical detectors:

[0027] The second optical detector, the input end is connected to the through output port of the silicon nitride micro-ring cavity, and the output end is connected to the control module to monitor the working state of the pump laser;

[0028] The third optical detector, the input end is connected to the drop output port of the silicon nitride micro-ring cavity, and the output end is connected to the control module to monitor the working state of the resonant light in the silicon nitride micro-ring cavity;

[0029] The fourth optical detector, the input end is connected to the optical splitter between the optical polarization beam splitter and the photon filtering module, and the output end is connected to the controller to monitor the working state of the Kerr optical frequency comb in the micro-ring cavity.

[0030] Further, the second optical detector and the third optical detector cooperate with the regulation of the pump laser process in the initial setting; the fourth optical detector cooperates with the regulation of the further adjustment of the pump laser process.

[0031] Further, the photon filtering module includes an independent one with a spectral line interval FSR 滤波The photon filter filters the orthogonal-mode Brillouin laser Kerr optical frequency comb signal; FSR 滤波 = M × FSR 布里渊 , where M is an integer and FSR 布里渊 is the spectral line interval of the resonance peaks of the silicon nitride micro-ring cavity.

[0032] Furthermore, the photon filtering module includes an optical splitter, a first photon filter, a second photon filter, and an optical combiner. The optical splitter receives the laser from the optical polarization beam splitter and splits it into two beams with a 50:50 ratio, which enter the first photon filter and the second photon filter respectively. According to the required microwave signal band, the corresponding Kerr optical frequency comb tooth photon signals are selected. The two photon signals are combined and then input into the first photodetector;

[0033] Among them, the spectral line interval FSR of the first photon filter and the second photon filter 滤波 is relatively large and needs to be greater than the signal response bandwidth of the first photodetector, and FSR 滤波 is not an integer multiple of the FSR of the Kerr optical frequency comb 布里渊 relationship.

[0034] Furthermore, the resonance peak frequencies of the laser in the TE mode and the laser in the TM mode in the silicon nitride micro-ring cavity are distributed at intervals of the free spectral range FSR 布里渊 GHz, and there are n*FSR 布里渊 resonance peak distributions. n is an integer. The resonance peak frequencies of the orthogonally polarized TE mode laser and the TM mode laser have a slight interval difference, and the difference is Δυ MHz;

[0035] Based on the Brillouin laser frequency offset of the pump light in the silicon nitride micro-ring cavity being f ΔSBL , design the FSR 布里渊 value of the silicon nitride micro-ring cavity as (f ΔSBL +Δυ) = m*FSR 布里渊 , where m is an integer; based on this FSR 布里渊 value, design the size of the silicon nitride micro-ring cavity according to the formula FSR = Δλ = λ 2 / n g L, where λ is the optical wavelength, n g is the group refractive index of the waveguide, and L is the length of the optical microcavity, that is, the length of the silicon nitride micro-ring cavity.

[0036] Furthermore, after determining the FSR 布里渊 , design the wavelength of the Brillouin gain region to overlap with the FSR 布里渊 resonance peaks of the silicon nitride micro-ring cavity of the TM polarization photon comb teeth, and design the peak of the wavelength of the Brillouin gain region to be slightly red-detuned from the resonance peak wavelength. According to the Brillouin frequency shift f ΔSBLThe value selection corresponds to the TE-polarized photon as the central wavelength of the input pump light; through dispersion engineering design, the TM-mode polarized photon is optimized to have anomalous dispersion in the BGS wavelength region.

[0037] Further, the tunable wavelength laser is a 1550 nm communication band laser, the photon signal obtained by the photon filtering module is in the Ka band, m is 4, and the value of f ΔSBL is 11, and M is 12 or 13.

[0038] The beneficial effects of the present invention are:

[0039] (1) In an exemplary embodiment of the present invention, based on a silicon nitride microring cavity, a Kerr optical frequency comb is formed by secondarily pumping the stimulated Brillouin laser of the orthogonal polarization mode, and the optical wave with a specific comb tooth interval of the optical frequency comb is filtered. The filtered optical wave signal is beat to obtain the required microwave signal output; among them, the input laser signal is used to pump the silicon nitride microcavity to generate the stimulated Brillouin laser. The generated Brillouin laser has a narrow linewidth and low noise. As the second pump light to generate the Kerr optical frequency comb, it can effectively isolate and reduce the noise influence brought by the conversion of the input pump laser signal, effectively improve the spectral purity of the microwave signal generated by the beat light, and obtain an ultra-low phase noise microwave signal; at the same time, the Kerr optical frequency comb signal is formed by secondarily pumping the stimulated Brillouin laser of the orthogonal polarization mode, and the polarization beam splitter is used to separate the input pump laser signal from the Kerr optical frequency comb signal of the orthogonal polarization mode, which can effectively reduce the unstable influences such as amplitude and noise brought by the input pump laser signal, effectively improve the spectral purity of the microwave signal generated by the beat light, and obtain an ultra-low phase noise microwave signal.

[0040] (2) In another exemplary embodiment of the present invention, when the input pump laser is input, it first enters from the blue detuning position of the resonant peak wavelength corresponding to the TE-mode polarized photon and gradually blue-shifts, while the stimulated Brillouin laser of the second pump is located at the red detuning position of the TM-mode polarized photon. Initially, the optical heat generated in the microcavity is mainly contributed by the Brillouin laser of the TM-mode polarized photon. As the input pump light continues to blue-shift, the optical frequency comb is formed and evolves towards the soliton state, and the Brillouin laser will also gradually red-shift away from the microcavity resonance peak, which will cause the heat in the microcavity to decrease. At this time, the input pump light blue-shifts close to the corresponding TE-mode polarized photon resonance peak, which can compensate for the decrease in the intracavity heat caused by the red-shift of the Brillouin laser SBL, thereby overcoming the thermal instability phenomenon of the traditional silicon nitride microring cavity Kerr optical frequency comb under red detuning and realizing the stable operation of the Brillouin Kerr optical frequency comb.

[0041] (3) In yet another exemplary embodiment of the present invention, the present invention uses a photon filter with a spectral line interval FSR filtering to filter the orthomode Brillouin laser Kerr optical frequency comb signal. The optical comb tooth interval of the silicon nitride microring cavity spectral line interval FSR Brillouin is small, and the interval of the FSR filtering is large. The design selects FSR filtering = M × FSR Brillouin (M is an integer) = Ka-band microwave frequency, which can effectively reduce the number of beat-frequency photons, effectively reduce the generation of spurious signals, and obtain a microwave signal with high spectral purity.

[0042] (4) In yet another exemplary embodiment of the present invention, the Brillouin radiation optical frequency shift is f ΔSBL , the optical resonance peak frequency difference between the orthogonally polarized modes (TM and TE) in the silicon nitride microcavity is Δυ, and the silicon nitride microcavity design selects the resonance spectral line interval as FSR 布里渊 , according to (f ΔSBL + Δυ) = m*FSR 布里渊 , m = 1, 2, 3, 4,.. m is an integer. When m is selected to be larger, the spectral line interval is small, and it is easy for the Brillouin radiation gain region to overlap with the resonance center wavelength of the microring cavity with small error. However, a small spectral line interval will make it difficult to obtain a single photon comb tooth spectrum by photon filtering, and the spurious signals of the optically generated microwave signal may increase, resulting in a decrease in the spectral purity of the microwave signal. Therefore, when designing the m value here, it is necessary to consider comprehensively. Generally, according to the required Ka-band microwave signal frequency, m = 4 or 6, etc. are preferably selected, and it needs to be flexibly adjusted according to specific application requirements.

[0043] (5) In yet another exemplary embodiment of the present invention, based on the silicon nitride microring cavity, according to (f ΔSBL + Δυ) = m*FSR 布里渊 , m = 1, 2, 3, 4,.. m is an integer, the FSR of the microring cavity design is determined 布里渊 , the wavelength of the Brillouin gain region (BGS) is designed to overlap with the FSR of the TM-polarized photon comb teeth 布里渊 microring cavity resonance peak, and the BGS peak is designed to be slightly red-detuned from the resonance peak wavelength. According to the Brillouin frequency shift f ΔSBL value, the corresponding TE-polarized photon is selected as the central wavelength of the input pump light. Through dispersion engineering design, the TM mode polarization photon is optimized to have anomalous dispersion in the BGS wavelength region, which is convenient for optimizing the excitation of the Kerr optical frequency comb in the TM mode in this wavelength region.

[0044] (6) In yet another exemplary embodiment of the present invention, the control module issues commands to control the wavelength change and power change of the input pump laser. By monitoring the resonant optical state of the micro-ring cavity and the output state of the optical frequency comb, and through big data analysis and look-up table analysis, an optimized input pump light drive control is obtained, realizing the stable operation of the orthogonally polarized mode Brillouin laser Kerr optical frequency comb of the present invention, and obtaining an ultra-low phase noise microwave signal generated by optical signal beat frequency. Description of the Drawings

[0045] Figure 1 Schematic connection structure diagram of a microwave generating device of a temperature-controlled Brillouin laser Kerr optical frequency comb provided in an exemplary embodiment of the present invention;

[0046] Figure 2 Schematic diagram of one of the photon filtering modules provided in an exemplary embodiment of the present invention;

[0047] Figure 3 Schematic diagram of another photon filtering module provided in an exemplary embodiment of the present invention;

[0048] Figure 4 Schematic diagram of the principle of the orthogonally polarized mode Brillouin laser Kerr optical frequency comb provided in an exemplary embodiment of the present invention. Detailed Embodiments

[0049] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0050] In the description of the present invention, it should be noted that the directions or positional relationships indicated by terms such as "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. are based on the directions or positional relationships shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be construed as a limitation to the present invention. In addition, terms such as "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0051] In the description of the present invention, it should be noted that unless otherwise clearly specified and defined, the terms "installation", "connection", and "coupling" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0052] In addition, the technical features involved in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0053] See Figure 1 , Figure 1 which shows a microwave generating device of a temperature-controlled Brillouin laser Kerr optical frequency comb provided by an exemplary embodiment of the present invention, including:

[0054] A control module;

[0055] An adjustable wavelength laser that outputs pump laser with corresponding wavelength and power according to the command of the control module;

[0056] An optical amplifier that amplifies the pump laser;

[0057] An optical circulator, the first port of which is used to receive the amplified pump laser;

[0058] A silicon nitride micro-ring cavity, the optical input end of which receives the pump laser through the second port of the optical circulator, and after generating Brillouin laser inside the cavity, together with the reflected pump laser, outputs the mixed laser to the second port of the optical circulator through the optical input end;

[0059] An optical polarization beam splitter that receives the mixed laser output from the third port of the optical circulator, filters the pump laser in the mixed laser, and outputs the split Brillouin laser;

[0060] A photon filtering module that selects the corresponding frequency interval after receiving the Brillouin laser from the optical polarization beam splitter and outputs the filtered photon signal;

[0061] A first optical detector that receives the photon signal, performs beat frequency, and outputs a microwave signal;

[0062] The silicon nitride micro-ring cavity generates resonant light under the coupled input pump laser and excites orthogonally polarized Brillouin laser in the micro-ring cavity as a secondary pump laser to form a Kerr optical frequency comb.

[0063] Specifically, in this exemplary embodiment, the tunable wavelength laser outputs laser light with corresponding wavelength and power according to the command of the control module. The laser signal is input into the first port of the optical circulator after optical amplification, and then output from the second port of the circulator and enters the silicon nitride (Si3N4) microring cavity as the input pump laser signal. The orthogonally polarized Brillouin laser (TM mode or TE mode, which will be elaborated in the following exemplary embodiments) excited by the resonant light in the silicon nitride microring cavity travels in the opposite direction to the input pump laser in the form of reflected light in the silicon nitride microring cavity and outputs from the port of the silicon nitride microring cavity into the second port of the optical circulator, and then outputs from the third port of the optical circulator. The output optical signal from the third port of the optical circulator contains orthogonally polarized TE and TM mode polarized photons. After passing through the optical polarization beam splitter, the photon signals related to the input pump laser are filtered out, and only the polarized photons related to the Brillouin laser are output. A photon filter with a corresponding frequency interval is selected to filter out the photon signals with relevant comb tooth intervals in the Kerr optical frequency comb to obtain two or more photon signals with equal spectral line intervals, and then the filtered photon signals are input into the first optical detector. After beat frequency, a microwave signal is output by the first optical detector, thereby obtaining the required ultra-low phase noise microwave signal.

[0064] After that, the control module adjusts the pump laser in terms of wavelength and power and then performs secondary pumping until the Kerr optical frequency comb state appears in the silicon nitride microring cavity.

[0065] In this exemplary embodiment, based on the silicon nitride microring cavity, the Kerr optical frequency comb is formed by generating orthogonally polarized mode stimulated Brillouin laser for secondary pumping, and the light waves with specific comb tooth intervals of the optical frequency comb are filtered. The filtered optical wave signals are subjected to beat frequency to obtain the required microwave signal output. Among them, the input laser signal is used to pump the silicon nitride microcavity to generate stimulated Brillouin laser. The generated Brillouin laser has a narrow linewidth and low noise. As the secondary pump to generate the Kerr optical frequency comb, it can effectively isolate and reduce the noise influence brought by the conversion of the input pump laser signal, and can effectively improve the spectral purity of the microwave signal generated by the beat frequency light to obtain an ultra-low phase noise microwave signal. At the same time, the Kerr optical frequency comb signal is formed by using the orthogonally polarized mode stimulated Brillouin laser for secondary pumping. By using the polarization beam splitter, the input pump laser signal is separated from the orthogonally polarized mode Kerr optical frequency comb signal, which can effectively reduce the unstable influences such as amplitude and noise brought by the input pump laser signal, and can effectively improve the spectral purity of the microwave signal generated by the beat frequency light to obtain an ultra-low phase noise microwave signal.

[0066] In addition, based on a silicon nitride micro-ring cavity, the present invention controls the wavelength and power changes of an input pump laser by issuing commands from a control module. By monitoring the resonant light state of the silicon nitride micro-ring cavity and the output state of the optical frequency comb, through big data analysis and look-up table analysis, an optimized input pump light drive control is obtained, realizing the stable operation of the orthogonally polarized mode Brillouin laser Kerr optical frequency comb of the present invention, and obtaining an ultra-low phase noise microwave signal generated by optical signal beat frequency.

[0067] It should be noted that in an exemplary embodiment, the Brillouin laser and the pump laser are two orthogonally polarized laser signals; among them, the Brillouin laser is in the TM mode and the pump laser is in the TE mode, or the Brillouin laser is in the TE mode and the pump laser is in the TM mode. In the following exemplary embodiments, the case where the Brillouin laser is in the TM mode and the pump laser is in the TE mode will be described.

[0068] More preferably, in an exemplary embodiment, the control of the tunable wavelength laser by the control module (i.e., primary pump and secondary pump) includes:

[0069] Primary pump: The tunable wavelength laser outputs laser with a corresponding wavelength and power according to the command of the control module. This laser signal is amplified by an optical amplifier and then input into the first port of an optical circulator, and then output from the second port of the circulator and enter into a silicon nitride (Si3N4) micro-ring cavity as an input pump laser signal. Initially, the input pump laser wavelength is set at the blue detuning of the resonant peak wavelength corresponding to the TE mode polarized photons in the silicon nitride micro-ring cavity, and the wavelength blue shift is gradually increased so that the pump laser approaches the resonant peak. The input pump laser is coupled into the silicon nitride micro-ring cavity to resonate, and the resonant power gradually increases (in an exemplary embodiment, the microwave generating device further includes one or more of the following optical detectors: as Figure 1 shown, the second optical detector, with its input end connected to the through output port of the silicon nitride micro-ring cavity and its output end connected to the control module, monitors the working state of the pump laser; the third optical detector, with its input end connected to the drop output port of the silicon nitride micro-ring cavity and its output end connected to the control module, monitors the working state of the resonant light in the silicon nitride micro-ring cavity; the second optical detector and the third optical detector cooperate with the regulation of the pump laser process in the initial setting), and the orthogonally polarized TM mode Brillouin laser excited by the resonant light in the silicon nitride micro-ring cavity; in the silicon nitride micro-ring cavity, in the form of reflected light, in the direction opposite to the transmission direction of the input pump laser, it outputs from the port of the silicon nitride micro-ring cavity and enters the second port of the optical circulator, and then is output from the third port of the optical circulator. The optical signal output from the third port of the optical circulator contains orthogonally polarized TE and TM mode polarized photons. After passing through an optical polarization beam splitter, the photon signals related to the input pump laser are filtered out, and only the TM mode polarized photons related to the Brillouin laser are output.

[0070] Second pumping: The control module further adjusts the blue-shift speed and optical power of the pump laser (in an exemplary embodiment, the microwave generating device further includes one or more of the following optical detectors: as Figure 1 shown, the fourth optical detector, the input end of which is connected to an optical splitter (90:10 splitter) located between the optical polarization beam splitter and the photon filtering module, and the output end is connected to the controller, and is used to monitor the working state of the Kerr optical frequency comb in the micro-ring cavity. The fourth optical detector cooperates with the regulation of the further adjustment of the pump laser process; in this step, the stimulated Brillouin laser state of the cross-polarized TM mode is monitored through the fourth optical detector), until the Kerr optical frequency comb state appears (which can be monitored through a preset empirical time, or preferably the fourth optical detector in the exemplary embodiment), continue to finely adjust the input pump laser in the blue-shift direction. The stimulated Brillouin laser of the second pump laser will red-shift from the red-detuned position of the TM mode resonance peak wavelength, gradually move away from the resonance peak of the silicon nitride micro-ring cavity, and the power of the Kerr optical frequency comb excited in the silicon nitride micro-ring cavity will decrease in a stepwise manner until the desired soliton state optical frequency comb output is obtained, and the optical comb tooth interval is stable. At this time, since the input pump light gradually blue-shifts and more photons are coupled into the micro-ring cavity, the photo-induced heating in the cavity caused by the red-shift of the stimulated Brillouin SBL light leaving is compensated, so that the photo-induced heating in the micro-ring cavity is maintained in a relatively stable continuous state, and the thermal instability state that occurs when the optical power in the cavity rapidly decreases and the heating decreases in the soliton state of the Kerr optical frequency comb in the traditional silicon nitride micro-ring cavity will not occur. Through the fine control of the control module, the optical resonance in the micro-ring cavity and the output state of the Kerr optical frequency comb fed back by each optical detector are received and analyzed in real time, so as to realize the stable operation of the orthogonal polarization mode Brillouin laser Kerr optical frequency comb photon microwave generating device of the present invention.

[0071] Specifically, in this exemplary embodiment, when the input pump laser is input, it first enters from the blue-detuned position corresponding to the resonance peak wavelength of the TE-mode polarized photons and gradually blue-shifts. The stimulated Brillouin laser of the second pump is located at the red-detuned position of the TM-mode polarized photons. Initially, the photo-generated heat in the micro-cavity is mainly contributed by the Brillouin laser of the TM-mode polarized photons. As the input pump light continues to blue-shift and the optical frequency comb forms and evolves towards the soliton state, the Brillouin laser will also gradually red-shift away from the micro-cavity resonance peak value, which will cause the heat in the micro-cavity to decrease. At this time, the input pump light blue-shifts close to the resonance peak of the corresponding TE-mode polarized photons, which can compensate for the decrease in the cavity heat caused by the SBL red-shift, thereby overcoming the thermal instability phenomenon under the red-detuning of the traditional silicon nitride micro-ring cavity Kerr optical frequency comb and realizing the stable operation of the Brillouin Kerr optical frequency comb.

[0072] More preferably, in an exemplary embodiment, the resonance peak frequencies of the lasers in the TE mode and the lasers in the TM mode in the silicon nitride micro-ring cavity are distributed at intervals of the free spectral range FSR 布里渊 GHz intervals, which is n*FSR 布里渊The resonant peak distribution, where n is an integer, and there is a slight frequency interval difference between the resonant peak frequencies of the orthogonally polarized TE-mode laser and the TM-mode laser, with a difference of Δυ MHz;

[0073] Based on the Brillouin laser frequency offset of the pump light in the silicon nitride microring cavity being f ΔSBL , design the FSR of the silicon nitride microring cavity 布里渊 value to be (f ΔSBL + Δυ) = m * FSR 布里渊 , where m is an integer; based on this FSR 布里渊 value, design the size of the silicon nitride microring cavity according to the formula FSR = Δλ = λ 2 / n g L, where λ is the optical wavelength, n g is the group refractive index of the waveguide, and L is the length of the optical microcavity, i.e., the length of the silicon nitride microring cavity.

[0074] More specifically, for the silicon nitride microring cavity itself, the pump light is output from the second port of the optical circulator and then enters the silicon nitride microring cavity. This microring cavity is a double-runway up-down path type ring cavity structure, with an optical input end, an optical through-output end, and an optical drop-output end. The input pump light with a certain power is coupled into the microring cavity and resonates to excite two orthogonally polarized polarized photons. The two orthogonally polarized photons are the TE mode and the TM mode. The resonant peak frequencies of the TE mode and TM mode photons in the microring resonator are distributed at intervals of FSR 布里渊 (free spectral range) GHz intervals, with a distribution of n * FSR 布里渊 (n is an integer) resonant peak distributions. There is a slight frequency interval difference between the resonant peak frequencies of the orthogonally polarized TE mode and TM mode photons, with a difference of Δυ MHz. In the device of the present invention, the input pump light and the Brillouin laser (SBL) respectively correspond to the two orthogonally polarized photon signals. For simplicity of description, it is assumed here that the polarization direction of the input pump light is aligned with the TE mode polarized photon transmission, and the Brillouin light (SBL) excited by the microring resonator is aligned with the orthogonally polarized TM mode polarized photon transmission. According to the working principle of the Brillouin laser, the Brillouin laser frequency offset of the pump light in the silicon nitride-based microring cavity is approximately f ΔSBL = 11 GHz. Design the FSR value of the microring cavity to be (f ΔSBL + Δυ) = m * FSR, m = 1, 2, 3, 4,..., m is an integer. For simplicity of description, m = 4 is taken here, and FSR = ((Δυ / 4) + 2.75) GHz. Based on this FSR value, according to the formula FSR 布里渊 = Δλ = λ 2 / n gDesign the size of the microring cavity with L and conduct specialized dispersion engineering for the silicon nitride microring cavity, so that at the corresponding SBL wavelength in the 1550 nm band, the orthogonally polarized TM-mode photons have optimized anomalous dispersion. Make the spectral range (BGS) of the Brillouin radiation gain region excited by the pump light close to overlap with the resonant peak frequency of the TM-mode photons in the anomalous dispersion region. Select the resonant peak frequency value of the corresponding TE-mode photons at this place at intervals of (4*FSR 布里渊 -Δυ), and select it as the input pump light frequency, as Figure 4 shown (in the figure, SBL represents Brillouin laser). Among them, if m is selected to be larger, the spectral line interval is smaller, and it is easier to overlap the Brillouin radiation gain region with the resonant center wavelength of the microring cavity and the error is smaller. However, a smaller spectral line interval will make it difficult to obtain a single photon comb tooth spectrum by photon filtering, and the spurious signals of the optogenerated microwave signal may increase, resulting in a decrease in the spectral purity of the optogenerated microwave signal. Therefore, when designing the value of m here, it needs to be comprehensively considered. Generally, according to the required microwave signal frequency in the Ka band, etc., m = 4 or 6 is preferably selected, and it needs to be flexibly adjusted according to specific application requirements.

[0075] According to the formation mechanism of the silicon nitride microring cavity Kerr optical frequency comb, the control module adjusts the output optical power and optical wavelength of the pump laser. When the pump light power exceeds the Brillouin radiation threshold, Brillouin laser is excited and generated in the cavity. Continue to increase the pump power, and set the initial input pump light wavelength at the blue detuning of the resonant peak wavelength corresponding to the relevant TE mode, and gradually blue-shift the pump light wavelength towards the resonant peak. At this time, the Brillouin laser initially set at the red detuning of the resonant peak wavelength of the corresponding relevant TM-mode photons becomes the pump light of the Kerr optical frequency comb. The optical power of this Brillouin laser will gradually increase, and when it exceeds the Kerr optical frequency comb excitation threshold, a Kerr optical frequency comb of TM-mode photons will appear, and its comb tooth interval is k*FSR 布里渊 (k = 1, 2, 3, 4... integers). When the input pump light is further adjusted to blue-shift and approach the resonant peak, the optical wavelength of the Brillouin laser SBL as the secondary pump will also move accordingly, and gradually red-shift away from the resonant peak of the corresponding TM mode at the red detuning position, and a stepped change in the intracavity power of the Kerr optical frequency comb will appear accordingly. Finally, a Kerr optical frequency comb single soliton state with a comb tooth interval of 1*FSR is formed. Maintaining the pump light power and wavelength unchanged, the system will continue to work stably in the Kerr optical frequency comb single soliton state.

[0076] The input pump light is in a blue-detuned position with respect to the resonance peak wavelength of the corresponding TE-mode photons. The Brillouin laser serving as the secondary pump is in a red-detuned position with respect to the resonance peak wavelength of the corresponding TM-mode photons. When the pump light is gradually blue-shifted to stimulate the generation of the initial state of the Kerr optical frequency comb by the Brillouin laser, the optical heating in the cavity is mainly due to the Brillouin laser of the secondary pump. Under continuous blue-shifting of the pump light, the Brillouin laser will red-shift away from the resonance peak, reducing the optical heating in the cavity. At this time, the Kerr soliton state is formed. Since there is pump light continuously entering the resonant cavity through the blue-detuned position, the total heat generation in the cavity can be maintained without a large sudden drop. Thus, a stable operation of the Kerr soliton state for a long time can be obtained.

[0077] Therefore, in this exemplary embodiment, the frequency shift amount of the Brillouin radiation light is f ΔSBL , the optical resonance peak frequency difference between the orthogonally polarized modes (TM and TE) in the silicon nitride microcavity is Δυ, and the silicon nitride microcavity is designed to have a resonance spectral line interval of FSR 布里渊 , according to (f ΔSBL + Δυ) = m * FSR 布里渊 , where m = 1, 2, 3, 4,.. m is an integer. A larger m value is selected, the spectral line interval is smaller, and it is easier for the Brillouin radiation gain region to overlap with the resonance center wavelength of the micro-ring cavity with a smaller error. However, a smaller spectral line interval will make it difficult to obtain a single photon comb tooth spectrum line through photon filtering, and the spurious signals of the optically generated microwave signals may increase, resulting in a decrease in the spectral purity of the microwave signals. Therefore, when designing the m value, comprehensive consideration is required. Generally, according to the required microwave signal frequency in, for example, the Ka band, m = 4 or 6, etc. is preferably selected, and it needs to be flexibly adjusted according to specific application requirements.

[0078] More preferably, in an exemplary embodiment, as Figure 2 shown, the photon filtering module includes an independent photon filter with a spectral line interval of FSR 滤波 , and the photon filter filters the Kerr optical frequency comb signals of the orthogonally polarized mode Brillouin laser; FSR 滤波 = M × FSR 布里渊 , where M is an integer, and FSR 布里渊 is the resonance peak spectral line interval of the silicon nitride micro-ring cavity.

[0079] In this exemplary embodiment, the optical comb tooth interval of the silicon nitride micro-ring cavity spectral line interval FSR 布里渊 is smaller, and the interval of FSR 滤波 is larger. By designing and selecting FSR 滤波 = M × FSR 布里渊 (M is an integer) = Ka band microwave frequency, the number of beat frequency lights can be effectively reduced, the spurious signals can be effectively reduced, and a microwave signal with high spectral purity can be generated and obtained.

[0080] For example, according to the microwave frequency RF required in practice, the photonic filter is designed according to RF = p * FSR 滤波 For example, if it is desired to obtain a Ka-band microwave signal output, according to the FSR = ((Δυ / 4) + 2.75) GHz, approximately 2.81 GHz, exemplified in the solution of the present invention, the FSR of the photonic filter is obtained 滤波 = 13 * 2.81 = 36.53 GHz or FSR 滤波 = 12 * 2.81 = 33.72 GHz. According to the formula FSR = Δλ = λ 2 / n g L to design and optimize the photonic microcavity filter. Align the two consecutive intervals FSR 滤波 channels of the photonic filter with the 0# optical comb tooth and the 12# / or 13# optical comb tooth of the Brillouin Kerr optical frequency comb output, and two or multiple optical signals with the required wavelength interval can be filtered out. These two or multiple optical signals with an interval of FSR 滤波 enter the high-speed detector PD1. After beating frequency by the high-speed detector, the required microwave signal is obtained, and the output FSR 滤波 = 12 * 2.81 = 33.72 GHz or FSR 滤波 = 13 * 2.81 = 36.53 GHz microwave signal; considering the alignment and debugging of the photon center wavelength, the photonic filter uses a TEC temperature control module to adjust and control its temperature to finely adjust and adapt to the frequency alignment between the center wavelength of the photonic filter and the photonic frequency comb.

[0081] More preferably, in an exemplary embodiment, as Figure 3 shown, the photonic filtering module includes an optical splitter, a first photonic filter, a second photonic filter, and an optical combiner. The optical splitter receives the laser from the optical polarization beam splitter and splits it into two beams with a 50:50 ratio, which respectively enter the first photonic filter and the second photonic filter. According to the microwave signal of the required band (such as the Ka band), the corresponding Kerr optical frequency comb tooth photon signal is selected (such as aligning the center wavelength of photonic filter 1 with the 0# comb tooth of the Kerr optical frequency comb, and aligning the center wavelength of photonic filter 2 with the 12# comb tooth of the Kerr optical frequency comb). The two photon signals are combined by optical wave and then input into the first optical detector;

[0082] Among them, the spectral line interval FSR of the first photonic filter and the second photonic filter 滤波 is relatively large and needs to be greater than the signal response bandwidth of the first optical detector, and FSR 滤波 does not coincide with the FSR of the Kerr optical frequency comb 布里渊They are in an integer multiple relationship to avoid the output of redundant optical comb tooth signals after filtering. In this way, two optical signals can be obtained after passing through two optical filters. After the two optical signals are combined by optical multiplexing, they are input into the first high-speed detector for beat frequency, and the required microwave signal is output, obtaining a microwave signal with ultra-low phase noise.

[0083] According to the output optical comb tooth frequency of the Brillouin Kerr optical frequency comb, the central wavelength of the optical filter is aligned with a wavelength of the optical frequency comb, such as the 0# optical comb tooth. According to the formula FSR = Δλ = λ 2 / n g L to design and optimize the photonic microcavity filter. According to the actual required microwave signal, such as the Ka band, align the central wavelength of another optical filter with the 12# or 13# comb tooth wavelength. Similarly, according to the formula FSR = Δλ = λ 2 / n g L to design and optimize the photonic microcavity filter. The spectral spacing FSR of the optical filter 滤波 is designed to be greater than the receiving signal bandwidth of the detector. For example, for Ka band reception, FSR 滤波 about 50 GHz can be selected so that except for the central wavelength such as 0# alignment, the other spectral lines of the comb-shaped filtering spectrum of the optical filter do not coincide with the optical comb tooth wavelengths output by the optical frequency comb. In this way, only the two optical comb tooth signals aligned with the central wavelength can pass through after filtering. Then, the two optical signals are combined and output to the first optical detector, and the required Ka band microwave signal can be obtained through beat frequency. Considering the alignment and debugging of the central wavelength of the photon for the two optical filters, the TEC temperature control module is used to adjust and control its temperature to finely adjust and adapt to the frequency alignment between the optical center wavelength and the photon frequency comb.

[0084] More preferably, in an exemplary embodiment, after determining FSR 布里渊 , design the wavelength of the Brillouin gain region to overlap with the FSR 布里渊 of the TM-polarized photon comb teeth, and design the peak of the wavelength of the Brillouin gain region to be slightly red-detuned from the resonance peak wavelength. According to the Brillouin frequency shift f ΔSBL value, select the corresponding TE-polarized photon as the central wavelength of the input pump light; through dispersion engineering design, optimize the TM mode polarization photon to have anomalous dispersion in the BGS wavelength region.

[0085] Specifically, in this exemplary embodiment, the present invention is based on a silicon nitride microcavity. According to (f ΔSBL +Δυ) = m*FSR 布里渊 , m = 1, 2, 3, 4,..m is an integer, determine the FSR 布里渊 of the microcavity design, and design the wavelength of the Brillouin gain region (BGS) to be the same as the FSR 布里渊The resonant peaks of the microring cavity overlap, and the peak of the designed BGS is located at a slightly red-detuned position with respect to the resonant peak wavelength. According to the Brillouin frequency shift f ΔSBL value, the corresponding TE-polarized photons are selected as the central wavelength of the input pump laser. Through dispersion engineering design, the TM-mode polarized photons are optimized to have anomalous dispersion in the BGS wavelength region, facilitating the optimized excitation of Kerr optical frequency combs in this wavelength region in the TM mode.

[0086] Preferably, in an exemplary embodiment, the tunable wavelength laser is a 1550 nm communication-band laser, the photon signal obtained by the photon filtering module is in the Ka band, m is 4, and f ΔSBL value is 11, and M is 12 or 13.

[0087] In another exemplary embodiment of the present invention, a control method for a Brillouin laser Kerr optical frequency comb based on orthogonal polarization modes is provided. Based on a control module, the method includes:

[0088] Initial control step: Send a first control command to the tunable wavelength laser, set the input pump laser wavelength at a blue-detuned position with respect to the resonant peak wavelength of the TE-mode polarized photons in the silicon nitride microring cavity, and gradually increase the wavelength blue shift based on the monitoring data of the second photodetector for monitoring the working state of the pump laser at the through output port of the silicon nitride microring cavity and the third photodetector for monitoring the working state of the resonant light at the drop output port of the silicon nitride microring cavity, so that the pump laser approaches the resonant peak;

[0089] Secondary pump control step: Send a second control command to the tunable wavelength laser, and further adjust the wavelength blue shift speed and optical power of the pump laser based on the monitoring data of the fourth photodetector for monitoring the state of the stimulated Brillouin laser in the cross-polarized TM mode after optical polarization beam splitting until the Kerr optical frequency comb state appears.

[0090] Preferably, in an exemplary embodiment, in this control method, the connection relationship between the control module and external components includes:

[0091] A tunable wavelength laser that receives commands from the control module and outputs pump laser with corresponding wavelength and power;

[0092] An optical amplifier that amplifies the pump laser;

[0093] An optical circulator, the first port of which is used to receive the amplified pump laser;

[0094] A silicon nitride microring cavity, the optical input end of which receives the pump laser through the second port of the optical circulator, and after exciting Brillouin laser inside the cavity, outputs the mixed laser together with the pump laser to the second port of the optical circulator through the optical input end;

[0095] An optical polarization beam splitter receives the combined laser output from the third port of the optical circulator, filters the pump laser in the combined laser, and outputs the split Brillouin laser.

[0096] A photon filtering module receives the Brillouin laser from the optical polarization beam splitter, selects the corresponding frequency interval, and outputs the filtered photon signal.

[0097] A first optical detector receives the photon signal, performs beat frequency, and outputs a microwave signal.

[0098] A second optical detector has its input end connected to the through output port of the silicon nitride micro-ring cavity and its output end connected to the control module to monitor the working state of the pump laser.

[0099] A third optical detector has its input end connected to the drop output port of the silicon nitride micro-ring cavity and its output end connected to the control module to monitor the working state of the resonant light in the silicon nitride micro-ring cavity.

[0100] A fourth optical detector has its input end connected to an optical splitter located between the optical polarization beam splitter and the photon filtering module and its output end connected to the controller to monitor the working state of the Kerr optical frequency comb in the micro-ring cavity.

[0101] The silicon nitride micro-ring cavity forms a Kerr optical frequency comb through the secondary pumping of the tunable wavelength laser by the control module.

[0102] More preferably, in an exemplary embodiment, in this control method, the photon filtering module includes an independent photon filter having a free spectral range (FSR). 滤波 The photon filter filters the orthomode Brillouin laser Kerr optical frequency comb signal; FSR 滤波 = M × FSR 布里渊 , where M is an integer, and FSR 布里渊 is the spectral line interval of the resonant peak of the silicon nitride micro-ring cavity.

[0103] More preferably, in an exemplary embodiment, in this control method, the photon filtering module includes an optical splitter, a first photon filter, a second photon filter, and an optical combiner. The optical splitter receives the laser from the optical polarization beam splitter and splits it 50:50 into two beams of light, which respectively enter the first photon filter and the second photon filter. According to the required band microwave signal, the corresponding Kerr optical frequency comb tooth photon signals are selected. The two photon signals are combined by the optical combiner and then input into the first optical detector.

[0104] Among them, the free spectral range (FSR) of the first photon filter and the second photon filter 滤波 is relatively large and needs to be greater than the signal response bandwidth of the first optical detector, and FSR 滤波 does not coincide with the FSR of the Kerr optical frequency comb 布里渊Are in an integer multiple relationship.

[0105] More preferably, in an exemplary embodiment, in this control method, the lasers in the TE mode and the lasers in the TM mode have resonant peak frequencies in the silicon nitride micro-ring cavity that are distributed at intervals of the free spectral range FSR 布里渊 GHz intervals, with n * FSR 布里渊 resonant peak distributions, where n is an integer, and there is a slight interval difference between the resonant peak frequencies of the orthogonally polarized TE-mode laser and the TM-mode laser, and the difference is Δυ MHz;

[0106] Based on the fact that the frequency shift of the pump light-excited Brillouin laser in the silicon nitride micro-ring cavity is f ΔSBL , design the FSR 布里渊 value of the silicon nitride micro-ring cavity to be (f ΔSBL +Δυ) = m * FSR 布里渊 , where m is an integer; based on this FSR 布里渊 value, design the size of the silicon nitride micro-ring cavity according to the formula FSR = Δλ = λ 2 / n g L, where λ is the optical wavelength, n g is the group refractive index of the waveguide, and L is the length of the optical micro-cavity, that is, the size of the silicon nitride micro-ring cavity.

[0107] More preferably, in an exemplary embodiment, in this control method, after determining the FSR 布里渊 , design the wavelength of the Brillouin gain region to overlap with the FSR 布里渊 of the TM-polarized photon comb teeth of the silicon nitride micro-ring cavity, and design the peak of the wavelength of the Brillouin gain region to be slightly red-detuned from the resonant peak wavelength. Select the corresponding TE-polarized photon as the central wavelength of the input pump light according to the Brillouin frequency shift f ΔSBL value; through dispersion engineering design, optimize the TM-mode polarized photons to have anomalous dispersion in the BGS wavelength region.

[0108] More preferably, in an exemplary embodiment, in this control method, the tunable wavelength laser is a 1550 nm communication band laser, the photon signal obtained by the photon filtering module is in the Ka band, m ΔSBL is 4, the value of f

[0109] Another exemplary embodiment of the present invention provides a storage medium on which computer instructions are stored, and when the computer instructions run, they execute the steps of the control method of a Brillouin laser Kerr optical frequency comb based on an orthogonally polarized mode described in any of the above exemplary embodiments.

[0110] Another exemplary embodiment of the present invention provides a terminal, including a memory and a processor. A computer instruction that can run on the processor is stored on the memory. When the processor runs the computer instruction, it executes the steps of a control method of a Brillouin laser Kerr optical frequency comb based on an orthogonal polarization mode described in any of the above exemplary embodiments.

[0111] Based on such an understanding, the technical solution of this embodiment, in essence, or the part that contributes to the prior art, or a part of this technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions for causing a computer device (which may be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in various embodiments of the present invention. The aforementioned storage medium includes: various media that can store program codes, such as a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disc.

[0112] Obviously, the above embodiments are merely examples given for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A microwave generating device for a temperature-controlled Brillouin laser Kerr optical frequency comb, characterized in that: Comprising: A control module; An adjustable wavelength laser that receives commands from the control module and outputs pump laser with corresponding wavelength and power; An optical amplifier that amplifies the pump laser; An optical circulator, the first port of which is used to receive the amplified pump laser; A silicon nitride microring resonator, the optical input end of which receives the pump laser through the second port of the optical circulator, and after exciting Brillouin laser inside the cavity, together with the reflected pump laser, outputs the mixed laser to the second port of the optical circulator through the optical input end; An optical polarization beam splitter that receives the mixed laser output from the third port of the optical circulator and filters the pump laser in the mixed laser and then outputs the split Brillouin laser; A photon filtering module that receives the Brillouin laser from the optical polarization beam splitter, selects the corresponding frequency interval, and then outputs the filtered photon signal; A first optical detector that receives the photon signal, performs beat frequency, and then outputs a microwave signal; The silicon nitride microring resonator generates resonant light under the coupled input pump laser and excites orthogonally polarized Brillouin laser in the microring cavity as a secondary pump light to form a Kerr optical frequency comb; The Brillouin laser and the pump laser are two orthogonally polarized laser signals; where the Brillouin laser is in the TM mode and the pump laser is in the TE mode, or the Brillouin laser is in the TE mode and the pump laser is in the TM mode; The photon filtering module includes an independent photon filter with a spectral line interval FSR filtering, and the photon filter filters the Kerr optical frequency comb signal of the orthomode Brillouin laser; FSR filtering = M×FSR Brillouin, M is an integer, and FSR Brillouin is the spectral line interval of the resonant peak of the silicon nitride microring resonator; or: The photon filtering module includes an optical splitter, a first photon filter, a second photon filter, and an optical combiner. The optical splitter receives the laser from the optical polarization beam splitter and splits it into two beams with a ratio of 50:50, which respectively enter the first photon filter and the second photon filter. According to the required band microwave signal, the corresponding Kerr optical frequency comb tooth photon signals are selected. The two photon signals are combined and then input into the first optical detector; where the spectral line intervals FSR filtering of the first photon filter and the second photon filter are larger and need to be greater than the signal response bandwidth of the first optical detector, and FSR filtering is not an integer multiple relationship with the FSR Brillouin of the Kerr optical frequency comb; Considering the alignment and debugging of the photon center wavelength, a TEC temperature control module is used to adjust the temperature of the photon filter to finely adjust and adapt to the frequency alignment between the center wavelength of the photon filter and the photon frequency comb.

2. The microwave generating device of a temperature-controlled Brillouin laser Kerr optical frequency comb according to claim 1, characterized in that: The control of the adjustable wavelength laser by the control module includes: Initially set the input pump laser wavelength to be blue-detuned from the resonant peak wavelength corresponding to the TE mode polarized photons of the silicon nitride microring resonator, gradually increase the wavelength blue shift so that the pump laser approaches the resonant peak, the input pump laser is coupled into the silicon nitride microring resonator to resonate, the resonant power gradually increases, and the resonant light in the silicon nitride microring resonator excites orthogonally polarized TM mode Brillouin laser; The control module further adjusts the blue-shift speed and optical power of the pump laser until the Kerr optical frequency comb state appears. Then, it continues to finely tune the input pump laser for blue-shifting. The stimulated Brillouin laser of the secondary pump laser will redshift from the red-detuned position of the TM mode resonance peak wavelength and gradually move away from the resonance peak of the silicon nitride micro-ring cavity. The power of the Kerr optical frequency comb excited in the silicon nitride micro-ring cavity will decrease in a step-like manner until the desired soliton state optical frequency comb output is obtained, and the optical comb tooth interval is stabilized.

3. The microwave generating device of a temperature-controlled Brillouin laser Kerr optical frequency comb according to claim 2, characterized in that: The microwave generating device further includes one or more of the following optical detectors: The second optical detector, whose input end is connected to the through-output port of the silicon nitride micro-ring cavity, and the output end is connected to the control module to monitor the working state of the pump laser; The third optical detector, whose input end is connected to the drop-output port of the silicon nitride micro-ring cavity, and the output end is connected to the control module to monitor the working state of the resonant light in the silicon nitride micro-ring cavity; The fourth optical detector, whose input end is connected to an optical splitter located between the optical polarization beam splitter and the photon filtering module, and the output end is connected to the controller to monitor the working state of the Kerr optical frequency comb in the micro-ring cavity.

4. The microwave generating device of a temperature-controlled Brillouin laser Kerr optical frequency comb according to claim 3, characterized in that: The second optical detector and the third optical detector cooperate with the regulation and control of the pump laser process in the initial setting; the fourth optical detector cooperates with the regulation and control of the further adjustment of the pump laser process.

5. The microwave generating device of a temperature-controlled Brillouin laser Kerr optical frequency comb according to claim 1, characterized in that: The lasers in TE mode and the lasers in TM mode have resonant peak frequencies in the silicon nitride micro-ring cavity that are spaced according to the free spectral range FSR 布里渊 at intervals of GHz, and are distributed as n*FSR 布里渊 resonant peak distributions, where n is an integer. The resonant peak frequencies of the orthogonally polarized TE-mode laser and the TM-mode laser have a slight interval difference, and the difference is Δυ MHz; Based on the fact that the pump light in the silicon nitride microring cavity stimulates the Brillouin laser frequency shift to be f ΔSBL , design the FSR of the silicon nitride microring cavity 布里渊 value to be (f ΔSBL +Δυ) = m * FSR 布里渊 , where m is an integer; based on this FSR 布里渊 value, design the size of the silicon nitride microring cavity according to the formula FSR = Δλ = λ 2 / n g L, where λ is the optical wavelength, n g is the group refractive index of the waveguide, and L is the length of the optical microcavity, i.e., the length of the silicon nitride microring cavity.

6. The microwave generating device of a temperature-controlled Brillouin laser Kerr optical frequency comb according to claim 5, characterized in that: After determining the FSR 布里渊 the wavelength of the Brillouin gain region is designed to overlap with the FSR 布里渊 of the TM-polarized photon comb teeth, and the peak of the wavelength of the Brillouin gain region is located at a slightly red-detuned position from the resonance peak wavelength. According to the Brillouin frequency shift f ΔSBL value, the corresponding TE-polarized photon is selected as the central wavelength of the input pump light; through dispersion engineering design, the TM-mode polarized photon is optimized to have anomalous dispersion in the Brillouin gain spectrum (BGS) wavelength region.

7. The microwave generating device of a temperature-controlled Brillouin laser Kerr optical frequency comb according to claim 6, characterized in that: The tunable wavelength laser is a 1550 nm communication band laser, the photon signal obtained by the photon filtering module is in the Ka band, m is 4, the value of f ΔSBL is 11, and M is 12 or 13.

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