A high-stable photonic millimeter wave / terahertz signal generation chip and a signal generation method thereof

Abstract

A high-stability photonic millimeter wave / terahertz signal generation chip and a signal generation method thereof belong to the field of photonic-assisted millimeter wave / terahertz communication. In view of the problems of poor frequency stability, high phase noise and large integrated loss of the existing system, the system comprises a common-cavity dual-wavelength laser and a heterogeneous integrated IQ modulator. The dual-wavelength laser is composed of two distributed Bragg reflection lasers connected to the same high-Q silicon nitride micro-ring through a multimode interferometer, so that the two lasers are self-injection locked at different resonant frequencies of the micro-ring. One of the lasers is modulated by a lithium niobate-silicon nitride heterogeneous integrated IQ modulator, and then input to an optical frequency mixer together with the other laser to generate a millimeter wave / terahertz signal. The common-mode characteristic of the common-cavity thermal refractive index fluctuation is used to offset the beat frequency thermal noise, which greatly improves the phase purity and frequency stability of the millimeter wave / terahertz signal, and significantly reduces the transmission and integrated loss.

Description

Technical Field

[0001] This invention relates to the fields of integrated photonics technology, microwave photonics, terahertz communication and radio frequency microwave technology, specifically to a highly stable photonic millimeter-wave / terahertz signal generation chip and method based on a common-cavity dual-wavelength self-injection locked laser, which is particularly suitable for application scenarios such as ultra-high-speed wireless communication, high-resolution radar, short-range high-capacity transmission and high-precision sensing in sixth-generation mobile communication (6G). Background Technology

[0002] As 6G communication technology evolves towards "Internet of Everything," the exponential growth in single-device traffic places stringent demands on communication speed, latency, and reliability, driving the need for wider spectrum usage. It is projected that around 2030, millimeter-wave / terahertz communication technology will support 6G networks achieving peak speeds of Tbps and experience speeds of 10–100 Gbps, becoming a core support for overcoming future communication capacity bottlenecks. Millimeter-wave / terahertz waves, with their abundant spectrum resources, ultra-wideband transmission potential, and high-precision positioning and sensing capabilities, possess irreplaceable advantages in 6G mobile communication, high-resolution radar, and ultra-high-speed short-range transmission. The efficient and stable generation of millimeter-wave / terahertz signals is fundamental to these applications and represents a key breakthrough for millimeter-wave / terahertz communication technology in moving from the laboratory to practical deployment, thus becoming one of the key aspects of global 6G technology competition.

[0003] Currently, the generation and processing of millimeter-wave / terahertz signals mainly fall into two major technological categories: electronics and photonics. The former, based on electronic devices, boasts advantages such as miniaturization and integration, enabling high-power signal radiation. However, its system capacity is limited by factors such as the operating bandwidth of electronic devices, modulation efficiency, and harmonic interference, particularly the performance bottleneck of electronic devices in the high-frequency band, making it difficult to meet the demands of future high-speed, high-capacity communication. The latter, utilizing photonic principles to generate and process millimeter-wave / terahertz signals, features ultra-wideband, flexible reconfigurability, and low harmonic interference, making it more conducive to achieving ultra-high-speed wireless communication.

[0004] Currently, photonic millimeter-wave / terahertz signals are mainly generated using methods such as photoelectric heterodyne beat frequency generation and quantum cascade lasers (QCLs). While QCL schemes can generate millimeter-wave / terahertz signals with frequencies above 1 THz, their application in practical systems is limited by the need for cryogenic operation. The photoelectric heterodyne beat frequency method mixes two laser beams with similar frequencies in a UTC-PD or photoconductive antenna (PC antenna) to generate a millimeter-wave / terahertz photocurrent with a frequency equal to their frequency difference. Compared to PC antennas, UTC-PDs offer higher efficiency and output power, making them more suitable for millimeter-wave / terahertz communication applications.

[0005] In the process of generating millimeter-wave / terahertz signals using optical heterodyne beat frequency, the frequency noise of the signal is often the superposition of the noise from two independent lasers (carrier and reference beams). Limited by the linewidth of traditional semiconductor lasers, and the random frequency drift of the two freely operating lasers, the resulting millimeter-wave / terahertz signal suffers from severe phase noise degradation. Furthermore, one of the main sources of frequency noise in chip-scale lasers is thermal refractive index noise (TRN). Temperature fluctuations in the micro-ring waveguide cause continuous fluctuations in the refractive index, leading to frequency jitter in the resonant frequency. Since the thermal refractive index noise of the two independent self-injection locked lasers is completely uncorrelated, the frequency noise of the microwave signal generated by beat frequency is equivalent to the direct addition of the frequency noise from the two laser beams. This TRN limitation becomes particularly pronounced after the Q value of the micro-ring increases to a certain level, severely restricting the signal quality and receiving sensitivity of millimeter-wave / terahertz communication systems.

[0006] From a global technological competition perspective, millimeter-wave / terahertz communication, as a core technology of 6G, has become a key strategic focus for many countries. The United States, through DARPA's TMIC project, focuses on fundamental research into photonic millimeter-wave / terahertz communication chips; the European Union, under the "Horizon 2020" framework, launched joint research projects such as THOR and TERAWAY to promote technology implementation; and Japan, relying on institutions like NTT and NICT, maintains its technological leadership in core devices such as UTC-PD. Domestically, while achieving phased results in single-point technologies such as millimeter-wave / terahertz signal generation and transmission, China remains in the exploratory stage in the crucial field of millimeter-wave / terahertz communication, particularly lacking a photonic millimeter-wave / terahertz signal generation solution that balances high frequency stability, high integration, wide tuning range, and low power consumption. This technological gap not only restricts the overall advancement of my country's 6G communication technology, but also forms potential technological barriers in key areas such as high-end communication equipment and precision sensing. Therefore, it is urgent to break through existing bottlenecks through core technology innovation and build a photonic millimeter-wave / terahertz signal generation technology system with independent intellectual property rights, so as to provide core support for my country to seize the initiative in the global 6G competition. Summary of the Invention

[0007] The purpose of this invention is to provide a highly stable, frequency-tunable, and high-performance photonic millimeter-wave / terahertz signal generation chip and method, aiming to solve the following technical problems existing in the current photonic-assisted millimeter-wave / terahertz signal generation schemes: First, the two independently operating lasers each have random frequency drift, and their thermal refractive index noise is superimposed during the photoelectric heterodyne beat frequency process, resulting in severe phase noise degradation and poor frequency stability of the generated millimeter-wave / terahertz signal; Second, the traditional discrete devices introduce large insertion loss and mechanical instability through fiber coupling, and the pure lithium niobate waveguide has high transmission loss due to etching roughness, making it difficult to simultaneously achieve high frequency stability, high integration, wide tuning range, and low power consumption.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows: A highly stable photonic millimeter-wave / terahertz signal generation chip includes: A common-cavity dual-wavelength laser includes a first distributed Bragg reflector (DBR) laser, a second DBR laser, a coupler, and a high-Q microring resonator. The rear output terminals of the first and second DBR lasers are optically coupled to the two input terminals of the coupler, respectively. The output terminal of the coupler is optically coupled to the high-Q microring resonator. Two optical signals output from the first and second DBR lasers are injected into the high-Q microring resonator via the coupler. Feedback optical signals generated by the high-Q microring resonator are returned to their respective DBR lasers via the coupler, so that the two optical signals are self-injected and locked to different resonant frequencies of the same high-Q microring resonator. The common-cavity dual-wavelength laser has a first output terminal and a second output terminal, respectively used to output the two locked laser beams.

[0009] The heterogeneous integrated IQ modulator has its input terminal optically coupled to the first output terminal of the common cavity dual-wavelength laser, and is used to digitally modulate one of the laser beams and output the modulated optical signal.

[0010] The micro-ring combiner has its first input terminal optically coupled to the output terminal of the heterogeneous integrated IQ modulator, and its second input terminal optically coupled to the second output terminal of the common cavity dual-wavelength laser. It is used to combine the modulated optical signal with another unmodulated reference optical signal and output the combined optical signal.

[0011] A unidirectional carrier transport photodetector, whose input end is optically coupled to the output end of the micro-ring combiner, is used to receive the combined optical signal and convert it into a millimeter-wave / terahertz signal through heterodyne beat frequency.

[0012] Furthermore, the distributed Bragg reflector laser includes a semiconductor optical amplifier based on an indium phosphide material system and a Bragg grating based on a silicon nitride material. The semiconductor optical amplifier is disposed above the silicon nitride waveguide using micro-transfer technology, and an interlayer coupler composed of a silicon intermediate layer is provided between the semiconductor optical amplifier and the silicon nitride waveguide. The distributed Bragg reflector laser adopts a tail-emission mode, and the reflectivity of the Bragg grating on its front and rear cavity surfaces is set to 15% and 40%, respectively; a heater is disposed above the Bragg grating for thermally tuning the feedback.

[0013] Furthermore, the coupler is a 2×2 Mach-Zehnder interferometer, with its two input terminals optically coupled to the rear output terminals of the first and second distributed Bragg reflector lasers, respectively, and its output terminal optically coupled to the high-Q microring resonator. The Mach-Zehnder interferometer integrates microheaters on both phase-shifting arms, adjusting the phase difference between the two arms through a thermo-optical effect. It can be considered a tunable Sagnarc ring reflector (TSL). By changing the phase difference between the two arms of the MZI through the heaters, the equivalent coupling coefficient of the loop can be continuously changed, thereby achieving adjustable reflectivity from 0 to 100% and preventing mutual injection between the two lasers.

[0014] Furthermore, the high-Q microring resonator is constructed using a multimode waveguide with a width of 3μm, and all its curved sections are Euler bends, which maintain stable transmission of the TE fundamental mode in a 90° bend, and suppress higher-order mode excitation to below -30dB.

[0015] Furthermore, the heterogeneous integrated IQ modulator adopts a dual-embedded Mach-Zehnder modulator structure, consisting of two independent equal-arm Mach-Zehnder modulators connected in parallel, corresponding to the loading of I-channel and Q-channel digital signals, respectively. The phase-shifting arm of the heterogeneous integrated IQ modulator employs a hybrid waveguide scheme with thin-film lithium niobate bonded above a silicon nitride waveguide. Its bottom layer is a silicon nitride single-mode waveguide with a thickness of 400 nm and a width of 1 μm, and a thin-film lithium niobate plate with a thickness of 300 nm is bonded on top, forming an inverted ridge waveguide structure. In the heterogeneous integrated IQ modulator, the passive optical path except for the phase-shifting region is constructed using silicon nitride waveguides, and the 3dB coupling between its input and output ends is achieved by a 1×2 multimode interference coupler.

[0016] Furthermore, the heterogeneous integrated IQ modulator also includes a multi-segment interlayer coupler, which is disposed between the ordinary silicon nitride waveguide and the hybrid waveguide to achieve a low-loss connection between the two. The multi-segment interlayer coupler is composed of three linear tapered waveguides. The lower silicon nitride waveguide gradually narrows from a width of 3 μm to a single-mode width of 1 μm along the optical transmission direction, while the upper thin-film lithium niobate waveguide gradually widens from a 150 nm tip to a 7 μm planar structure to achieve adiabatic evolution of the optical field. The physical length of the multi-segment interlayer coupler is 120 μm, and it has an alignment tolerance of 1.5 μm in the vertical direction.

[0017] Furthermore, the heterogeneous integrated IQ modulator is equipped with independently configured thermo-optical phase shifters in both the I and Q branches. These thermo-optical phase shifters are optically coupled to the phase-shifting arms of the corresponding Mach-Zehnder modulators, controlling their respective modulation bias points to operate at orthogonal points. Simultaneously, a third thermo-optical phase shifter is located in the front-end optical path of both Mach-Zehnder modulators to statically introduce a π / 2 phase shift, ensuring strict orthogonality between the I and Q branch signals. A traveling-wave metal electrode with a ground-signal-ground structure is positioned above each phase-shifting arm, and the device operates in push-pull drive mode. The parameters of the traveling-wave metal electrode are: S-electrode width 13.5 μm, G-electrode width 100 μm, electrode thickness 1 μm, and a 4.5 μm gap between the signal and ground electrodes.

[0018] Furthermore, the unidirectional carrier transport photodetector is heterogeneously integrated above a passive waveguide, employing an indium phosphide / indium gallium arsenide material system or a germanium-silicon material system. A refractive index-matching intermediate material layer is introduced between the unidirectional carrier transport photodetector's absorption layer and the silicon nitride waveguide, forming a double-mesa structure with a double-matching layer configuration, used to achieve adiabatic evolution of the optical field from the silicon nitride waveguide to the active region of the detector. The absorption region of the unidirectional carrier transport photodetector has a length of 7 μm, a width of 2 μm, and a responsivity of 0.65 A / W.

[0019] Furthermore, the common-cavity dual-wavelength laser, the heterogeneous integrated IQ modulator, the micro-ring combiner, and the unidirectional carrier transport photodetector are integrated on the same chip using a heterogeneous integration process.

[0020] This invention also provides a method for generating highly stable photonic millimeter-wave / terahertz signals based on the above-mentioned chip, characterized by comprising the following steps: By using the same high-Q microring resonator as the common feedback element for the two laser beams, the two laser beams output from the first distributed Bragg reflector laser and the second distributed Bragg reflector laser are respectively self-injected and locked at different resonant frequencies of the high-Q microring resonator. The two laser beams generate frequency jitter with the same trend due to the refractive index jitter of the same microring. One locked laser beam is input into a heterogeneous integrated IQ modulator for digital signal modulation to obtain a modulated optical signal; the other locked laser beam is used as an unmodulated reference light. The modulated optical signal and the reference light are combined using a micro-ring combiner. The combined optical signal is input into a unidirectional carrier transport photodetector for heterodyne beat frequency generation to generate a millimeter-wave / terahertz signal.

[0021] Specifically, by utilizing the common-mode property of the thermal refractive index fluctuation of the same high-Q microring resonant cavity, the frequency noise caused by the microring carried by the two laser beams is subtracted and canceled out during the beat frequency process, thereby outputting a highly stable, low-phase-noise photonic millimeter-wave / terahertz signal.

[0022] Furthermore, by thermally tuning the temperature of the Bragg grating of the distributed Bragg reflector laser or the high-Q microring resonator, the position of the resonance peak locked by the two laser beams is changed, thereby tuning the frequency of the generated millimeter-wave / terahertz signal in steps with the free spectral range of the high-Q microring resonator.

[0023] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention employs a common-cavity self-injection locking mechanism, enabling two laser beams of different wavelengths to be simultaneously locked at different resonant frequencies within the same high-Q microring resonant cavity. Since the refractive index jitter trends of the same microring are consistent, the frequency jitter directions of the two laser beams are highly correlated. During the beat frequency operation of the optical mixer, this common-mode characteristic of thermal refractive index fluctuations is utilized to subtract and cancel out thermal noise (for example, frequency jitter can be reduced by approximately 32.4 dB for a 220 GHz signal), significantly improving the phase purity and long-term frequency stability of millimeter-wave / terahertz carrier waves.

[0024] 2. This invention utilizes a single high-Q microring resonator as the feedback locking element of a dual-wavelength laser. The frequency of the millimeter-wave / terahertz signal generated by the beat frequency is determined by the difference in the different resonant frequencies of the microring. Therefore, by changing the position of the resonant peak locked by the two laser beams, the frequency of the generated millimeter-wave / terahertz signal can be flexibly tuned over a wide range, in multiples of the free spectral range (FSR) of the high-Q microring, thus broadening the applicable frequency band of the system.

[0025] 3. This invention achieves heterogeneous integration of a dual-wavelength light source, modulator, and unidirectional carrier transport photodetector (UTC-PD) on a single chip, eliminating the significant insertion loss and mechanical instability caused by fiber coupling between traditional discrete devices. Furthermore, the modulator employs an electro-optic thin-film-silicon nitride heterogeneous integrated hybrid waveguide structure. Its inverted ridge waveguide design effectively reduces the physical overlap between the optical mode and the rough sidewalls of the waveguide, ensuring efficient and low-loss transmission of the optical signal. Combined with the high-power output characteristics of the UTC-PD, this significantly improves the overall performance of millimeter-wave / terahertz signal generation. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the overall architecture of the high-stability photonic millimeter-wave / terahertz signal generation chip of the present invention; Figure 2 This is a schematic diagram of the structure of a common cavity dual-wavelength laser in the first embodiment of the present invention, wherein (a) is a schematic diagram of the three-dimensional structure of the laser, (b) is a schematic diagram of the III-V gain chip structure, (c) is a schematic diagram of the Bragg grating structure, and (d) is a schematic diagram of the interlayer coupler structure. Figure 3 This is a schematic diagram illustrating the working principle of common-mode cancellation of thermal refraction noise in a common-cavity laser according to the first embodiment of the present invention; Figure 4 The diagram shows the high-Q microring resonator structure and simulation results in the first embodiment of the present invention, where (a) is a top view of the microring structure and (b) is a simulation result of the microring resonant spectrum. Figure 5 This is a schematic diagram of the structure of the SiN-LN heterogeneous integrated IQ modulator provided in the second embodiment of the present invention. Detailed Implementation

[0027] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. These embodiments are implemented based on the technical solutions of the present invention and provide detailed implementation methods and operation processes. However, the scope of protection of the present invention is not limited to the following embodiments.

[0028] Example 1: System Overall Architecture and Common Cavity Dual-Wavelength Laser Design This embodiment provides a highly stable photonic millimeter-wave / terahertz signal generation chip, whose overall system architecture is as follows: Figure 1 As shown, it includes two distributed Bragg reflector (DBR) lasers 1, a high-Q silicon nitride (Si3N4) microring resonator 2, a heterogeneous integrated IQ modulator 3, a microring combiner 4, and a unidirectional carrier transport photodetector 5.

[0029] The output ends of the two DBR lasers 1 are optically coupled to the two input ends of a 2×2 Mach-Zehnder interferometer (2×2MZI) with integrated microheaters in both arms. The output end of the 2×2MZI is optically coupled to the high-Q Si3N4 microring resonator 2. The optical signals output from the two DBR lasers 1 are injected into the high-Q microring resonator 2 after passing through the 2×2MZI. The feedback optical signals generated by the microring return to the corresponding DBR lasers 1 through the same MZI, thereby locking the two laser beams to different resonant frequencies of the same microring. One laser output is sent to a heterogeneous integrated IQ modulator 3 for digital signal modulation, while the other is directly output as an unmodulated reference beam. The modulated optical signal output from the IQ modulator 3 and the reference optical signal are input together to a microring combiner 4 for beam combining. The combined optical signal enters a UTC-PD 5 for heterodyne beat frequency generation, ultimately generating a millimeter-wave / terahertz electrical signal.

[0030] like Figure 2 As shown, in the physical structure design of the dual-wavelength light source, the co-cavity dual-wavelength laser adopts a composite cavity structure, consisting of two distributed Bragg reflector (DBR) lasers, a 2×2 Mach-Zehnder interferometer (MZI), and a single high-Q silicon nitride (Si3N4) microring resonator. Specifically, as... Figure 2 As shown in (a), the DBR laser includes a semiconductor optical amplifier (SOA) that provides gain and Bragg gratings that form the front and rear cavity surfaces. Figure 2 As shown in (b), the SOA is based on the InP material system and is precisely transferred onto the Si3N4 waveguide using micro-transfer technology. Due to the large refractive index difference between InP and Si3N4, a Si interlayer is introduced between them in this embodiment to achieve low-loss interlayer mode switching. To improve output power, the laser adopts a tail-emission method, and the reflectivities of the Bragg gratings on the front and rear cavity surfaces are designed to be 15% and 40%, respectively, to balance output power and feedback. A heater is installed above the grating, which allows for dynamic adjustment of the feedback through thermal tuning.

[0031] To achieve a common cavity and avoid mutual interference between the two laser beams, the back-end outputs of the two DBR lasers are respectively connected to the two inputs of the 2×2 Mach-Zehnder interferometer. The output of the MZI is connected to the high-Q Si3N4 microring. This structure acts as a tunable Sagnac ring reflector (TSL), enabling continuous adjustment of the optical feedback intensity. This not only prevents mutual injection between the two laser beams (ensuring stable output of the two wavelengths at the front cavity surfaces of their respective DBR lasers), but also achieves a common resonant cavity function, allowing the two laser beams to self-inject and lock onto different resonant frequencies of the same microring.

[0032] like Figure 4As shown in (a) and 4(b), the high-Q microring is constructed using a 3 μm wide multimode waveguide to reduce the overlap between the waveguide sidewalls and the optical field, thereby reducing transmission loss. It also reduces thermal refractive index noise by increasing the optical mode volume. All bends in the microring are Euler bends, ensuring stable transmission of the TE fundamental mode within a 90° bend, and successfully suppressing higher-order mode excitation to below -30 dB.

[0033] like Figure 3 As shown, ambient temperature and random molecular motion cause continuous fluctuations in the refractive index of the microring, resulting in thermal refractive index noise (TRN). Since the two laser beams are locked in the same microring, their refractive index fluctuations are consistent, therefore the frequencies of the two laser beams ( and The direction of the jitter is consistent. The frequency of the millimeter-wave / terahertz signal obtained by the beat frequency can be expressed as: in, This represents the free spectral range of the microring. Through this common-mode cancellation mechanism, TRN is significantly reduced. Taking the generation of a 220 GHz microwave signal as an example, compared to the 193 THz optical frequency jitter, the frequency jitter can be reduced. .

[0034] Example 2: Thin-film lithium niobate-silicon nitride heterogeneous integrated IQ modulator Based on Example 1, this example provides a detailed description of the heterogeneous integrated IQ modulator.

[0035] like Figure 5 As shown, this modulator is used to digitally modulate one wavelength of the output from a dual-wavelength laser. It employs a dual embedded Mach-Zehnder (MZM) structure, consisting of two independent equal-arm MZMs connected in parallel, corresponding to the I and Q paths respectively. Except for the phase-shifting region, the passive optical path of the device uses Si3N4 waveguides, and the 3dB coupling between the input and output is achieved by a 1×2 MMI. To overcome the DC drift effect of lithium niobate material, the I and Q branches are each independently configured with a thermo-optical phase shifter to control the modulation bias point; simultaneously, a third thermo-optical phase shifter is added to the front-end optical path of the two MZMs, statically introduced... Phase shifting ensures that the I / Q signals are strictly orthogonal.

[0036] In its core waveguide structure, the MZM employs a hybrid waveguide approach where thin-film lithium niobate (TFLN) is bonded to a silicon nitride waveguide. Specifically, the bottom silicon nitride layer is a 400 nm thick, 1 μm wide single-mode waveguide, with a 300 nm thick thin-film lithium niobate plate bonded on top. This design confines most of the optical field within the lithium niobate plate region, reducing the physical overlap between the transmission modes and the rough sidewalls, thus lowering optical transmission loss.

[0037] To achieve low-loss connection between the conventional Si3N4 waveguide and the hybrid waveguide, this embodiment optimizes the design of a multi-segment interlayer coupler. The bottom Si3N4 waveguide of the coupler gradually narrows from a width of 3 μm to a single-mode width of 1 μm, while the upper TFLN waveguide gradually widens from a 150 nm tip to a 7 μm planar structure. Based on the nonlinear slope variation of the effective refractive index, the coupler is designed as a combination of three linear tapered waveguides. This structure compresses the physical length of the coupler to 120 μm and provides the device with a large alignment tolerance of up to 1.5 μm in the Y direction, reducing the difficulty of heterogeneous integration processes.

[0038] In the microwave electrode design, the phase-shifting region is configured with a traveling-wave metal electrode of ground-signal-ground (GSG) structure, operating in push-pull drive mode. The electrode dimensions are specifically optimized as follows: S-electrode width 13.5 μm, G-electrode width 100 μm, electrode thickness 1 μm, and the gap between the signal and ground electrodes is set to 4.5 μm. This configuration achieves an optimal balance between improving modulation efficiency and reducing metal absorption loss, resulting in an effective microwave refractive index of approximately 2.256 and a characteristic impedance of approximately 52 Ω at 40 GHz, ensuring low microwave loss and a wide electro-optical response bandwidth.

[0039] Example 3: Heterogeneous Integration Design of Micro-Ring Combiner and UTC-PD and Generation of Millimeter Wave / Terahertz Signals This embodiment provides a detailed description of the system's back-end micro-ring combiner and the heterogeneous integrated structure of the UTC-PD.

[0040] At the end of the chip's optical path, the micro-ring combiner 4 combines the modulated signal output from the IQ modulator with the unmodulated reference light from the light source. Its high wavelength selectivity effectively filters out broadband spontaneous emission (ASE) noise in the link, optimizing the optical signal-to-noise ratio before entering the detector.

[0041] The combined optical signal is input into the UTC-PD. To address the refractive index mismatch between the silicon nitride waveguide (n=2.016) and the InGaAs absorber layer (n=3.59), the UTC-PD introduces a dual-mesa structure with a double-matching layer configuration between the two, achieving adiabatic evolution of the optical field. Simulations show that, with a width of 2μm and a length of 7μm, the responsivity of this heterogeneous integrated structure can reach 0.65 A / W. The two optical signals carrying information undergo heterodyne beat frequency matching in this UTC-PD. Combined with the thermal noise common-mode cancellation mechanism in Example 1, the system directly outputs a high-power, low-phase-noise millimeter-wave / terahertz electrical signal at the chip level.

[0042] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A highly stable photonic millimeter-wave / terahertz signal generation chip, characterized in that, include: A common-cavity dual-wavelength laser includes a first distributed Bragg reflector (DBR) laser, a second DBR laser, a coupler, and a high-Q microring resonator. The rear output terminals of the first and second DBR lasers are optically coupled to the two input terminals of the coupler, respectively. The output terminal of the coupler is optically coupled to the high-Q microring resonator. Two optical signals output from the first and second DBR lasers are injected into the high-Q microring resonator via the coupler. Feedback optical signals generated by the high-Q microring resonator are returned to their respective DBR lasers via the coupler, so that the two optical signals are self-injected and locked to different resonant frequencies of the same high-Q microring resonator. The common-cavity dual-wavelength laser has a first output terminal and a second output terminal, respectively used to output two locked laser beams. A heterogeneous integrated IQ modulator, whose input terminal is optically coupled to the first output terminal of the common-cavity dual-wavelength laser, is used to digitally modulate one of the laser beams and output a modulated optical signal. The micro-ring combiner has its first input terminal optically coupled to the output terminal of the heterogeneous integrated IQ modulator, and its second input terminal optically coupled to the second output terminal of the common cavity dual-wavelength laser. It is used to combine the modulated optical signal with another unmodulated reference optical signal and output the combined optical signal. A unidirectional carrier transport photodetector, whose input end is optically coupled to the output end of the micro-ring combiner, is used to receive the combined optical signal and convert it into a millimeter-wave / terahertz signal through heterodyne beat frequency.

2. The high-stability photonic millimeter-wave / terahertz signal generation chip according to claim 1, characterized in that, The distributed Bragg reflector laser includes a semiconductor optical amplifier based on an indium phosphide material system and a Bragg grating based on a silicon nitride material. The semiconductor optical amplifier is transferred onto the silicon nitride waveguide using micro-transfer technology, and an interlayer coupler composed of a silicon intermediate layer is provided between the semiconductor optical amplifier and the silicon nitride waveguide to achieve low-loss interlayer mode conversion. The distributed Bragg reflector laser adopts a tail-emission mode, and the reflectivity of the Bragg grating, which serves as the front and rear cavity surfaces of the distributed Bragg reflector laser, can be adjusted by a heater above the grating to balance the output power and the feedback.

3. The high-stability photonic millimeter-wave / terahertz signal generation chip according to claim 1, characterized in that, The coupler is a 2×2 multimode interferometer, with its two input terminals optically coupled to the rear output terminals of the first distributed Bragg reflector laser and the second distributed Bragg reflector laser, respectively, and its output terminal optically coupled to the high-Q microring resonator.

4. The high-stability photonic millimeter-wave / terahertz signal generation chip according to claim 1, characterized in that: The heterogeneous integrated IQ modulator adopts a dual embedded Mach-Zehnder modulator (MZM) structure, consisting of two independent equal-arm MZMs connected in parallel, corresponding to the loading of I-channel and Q-channel digital signals, respectively. The phase-shifting arm of the heterogeneous integrated IQ modulator adopts a heterogeneous integrated hybrid waveguide scheme of electro-optic thin film and passive waveguide. The bottom layer is a single-mode passive waveguide, and the top layer is an electro-optic thin film material bonded to form an inverted ridge waveguide structure. The electro-optic thin film material is a thin film material with electro-optic effect. The passive optical path of the device is composed of a passive waveguide, and the coupling between the input and output ends is achieved through a multimode interference coupler.

5. The high-stability photonic millimeter-wave / terahertz signal generation chip according to claim 4, characterized in that, The heterogeneous integrated IQ modulator also includes a multi-segment interlayer coupler for connecting the ordinary silicon nitride waveguide and the hybrid waveguide; the multi-segment interlayer coupler is composed of three linear tapered waveguides, wherein the lower silicon nitride waveguide gradually narrows along the optical transmission direction, and the upper thin film material waveguide gradually widens from the tip to a planar structure to achieve adiabatic evolution of the optical field.

6. The high-stability photonic millimeter-wave / terahertz signal generation chip according to claim 5, characterized in that, The heterogeneous integrated IQ modulator has independently configured thermo-optical phase shifters in the I and Q branches to control their respective modulation bias points. At the same time, a third thermo-optical phase shifter is provided in the front-end optical path of the two MZMs to introduce a static π / 2 phase shift, thereby ensuring strict orthogonality between the I and Q branch signals. The phase shifting arm is configured with a traveling wave metal electrode with a ground-signal-ground structure, and the device operates in push-pull drive mode.

7. The high-stability photonic millimeter-wave / terahertz signal generation chip according to claim 1, characterized in that, The unidirectional carrier transport photodetector is heterogeneously integrated above a passive waveguide and adopts an indium phosphide / indium gallium arsenide material system or a germanium silicon material system. The unidirectional carrier transport photodetector introduces an intermediate material layer with refractive index matching between its absorption layer and the silicon nitride waveguide to form a double-mesa structure with a double matching layer, which is used to realize the adiabatic evolution of the light field from the silicon nitride waveguide to the active region of the detector.

8. The high-stability photonic millimeter-wave / terahertz signal generation chip according to any one of claims 1 to 8, characterized in that, The common cavity dual-wavelength laser, the heterogeneous integrated IQ modulator, the micro-ring combiner, and the unidirectional carrier transport photodetector are integrated on the same chip using a heterogeneous integration process.

9. A signal generation method for a high-stability photonic millimeter-wave / terahertz signal generation chip as described in any one of claims 1 to 8, characterized in that, Includes the following steps: Using a common feedback element of a high-Q microring resonator for two laser beams, the two laser beams output from the first and second distributed Bragg reflector lasers are self-injected and locked at different resonant frequencies of the high-Q microring resonator. The two laser beams exhibit frequency jitter with the same trend due to the refractive index fluctuation of the same microring. One locked laser beam is input into a heterogeneous integrated IQ modulator for digital signal modulation to obtain a modulated optical signal. The other locked laser beam is used as an unmodulated reference beam. The modulated optical signal and the reference beam are combined using a microring combiner. The combined optical signal is input into a unidirectional carrier transport photodetector for heterodyne beat frequency generation to produce a millimeter-wave / terahertz signal. Utilizing the common-mode property of the thermal refractive index fluctuation of the same high-Q microring resonator, the frequency noise carried by the two laser beams and caused by the microring is subtracted and canceled out during the beat frequency process, thereby outputting a highly stable, low-phase-noise photonic millimeter-wave / terahertz signal.

10. The signal generation method according to claim 9, characterized in that, By thermally tuning the temperature of the Bragg grating of the distributed Bragg reflector laser or the high-Q microring resonator, the position of the resonance peak locked by the two laser beams is changed, thereby tuning the frequency of the generated millimeter-wave / terahertz signal in steps with the free spectral range of the high-Q microring resonator.

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