Low-loss coherent Doppler pulse wind lidar system architecture

Abstract

The invention discloses a low-loss coherent Doppler pulse wind measurement laser radar system architecture, and relates to the field of laser radars. The system architecture comprises a photon chip, an amplifier and a transceiver. The photon chip generates incident laser, and pulse light and local oscillation light are output through pulse modulation; the amplifier receives the pulsed light and amplifies the pulsed light; the transceiver transmits pulsed light, receives backscattered light of a target object and sends the backscattered light back to the photon chip; the photon chip carries out frequency shift on the local oscillation light and carries out coupling frequency mixing on the local oscillation light and the obtained back scattering light, then photoelectric conversion is achieved, and electric signals output by the photoelectric conversion are used for processing and analyzing wind speed and wind direction information. According to the scheme, through the integrated design of the photon chip, the amplifier and the transceiver and in combination with a complementary waveform and blind area light section matching mechanism, the optical path loss is remarkably reduced and the stray light interference is inhibited while the system miniaturization is maintained, and the advantages of reducing the device loss and reducing the radar blind area are achieved.

Description

Technical Field

[0001] This application relates to the field of wind lidar, and in particular to a low-loss coherent Doppler pulse wind lidar system architecture. Background Technology

[0002] In recent years, with the continuous upgrading of equipment miniaturization requirements in fields such as low-altitude wind measurement, coherent Doppler pulse wind measurement lidar based on on-chip photonic integration technology has gradually become the core direction of the next generation of laser wind measurement technology.

[0003] However, this technical approach is currently hampered by the high loss of on-chip devices. Especially in coherent heterodyne detection, frequency shifting is required to control the frequency difference between the local oscillator and the echo light, but existing frequency shifting schemes have failed to effectively avoid the high loss problem. The mainstream solutions fall into three categories: I. Electro-optic frequency shifting scheme based on dual parallel Mach-Zehnder modulator (DPMZM): The frequency shift is achieved by suppressing the carrier and generating a single sideband signal using the electro-optic effect, but the insertion loss caused by its complex device structure often exceeds 10dB. II. Frequency shifting scheme based on on-chip acousto-optic frequency shifter (AOFS): Relying on the acousto-optic effect, sound waves are excited by interdigital transducers on the chip, forming a moving ultrasonic grating in the medium. After the laser is diffracted by Bragg, the frequency is superimposed on the ultrasonic frequency to complete the frequency shift. Its actual loss generally exceeds 12dB. III. Nonlinear frequency shifting scheme based on microring resonators: The resonance enhancement effect of microrings is used to increase the light field intensity and excite nonlinear optical effects such as four-wave mixing, so that the pump light and signal light interact to generate a new frequency light signal to achieve frequency shifting. However, factors such as two-photon absorption of silicon-based materials and coupling mismatch between microrings and waveguides cause the total loss to generally exceed 10dB.

[0004] The high loss issues of these on-chip frequency shifting schemes directly lead to a decrease in the transmitted light power of wind lidar, becoming a core bottleneck restricting the large-scale application of on-chip integrated coherent wind lidar. Furthermore, in coherent Doppler pulse wind lidar systems, the stray light power introduced by return loss of optical path components, reflection from fiber optic jumper end faces, and reflection within the telescope lens is typically several orders of magnitude higher than the backscattered light power of atmospheric aerosols. This intense light easily causes the detector to reach gain saturation, resulting in pulse trailing, which is equivalent to pulse width broadening, thereby expanding the original physical blind zone and compressing the radar's effective near-field detection window.

[0005] To address the aforementioned issues, the relevant technologies urgently need improvement. Summary of the Invention

[0006] This application provides a low-loss coherent Doppler pulse wind lidar system architecture, which has the advantages of effectively reducing device losses and shrinking the physical blind zone.

[0007] The system architecture includes: A photonic chip that generates incident laser light and outputs pulsed light and local oscillator light through pulse modulation; An amplifier that receives pulsed light and amplifies the pulsed light; A transceiver is used to transmit pulsed light and receive backscattered light from the target object, and send it back to the photonic chip. Stray light introduced by return loss of optical path components, reflection from fiber optic jumper end face and reflection from inside the telescope lens will cause radar blind zone. Therefore, the backscattered light includes a section of blind zone light, and the blind zone light is stronger than other backscattered light. The photonic chip shifts the frequency of the local oscillator light and couples it with the acquired backscattered light for frequency mixing, thereby achieving photoelectric conversion. The electrical signal output from the photoelectric conversion is used to process and analyze wind speed and wind direction information.

[0008] Specifically, the photonic chip includes a seed laser, an optical chopper, and a frequency shifter; The seed laser generates continuous incident laser light, and the optical chopper is driven by a pulse radio frequency signal to chop and output two split beams; one split beam is output as a pulse beam, and the other split beam is sent as a local oscillator beam to the frequency shifter. The frequency shifter will shift the local oscillator light to generate local oscillator light with a frequency that satisfies the coherent heterodyne condition, and attenuate the light to the target power.

[0009] Specifically, the photonic chip also includes a mixer and a photodetector; the mixer receives the local oscillator light output after frequency shifting and the backscattered light input from the transceiver, and performs coupling mixing; the mixed output light is sent into the photodetector to convert the optical signal into an electrical signal carrying target distance and speed information.

[0010] Specifically, the pulsed light output by the optical chopper has a waveform that is complementary to the local oscillator light.

[0011] Specifically, the local oscillator light includes a dark segment, and the time domain length of the dark segment is the same as the time domain length of the blind zone light in the backscattered light.

[0012] Specifically, the seed laser is a distributed feedback laser (DFB) with an output optical power of 10-100mW; The optical chopper contains several cascaded microring resonators (MRRs). The duty cycle of the pulse signal applied to the chopper is 0.6% - 0.9%. Without considering additional losses, the average power of the pulsed light output is 60μW - 900μW, and the average power of the local oscillator light output is close to the input light power, which is 9.94mW - 99.1mW. The frequency shifter is a dual parallel Mach-Zehnder modulator (DPMZM).

[0013] Specifically, the mixer is a 2×2 directional coupler DC, which couples the backscattered light with the local oscillator light before outputting the signal. The photodetector is a balanced photodetector (BPD), which performs beat frequency processing on the coupled local oscillator light and backscattered light.

[0014] Specifically, the 20mW optical signal output by the DFB directly enters the optical chopper. The duty cycle of the pulse signal is 0.6%. Without considering additional losses, the average power of the pulse signal after chopping is 120μW. The average power of the local oscillator output is close to the input optical power, which is 19.88mW.

[0015] Specifically, the MRR has a total insertion loss of 5dB, a pulse repetition frequency of 30kHz, a pulse width of 200ns, and an average power of 37.9μW for the on-chip architecture output pulse signal. The DPMZM has a combined insertion loss of 10dB and a local oscillator power of 1.988mW.

[0016] Specifically, the optical chopper includes two straight waveguides and four MRRs. The incident laser outputs local oscillator light after passing through the first straight waveguide, and the remaining lasers output pulsed light after passing through the straight waveguide and the four MRRs.

[0017] The beneficial effects of the technical solution provided in this application include at least the following: This application solves the high loss problem in the on-chip frequency shifting process, improves the utilization rate of emitted light power, and suppresses blind zone light through time-domain waveform matching, thus avoiding detector saturation caused by blind zone light. This architecture effectively expands the effective window of near-field detection while maintaining high detection sensitivity, providing a feasible solution for the practical application of miniaturized coherent wind lidar. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the architecture of a low-loss coherent Doppler pulse wind lidar system according to an embodiment of this application; Figure 2 This is a schematic diagram of the structure of the photonic chip provided in the embodiments of this application; Figure 3 This diagram shows the two optical signals output from the seed signal optical path after passing through the optical chopper; Figure 4 This is an on-chip architecture diagram that uses an optical chopper to generate shunt light; Figure 5 This diagram illustrates the on-chip architecture using a directional coupler for shunting. Figure 6 It is an on-chip architecture with two straight waveguides and four MRR optical choppers; Figure 7 It is a timing diagram of pulsed light and local oscillator light under ideal conditions. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this application clearer, the embodiments of this application will be described in further detail below with reference to the accompanying drawings.

[0020] In this article, "multiple" refers to two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0021] In on-chip integrated radar detection schemes, the frequency shifting process is achieved through on-chip dual parallel Mach-Zehnder modulators, acousto-optic frequency shifters, or micro-ring resonators. However, these methods all suffer from insertion losses exceeding 10 dB, resulting in severely insufficient pulse light energy transmitted by the radar. Furthermore, the radar cannot effectively suppress interference from strong stray light on the detector. For example, when the backscattered light received by the transceiver contains high-intensity blind zone light, the detector is prone to saturation, compressing the radar's effective detection window.

[0022] To address the aforementioned issues, this application addresses the low energy utilization of conventional methods during pulse modulation by optimizing the local oscillator (LOA) configuration. Analysis reveals that in conventional methods, over 99% of the optical energy is wasted after pulse modulation. Furthermore, the cascaded frequency shifter in the pulse optical path results in a weak pulse due to high losses, hindering subsequent amplification and leading to severely insufficient pulse energy emitted by the radar. Additionally, the mixing of the blind zone light with the LOA exacerbates the risk of detector saturation. Therefore, this application proposes using the wasted light from pulse modulation as the LOA, optimizing the frequency shifting from the conventional pulse to the LOA, thus mitigating the insufficient radar pulse energy caused by the high insertion loss of the on-chip frequency shifter. Simultaneously, the waveforms of the LOA and pulse are complementary. This ensures that when the blind zone light generated by the pulse within the radar (due to return loss from optical path components, reflection from fiber optic jumper ends, and reflection from the telescope lens) reaches the mixer, the corresponding time domain of the LOA is dark, effectively blocking the mixing path between the blind zone light and the LOA. Meanwhile, by optimizing the optical path structure, the losses caused by the pulse modulation scheme of traditional radar are reduced, thereby improving energy utilization efficiency.

[0023] Therefore, this application provides a low-loss coherent Doppler pulse wind measurement lidar system architecture, such as... Figure 1 As shown, the system architecture specifically includes an on-chip photonic chip 1, an amplifier 2, and a transceiver 3. The generation, modulation, mixing, and reception of laser signals are all completed by the photonic chip 1, the signal amplification is completed by the amplifier 2, and the signal transmission and reception are completed by the transceiver 3.

[0024] Photonic chip 1 generates incident laser light and outputs pulsed light and local oscillator light through pulse modulation. Amplifier 2 receives the pulsed light and amplifies it; the amplification factor is determined by factors such as the application scenario. Transceiver 3 is used to transmit pulsed light and receive backscattered light from the target object, sending it back to photonic chip 1. The backscattered light received after transmission by transceiver 3 includes a blind zone, which is stronger than the other backscattered light. Photonic chip 1 then shifts the frequency of the local oscillator light and couples it with the acquired backscattered light for mixing, thus achieving photoelectric conversion. The electrical signal output from the photoelectric conversion is used to process and analyze wind speed and direction information.

[0025] The laser generated by photonic chip 1 is pulse-modulated and split into two paths. One path serves as the local oscillator beam, which is frequency-shifted by a frequency shifter before being input into the mixer. Because the pulse modulation duty cycle is over 99%, the split local oscillator beam is very strong, almost equal to the input optical power. However, the insertion loss of the frequency shifter is over 10dB, and conventional solutions place it in the pulse optical path, severely limiting the radar's pulse light energy. Placing the high-insertion-loss frequency shifter in the local oscillator beam path solves the problem of reduced pulse light energy caused by the high insertion loss of the frequency shifter, and also attenuates the local oscillator beam to a suitable power (the optimal local oscillator beam power for radar is approximately on the order of 1-2mW).

[0026] The laser generated by photonic chip 1 is pulse-modulated and then transmitted as a pulse beam. This pulse beam is amplified by amplifier 2 and emitted outward by transceiver 3. The target backscattered light is received by the transceiver and fed back into photonic chip 1. Inside the radar, due to return loss from optical components, reflections from fiber optic jumper ends, and reflections within the telescope lens, the pulse beam enters a blind zone. Upon reaching the mixer, the local oscillator light is in a dark state in the corresponding time domain. After coupling with the local oscillator light in the mixer, the backscattered light, unaffected by the blind zone light, can generate an effective beat frequency signal with the local oscillator light, while the blind zone light, lacking the support of the local oscillator light, cannot form beat frequency interference. The photodetector converts the beat frequency signal into an electrical signal, and the target distance and velocity information are extracted through spectral analysis.

[0027] The comparison shows that after pulse modulation, over 99% of the optical energy is wasted in the traditional scheme, and the high insertion loss frequency shifter cascaded in the pulse optical path severely restricts the pulse optical energy of the radar. At the same time, the blind zone light in the backscattered light will beat with the local oscillator light, causing the detector to saturate and expanding the radar's blind zone.

[0028] This solution utilizes a chopper-based optical splitter technique to convert wasted optical energy into local oscillator light. A high-insertion-loss frequency shifter is cascaded into the local oscillator optical path, solving the problem of reduced pulsed light energy caused by the high insertion loss of the frequency shifter while maintaining local oscillator power. Furthermore, a unique waveform complementarity mechanism is designed to suppress blind zone interference. This mechanism maintains the functionality of the local oscillator while disrupting the beat frequency conditions of the blind zone light in the backscattered light, thus shortening the radar blind zone.

[0029] Through the above technical solutions, this application solves the problem of reduced radar pulse light energy caused by high loss of on-chip frequency shifters, and simultaneously suppresses detector saturation effects caused by blind zone light through time-domain waveform matching. This architecture effectively expands the effective window for near-field detection while maintaining high detection sensitivity, providing a feasible solution for the practical application of miniaturized coherent wind lidar.

[0030] Figure 2 This is a schematic diagram of the structure of the photonic chip provided in the embodiment of this application. The photonic chip 1 includes a seed laser 11, an optical chopper 12, and a frequency shifter 13.

[0031] Seed laser 11 generates continuous incident laser light. Optical chopper 12 is driven by pulsed radio frequency signal to chop and output two split beams. One split beam is output as pulsed light, and the other split beam is sent to frequency shifter 13 as local oscillator light. Frequency shifter 13 shifts the frequency of local oscillator light to generate local oscillator light with a frequency that satisfies the coherent heterodyne condition.

[0032] A seed laser is a light source device that directly generates continuous laser light; for example, it can be implemented using a distributed feedback laser.

[0033] An optical chopper is a pulse modulation device based on pulse radio frequency signal control. For example, it can be implemented using a micro-ring resonator array. By timing control, continuous light is split into two complementary waveforms, so that the local oscillator path retains most of the light energy.

[0034] The frequency shifter is a functional module that realizes optical frequency shifting. Specifically, it can be implemented using a dual parallel Mach-Zehnder modulator. By controlling the frequency of the local oscillator light through carrier-suppressed single-sideband modulation, it can form a stable frequency difference with the emitted pulse light.

[0035] Specifically, continuous-incident laser light is pulse-modulated in an optical chopper using a pulsed radio frequency (RF) signal. The pulsed light path is only active within a specific time window, while the light during the remaining time periods is transmitted to the frequency shifter via the local oscillator (LO) path. Since the LO path occupies the majority of the time period, most of the light energy is retained within the LO path. The frequency shifter applies a precise frequency offset to the LO light, generating LO light with a fixed frequency difference from the emitted pulse light by adjusting the modulator bias voltage and RF drive signal. This pulse modulation method achieves energy distribution in the time domain. Compared to traditional pulse modulation schemes, it avoids energy waste caused by filtering out residual light. Furthermore, placing the high-insertion-loss frequency shifter in the LO path solves the problem of pulse light energy reduction due to the high insertion loss of the frequency shifter and attenuates the LO light to an appropriate power.

[0036] In addition, to achieve coupling mixing and beat frequency processing, the photonic chip 1 also includes a mixer 14 and a photodetector 15. The mixer 14 receives the local oscillator light output from the frequency shift operation and the backscattered light input from the transceiver 3, and performs coupling mixing; the mixed output light is sent to the photodetector 15 to convert the optical signal into an electrical signal carrying target distance and speed information.

[0037] The mixer here is an optical device that couples and superimposes two optical signals. Specifically, it can be implemented using a 2×2 directional coupler, with a waveguide structure achieving energy distribution and phase matching between the backscattered light and the local oscillator light. The photodetector is an optoelectronic device that converts the optical signal into an electrical signal. Specifically, it can be implemented using a balanced detector, eliminating common-mode noise and extracting the effective beat frequency signal through differential detection. The mixer is directly integrated inside the photonic chip, reducing insertion loss caused by optical path coupling in traditional beam splitting schemes and ensuring that the local oscillator light power is maintained at the required level. The photodetector suppresses common-mode noise through a balanced detection mechanism, improving the detection sensitivity of weak echo signals. Specifically, the frequency-shifted local oscillator light and the target backscattered light are coupled and mixed in a mixer to form a composite optical signal containing two light sources with different frequencies. This composite optical signal enters the photodetector, where envelope detection technology generates an electrical signal corresponding to the frequency difference. During the time slot corresponding to the blind zone light, the local oscillator light is in a dark state. At this time, the strong stray light in the backscattered light cannot form an effective beat frequency signal due to the lack of local oscillator light participating in the mixing, thus preventing the detector from entering a saturation state. The integrated design of the mixer and photodetector eliminates the optical path coupling loss between discrete components in traditional schemes, allowing the local oscillator light power to be maintained within the effective operating range.

[0038] Figure 3The diagram illustrates the two optical paths output from the seed signal optical path via an optical chopper. The pulsed light output by the optical chopper has a waveform complementary to the local oscillator light. The local oscillator light includes a dark segment, the time domain length of which is the same as the time domain length of the blind zone light in the backscattered light. This blind zone light is typically caused by return loss of optical path components, reflection from fiber optic jumper end faces, and reflection from within the telescope lens during the transmission of the pulsed light inside the radar. Therefore, the backscattered light includes a blind zone light segment, and its intensity is much higher than the effective backscattered light. To detect weak target signals, the detector must have high gain. However, high gain leads to detector saturation caused by the blind zone light, producing a "saturation tail" effect, i.e., the saturation recovery time is prolonged, causing subsequent weak signals to be masked. This not only expands the actual blind zone range but may even lead to the loss of near-range target signals.

[0039] The optical chopper can be implemented using a periodically alternating switching optical chopper structure, by controlling the generation timing of the pulsed light and the local oscillator light to make them staggered on the time axis. In this scheme, the "splitter light" after pulse modulation by the chopper is used as the local oscillator light input to the frequency shifter, eliminating the influence of the high insertion loss of the frequency shifter on the pulsed light path and greatly improving the pulsed light intensity.

[0040] When the blind zone light in the target backscattered light arrives, the local oscillator light remains in a dark state, preventing the strong blind zone light from coherently mixing with the local oscillator light. During the non-blind zone period, the local oscillator light resumes effective output and completes beat frequency processing with the normal backscattered light signal. This timing control mechanism eliminates the interaction conditions between strong interference signals and the local oscillator light through time isolation of the optical signals.

[0041] In some embodiments, the seed laser 11 is a distributed feedback laser (DFB) with an output optical power of 10-100mW; the optical chopper 12 contains several cascaded microring resonators (MRRs), the duty cycle of the chopping pulse signal is 0.6%-0.9%, and without considering additional losses, the average power of the chopper output is 60μW-900μW, while the average power of the local oscillator output is almost equal to the input optical power, which is 9.94mW-99.1mW. The frequency shifter 13 is a dual parallel Mach-Zehnder modulator (DPMZM). Figure 4This is an on-chip architecture diagram using an optical chopper to generate split beams. A distributed feedback laser refers to a semiconductor laser that achieves single-mode output through an integrated Bragg grating. Specifically, it can be implemented using an integrated light source fabricated from InP-based materials, whose high-power output characteristics provide ample energy reserves for subsequent optical paths. A microring resonator refers to a resonant structure formed by coupling a ring waveguide and a straight waveguide. Specifically, it can be implemented using a cascaded microring array fabricated from silicon-based or silicon nitride materials, achieving low duty cycle pulse modulation through multi-stage resonance enhancement. A dual-parallel Mach-Zehnder modulator refers to an electro-optic modulation device composed of two parallel Mach-Zehnder interferometers. Specifically, it can be implemented using an integrated modulator fabricated from silicon or thin-film lithium niobate materials, achieving frequency shifting operation through carrier suppression.

[0042] Specifically, when the continuous light output from the distributed feedback laser is pulse-modulated by a microring resonator array, the resonant state and coupling coefficient of the microrings are adjusted to form optical pulses within a 0.6%–0.9% time window, while the light energy during the remaining time periods is directly transmitted through a straight waveguide as the local oscillator. This pulse modulation mechanism enables the pulsed light and the local oscillator to form complementary waveforms, avoiding the energy waste caused by traditional pulse modulation methods. When the dual parallel Mach-Zehnder modulator performs frequency shifting on the retained local oscillator, it suppresses the carrier component by balancing the phase difference between the two interferometer arms, achieving precise frequency shift control while reducing the device's own losses.

[0043] The solution will now be illustrated through the following examples: The seed laser is a distributed feedback laser (DFB), the chopper (OC) is a cascaded multi-micro-ring resonator (MRR), the frequency shifter is a dual parallel Mach-Zehnder modulator (DPMZM), the mixer is a 2×2 directional coupler (DC), and the detector is a balanced photodetector (BPD). The directional coupler (DC) couples the backscattered light with the local oscillator light before outputting the photodetector. The photodetector 15 is a balanced photodetector (BPD) that performs beat frequency processing on the coupled local oscillator light and the backscattered light.

[0044] A 2×2 directional coupler (DC) is an optical coupling device with two input ports and two output ports. It can be implemented using silicon-based or silicon nitride waveguide structures, and the optical energy distribution is achieved by controlling the waveguide spacing. This device achieves uniform mixing of backscattered light and local oscillator light through symmetrical coupling characteristics, avoiding the power imbalance problem introduced by traditional beam splitting structures and providing stable interference conditions for subsequent beat frequency processing.

[0045] A balanced photodiode (BPD) is a photoelectric conversion device with differential detection capabilities, specifically implemented using a combination of dual photodiodes and a differential amplifier circuit. This device eliminates common-mode noise, suppresses DC component interference generated in the dead-zone optical section, prevents the detector from saturating due to strong light signals, and simultaneously improves the sensitivity for weak signal detection.

[0046] Specifically, the backscattered light and the local oscillator light are coupled through a 2×2 directional coupler. During coupling, the symmetry of the waveguide structure ensures that the optical path difference between the two optical signals remains constant, avoiding beat frequency signal attenuation caused by phase mismatch. After receiving the two coupled optical signals, the balanced detector cancels common-mode noise through a differential amplifier circuit, while simultaneously extracting the AC signal component carrying target information. During this process, the strong DC component generated by the blind zone light is suppressed, preventing the detector from entering the nonlinear operating region and thus avoiding pulse trailing.

[0047] In one possible embodiment, the DFB output power is 20mW, the MRR insertion loss is 5dB, the pulse signal repetition frequency is 30kHz, the pulse width is 200ns, the DPMZM insertion loss is 10dB, and the local oscillator power required by the system is approximately 1-2mW (i.e., 0.5-1mW of local oscillator power per arm during balanced detection).

[0048] Figure 5 The diagram shows an on-chip architecture using a directional coupler for shunting. When using a conventional directional coupler shunting on-chip architecture, a 1×2 DC with a fixed splitting ratio separates the local oscillator light from the DFB. To ensure the local oscillator light power is greater than 1mW, the 1×2 DC ratio must be at least 19:1 (for ease of calculation, the loss of the 1×2 DC is not considered). The optical power entering the chopper MRR is 19mW. The duty cycle of the pulsed light is 0.6% (repetition frequency of 30kHz, pulse width of 200ns), and the average power of the pulsed light after chopping is 114μW. The total insertion loss of the MRR and DPMZM is 15dB, therefore the average power of the pulsed light output by the chip is 3.6μW.

[0049] When using the on-chip structure provided in this embodiment, the 20mW optical signal output from the DFB directly enters the MRR. The duty cycle of the pulsed light is 0.6%, and the average power of the pulsed light after chopping is 120μW. The average power of the local oscillator output is close to the input optical power, at 19.88mW. Based on the MRR's overall insertion loss of 5dB, the average power of the pulsed light output by the chip is 37.9μW, which is much higher than the 3.6μW average power of the traditional solution. The pulse-modulated "shunt light" is used as the local oscillator light and passes through DPMZM. The overall insertion loss is 10dB, so the local oscillator light power is approximately 2mW (meeting the requirement of 1-2mW for local oscillator light), which is still comparable to the traditional solution.

[0050] Compared to traditional methods, which directly filter out residual light through pulse modulation, resulting in the direct loss of over 99% of optical energy, this solution utilizes a dynamic complementary beam splitting mechanism to directly convert the chopper-splittered light into local oscillator light, thus significantly improving optical energy utilization.

[0051] Through the above technical solution, this application increases the average power of the pulse signal to 10 times that of traditional solutions while maintaining the local oscillator power level. Simultaneously, complementary waveform design avoids saturation interference from blind zone signals to the detector. This technical solution effectively overcomes the problem of reduced transmission power caused by high losses in on-chip frequency shifting devices, providing a feasible optical path architecture for on-chip integration of coherent Doppler pulse wind lidar.

[0052] In another possible embodiment, an on-chip architecture is designed using an optical chopper 12 comprising two straight waveguides and four MRRs, see [link to relevant documentation]. Figure 6 As shown, the incident laser outputs local oscillator light after passing through the first straight waveguide, while the remaining laser light outputs pulsed light after passing through the straight waveguide and four MRRs. The duty cycle of the pulsed light is 0.6%, meaning that only 0.6% of the light passes through multiple MRRs to form pulsed light, while the vast majority of the light passes through the straight waveguide to become local oscillator light. Therefore, compared to traditional schemes, energy is fully utilized. From the results, although the blind zone light in the backscattered light does not completely overlap with the non-light segment of the local oscillator signal in terms of timing, it further reduces the optical signal strength. Figure 7 This is the timing diagram of the pulsed light and the local oscillator light under ideal conditions, in which they are completely overlapping and lossless. However, this is impossible to achieve when different optical path differences arise due to the detection of the target object (introducing long-distance delay fibers would inevitably lead to difficulties in on-chip integration or huge insertion losses, making it difficult to apply). Figure 6 The results compared to Figure 5 The solution has been greatly improved.

[0053] In summary, traditional methods generate pulsed light using pulse modulators and then filter out the remaining light, wasting over 99% of optical energy. This new method, through a combination of a straight waveguide and a micro-ring resonator, allows the local oscillator light to be output directly through a low-loss transmission path without any modulation devices, while reducing the proportion of light requiring modulation to 0.6%. This structural innovation increases the optical energy utilization rate from less than 1% in traditional methods to over 99%, and avoids the loss of main optical power by modulation devices.

[0054] Through the above technical solution, this application achieves the optimal allocation of optical energy between the detection signal generation path and the local oscillator light transmission path, effectively solving the energy waste problem caused by pulse modulation loss in traditional systems. By cascading a high insertion loss frequency shifter into the local oscillator light path, the impact of the frequency shifting stage on the pulse light energy emitted by the radar is significantly reduced.

[0055] This specific embodiment is merely an explanation of the present invention and is not intended to limit the invention. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A low-loss coherent Doppler pulse wind measurement lidar system architecture, characterized in that, The system architecture includes: Photonic chip (1), which generates incident laser light and outputs pulsed light and local oscillator light through pulse modulation; Amplifier (2), which receives pulsed light and amplifies the pulsed light; Transceiver (3), the transceiver (3) is used to emit pulsed light and receive backscattered light from the target object and send it back to the photonic chip (1); the backscattered light contains a blind zone light; The photonic chip (1) shifts the frequency of the local oscillator light and couples it with the acquired backscattered light to achieve photoelectric conversion; the electrical signal output by the photoelectric conversion is used to process and analyze wind speed and wind direction information.

2. The low-loss coherent Doppler pulse wind lidar system architecture according to claim 1, characterized in that, The photonic chip (1) includes a seed laser (11), an optical chopper (12), and a frequency shifter (13); The seed laser (11) generates continuous incident laser light, and the optical chopper (12) is driven by a pulse radio frequency signal to chop and output two split beams. One of the split beams is output as pulse light, and the other split beam is sent to the frequency shifter (13) as local oscillator light; The frequency shifter (13) shifts the local oscillator light to generate local oscillator light with a frequency that satisfies the coherent heterodyne condition, and attenuates the light to the target power.

3. The low-loss coherent Doppler pulse wind lidar system architecture according to claim 2, characterized in that, The photonic chip (1) also includes a mixer (14) and a photodetector (15); the mixer (14) receives the local oscillator light output after frequency shifting and the backscattered light input from the transceiver (3), and performs coupling mixing; The mixed-frequency output light is sent into the photodetector (15) to convert the optical signal into an electrical signal carrying target distance and speed information.

4. The low-loss coherent Doppler pulse wind lidar system architecture according to claim 3, characterized in that, The pulsed light output by the optical chopper (12) has a waveform that is complementary to the local oscillator light.

5. The low-loss coherent Doppler pulse wind lidar system architecture according to claim 4, characterized in that, The local oscillator light includes a dark segment, and the time domain length of the dark segment is the same as the time domain length of the blind zone light in the backscattered light.

6. The low-loss coherent Doppler pulse wind lidar system architecture according to claim 2, characterized in that, The seed laser (11) is a distributed feedback laser (DFB) with an output optical power of 10-100mW; The optical chopper (12) contains several cascaded microring resonators (MRRs), the duty cycle of the pulse signal applied to the chopper is 0.6% - 0.9%, and the average power of the chopper output is 60μW - 900μW; The frequency shifter (13) is a dual parallel Mach-Zehnder modulator (DPMZM).

7. The low-loss coherent Doppler pulse wind lidar system architecture according to claim 3, characterized in that, The mixer (14) is a 2×2 directional coupler DC, which couples the backscattered light with the local oscillator light and outputs the output. The photodetector (15) is a balanced detector (BPD) that performs beat frequency processing on the coupled local oscillator light and backscattered light.

8. The low-loss coherent Doppler pulse wind lidar system architecture according to claim 6, characterized in that, The 20mW optical signal output by the DFB goes directly into the optical chopper. The duty cycle of the pulse signal is 0.6%, and the average power of the pulse signal after chopping is 120μW.

9. The low-loss coherent Doppler pulse wind lidar system architecture according to claim 8, characterized in that, The MRR has a total insertion loss of 5dB, a pulse repetition frequency of 30kHz, a pulse width of 200ns, and an average power of 37.9μW for the on-chip architecture output pulse signal. The DPMZM has a combined insertion loss of 10dB and a local oscillator power of 2mW.

10. The low-loss coherent Doppler pulse wind lidar system architecture according to claim 6, characterized in that, The optical chopper (12) includes two straight waveguides and four MRRs. The incident laser outputs local oscillator light after passing through the first straight waveguide, and the remaining laser outputs pulse light after passing through the straight waveguide and the four MRRs.

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