Circuit for transmitting chirped light and lidar

Abstract

This disclosure provides a circuit for emitting linear frequency modulated light and a lidar. The circuit for emitting linear frequency modulated light includes: a light source configured to emit frequency modulated light; a frequency discrimination circuit coupled to the light source and configured to output a frequency discrimination signal; and a first feedback circuit, with its input terminal coupled to the frequency discrimination circuit and its output terminal coupled to the light source, configured to output a first feedback signal based on the frequency discrimination signal and a first reference signal to adjust the linearity of the frequency modulated light.

Description

Technical Field

[0001] This disclosure relates to the field of lidar technology, and more particularly to a circuit for emitting linear frequency modulated light and a lidar. Background Technology

[0002] Frequency Modulated Continuous Wave (FMCW) lidar typically requires a linearly frequency-modulated light source with high coherence and high power. The frequency of the detection signal of an FMCW lidar changes linearly with time, and the time of flight (TOF) or velocity of an object can be accurately obtained based on the frequency shift.

[0003] However, due to factors such as uneven stress tension, circuit noise, and temperature changes within the laser cavity, existing frequency-modulated light sources often struggle to output highly linear frequency-modulated light, which can easily lead to a decrease in the ranging accuracy and resolution of FMCW lidar, thus reducing the reliability of FMCW lidar.

[0004] Therefore, improving the linearity of frequency-modulated light has become a challenge. Summary of the Invention

[0005] This disclosure provides a circuit for emitting linear frequency modulated light, which can emit frequency modulated light with high linearity.

[0006] In a first aspect, embodiments of this disclosure provide a circuit for emitting linearly frequency-modulated light, comprising:

[0007] The light source is configured to emit frequency-modulated light;

[0008] The frequency discrimination circuit is coupled to the light source and configured to output a frequency discrimination signal;

[0009] The first feedback circuit has its input terminal coupled to the frequency discrimination circuit and its output terminal coupled to the light source. It is configured to output a first feedback signal based on the frequency discrimination signal and the first reference signal to adjust the linearity of the frequency-modulated light.

[0010] Optionally, the first feedback circuit includes:

[0011] The subtractor is configured to output an error signal based on the frequency discrimination signal and the first reference signal;

[0012] The PID controller, coupled to the subtractor, is configured to receive the error signal and output the first feedback signal.

[0013] Optionally, the frequency discrimination circuit includes:

[0014] Frequency discriminator;

[0015] A phase modulation circuit, coupled to the frequency discriminator, is configured to adjust the operating point of the frequency discriminator based on a second feedback signal.

[0016] Optionally, the circuit for emitting linearly modulated light further includes:

[0017] The second feedback circuit, coupled to the frequency discrimination circuit, is configured to receive the frequency discrimination signal and the second reference signal, and output the second feedback signal to the phase modulation circuit to adjust the operating point of the frequency discrimination circuit.

[0018] Optionally, the second feedback circuit includes at least one of the following:

[0019] Analog signal processing circuit; or

[0020] Digital signal processing circuit.

[0021] Optionally, the analog signal processing circuit includes:

[0022] The multiplier is configured to output a phase detection signal based on the frequency discrimination signal and the second reference signal;

[0023] The filter, coupled to the multiplier, is configured to receive the phase detection signal and output a second feedback signal.

[0024] Optionally, the digital signal processing circuit is configured to perform at least one of Hilbert transform and sine signal fitting on the frequency discrimination signal to determine the second feedback signal.

[0025] Optionally, the frequency discriminator includes any of the following:

[0026] Mach-Zehnder interferometer,

[0027] Fiber Bragg grating

[0028] Bandpass filter,

[0029] Fabry-Perot resonator, or

[0030] Microrings.

[0031] Optionally, the phase modulation circuit includes at least one of the following:

[0032] Phase modulator,

[0033] Semiconductor optical amplifier,

[0034] piezoelectric ceramics

[0035] Thermally adjustable phase shifter, or

[0036] Electrically adjustable phase shifter.

[0037] Optionally, the frequency discrimination circuit also includes:

[0038] The balanced detection circuit has its input terminal coupled to the frequency discriminator and its output terminal coupled to the first feedback circuit and the second feedback circuit.

[0039] Optionally, the balance detection circuit includes:

[0040] A first photodetector and a second photodetector, wherein the anode of the first photodetector is coupled to the cathode of the second photodetector, and the first photodetector and the second photodetector are configured to convert optical signals into electrical signals.

[0041] Secondly, embodiments of this disclosure provide a lidar, including the circuit for emitting linear frequency modulated light according to any of the above embodiments. Attached Figure Description

[0042] Figure 1 A structural example diagram of an FMCW lidar is shown.

[0043] Figure 2 An example spectrum diagram of the local oscillator light and probe echo signal of an FMCW lidar is shown.

[0044] Figure 3 An example circuit diagram for emitting linear frequency modulated light is shown in this disclosure.

[0045] Figure 4 An example diagram of the transmittance curve of a frequency discriminator according to the present disclosure is shown.

[0046] Figure 5 An example diagram of the frequency-to-amplitude conversion result of a frequency discriminator of this disclosure is shown, wherein, sub Figure 5 a shows an example diagram of frequency variation of the light source, sub- Figure 5 b shows the relationship with the child Figure 5 Figure a shows an example of the amplitude change of the frequency discrimination signal corresponding to the frequency change of the light source.

[0047] Figure 6 An example diagram of a Mach-Zehnder interferometer of this disclosure is shown.

[0048] Figure 7 An example diagram of a first feedback circuit of this disclosure is shown.

[0049] Figure 8 An example diagram of a frequency discrimination circuit of this disclosure is shown.

[0050] Figure 9 An example circuit diagram for emitting linear frequency modulated light is shown in this disclosure.

[0051] Figure 10 An example diagram of a phase modulation circuit of this disclosure is shown.

[0052] Figure 11 An example diagram of a frequency discrimination circuit of this disclosure is shown.

[0053] Figure 12 An example diagram of a second feedback circuit of this disclosure is shown.

[0054] Figure 13 An example diagram of a balanced detection circuit of this disclosure is shown.

[0055] Figure 14 An example circuit diagram for emitting linear frequency modulated light is shown in this disclosure. Detailed Implementation

[0056] Due to factors such as uneven stress tension, circuit noise, and temperature changes within the laser cavity, existing frequency-modulated light sources often struggle to output highly linear frequency-modulated light, which can easily lead to a decrease in the ranging accuracy and resolution of FMCW lidar, thus reducing the reliability of FMCW lidar.

[0057] To facilitate understanding, the following is a brief introduction to linear frequency modulated light based on the detection principle of FMCW lidar.

[0058] Figure 1 A structural example diagram of an FMCW lidar is shown. (Refer to...) Figure 1 The FMCW lidar 100 may include a laser 102 and a detector 104. The FMCW lidar 100 can generate an optical signal through the laser 102. The optical signal may be a linearly frequency-modulated (LFM) optical signal. A portion of the LFM optical signal is emitted into external space as a probe signal, and another portion is transmitted to the detector 104 as a local oscillator. The probe signal is reflected by an object to obtain a probe echo signal, which is also transmitted to the detector 104. By performing beat frequency analysis on the local oscillator and the probe echo signals, a beat frequency signal can be obtained, and relevant information about the object can be determined based on the beat frequency signal. For example, one or more parameters such as the object's distance, flight time, and speed.

[0059] Figure 2 An example spectrum diagram of the local oscillator light and probe echo signal of an FMCW lidar is shown. For example, refer to... Figure 2 The frequencies of the local oscillator light and the probe echo signal change linearly with time, exhibiting a triangular wave pattern. Based on the beat frequency of the local oscillator light and the probe echo signal, the distance information of the obstacle can be obtained according to the following formula (1).

[0060] D=(fb*c*ts) / (2Δf) (1)

[0061] Where fb represents the frequency of the beat frequency signal of the local oscillator and the probe echo signal, c represents the speed of light, ts represents the period of the probe light signal sweeping band, and Δf represents the frequency modulation bandwidth of the probe light signal sweeping band.

[0062] When there is a relative velocity between the object and the FMCW lidar, the object's velocity information can also be obtained based on the beat frequency signal.

[0063] The frequency of the probe optical signal changes linearly with time, which ensures the accuracy of the acquired detection information. In other words, if the probe optical signal meets the preset linearity requirement, it is beneficial to obtain accurate detection information.

[0064] However, due to factors such as uneven stress tension, circuit noise, and temperature variations within the laser cavity, existing frequency-modulated light sources often struggle to output linearly frequency-modulated light with high linearity. Therefore, improving the linearity of frequency-modulated light is of great significance for enhancing the detection accuracy and reliability of FMCW lidar.

[0065] To address the aforementioned problems, this disclosure provides a circuit for emitting linearly frequency-modulated (LFM) light. The circuit includes a light source, a frequency discriminator circuit, and a first feedback circuit. The light source can emit LFM light. The frequency discriminator circuit is coupled to the light source and can output a frequency discriminator signal. The input terminal of the first feedback circuit is coupled to the frequency discriminator circuit, and its output terminal is coupled to the light source. Based on the frequency discriminator signal and a first reference signal, it can output a first feedback signal. The first feedback signal can adjust the linearity of the LFM light to improve linearity.

[0066] Figure 3 An example circuit diagram for emitting linearly frequency-modulated light according to this disclosure is shown. (Refer to...) Figure 3 In some embodiments, circuit 300 may include light source 302, frequency discrimination circuit 304 and first feedback circuit 306.

[0067] Light source 302 can emit frequency-modulated light. The frequency-modulated light is, for example, linearly frequency-modulated light, that is, the frequency of the light changes linearly with time. The change pattern can be in the form of triangular waves, sawtooth waves, trapezoidal waves, etc.

[0068] For example, continue to refer to Figure 3 The frequency-modulated light emitted by the light source 302 is split by a coupler (not shown in the figure). One part is output as the probe light Out1, which can be emitted into external space for object detection. The other part is input as the detection light Out2 to the frequency discriminator circuit 304.

[0069] In some embodiments, the light source 302 may include a laser. For example, the laser may include, but is not limited to, a distributed feedback semiconductor laser (DFBL), a distributed Bragg reflector laser (DBRL), or a vertical-cavity surface-emitting semiconductor laser (VCSEL).

[0070] It is understood that the embodiments disclosed herein do not impose specific limitations on the light source, and the above embodiments are merely illustrative examples.

[0071] Frequency discrimination circuit 304 is coupled to light source 302, and can receive detection light Out2 and output frequency discrimination signal S. f .

[0072] In some embodiments, the frequency discrimination circuit 304 may include a frequency discriminator (not shown in the figure).

[0073] The detection light Out2 is input from the input terminal of the frequency discriminator. The output terminal of the frequency discriminator outputs the discriminated light signal.

[0074] For a light source emitting frequency-modulated light, the frequency of the emitted linearly frequency-modulated light can be quantized as f = f0 + kt + δ. Here, f0 is the initial frequency of the light source, k is the frequency modulation slope of the linearly frequency-modulated light, and δ is the frequency modulation nonlinearity that needs to be adjusted. Figure 4 An example transmittance curve of a frequency discriminator according to this disclosure is shown. (Refer to...) Figure 4 The initial frequency f0 of the light source is located at the full width at half maximum (FWHM) of the transmission peak of the frequency discriminator, which is the operating point of the discriminator. When the frequency of the light source changes with time, the reference... Figure 4 As shown, the frequency changes to f2 at the first moment and to f1 at the second moment. The frequency discriminator can convert this frequency change into an amplitude change. The frequency discriminator is very sensitive to changes in the frequency of the light source; even a small change in the frequency of the light source can cause a significant change in the amplitude of the discriminator's output signal. For example, Figure 5 An example diagram showing the frequency-amplitude conversion result of a frequency discriminator according to this disclosure is illustrated. (Refer to...) Figure 5 son Figure 5 a. The frequency of the light source varies around f0. (Refer to...) Figure 5 son Figure 5 b. Correspondingly, the amplitude of the frequency discrimination signal changes around the value P0. The amplitude change of the frequency discrimination signal is significantly greater than the amplitude change of the light source frequency.

[0075] In some embodiments, the frequency discriminator may include a Mach-Zehnder interferometer.

[0076] For example, Figure 6 An example diagram of a Mach-Zehnder interferometer of this disclosure is shown. (Refer to...) Figure 6 The Mach-Zehnder interferometer 600 may include coupler 602, coupler 604, waveguide arm 606, and waveguide arm 608. The optical path lengths of waveguide arm 606 and waveguide arm 608 are different.

[0077] When the detection light Out2 is transmitted to coupler 602, it is split into two optical signals. One signal enters waveguide arm 606, and the other enters waveguide arm 608. Because the optical path length of waveguide arm 606 is greater than that of waveguide arm 608, the optical signal located in waveguide arm 606 is delayed, resulting in an optical path difference (i.e., a phase difference) between the two optical signals. The two beams are coherently coupled and combined into a single output beam at coupler 604. The frequency discriminator 600 outputs the frequency-discriminated optical signal S. f, The amplitude is related to the frequency of the detection light. Figure 4 As shown in the diagram, the frequency of the detection light can be determined by detecting the amplitude of the frequency-discriminating optical signal, thus achieving frequency discrimination of the detection light Out2.

[0078] In some embodiments, the frequency discriminator may include a microring.

[0079] For example, a frequency discriminator may include a single-waveguide-coupled microring. The single-waveguide-coupled microring consists of a ring waveguide and a straight waveguide. When the frequency of the input optical signal meets the resonance condition, the optical signal interferes and is enhanced within the microring, reducing the coupling strength with the straight waveguide and decreasing the output light intensity. When the frequency of the input light matches the resonant frequency of the microring, the optical signal within the microring interferes and is enhanced, a large amount of light energy is absorbed by the microring, and the output light intensity is minimal. When the frequency of the input light deviates from the resonant frequency, the resonance effect weakens, and the output light intensity gradually increases. The output light intensity is related to the frequency of the input light. By measuring the output light intensity of the microring, the frequency of the input light can be determined based on the relationship between the output light intensity and the input light frequency.

[0080] In some embodiments, the frequency discriminator may include fiber Bragg gratings (FBG).

[0081] For example, FBG is used for optical signals of a specific wavelength (i.e., the Bragg wavelength λ). B It has a strong reflective effect. For a specific FBG, when the wavelength corresponding to the incident light frequency is close to λ... B When the incident light frequency is close to λ, the reflected light intensity is close to its maximum value; when the wavelength corresponding to the incident light frequency is far from λ... BAs the incident light frequency increases, the intensity of reflected light decreases while the intensity of transmitted light increases. The intensity of reflected or transmitted light detected at the output of the FBG is related to the frequency of the incident light. Therefore, based on the relationship between the intensity of reflected or transmitted light and the frequency of the incident light, the frequency of the incident light can be determined by detecting the intensity of reflected or transmitted light.

[0082] In some embodiments, the frequency discriminator may include a bandpass filter.

[0083] For example, a bandpass filter allows optical signals within a certain frequency range to pass through, while attenuating optical signals outside that range. The frequency at which the bandpass filter has the maximum gain for optical signals is its center frequency f. c When the frequency of the input optical signal is close to the center frequency f of the bandpass filter. c At a certain frequency, the optical signal transmission efficiency is highest, and the output signal amplitude is largest. When the input optical signal frequency is far from f... c When the bandpass filter attenuates the optical signal more, the amplitude of the output light decreases. The amplitude of the output optical signal varies with the frequency of the input optical signal; the magnitude of the amplitude reflects the deviation of the input light frequency from f. c The degree of intensity. By detecting changes in the amplitude of the output optical signal, the frequency information of the input optical signal can be obtained.

[0084] In some embodiments, the frequency discriminator may include a Fabry-Perot resonator.

[0085] The Fabry-Perot resonator responds to the frequency selective response of optical signals based on its resonance characteristics. By measuring the light intensity of the resonator, it can be determined whether the frequency of the input optical signal meets the resonance condition of the resonator, thereby achieving frequency discrimination.

[0086] It is understood that the embodiments disclosed herein do not impose specific limitations on the frequency discriminator.

[0087] Continue to refer to Figure 3 The input terminal of the first feedback circuit 306 is coupled to the frequency discrimination circuit 304, and the output terminal is coupled to the light source 302. The first feedback circuit 306 can be based on the frequency discrimination signal S. f With the first reference signal S r1 Output the first feedback signal S b1 This is to adjust the linearity of the light produced by the frequency-modulated light source 302.

[0088] For example, a directly modulated light source can adjust its emission frequency by regulating the drive current. Therefore, when the light source is directly modulated, the drive current of the light source can be adjusted based on a first feedback signal, thereby adjusting the linearity of the frequency-modulated light. Specifically, a current regulating element can be used to adjust the drive current of the light source.

[0089] For example, an externally modulated light source can generate fixed-frequency light using a laser, and then use an external modulator to modulate the frequency of the fixed-frequency light to generate frequency-modulated light. The frequency of the frequency-modulated light can be adjusted by adjusting the input electrical signal of the external modulator. Therefore, when the light source is an externally modulated light source, the linearity of the frequency-modulated light can be adjusted based on the first feedback signal by adjusting the electrical signal of the external modulator. For example, a voltage-controlled oscillator (VCO) can be used as the external modulator, with a voltage adjustment element, and the frequency of the frequency-modulated light can be adjusted by adjusting the input voltage of the VCO.

[0090] Figure 7 An example diagram of a first feedback circuit according to this disclosure is shown. (Refer to...) Figure 7 In some embodiments, the first feedback circuit 700 may include a subtractor 702 and a PID controller 704.

[0091] The first input of the subtractor 702 is coupled to the frequency discriminator and can receive the frequency discrimination signal S. f The second input of subtractor 702 can receive the first reference signal S. r1 The subtractor 702 can be based on the frequency discrimination signal S. f With the first reference signal S r1 Output error signal S e .

[0092] In some embodiments, the first reference signal S r1 It can be generated by a sinusoidal oscillator. For example, the first reference signal S r1 It can be the frequency discrimination signal output by the frequency-modulated light that meets the preset linearity requirements after passing through the frequency discrimination circuit.

[0093] In some embodiments, the subtractor 702 may include a differential amplifier. The first input of the differential amplifier receives a frequency discrimination signal S. f The second input terminal of the differential amplifier receives the first reference signal S. r1 After passing through the differential amplifier, the output terminal of the differential amplifier outputs an error signal S. e .

[0094] The PID controller 704 is coupled to the subtractor 702 and can receive the error signal S. e Output the first feedback signal S b1 .

[0095] A PID controller processes error signals through a combination of proportional, integral, and derivative control actions, thereby achieving precise control of the target value. For example, a PID controller, based on the error signal S... e Calculate the outputs of the proportional, derivative, and integral components. Combine the outputs of the three components into a control signal, which serves as the first feedback signal S. b1 Output.

[0096] In some embodiments, the light source emits frequency-modulated light, the frequency of which changes over time. This real-time change in light frequency can cause instability in the frequency discrimination signal output by the frequency discrimination circuit, thereby affecting the accuracy of the first feedback signal output by the first feedback circuit.

[0097] To address the aforementioned issues, the circuit disclosed herein for transmitting linear frequency modulated light includes a frequency discriminator and a phase modulation circuit. The phase modulation circuit is coupled to the frequency discriminator and adjusts the operating point of the frequency discriminator based on a second feedback signal. The phase modulation circuit ensures that the operating point of the frequency discriminator is consistent with the real-time frequency of the frequency-modulated light.

[0098] For example, Figure 8 An example diagram of a frequency discriminator circuit according to this disclosure is shown. (Refer to...) Figure 8 In some embodiments, the frequency discrimination circuit 800 may include a frequency discriminator 802 and a phase modulation circuit 804.

[0099] The input of frequency discriminator 802 receives the detection light Out2, and the output of frequency discriminator 802 outputs the discriminated optical signal S. f′ .

[0100] The phase modulation circuit 804 is coupled to the frequency discriminator 802, and the operating point of the frequency discriminator 802 can be adjusted.

[0101] Further embodiments of the frequency discriminator 802 can be found in the foregoing embodiments, and will not be repeated here.

[0102] The phase modulation circuit 804 can make the modulation signal of the frequency discriminator 802 correspond to the modulation signal of the light source, so that the frequency corresponding to the operating point of the frequency discriminator 802 is consistent with the instantaneous frequency of the frequency-modulated light emitted by the light source.

[0103] In some embodiments, the circuit for emitting linear frequency-modulated light provided in this disclosure includes a light source, a frequency discriminator circuit, a first feedback circuit, and a second feedback circuit. The light source can emit frequency-modulated light. The frequency discriminator circuit is coupled to the light source and can output a frequency discriminator signal. The input terminal of the first feedback circuit is coupled to the frequency discriminator circuit, and the output terminal is coupled to the light source. It can output a first feedback signal based on the frequency discriminator signal and a first reference signal. The second feedback circuit is coupled to the frequency discriminator circuit, can receive the frequency discriminator signal and a second reference signal, and output a second feedback signal. The second feedback signal is used to adjust the operating point of the frequency discriminator circuit. The first feedback signal can correct the nonlinear deviation of the frequency-modulated light, so that the frequency-modulated light reaches a preset linearity requirement. The second feedback signal can adjust the operating point of the frequency discriminator circuit. Through the second feedback signal, the nonlinear deviation existing in the frequency-modulated light is corrected at the frequency corresponding to the operating point of the frequency discriminator, so that the operating point of the frequency discriminator is consistent with the real-time frequency of the corrected frequency-modulated light, thereby improving the accuracy of the frequency discriminator signal.

[0104] Figure 9 An example circuit diagram for emitting linearly frequency-modulated light according to this disclosure is shown. (Refer to...) Figure 9 In some embodiments, circuit 900 may include light source 902, frequency discrimination circuit 904, first feedback circuit 906 and second feedback circuit 908.

[0105] Light source 902 can emit frequency-modulated light.

[0106] Further embodiments of the light source 902 can be found in the foregoing embodiments, and will not be repeated here.

[0107] The frequency discrimination circuit 904 is coupled to the light source 902 and can output a frequency discrimination signal S. f .

[0108] In some embodiments, the frequency discrimination circuit 904 includes a frequency discriminator and a phase modulation circuit. The phase modulation circuit may include a phase modulator.

[0109] For example, Figure 10 An example diagram of a phase modulation circuit according to this disclosure is shown. (Refer to...) Figure 10 In some embodiments, the phase modulation circuit 1000 may include electrodes 1002 and 1004. The phase modulation circuit 1000 may apply a phase that varies linearly with voltage to the input optical field according to the following formula (2) to adjust the operating point of the frequency discriminator.

[0110]

[0111] in, For phase, α EO λ is the electro-optic coefficient, L is the electrode length, d is the distance between electrodes 1002 and 1004, λ is the wavelength of the input light, and V is the applied voltage.

[0112] In some embodiments, the phase modulation circuit may include a semiconductor optical amplifier.

[0113] For example, the phase of the optical signal can be adjusted by regulating the injection current of the semiconductor optical amplifier, thereby adjusting the operating point of the frequency discriminator.

[0114] In some embodiments, the phase modulation circuit may include piezoelectric ceramics.

[0115] For example, the phase of an optical signal can be adjusted by regulating the modulation voltage applied to the piezoelectric ceramic, thereby adjusting the operating point of the frequency discriminator.

[0116] In some embodiments, the phase modulation circuit may include a thermally modulated phase shifter.

[0117] For example, a thermally modulated phase shifter can adjust the phase of an optical signal by changing the temperature, thereby adjusting the operating point of the frequency discriminator.

[0118] In some embodiments, the phase modulation circuit may include an electrically tunable phase shifter.

[0119] For example, an electrically tunable phase shifter can adjust the phase of an optical signal by adjusting the electrical signal applied to the optical path, thereby adjusting the operating point of the frequency discriminator.

[0120] Figure 11 An example diagram of a frequency discriminator circuit according to this disclosure is shown. (Refer to...) Figure 11 In some embodiments, the frequency discrimination circuit 1100 includes a Mach-Zehnder interferometer 1110 and an electrically tunable phase shifter 1120. The Mach-Zehnder interferometer 1110 includes couplers 1112 and 1114, waveguide arm 1116, and waveguide arm 1118. The optical path lengths of waveguide arm 1116 and waveguide arm 1118 are different.

[0121] An electrically tunable phase shifter 1120 can be mounted on the waveguide arm 1118. The electrically tunable phase shifter 1120 controls the refractive index of the waveguide arm 1118 by applying an external electric field. Adjusting the magnitude of the electric field can change the refractive index of the waveguide arm 1118, thereby changing the phase of the light transmitted through the waveguide arm 1118 and thus adjusting the operating point of the Mach-Zehnder interferometer 1110.

[0122] Continue to refer to Figure 9 The input terminal of the first feedback circuit 906 is coupled to the frequency discriminator circuit 904, and the output terminal is coupled to the light source 902. The first feedback circuit 906 can be based on the frequency discriminator signal S. f With the first reference signal S r1 Output the first feedback signal S b1 This is to correct the nonlinear deviation of frequency-modulated light and improve the linearity of frequency-modulated light.

[0123] Further embodiments of the first feedback circuit 906 can be found in the foregoing embodiments, and will not be repeated here.

[0124] The second feedback circuit 908 is coupled to the frequency discrimination circuit 904. The second feedback circuit 908 can receive the frequency discrimination signal S. f With the second reference signal S r2 Output the second feedback signal S b2 The frequency discriminator circuit 904 is used to adjust its operating point.

[0125] In some embodiments, the second feedback circuit may include an analog signal processing circuit.

[0126] Figure 12 An example diagram of a second feedback circuit according to this disclosure is shown. (Refer to...) Figure 12 In some embodiments, the second feedback circuit 1200 may include a multiplier 1202 and a filter 1204.

[0127] The first input of multiplier 1202 receives the frequency discrimination signal S. f The second input terminal receives the second reference signal S. r2 Multiplier 1202 can be based on the frequency discrimination signal S. f With the second reference signal S r2 Output phase detection signal

[0128] In some embodiments, the second reference signal S r2 It can be generated by a sinusoidal oscillator.

[0129] Filter 1204 is coupled to multiplier 1202. Filter 1204 can receive phase detection signals. Output the second feedback signal S b2 .

[0130] Second feedback signal S b2 The nonlinear deviation of the frequency-modulated light can be eliminated in the frequency corresponding to the operating point of the frequency discriminator, so that the frequency corresponding to the operating point of the frequency discriminator is consistent with the real-time frequency of the frequency-modulated light emitted by the light source, thereby improving the accuracy of the frequency discrimination signal.

[0131] In some embodiments, filter 1204 may include a low-pass filter.

[0132] In some embodiments, the second feedback circuit may include a digital signal processing circuit.

[0133] For example, a digital signal processing circuit can perform a Hilbert transform on the frequency discrimination signal to determine the second feedback signal.

[0134] For example, a digital signal processing circuit can perform sinusoidal signal fitting on the frequency discrimination signal to determine the second feedback signal.

[0135] In some embodiments, the circuit for emitting linearly frequency-modulated light provided in this disclosure includes a light source, a frequency discriminator circuit, a first feedback circuit, and a second feedback circuit. The frequency discriminator circuit may further include a balanced detection circuit. The input terminal of the balanced detection circuit is coupled to the frequency discriminator, and the output terminal is coupled to the first feedback circuit and the second feedback circuit. The balanced detection circuit can perform photoelectric conversion, converting the frequency-discriminated light signal output by the frequency discriminator into the frequency-discriminated signal.

[0136] For example, Figure 13 An example diagram of a balanced detection circuit according to this disclosure is shown. (Refer to...) Figure 13In some embodiments, the balanced detection circuit 1300 may include a first photodetector 1302 and a second photodetector 1304. The anode of the first photodetector 1302 is coupled to the cathode of the second photodetector 1304. The first photodetector 1302 and the second photodetector 1304 can convert optical signals into electrical signals.

[0137] Frequency discrimination optical signal S f′ The signal can be divided into two equal parts. The two frequency-discriminating optical signals are received by the first photodetector 1302 and the second photodetector 1304, respectively. The first photodetector 1302 and the second photodetector 1304 are connected in series. The DC components of the currents generated by the two photodetectors are the same, while the AC components are opposite. The currents generated by the two photodetectors are combined to form the frequency-discriminating signal S. f The output can eliminate the DC component in the current, thus suppressing common-mode signals. Therefore, it can ensure the normal operation of the first and second feedback circuits.

[0138] Figure 14 An example circuit diagram for emitting linearly frequency-modulated light according to this disclosure is shown. (Refer to...) Figure 14 The light source 1410 emits frequency-modulated light under the modulation of the modulation signal. After being split by a coupler (not shown in the figure), part of the emitted frequency-modulated light is output as the probe light Out1 to determine relevant information about objects in the detection space. The other part is input to the frequency discriminator circuit 1420 as the detection light Out2.

[0139] In some embodiments, the frequency discrimination circuit 1420 may include a frequency discriminator 1422 and a phase modulator 1424. For example... Figure 14 As shown, the frequency discriminator 1422 includes a Mach-Zehnder interferometer 1422. The Mach-Zehnder interferometer 1422 may include coupler 14222, coupler 14224, waveguide arm 14226, and waveguide arm 14228. The optical path lengths of waveguide arm 14226 and waveguide arm 14228 are different. A phase modulator 1424 may be disposed on waveguide arm 14228.

[0140] Frequency discriminator 1422 performs frequency discrimination processing on the detection light Out2 to obtain the frequency-discriminated optical signal S. f′ Frequency discrimination optical signal S f′ It is transmitted to the balance detection circuit 1426.

[0141] In some embodiments, coupler 14222 and coupler 14224 are both 1:1 couplers. Based on the transmission matrix of the Mach-Zehnder interferometer, the frequency-discriminating optical signal S can be obtained. f′ The two optical signals S after being split by coupler 14224 f′1 and S f′2It can be expressed by the following formulas (3) and (4).

[0142]

[0143]

[0144] Among them, P in Let f0 be the initial frequency of the input frequency-modulated light, k be the frequency modulation slope of the linearly frequency-modulated light, δ be the frequency modulation nonlinearity deviation to be adjusted, and τ be the delay difference between the two waveguide arms of the Mach-Zehnder interferometer. The operating point phase of the Mach-Zehnder interferometer, The operating point phase component that needs adjustment.

[0145] In some embodiments, the balanced detection circuit 1426 may include a first photodetector 14262 and a second photodetector 14264. The first photodetector 14262 and the second photodetector 14264 are connected in series.

[0146] The output terminal of the balanced detection circuit 1426 is located between the first photodetector 14262 and the second photodetector 14264. The currents generated by the first photodetector 14262 and the second photodetector 14264 are combined into a frequency discrimination signal S. f This eliminates the DC component in the current generated by the first photodetector 14262 and the second photodetector 14264, thus suppressing common-mode signals. Frequency discrimination signal S f They are respectively transmitted to the first feedback circuit 1430 and the second feedback circuit 1440.

[0147] Optical signal S f′1 and light signal S f′2 The equivalent optical signal after balanced detection can be represented by the following formula (5).

[0148]

[0149] Optical signal S f′1 and light signal S f′2 The frequency discrimination signal after balanced detection can be represented by the following formula (6).

[0150]

[0151] This electrical signal is only related to kt+δ. Here, R is the gain coefficient of the photodetector.

[0152] In some embodiments, the first feedback circuit 1430 may include a subtractor 1432 and a PID controller 1434.

[0153] In the first feedback circuit 1430, the subtractor 1432 can be based on the frequency discrimination signal S f With the first reference signal S r1 Output error signal S e The PID controller 1434 receives the error signal S. e Then, it is processed to output the first feedback signal S. b1 To the light source 1410.

[0154] First reference signal S r1 It can be an ideal signal output from linearly modulated light that meets preset linearity requirements after passing through a frequency discrimination circuit and a balanced detection circuit. In some embodiments, the first reference signal S r1 It is a sine wave or a cosine wave. First reference signal S r1 It can be represented by the following formula (7).

[0155]

[0156] In some embodiments, based on the first feedback signal S b1 The current adjustment element can be set to adjust the driving current of the light source 1410, thereby correcting the nonlinear deviation of the frequency-modulated light and making the frequency-modulated light meet the preset linearity requirements.

[0157] In some embodiments, the first reference signal S r1 It can be any type of wave, such as a triangular wave, sawtooth wave, trapezoidal wave, or straight line.

[0158] In some embodiments, the second feedback circuit 1440 may include a multiplier 1442 and a low-pass filter 1444.

[0159] In the second feedback circuit 1440, the multiplier 1442 can be based on the frequency discrimination signal S f With the second reference signal S r2 Output phase detection signal Low-pass filter 1444 receives phase detection signal Then, it is low-pass filtered to output the second feedback signal S. b2 To phase modulator 1424. Phase modulator 1424 adjusts the optical path of waveguide arm 14228 by applying an external electric field, so that the operating point phase of the Mach-Zehnder interferometer is adjusted. To stabilize the operating point of the Mach-Zehnder interferometer.

[0160] In some embodiments, the second reference signal S r2 It can be represented by the following formula (8).

[0161] s(t)=sin(2πτkt) (8)

[0162] Combining formulas (6) and (8), multiplier 1442 is based on the frequency discrimination signal S. f Second reference signal S r2 Output phase detection signal It can be represented by the following formula (9).

[0163]

[0164] Low-pass filter 1444 receives phase detection signal Then, the second feedback signal S is output after low-pass filtering. b2 It can be represented by the following formula (10).

[0165]

[0166] The frequency modulation nonlinear deviation δ has a large bandwidth and varies at high frequencies. In comparison, It's just a low-frequency change. By setting the low-pass filter 1444, the second feedback circuit 1440 feeds back the low frequency. Used to adjust the operating point of the frequency discriminator.

[0167] Based on the second feedback signal S b2 The feedback phase change can eliminate the nonlinear deviation of the frequency-modulated light at the frequency corresponding to the operating point of the frequency discriminator, so that the frequency corresponding to the operating point of the frequency discriminator is consistent with the real-time frequency of the frequency-modulated light emitted by the light source.

[0168] This disclosure also provides a lidar. The lidar includes the circuitry described in any of the foregoing embodiments for emitting linearly frequency-modulated light.

[0169] In some embodiments, the lidar includes a frequency-modulated light source, a receiving component, and a processor. The frequency-modulated light source may include circuitry for emitting linearly frequency-modulated light, as described in the foregoing embodiments of this disclosure. The frequency-modulated light source can generate a local oscillator light and a probe light signal. The probe light signal is emitted outside the lidar and, after being reflected by an object, forms an echo light signal. The receiving component receives the echo light signal. The receiving component can also beat the local oscillator light and the echo light signal to obtain a beat frequency signal. The receiving component may, for example, include a detector that can convert the beat frequency signal into an electrical signal. The processor can obtain one or more pieces of information, such as the distance and velocity of the object, based on the electrical signal obtained from the beat frequency signal conversion.

[0170] The lidar using some embodiments of this disclosure emits linearly frequency-modulated light that meets preset linearity requirements through a circuit for emitting linearly frequency-modulated light, thereby obtaining accurate detection results and improving the detection accuracy and reliability of the lidar.

[0171] Processors can be implemented as application-specific integrated circuits (ASICs), or as hardware circuits implemented with programmable logic devices (PLDs), such as field-programmable gate arrays (FPGAs), microcontroller units (MCUs), or digital signal processors (DSPs), which provide high processing efficiency. In other implementations, a central processing unit (CPU) can also be selected.

[0172] In this disclosure, unless otherwise expressly specified and limited, ordinal numbers, such as "first," "second," etc., are used only to distinguish and describe related objects, and should not be construed as indicating or implying the relative importance or order between related objects. Furthermore, ordinal numbers do not represent the quantity of related objects.

[0173] The terms "or" and "and / or" in this disclosure are used to describe relationships between related objects, indicating a non-exclusive inclusion. For example, "A and / or B" and "A or B" can both include: "A alone," "B alone," or "A and B," where "A" and "B" can include a single object or multiple objects. Similarly, "A, B and / or C," "A, B or C," and "A, B and C" can both include: "A alone," "B alone," "C alone," "A and B," "A and C," "B and C," or "A, B and C," where "A," "B," and "C" can include a single object or multiple objects. Additionally, the " / " in this disclosure is used to indicate an "or" relationship between related objects. The meanings of "at least one of A or B" and "one or more of A and B" in this disclosure are the same as the meaning of "A or B" above. The meanings of "one or more of A, B, and C" and "at least one of A, B, or C" are the same as the meaning of "A, B, or C" above. The meaning of "one or more of A, B, and C" is the same as the meaning of "A, B, or C" above.

[0174] In the above embodiments, the descriptions of each embodiment have their own emphasis. Parts not described in detail or recorded in a certain embodiment can be referred to in the relevant descriptions of other embodiments. Furthermore, the above embodiments can be freely combined as needed. Although the embodiments of this disclosure have been disclosed above, this disclosure is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of this disclosure.

Claims

1. A circuit for emitting linear frequency modulated light, comprising: The light source is configured to emit frequency-modulated light; A frequency discrimination circuit, coupled to the light source, is configured to output a frequency discrimination signal; The first feedback circuit has its input terminal coupled to the frequency discrimination circuit and its output terminal coupled to the light source. It is configured to output a first feedback signal based on the frequency discrimination signal and the first reference signal to adjust the linearity of the frequency-modulated light.

2. The circuit according to claim 1, characterized in that, The first feedback circuit includes: The subtractor is configured to output an error signal based on the frequency discrimination signal and the first reference signal; A PID controller, coupled to the subtractor, is configured to receive the error signal and output the first feedback signal.

3. The circuit according to claim 1, characterized in that, The frequency discrimination circuit includes: Frequency discriminator; A phase modulation circuit, coupled to the frequency discriminator, is configured to adjust the operating point of the frequency discriminator based on a second feedback signal.

4. The circuit according to claim 3, characterized in that, Also includes: The second feedback circuit, coupled to the frequency discrimination circuit, is configured to receive the frequency discrimination signal and the second reference signal, and output a second feedback signal to the phase modulation circuit to adjust the operating point of the frequency discrimination circuit.

5. The circuit according to claim 4, characterized in that, The second feedback circuit includes at least one of the following: Analog signal processing circuit; or Digital signal processing circuit.

6. The circuit according to claim 5, characterized in that, The analog signal processing circuit includes: The multiplier is configured to output a phase detection signal based on the frequency discrimination signal and the second reference signal; A filter, coupled to the multiplier, is configured to receive the phase detection signal and output the second feedback signal.

7. The circuit according to claim 5, characterized in that, The digital signal processing circuit is configured to perform at least one of Hilbert transform and sine signal fitting on the frequency discrimination signal to determine the second feedback signal.

8. The circuit according to claim 3, characterized in that, The frequency discriminator includes any of the following: Mach-Zehnder interferometer, Fiber Bragg grating Bandpass filter, Fabry-Perot resonator, or Microrings.

9. The circuit according to claim 3, characterized in that, The phase modulation circuit includes at least one of the following: Phase modulator, Semiconductor optical amplifier, piezoelectric ceramics Thermally adjustable phase shifter, or Electrically adjustable phase shifter.

10. The circuit according to claim 3, characterized in that, The frequency discrimination circuit also includes: The balanced detection circuit has its input terminal coupled to the frequency discriminator and its output terminal coupled to the first feedback circuit and the second feedback circuit.

11. The circuit according to claim 10, characterized in that, The balance detection circuit includes: A first photodetector and a second photodetector, wherein the anode of the first photodetector is coupled to the cathode of the second photodetector, and the first photodetector and the second photodetector are configured to convert optical signals into electrical signals.

12. A lidar, comprising: The circuit for emitting linear frequency modulated light according to any one of claims 1-11.

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