A laser radar that emits local oscillator light and phase coding signal simultaneously

Abstract

The present invention belongs to the technical field of laser radar ranging and speed measurement, and discloses a laser radar that simultaneously transmits local oscillator light and phase coded signal, including a continuous laser, an amplitude modulator, a phase modulator, an optical fiber amplifier, a transmitting telescope, a receiving telescope, a circulator, a polarization-independent interferometer chip, two photodetectors, a differential circuit and a main control module, wherein the main control module is used to drive the amplitude modulator to generate random binary bits to form a coding sequence to drive the phase modulator, and convert the in-phase component and the orthogonal component of the signal light output by the differential circuit into a decoding sequence, and perform correlation operations on the coding sequence and the decoding sequence to obtain the distance information of the target. Compared with the prior art, the present invention can greatly reduce the influence of the decoherence effect because the signal light and the local oscillator light experience the same path. In addition, the echo signal of any polarization can be received, and the background noise in the echo signal can be greatly reduced, thereby improving the signal-to-noise ratio of the system.

Description

Technical Field

[0001] The present invention relates to the technical field of laser radar ranging and speed measurement, and in particular to a laser radar that emits local oscillator light and a phase coding signal simultaneously. Background Art

[0002] Radar plays a very important role in the fields of military, civil aviation, and autonomous driving. LiDAR uses short-wavelength lasers as information carriers, so it has a higher resolution and can be used to detect, track, and identify targets, as well as perform distance measurement and imaging.

[0003] Signal-to-noise ratio is a very important indicator in laser radar detection, which can directly affect the performance of the system. In the prior art, laser radars using the photon counting method can achieve a longer ranging range. This is because the single-photon detector has a higher sensitivity, but it needs to be cooled to below -30°C to reduce dark counts when working, so the cost and complexity are high, which is not conducive to miniaturization. For daylight background noise, it can only be filtered through a filter. While filtering the noise, the real signal will have a certain loss. Therefore, the signal-to-noise ratio is low during the day, and it is difficult to work normally. Coherent laser radar has a natural filtering effect. Using local oscillator light and real echo signals for coherent detection can not only filter out irrelevant background noise, but also have a certain gain. However, at long distances, due to the more significant decoherence effect of the echo signal, the phase relationship between the local oscillator light and the echo signal cannot be determined, making coherent detection difficult. Summary of the invention

[0004] In view of the above defects in the prior art, the present invention proposes a laser radar that emits local oscillator light and phase coding signal simultaneously.

[0005] The technical solution of the present invention is achieved in this way:

[0006] A laser radar that simultaneously transmits local oscillator light and phase coding signal, comprising:

[0007] Continuous laser CWL, used to generate continuous laser signal;

[0008] Amplitude modulator AM, used to chop the continuous laser signal to generate signal light and local oscillator light pulses with a time interval of T and alternating appearance;

[0009] The phase modulator PM is used to modulate the phase of the signal light to 0 or π;

[0010] Fiber amplifier, used to amplify signal light and local oscillator light;

[0011] A transmitting telescope is used to expand the amplified signal light and local oscillator light and illuminate the target;

[0012] a receiving telescope for receiving an echo signal reflected from a target;

[0013] A polarization-independent interferometer chip, comprising an unequal-arm interferometer, for interfering the signal light in the echo signal with the local oscillator light to generate a first interference result and a second interference result; and for causing the background noise signal in the echo signal to be emitted from its two ports with equal amplitude;

[0014] The delay difference between the long and short arms of the unequal-arm interferometer chip of the polarization-independent interferometer is T, and a phase shifter is provided on the long arm to stabilize the phase difference between the long and short arms at π / 4;

[0015] A circulator CIR, used for transmitting the echo signal to an input port of the polarization-independent interferometer chip, and transmitting the first interference result to the first photodetector PD1;

[0016] The first photodetector PD1 and the second photodetector PD2 are used to detect the amplitudes of the first interference result and the second interference result respectively;

[0017] A differential circuit, used for differentiating the output electrical signals of the first photodetector PD1 and the second photodetector PD2 to obtain an alternating in-phase component and a quadrature component of the signal light, and eliminating background noise signals;

[0018] The main control module is used to drive the amplitude modulator AM, generate random binary bits to form a coding sequence to drive the phase modulator PM, and convert the in-phase component and orthogonal component of the signal light output by the differential circuit into a decoding sequence, and perform correlation operations on the coding sequence and the decoding sequence to obtain the distance information of the target.

[0019] Preferably, the polarization-independent interferometer chip comprises a beam splitter BS, a first polarization beam splitter PBS1 and a first phase shifter PS1.

[0020] The two input ports of the beam splitter BS serve as two ports of the polarization-independent interferometer chip respectively;

[0021] The two output ports of the beam splitter BS are connected to the two input ports of the first polarization beam splitter PBS1 through waveguides of different lengths; the first phase shifter PS1 is located on the longer waveguide;

[0022] The two output ports of the first polarization beam splitter PBS1 are directly connected through a waveguide to form a Sagnac ring.

[0023] Preferably, the polarization-independent interferometer chip comprises a second polarization beam splitter PBS2, a third polarization beam splitter PBS3, a fourth polarization beam splitter PBS4, a first half-wave plate HWP1, a second half-wave plate HWP2 and a second phase shifter PS2.

[0024] The two input ports of the second polarization beam splitter PBS2 are respectively used as the two ports of the polarization-independent interferometer chip; the two output ports thereof are respectively connected to the input port of the third polarization beam splitter PBS3 and the input port of the fourth polarization beam splitter PBS4 through the first optical waveguide and the second optical waveguide of equal length;

[0025] The first half-wave plate HWP1 and the second half-wave plate HWP2 are arranged to vertically penetrate the first optical waveguide and the second optical waveguide respectively;

[0026] The angles between the main axis directions of the first half-wave plate HWP1 and the second half-wave plate HWP2 and the polarization direction of the TE mode of the optical waveguide are both 22.5°;

[0027] The two output ports of the third polarization beam splitter PBS3 and the two output ports of the fourth polarization beam splitter PBS4 are respectively connected through optical waveguides of unequal lengths to form an unequal-arm interferometer; the second phase shifter PS2 is located on the longer waveguide.

[0028] Preferably, the polarization-independent interferometer chip comprises a second polarization beam splitter PBS2, a fifth polarization beam splitter PBS5, a third half-wave plate HWP3 and a third phase shifter PS3.

[0029] The two input ports of the second polarization beam splitter PBS2 are respectively used as the two ports of the polarization-independent interferometer chip; the two output ports thereof are respectively connected to an input port and an output port of the fifth polarization beam splitter PBS5 through a first optical waveguide and a second optical waveguide of equal length;

[0030] The third half-wave plate HWP3 is arranged to vertically penetrate the first optical waveguide and the second optical waveguide;

[0031] The angle between the main axis direction of the third half-wave plate HWP3 and the polarization direction of the TE mode of the optical waveguide is 22.5°;

[0032] Another input port and another output port of the fifth polarization beam splitter PBS5 are directly connected via an optical waveguide provided with a third phase shifter PS3 to form a long arm of an unequal-arm interferometer.

[0033] Preferably, the intensity of the local oscillation light is more than 100 times the intensity of the signal light.

[0034] Preferably, the time interval T between the signal light and the local oscillator light is no more than 1 ns.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] The present invention proposes a laser radar that emits local oscillator light and phase coded signal simultaneously, by irradiating the local oscillator light and phase coded signal to the target at the same time, using a polarization-independent unequal-arm interferometer chip and a pair of photodetectors to form a time-division multiplexing heterodyne detector to measure the in-phase component and the orthogonal component of the signal for decoding. Since the signal light and the local oscillator light experience the same path, the influence of the decoherence effect can be greatly reduced. In addition, the echo signal of any polarization can be received, and the background noise in the echo signal can be greatly reduced, thereby improving the signal-to-noise ratio of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 The schematic diagram of the laser radar of the present invention that emits the local oscillator light and the phase coding signal simultaneously;

[0038] Figure 2 This is a schematic diagram of a first embodiment of a laser radar that simultaneously transmits local oscillator light and phase coding signal according to the present invention;

[0039] Figure 3 This is a schematic diagram of a second embodiment of a laser radar that simultaneously transmits local oscillator light and phase coding signal according to the present invention;

[0040] Figure 4 This is a schematic diagram of a third embodiment of a laser radar in which local oscillation light and a phase coding signal are emitted simultaneously according to the present invention. DETAILED DESCRIPTION

[0041] The present invention will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present invention.

[0042] like Figure 1 As shown, a laser radar that simultaneously transmits local oscillator light and phase coding signal includes a continuous laser CWL, an amplitude modulator AM, a phase modulator PM, an optical fiber amplifier, a transmitting telescope, a receiving telescope, a circulator CIR, a polarization-independent interferometer chip, a first photodetector PD1, a second photodetector PD2, a differential circuit and a main control module.

[0043] The continuous laser CWL is used to generate a continuous laser signal;

[0044] The amplitude modulator AM is used to chop the continuous laser signal to generate signal light and local oscillator light pulses with a time interval of T and appearing alternately;

[0045] The phase modulator PM is used to modulate the phase of the signal light to 0 or π;

[0046] The fiber amplifier is used to amplify the signal light and the local oscillator light;

[0047] The transmitting telescope is used to expand the amplified signal light and the local oscillator light and irradiate them to the target;

[0048] The receiving telescope is used to receive the echo signal reflected from the target;

[0049] The polarization-independent interferometer chip includes an unequal-arm interferometer, which is used to interfere the signal light in the echo signal with the local oscillator light to generate a first interference result and a second interference result; and is used to make the background noise signal in the echo signal be emitted from its two ports with equal amplitude;

[0050] The delay difference between the long and short arms of the unequal-arm interferometer chip of the polarization-independent interferometer is T, and a phase shifter is provided on the long arm to stabilize the phase difference between the long and short arms at π / 4;

[0051] The CIR is used to transmit the echo signal to an input port of the polarization-independent interferometer chip, and transmit the first interference result to the first photodetector PD1;

[0052] The first photodetector PD1 and the second photodetector PD2 are used to detect the amplitudes of the first interference result and the second interference result respectively;

[0053] The differential circuit is used to differentiate the output electrical signals of the first photodetector PD1 and the second photodetector PD2 to obtain the alternating in-phase component and quadrature component of the signal light, and eliminate the background noise signal;

[0054] The main control module is used to drive the amplitude modulator AM, generate random binary bits to form a coding sequence to drive the phase modulator PM, and convert the in-phase component and the orthogonal component of the signal light output by the differential circuit into a decoding sequence, and perform correlation operation on the coding sequence and the decoding sequence to obtain the distance information of the target.

[0055] The specific working process is as follows:

[0056] The continuous laser CWL generates a narrow linewidth continuous optical signal. The main control module drives the amplitude modulator AM to chop the continuous optical signal to generate signal light and local oscillator light pulses that appear alternately with a time interval of T. The main control module generates random binary bits to form a coding sequence, and drives the phase modulator PM to perform random 0 or π phase modulation on the signal light pulse, that is, the coding sequence, thereby obtaining a coded optical signal in which the local oscillator light and the phase-coded signal light appear at intervals. The coded optical signal is then amplified to a predetermined power by a fiber amplifier, expanded by a transmitting telescope, and irradiated to the target.

[0057] After being reflected by the target, the coded light signal enters the receiving telescope and becomes an echo signal, which then enters the polarization-independent interferometer chip through the CIR for decoding. In the echo signal of any polarization state, the local oscillator light has the same polarization as the signal light. Assume that the i-th local oscillator light and signal light After entering the polarization-independent interferometer chip, the two beams are split into components with the same amplitude by the unequal-arm interferometer, and go through the long arm and short arm of the unequal-arm interferometer respectively, that is, and .like Figure 2 As shown, when interfering, and , and When the signal light phase code is 0, since the phase of each local oscillator light pulse is the same, the phase difference between the long and short arms of the unequal arm interferometer is adjusted to π / 4 by using the phase shift module. and The phase difference is π / 4, and The phase difference is -π / 4, so the phase difference of the local oscillator light when the signal light is measured by the local oscillator light at two moments is π / 2. The homodyne detector composed of the first photodetector PD1, the second photodetector PD2 and the differential circuit can realize the measurement of the signal light. The in-phase component and the orthogonal component of Figure 2 It can also be seen that and , and The signal light is also interfered with Therefore, the result of the differential circuit is the alternating in-phase component and quadrature component of the signal light.

[0058] Since the background noise signal accompanying the local oscillator light and the signal light in the echo signal has a random phase and does not interfere, the noise amplitude emitted from the two ports of the polarization-independent interferometer chip is the same, that is, , which can be eliminated through the differential circuit.

[0059] The phase result of the signal light is obtained by using the in-phase component and quadrature component of the signal light output by the differential circuit and converted into a decoding sequence. The encoding sequence is shifted bit by bit and cross-correlated with the decoding sequence to obtain the cross-correlation value at each shift. When the cross-correlation value reaches the peak, it indicates that the sending and receiving sequences correspond one to one. The corresponding target distance can be obtained by the number of bits shifted, realizing the ranging function.

[0060] like Figure 2 As shown, the first embodiment of the present invention:

[0061] The polarization-independent interferometer chip comprises a beam splitter BS, a first polarization beam splitter PBS1 and a first phase shifter PS1.

[0062] The two input ports of the beam splitter BS serve as two ports of the polarization-independent interferometer chip respectively;

[0063] The two output ports of the beam splitter BS are connected to the two input ports of the first polarization beam splitter PBS1 through waveguides of different lengths; the first phase shifter PS1 is located on the longer waveguide;

[0064] The two output ports of the first polarization beam splitter PBS1 are directly connected through a waveguide to form a Sagnac ring.

[0065] The specific working process of embodiment 1 is as follows:

[0066] The continuous laser CWL generates a narrow linewidth continuous optical signal. The main control module drives the amplitude modulator AM to chop the continuous optical signal to generate signal light and local oscillator light pulses that appear alternately with a time interval of T. The main control module generates random binary bits to form a coding sequence, and drives the phase modulator PM to perform random 0 or π phase modulation on the signal light pulse, that is, the coding sequence, thereby obtaining a coded optical signal in which the local oscillator light and the phase-coded signal light appear at intervals. The coded optical signal is then amplified to a predetermined power by a fiber amplifier, expanded by a transmitting telescope, and irradiated to the target.

[0067] After being reflected by the target, the coded light signal enters the receiving telescope and becomes an echo signal, which then enters the polarization-independent interferometer chip through the CIR for decoding. In the echo signal of any polarization state, the local oscillator light has the same polarization as the signal light. Assume that the i-th local oscillator light and signal light After entering the polarization-independent interferometer chip, the two are first split into components with the same amplitude by the beam splitter BS of the unequal-arm interferometer, and then go through the long arm and short arm of the unequal-arm interferometer respectively, that is, and .in and Going along the long arm, they enter an input port of the first polarization beam splitter PBS1. The TE polarization components of the two are directly transmitted, propagating in the clockwise direction in the Sagnac ring, and are still TE polarization; the TM polarization components of the two are reflected, propagating in the counterclockwise direction in the Sagnac ring, and become TE polarization. The two polarization components return to the first polarization beam splitter PBS1 for polarization beam combination, and the TE polarization and TM polarization are exchanged, and they return to the beam splitter BS after propagating through the long arm. and Going through the short arm, they enter the other input port of the first polarization beam splitter PBS1. The TM polarization components of the two are directly transmitted, propagating in the counterclockwise direction in the Sagnac ring, and are still TM polarization; the TE polarization components of the two are reflected, propagating in the clockwise direction in the Sagnac ring, and become TM polarization. The two polarization components return to the first polarization beam splitter PBS1 for polarization beam combining, and the TE polarization and TM polarization are exchanged. After propagating through the short arm, they return to the beam splitter BS. Figure 2 As shown, and , and When the signal light phase is coded as 0, the phase of each local oscillator light pulse is the same. The first phase shifter PS1 is used to adjust the phase difference between the long and short arms of the unequal-arm interferometer to π / 4. and The phase difference is π / 4, and The phase difference is -π / 4, so the phase difference of the local oscillator light when the signal light is measured by the local oscillator light at two moments is π / 2. The homodyne detector composed of the first photodetector PD1, the second photodetector PD2 and the differential circuit can realize the measurement of the signal light. The in-phase component and the orthogonal component of Figure 2 It can also be seen that and , and The signal light is also interfered with Therefore, the result of the differential circuit is the alternating in-phase component and quadrature component of the signal light.

[0068] Since the background noise signal accompanying the local oscillator light and the signal light in the echo signal has a random phase and does not interfere, the noise amplitude emitted from the two ports of the polarization-independent interferometer chip is the same, that is, , which can be eliminated through the differential circuit.

[0069] The phase result of the signal light is obtained by using the in-phase component and quadrature component of the signal light output by the differential circuit and converted into a decoding sequence. The encoding sequence is shifted bit by bit and cross-correlated with the decoding sequence to obtain the cross-correlation value at each shift. When the cross-correlation value reaches the peak, it indicates that the sending and receiving sequences correspond one to one. The corresponding target distance can be obtained by the number of bits shifted, realizing the ranging function.

[0070] like Figure 3 As shown, the second embodiment of the present invention:

[0071] The polarization-independent interferometer chip comprises a second polarization beam splitter PBS2, a third polarization beam splitter PBS3, a fourth polarization beam splitter PBS4, a first half-wave plate HWP1, a second half-wave plate HWP2, and a second phase shifter PS2.

[0072] The two input ports of the second polarization beam splitter PBS2 are respectively used as the two ports of the polarization-independent interferometer chip; the two output ports thereof are respectively connected to the input port of the third polarization beam splitter PBS3 and the input port of the fourth polarization beam splitter PBS4 through the first optical waveguide and the second optical waveguide of equal length;

[0073] The first half-wave plate HWP1 and the second half-wave plate HWP2 are arranged to vertically penetrate the first optical waveguide and the second optical waveguide respectively;

[0074] The angles between the main axis directions of the first half-wave plate HWP1 and the second half-wave plate HWP2 and the polarization direction of the TE mode of the optical waveguide are both 22.5°;

[0075] The two output ports of the third polarization beam splitter PBS3 and the two output ports of the fourth polarization beam splitter PBS4 are respectively connected through optical waveguides of unequal lengths to form an unequal-arm interferometer; the second phase shifter PS2 is located on the longer waveguide.

[0076] The specific working process of the second embodiment is as follows:

[0077] The continuous laser CWL generates a narrow linewidth continuous optical signal. The main control module drives the amplitude modulator AM to chop the continuous optical signal to generate signal light and local oscillator light pulses that appear alternately with a time interval of T. The main control module generates random binary bits to form a coding sequence, and drives the phase modulator PM to perform random 0 or π phase modulation on the signal light pulse, that is, the coding sequence, thereby obtaining a coded optical signal in which the local oscillator light and the phase-coded signal light appear at intervals. The coded optical signal is then amplified to a predetermined power by a fiber amplifier, expanded by a transmitting telescope, and irradiated to the target.

[0078] After being reflected by the target, the coded light signal enters the receiving telescope and becomes an echo signal, which then enters the polarization-independent interferometer chip through the CIR for decoding. In the echo signal of any polarization state, the local oscillator light has the same polarization as the signal light. Assume that the i-th local oscillator light and signal light After entering the polarization-independent interferometer chip, the two are first polarized and split into TE mode and TM mode by the second polarization beam splitter PBS2.

[0079] The TE mode local oscillator light and signal light The component is polarized by 45° after passing through the first half-wave plate HWP1 and is polarized by the third polarization beam splitter PBS3 to generate components that propagate along the long and short arms of the unequal-arm interferometer. and .like Figure 2 As shown, and , and They meet at the fourth polarization beam splitter PBS4, and the two are polarized and combined. After reaching the second half-wave plate HWP2, they interfere to produce two interference components, TE mode and TM mode, respectively. They are then polarized and split by the second polarization beam splitter PBS2 to produce the first TE interference result and the second TE interference result. When the signal light phase encoding is 0, since the phase of each local oscillator light pulse is the same, the second phase shifter PS2 is used to adjust the phase difference between the long and short arms of the unequal arm interferometer to π / 4. It can be seen that and The phase difference is π / 4, and The phase difference is -π / 4, so the phase difference of the local oscillator light when the signal light is measured by the local oscillator light at two moments is π / 2. The homodyne detector composed of the first photodetector PD1, the second photodetector PD2 and the differential circuit can realize the measurement of the signal light. The in-phase component and the orthogonal component of Figure 2 It can also be seen that and , and Polarization interference is performed separately, and the signal light is also realized Therefore, the result of the differential circuit is the alternating in-phase component and quadrature component of the signal light.

[0080] TM mode local oscillator light and signal light The component is polarized by 45° after passing through HWP2, and is polarized by the fourth polarization beam splitter PBS4, and undergoes the same process in the opposite direction to the component of the TE mode, thereby generating a first TM interference result and a second TM interference result;

[0081] Since the elapsed time is the same, the first TE interference result and the first TM interference result are emitted from one input port of the second polarization beam splitter PBS2 at the same time, and polarization synthesis is performed to generate the first interference result; the second TE interference result and the second TM interference result are emitted from the other input port of the first polarization beam splitter PBS1 at the same time, and polarization synthesis is performed to generate the second interference result. Since the second integrated optical chip performs polarization splitting on the echo optical signal of any polarization state, and then performs polarization synthesis after interference, the generated interference result is independent of polarization.

[0082] Since the background noise signal accompanying the local oscillator light and the signal light in the echo signal has a random phase and does not interfere, the noise amplitude emitted from the two ports of the polarization-independent interferometer chip is the same, that is, , which can be eliminated through the differential circuit.

[0083] The phase result of the signal light is obtained by using the in-phase component and quadrature component of the signal light output by the differential circuit and converted into a decoding sequence. The encoding sequence is shifted bit by bit and cross-correlated with the decoding sequence to obtain the cross-correlation value at each shift. When the cross-correlation value reaches the peak, it indicates that the sending and receiving sequences correspond one to one. The corresponding target distance can be obtained by the number of bits shifted, realizing the ranging function.

[0084] like Figure 4 As shown, the third embodiment of the present invention:

[0085] The polarization-independent interferometer chip comprises a second polarization beam splitter PBS2, a fifth polarization beam splitter PBS5, a third half-wave plate HWP3 and a third phase shifter PS3.

[0086] The two input ports of the second polarization beam splitter PBS2 are respectively used as the two ports of the polarization-independent interferometer chip; the two output ports thereof are respectively connected to an input port and an output port of the fifth polarization beam splitter PBS5 through a first optical waveguide and a second optical waveguide of equal length;

[0087] The third half-wave plate HWP3 is arranged to vertically penetrate the first optical waveguide and the second optical waveguide;

[0088] The angle between the main axis direction of the third half-wave plate HWP3 and the polarization direction of the TE mode of the optical waveguide is 22.5°;

[0089] Another input port and another output port of the fifth polarization beam splitter PBS5 are directly connected via an optical waveguide provided with a third phase shifter PS3 to form a long arm of an unequal-arm interferometer.

[0090] The specific working process of the third embodiment is as follows:

[0091] The continuous laser CWL generates a narrow linewidth continuous optical signal. The main control module drives the amplitude modulator AM to chop the continuous optical signal to generate signal light and local oscillator light pulses that appear alternately with a time interval of T. The main control module generates random binary bits to form a coding sequence, and drives the phase modulator PM to perform random 0 or π phase modulation on the signal light pulse, that is, the coding sequence, thereby obtaining a coded optical signal in which the local oscillator light and the phase-coded signal light appear at intervals. The coded optical signal is then amplified to a predetermined power by a fiber amplifier, expanded by a transmitting telescope, and irradiated to the target.

[0092] After being reflected by the target, the coded light signal enters the receiving telescope and becomes an echo signal, which then enters the polarization-independent interferometer chip through the CIR for decoding. In the echo signal of any polarization state, the local oscillator light has the same polarization as the signal light. Assume that the i-th local oscillator light and signal light After entering the polarization-independent interferometer chip, the two are first polarized and split into TE mode and TM mode by the second polarization beam splitter PBS2.

[0093] The TE mode local oscillator light and signal light The component is polarized by 45° after passing through the third half-wave plate HWP3 and is polarized by the fifth polarization beam splitter PBS5 to generate components that propagate along the long and short arms of the unequal-arm interferometer. and .like Figure 2 As shown, and , and They meet at the fifth polarization beam splitter PBS5, and the two are polarized and combined. After reaching the third half-wave plate HWP3, they interfere to generate two interference components, TE mode and TM mode, respectively. They are then polarized and split by the second polarization beam splitter PBS2 to generate the first TE interference result and the second TE interference result. When the signal light phase encoding is 0, since the phase of each local oscillator light pulse is the same, the third phase shifter PS3 is used to adjust the phase difference between the long and short arms of the unequal arm interferometer to π / 4. It can be seen that and The phase difference is π / 4, and The phase difference is -π / 4, so the phase difference of the local oscillator light when the signal light is measured by the local oscillator light at two moments is π / 2. The homodyne detector composed of the first photodetector PD1, the second photodetector PD2 and the differential circuit can realize the measurement of the signal light. The in-phase component and the orthogonal component of Figure 2 It can also be seen that and , and Polarization interference is performed separately, and the signal light is also realized Therefore, the result of the differential circuit is the alternating in-phase component and quadrature component of the signal light.

[0094] TM mode local oscillator light and signal light The component is polarized by 45° after passing through the third half-wave plate HWP3, and is polarized by the fifth polarization beam splitter PBS5, and undergoes the same process in the opposite direction to the component of the TE mode, thereby generating the first TM interference result and the second TM interference result;

[0095] Since the elapsed time is the same, the first TE interference result and the first TM interference result are emitted from one input port of the second polarization beam splitter PBS2 at the same time, and polarization synthesis is performed to generate the first interference result; the second TE interference result and the second TM interference result are emitted from the other input port of the first polarization beam splitter PBS1 at the same time, and polarization synthesis is performed to generate the second interference result. Since the second integrated optical chip performs polarization splitting on the echo optical signal of any polarization state, and then performs polarization synthesis after interference, the generated interference result is independent of polarization.

[0096] Since the background noise signal accompanying the local oscillator light and the signal light in the echo signal has a random phase and does not interfere, the noise amplitude emitted from the two ports of the polarization-independent interferometer chip is the same, that is, , which can be eliminated through the differential circuit.

[0097] The phase result of the signal light is obtained by using the in-phase component and quadrature component of the signal light output by the differential circuit and converted into a decoding sequence. The encoding sequence is shifted bit by bit and cross-correlated with the decoding sequence to obtain the cross-correlation value at each shift. When the cross-correlation value reaches the peak, it indicates that the sending and receiving sequences correspond one to one. The corresponding target distance can be obtained by the number of bits shifted, realizing the ranging function.

[0098] It can be seen from the various embodiments of the present invention that the present invention proposes a laser radar that simultaneously transmits local oscillator light and phase-coded signal, by irradiating the local oscillator light and phase-coded signal to the target at the same time, using a polarization-independent unequal-arm interferometer chip and a pair of photodetectors to form a time-division multiplexing heterodyne detector to measure the in-phase component and the orthogonal component of the signal for decoding. Since the signal light and the local oscillator light experience the same path, the influence of the decoherence effect can be greatly reduced. In addition, the echo signal of any polarization can be received, and the background noise in the echo signal can be greatly reduced, thereby improving the signal-to-noise ratio of the system.

Claims

1. A laser radar that emits local oscillator light and phase coded signal simultaneously, It is characterized in that include: Continuous laser CWL, used to generate continuous laser signal; Amplitude modulator AM, used to chop the continuous laser signal to generate signal light and local oscillator light pulses with a time interval of T and alternating appearance; A phase modulator PM is used to modulate the phase of the signal light to 0 or π; Fiber amplifier, used to amplify signal light and local oscillator light; A transmitting telescope is used to expand the amplified signal light and local oscillator light and illuminate the target; a receiving telescope for receiving an echo signal reflected from a target; A polarization-independent interferometer chip, comprising an unequal-arm interferometer, for interfering the signal light in the echo signal with the local oscillator light to generate a first interference result and a second interference result; and for making the background noise signal in the echo signal be emitted from its two ports with equal amplitude; The delay difference between the long and short arms of the unequal-arm interferometer chip of the polarization-independent interferometer is T, and a phase shifter is provided on the long arm to stabilize the phase difference between the long and short arms at π / 4; A circulator CIR, used for transmitting the echo signal to an input port of the polarization-independent interferometer chip, and transmitting the first interference result to the first photodetector PD1; The first photodetector PD1 and the second photodetector PD2 are used to detect the amplitudes of the first interference result and the second interference result respectively; A differential circuit, used for differentiating the output electrical signals of the first photodetector PD1 and the second photodetector PD2 to obtain an alternating in-phase component and a quadrature component of the signal light, and eliminating background noise signals; The main control module is used to drive the amplitude modulator AM, generate random binary bits to form a coding sequence to drive the phase modulator PM, and convert the in-phase component and orthogonal component of the signal light output by the differential circuit into a decoding sequence, and perform correlation operations on the coding sequence and the decoding sequence to obtain the distance information of the target.

2. The laser radar according to claim 1 that emits local oscillator light and phase coded signal simultaneously, It is characterized in that The polarization-independent interferometer chip comprises a beam splitter BS, a first polarization beam splitter PBS1 and a first phase shifter PS1. The two input ports of the beam splitter BS serve as two ports of the polarization-independent interferometer chip respectively; The two output ports of the beam splitter BS are connected to the two input ports of the first polarization beam splitter PBS1 through waveguides of different lengths; the first phase shifter PS1 is located on the longer waveguide; The two output ports of the first polarization beam splitter PBS1 are directly connected through a waveguide to form a Sagnac ring.

3. The laser radar according to claim 1 that emits local oscillator light and phase coded signal simultaneously, It is characterized in that The polarization-independent interferometer chip comprises a second polarization beam splitter PBS2, a third polarization beam splitter PBS3, a fourth polarization beam splitter PBS4, a first half-wave plate HWP1, a second half-wave plate HWP2, and a second phase shifter PS2. The two input ports of the second polarization beam splitter PBS2 are respectively used as two ports of the polarization-independent interferometer chip; Its two output ports are connected to the input port of the third polarization beam splitter PBS3 and the input port of the fourth polarization beam splitter PBS4 through the first optical waveguide and the second optical waveguide of equal length respectively; The first half-wave plate HWP1 and the second half-wave plate HWP2 are arranged to vertically penetrate the first optical waveguide and the second optical waveguide respectively; The angles between the main axis directions of the first half-wave plate HWP1 and the second half-wave plate HWP2 and the polarization direction of the TE mode of the optical waveguide are both 22.5°; The two output ports of the third polarization beam splitter PBS3 and the two output ports of the fourth polarization beam splitter PBS4 are respectively connected through optical waveguides of unequal lengths to form an unequal-arm interferometer; The second phase shifter PS2 is located on the longer waveguide.

4. The laser radar according to claim 1 that emits local oscillator light and phase coded signal simultaneously, It is characterized in that The polarization-independent interferometer chip comprises a second polarization beam splitter PBS2, a fifth polarization beam splitter PBS5, a third half-wave plate HWP3 and a third phase shifter PS3. The two input ports of the second polarization beam splitter PBS2 are respectively used as two ports of the polarization-independent interferometer chip; Its two output ports are connected to an input port and an output port of a fifth polarization beam splitter PBS5 through a first optical waveguide and a second optical waveguide of equal length, respectively; The third half-wave plate HWP3 is arranged to vertically penetrate the first optical waveguide and the second optical waveguide; The angle between the main axis direction of the third half-wave plate HWP3 and the polarization direction of the TE mode of the optical waveguide is 22.5°; Another input port and another output port of the fifth polarization beam splitter PBS5 are directly connected via an optical waveguide provided with a third phase shifter PS3 to form a long arm of an unequal-arm interferometer.

5. A laser radar that simultaneously transmits local oscillator light and phase coded signal according to any one of claims 1 to 4, It is characterized in that The intensity of the local oscillation light is more than 100 times that of the signal light.

6. A laser radar that simultaneously emits local oscillator light and phase coded signal according to any one of claims 1 to 4, It is characterized in that The time interval T between the signal light and the local oscillator light is no more than 1ns.

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