A phase-coded laser radar based on reference pulse

Abstract

The present invention belongs to the field of laser radar ranging and speed measurement, and discloses a phase-coded laser radar based on a reference pulse, including a continuous laser, an amplitude modulator, a first unequal-arm interferometer, a third beam splitter, a first phase modulator, a second phase modulator, an optical fiber amplifier, a transmitting telescope, a receiving telescope, an unequal-arm interferometer module, and two photodetectors. Compared with the prior art, the present invention transmits a reference pulse and a signal pulse to the target, and passes the local oscillator light and the echo signal through the same unequal-arm interferometer, and uses a homodyne detector to detect the in-phase component and the orthogonal component of the reference pulse and the signal pulse. By correcting the measurement result of the signal pulse with the phase measurement result of the reference pulse, since the signal light and the reference light have experienced the same path, the influence of the decoherence effect can be greatly reduced. In addition, the detection of the in-phase component and the orthogonal component can be achieved using a homodyne detector, which reduces the complexity 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 phase-coded laser radar based on a reference pulse. 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 phase-coded laser radar based on reference pulses.

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

[0006] A phase-coded laser radar based on a reference pulse comprises a continuous laser CWL, an amplitude modulator AM, a first beam splitter BS1, a second beam splitter BS2, a third beam splitter BS3, a first phase modulator PM1, a second phase modulator PM2, an optical fiber amplifier, a transmitting telescope, a receiving telescope, an unequal-arm interferometer module, a first photodetector PD1 and a second photodetector PD2,

[0007] The continuous laser CWL is used to generate a continuous laser signal;

[0008] The amplitude modulator AM is used to chop the continuous laser signal to generate a light pulse with a period of 2T;

[0009] The first beam splitter BS1 and the second beam splitter BS2 form a first unequal-arm interferometer, which is used to generate a transmission light pulse and a local oscillator light pulse with a period of T emitted from two output ports of the second beam splitter BS2 respectively;

[0010] The first phase modulator PM1 is used to perform 0 or π phase encoding on the even pulses of the transmitted light pulses as signal pulses and the odd pulses as reference pulses;

[0011] The optical fiber amplifier is used to amplify the reference pulse and the signal pulse;

[0012] The transmitting telescope is used to expand the amplified reference pulse and signal pulse and illuminate the target;

[0013] The receiving telescope is used to receive the echo signal reflected from the target;

[0014] An unequal-arm interferometer module, used to make each pulse in the echo signal generate two sub-pulses with a time difference t; and used to make the local oscillator light pulse generate a first local oscillator component and a second local oscillator component with a time difference t;

[0015] The second phase modulator PM2 is used for modulating the phase of the second local oscillator component to π / 2;

[0016] The third beam splitter BS3 is used to make the first local oscillator component and the second local oscillator component interfere with the two sub-pulses of the echo signal respectively;

[0017] The first photodetector PD1 and the second photodetector PD2 form a balanced homodyne detector through signal differential, which is used to alternately measure the in-phase component and the orthogonal component of the reference pulse, and the in-phase component and the orthogonal component of the signal pulse in sequence.

[0018] Preferably, the unequal-arm interferometer module comprises a first polarization beam splitter PBS1, a second polarization beam splitter PBS2, a fourth beam splitter BS4 and a fifth beam splitter BS5.

[0019] The two output ports of the fourth beam splitter BS4 and the two output ports of the fifth beam splitter BS5 are respectively connected through optical fibers of unequal lengths to form a second unequal-arm interferometer;

[0020] The input port of the fourth beam splitter BS4 is connected to the input port of the first polarization beam splitter PBS1 after 90° polarization rotation;

[0021] The input port of the fifth beam splitter BS5 is connected to the input port of the second polarization beam splitter PBS2;

[0022] Two output ports of the first polarization beam splitter PBS1 are connected to the receiving telescope and the second phase modulator PM2 respectively;

[0023] Two output ports of the second polarization beam splitter PBS2 are connected to one output port of the second beam splitter BS2 and one input port of the third beam splitter BS3 respectively.

[0024] Preferably, the unequal-arm interferometer module comprises a polarizer POL, a first circulator CIR1, a second circulator CIR2, a fourth beam splitter BS4 and a fifth beam splitter BS5.

[0025] The two output ports of the fourth beam splitter BS4 and the two output ports of the fifth beam splitter BS5 are respectively connected through optical fibers of unequal lengths to form a second unequal-arm interferometer;

[0026] The first port, the second port and the third port of the first circulator CIR1 are respectively connected to the output port of the polarizer POL, the input port of the fourth beam splitter BS4 and the input port of the second phase modulator PM2;

[0027] The first port, the second port and the third port of the second circulator CIR2 are respectively connected to an output port of the second beam splitter BS2, an input port of the fifth beam splitter BS5 and an input port of the third beam splitter BS3;

[0028] The input port of the polarizer POL is connected to the receiving telescope.

[0029] Preferably, the unequal-arm interferometer module comprises a polarizer POL, a fourth beam splitter BS4 and a fifth beam splitter BS5.

[0030] The two output ports of the fourth beam splitter BS4 and the two output ports of the fifth beam splitter BS5 are respectively connected through optical fibers of unequal lengths to form a second unequal-arm interferometer;

[0031] Two input ports of the fourth beam splitter BS4 are connected to the output port of the polarizer POL and the input port of the second phase modulator PM2 respectively;

[0032] Two input ports of the fifth beam splitter BS5 are respectively connected to an output port of the second beam splitter BS2 and an input port of the third beam splitter BS3;

[0033] The input port of the polarizer POL is connected to the receiving telescope.

[0034] Preferably, the time difference between the two sub-pulses is t=T / 2.

[0035] Preferably, the time interval T between the signal light and the local oscillator light is no more than 1 ns.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] The present invention proposes a phase-coded laser radar based on a reference pulse, which transmits a reference pulse and a signal pulse to a target, passes the local oscillator light and the echo signal through the same unequal-arm interferometer, and uses a homodyne detector to detect the in-phase component and the orthogonal component of the reference pulse and the signal pulse. By correcting the measurement result of the signal pulse with the phase measurement result of the reference pulse, the influence of the decoherence effect can be greatly reduced because the signal light and the reference light have experienced the same path. In addition, the detection of the in-phase component and the orthogonal component can be realized by using a homodyne detector, which reduces the complexity of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a principle diagram of the phase-coded laser radar based on reference pulse of the present invention;

[0039] Figure 2 This is a schematic diagram of Embodiment 1 of a phase-coded laser radar based on a reference pulse according to the present invention;

[0040] Figure 3 This is a schematic diagram of Embodiment 2 of the phase-coded laser radar based on reference pulses of the present invention;

[0041] Figure 4 This is a schematic diagram of Example 3 of a phase-coded laser radar based on a reference pulse according to the present invention. DETAILED DESCRIPTION

[0042] The present invention will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present invention.

[0043] like Figure 1 As shown, a phase-coded laser radar based on a reference pulse includes a continuous laser CWL, an amplitude modulator AM, a first beam splitter BS1, a second beam splitter BS2, a third beam splitter BS3, a first phase modulator PM1, a second phase modulator PM2, an optical fiber amplifier, a transmitting telescope, a receiving telescope, an unequal-arm interferometer module, a first photodetector PD1 and a second photodetector PD2.

[0044] The continuous laser CWL is used to generate a continuous laser signal;

[0045] The amplitude modulator AM is used to chop the continuous laser signal to generate a light pulse with a period of 2T;

[0046] The first beam splitter BS1 and the second beam splitter BS2 form a first unequal-arm interferometer, which is used to generate a transmission light pulse and a local oscillator light pulse with a period of T emitted from two output ports of the second beam splitter BS2 respectively;

[0047] The first phase modulator PM1 is used to perform 0 or π phase encoding on the even pulses of the transmitted light pulses as signal pulses and the odd pulses as reference pulses;

[0048] The optical fiber amplifier is used to amplify the reference pulse and the signal pulse;

[0049] The transmitting telescope is used to expand the amplified reference pulse and signal pulse and illuminate the target;

[0050] The receiving telescope is used to receive the echo signal reflected from the target;

[0051] An unequal-arm interferometer module, used to make each pulse in the echo signal generate two sub-pulses with a time difference t; and used to make the local oscillator light pulse generate a first local oscillator component and a second local oscillator component with a time difference t;

[0052] The second phase modulator PM2 is used for modulating the phase of the second local oscillator component to π / 2;

[0053] The third beam splitter BS3 is used to make the first local oscillator component and the second local oscillator component interfere with the two sub-pulses of the echo signal respectively;

[0054] The first photodetector PD1 and the second photodetector PD2 form a balanced homodyne detector through signal differential, which is used to alternately measure the in-phase component and the orthogonal component of the reference pulse, and the in-phase component and the orthogonal component of the signal pulse in sequence.

[0055] The specific working process is as follows:

[0056] The continuous laser CWL generates a narrow linewidth continuous optical signal. The amplitude modulator AM chops the continuous optical signal to generate an optical pulse with a time interval of 2T. After passing through the first unequal-arm interferometer, the two output ports of the second beam splitter BS2 emit the emission optical pulse and the local oscillator optical pulse with a period of T respectively. When the emission optical pulse passes through the first phase modulator PM1, the first phase modulator PM1 encodes the even pulses with a period of 2T by 0 or π phase as the signal pulse, and obtains the encoding sequence; the odd pulses are not phase-modulated when passing through the first phase modulator PM1, and are used as reference pulses. Thus, a coded optical signal that appears at the interval between the reference pulse and the phase-coded signal pulse is obtained. 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, and then enters the unequal arm interferometer module, so that each pulse in the echo signal generates two sub-pulses with a time difference t. The reference pulse in the echo signal passes through the unequal arm interferometer module to generate the first reference component and the second reference component, and the signal pulse generates the first signal component and the second signal component accordingly. The local oscillator light pulse enters the unequal arm interferometer module from the opposite direction of the echo signal, generating the first local oscillator component and the second local oscillator component with a time difference t. Then the first local oscillator component interferes with the first reference component at the third beam splitter BS3, and the in-phase component of the reference pulse is measured by the balanced homodyne detector composed of the first photodetector PD1 and the second photodetector PD2. The second local oscillator component interferes with the second reference component after π / 2 phase modulation at the third beam splitter BS3, and the orthogonal component of the reference pulse is measured by the balanced homodyne detector. The first local oscillator component and the second local oscillator component generated by the unequal arm interferometer module of the next local oscillator light pulse respectively interfere with the first signal component and the second signal component at the third beam splitter BS3, respectively generating the in-phase component and the orthogonal component of the signal pulse. Therefore, the output result of the balanced homodyne detector is the in-phase component and quadrature component of the reference pulse, the in-phase component and quadrature component of the signal pulse that appear alternately in sequence, so that the phase of the reference pulse and the signal pulse can be obtained. The phase of the signal pulse can be corrected by using the phase of the reference pulse to obtain the encoding phase of the signal pulse, that is, decoding is achieved to obtain the decoding sequence. Since the reference pulse and the signal pulse experience the same path, the phase change of the optical path to the two is exactly the same, but the phase difference between the two can still remain stable. Therefore, the influence of decoherence during signal transmission can be greatly reduced by phase correction of the reference pulse.

[0058] The coding 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.

[0059] like Figure 2 As shown, the first embodiment of the present invention:

[0060] The unequal-arm interferometer module comprises a first polarization beam splitter PBS1, a second polarization beam splitter PBS2, a fourth beam splitter BS4 and a fifth beam splitter BS5.

[0061] The two output ports of the fourth beam splitter BS4 and the two output ports of the fifth beam splitter BS5 are respectively connected through optical fibers of unequal lengths to form a second unequal-arm interferometer;

[0062] The input port of the fourth beam splitter BS4 is connected to the input port of the first polarization beam splitter PBS1 after 90° polarization rotation;

[0063] The input port of the fifth beam splitter BS5 is connected to the input port of the second polarization beam splitter PBS2;

[0064] Two output ports of the first polarization beam splitter PBS1 are connected to the receiving telescope and the second phase modulator PM2 respectively;

[0065] Two output ports of the second polarization beam splitter PBS2 are connected to one output port of the second beam splitter BS2 and one input port of the third beam splitter BS3 respectively.

[0066] The specific working process of embodiment 1 is as follows:

[0067] The continuous laser CWL generates a narrow linewidth continuous optical signal. The amplitude modulator AM chops the continuous optical signal to generate an optical pulse with a time interval of 2T. After passing through the first unequal-arm interferometer, the two output ports of the second beam splitter BS2 emit the emission optical pulse and the local oscillator optical pulse with a period of T respectively. When the emission optical pulse passes through the first phase modulator PM1, the first phase modulator PM1 encodes the even pulses with a period of 2T by 0 or π phase as the signal pulse, and obtains the encoding sequence; the odd pulses are not phase-modulated when passing through the first phase modulator PM1, and are used as reference pulses. Thus, a coded optical signal that appears at the interval between the reference pulse and the phase-coded signal pulse is obtained. 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.

[0068] After being reflected by the target, the coded light signal enters the receiving telescope and becomes an echo signal, which then enters the first polarization beam splitter PBS1. Its horizontal polarization component is directly transmitted, and after being polarized by 90°, it enters the second unequal-arm interferometer, where each pulse generates two sub-pulses with a time difference t. The reference pulse in the echo signal generates the first reference component and the second reference component, and the signal pulse generates the first signal component and the second signal component accordingly, which are reflected by the second polarization beam splitter PBS2 and enter an input port of the third beam splitter BS3. The local oscillator light pulse enters the second polarization beam splitter PBS2 and is directly transmitted, and enters the second unequal-arm interferometer from the opposite direction, generating the first local oscillator component and the second local oscillator component with a time difference t, and then is polarized by 90° and reflected by the first polarization beam splitter PBS1 and enters the second phase modulator PM2. Then the first local oscillator component interferes with the first reference component at the beam splitter BS3, and the in-phase component of the reference pulse is measured by a balanced homodyne detector composed of the first photodetector PD1 and the second photodetector PD2. The second local oscillator component interferes with the second reference component after π / 2 phase modulation at the beam splitter BS3, and the quadrature component of the reference pulse is measured by the balanced homodyne detector. The first local oscillator component and the second local oscillator component generated by the unequal arm interferometer module of the next local oscillator light pulse respectively interfere with the first signal component and the second signal component at the beam splitter BS3 to generate the in-phase component and the quadrature component of the signal pulse respectively. Therefore, the output result of the balanced homodyne detector is the in-phase component and the quadrature component of the reference pulse, and the in-phase component and the quadrature component of the signal pulse that appear alternately in sequence, so that the phase of the reference pulse and the signal pulse can be obtained. The phase of the signal pulse is corrected by the phase of the reference pulse to obtain the encoding phase of the signal pulse, that is, decoding is realized, and a decoding sequence is obtained. Since the reference pulse and the signal pulse have experienced the same path, the phase changes of the optical path to the two are exactly the same, but the phase difference between the two can still remain stable. Therefore, the influence of decoherence during signal transmission can be greatly reduced by phase correction of the reference pulse.

[0069] The coding 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 unequal-arm interferometer module comprises a polarizer POL, a first circulator CIR1, a second circulator CIR2, a fourth beam splitter BS4 and a fifth beam splitter BS5.

[0072] The two output ports of the fourth beam splitter BS4 and the two output ports of the fifth beam splitter BS5 are respectively connected through optical fibers of unequal lengths to form a second unequal-arm interferometer;

[0073] The first port, the second port and the third port of the first circulator CIR1 are respectively connected to the output port of the polarizer POL, the input port of the fourth beam splitter BS4 and the input port of the second phase modulator PM2;

[0074] The first port, the second port and the third port of the second circulator CIR2 are respectively connected to an output port of the second beam splitter BS2, an input port of the fifth beam splitter BS5 and an input port of the third beam splitter BS3;

[0075] The input port of the polarizer POL is connected to the receiving telescope.

[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 amplitude modulator AM chops the continuous optical signal to generate an optical pulse with a time interval of 2T. After passing through the first unequal-arm interferometer, the two output ports of the second beam splitter BS2 emit the emission optical pulse and the local oscillator optical pulse with a period of T respectively. When the emission optical pulse passes through the first phase modulator PM1, the first phase modulator PM1 encodes the even pulses with a period of 2T by 0 or π phase as the signal pulse, and obtains the encoding sequence; the odd pulses are not phase-modulated when passing through the first phase modulator PM1, and are used as reference pulses. Thus, a coded optical signal that appears at the interval between the reference pulse and the phase-coded signal pulse is obtained. 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. After being polarized by the polarizer POL, it enters the first circulator CIR1 and then enters the second unequal arm interferometer, where each pulse generates two sub-pulses with a time difference t. The reference pulse in the echo signal generates the first reference component and the second reference component, and the signal pulse generates the first signal component and the second signal component accordingly, and enters an input port of the third beam splitter BS3 through the second circulator CIR2. The local oscillator light pulse enters the second polarization beam splitter PBS2 and is directly transmitted, and enters the second unequal arm interferometer from the opposite direction, generating the first local oscillator component and the second local oscillator component with a time difference t, and then enters the second phase modulator PM2 through the first circulator CIR1. Then the first local oscillator component interferes with the first reference component at the third beam splitter BS3, and the in-phase component of the reference pulse is measured by the balanced homodyne detector composed of the first photodetector PD1 and the second photodetector PD2. The second local oscillator component interferes with the second reference component after π / 2 phase modulation at the third beam splitter BS3, and the orthogonal component of the reference pulse is measured by the balanced homodyne detector. The first local oscillator component and the second local oscillator component of the next local oscillator light pulse generated by the unequal-arm interferometer module respectively interfere with the first signal component and the second signal component at the third beam splitter BS3, respectively generating the in-phase component and the orthogonal component of the signal pulse. Therefore, the output result of the balanced zero-difference detector is the in-phase component and the orthogonal component of the reference pulse, the in-phase component and the orthogonal component of the signal pulse that appear alternately in sequence, so that the phase of the reference pulse and the signal pulse can be obtained, and the phase of the signal pulse can be corrected by using the phase of the reference pulse to obtain the encoding phase of the signal pulse, that is, decoding is realized to obtain the decoding sequence. Since the reference pulse and the signal pulse experience the same path, the phase change of the optical path to the two is exactly the same, but the phase difference between the two can still remain stable. Therefore, the influence of decoherence during signal transmission can be greatly reduced by phase correction of the reference pulse.

[0079] The coding 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.

[0080] like Figure 4 As shown, the third embodiment of the present invention:

[0081] The unequal-arm interferometer module comprises a polarizer POL, a fourth beam splitter BS4 and a fifth beam splitter BS5.

[0082] The two output ports of the fourth beam splitter BS4 and the two output ports of the fifth beam splitter BS5 are respectively connected through optical fibers of unequal lengths to form a second unequal-arm interferometer;

[0083] Two input ports of the fourth beam splitter BS4 are connected to the output port of the polarizer POL and the input port of the second phase modulator PM2 respectively;

[0084] Two input ports of the fifth beam splitter BS5 are respectively connected to an output port of the second beam splitter BS2 and an input port of the third beam splitter BS3;

[0085] The input port of the polarizer POL is connected to the receiving telescope.

[0086] The specific working process of the third embodiment is as follows:

[0087] The continuous laser CWL generates a narrow linewidth continuous optical signal. The amplitude modulator AM chops the continuous optical signal to generate an optical pulse with a time interval of 2T. After passing through the first unequal-arm interferometer, the two output ports of the second beam splitter BS2 emit the emission optical pulse and the local oscillator optical pulse with a period of T respectively. When the emission optical pulse passes through the first phase modulator PM1, the first phase modulator PM1 encodes the even pulses with a period of 2T by 0 or π phase as the signal pulse, and obtains the encoding sequence; the odd pulses are not phase-modulated when passing through the first phase modulator PM1, and are used as reference pulses. Thus, a coded optical signal that appears at the interval between the reference pulse and the phase-coded signal pulse is obtained. 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.

[0088] After being reflected by the target, the coded light signal enters the receiving telescope and becomes an echo signal. After being polarized by the polarizer POL, it enters the second unequal-arm interferometer from an input port of the fourth beam splitter BS4, where each pulse generates two sub-pulses with a time difference t. The reference pulse in the echo signal generates a first reference component and a second reference component, and the signal pulse correspondingly generates a first signal component and a second signal component, which are emitted from an input port of the fifth beam splitter BS5 and enter an input port of the third beam splitter BS3. The local oscillator light pulse enters the second unequal-arm interferometer from another input port of the fifth beam splitter BS5 in the opposite direction, generates a first local oscillator component and a second local oscillator component with a time difference t, and enters the second phase modulator PM2 after being emitted from another input port of the fourth beam splitter BS4. Then the first local oscillator component interferes with the first reference component at the beam splitter BS3, and the in-phase component of the reference pulse is measured by a balanced homodyne detector composed of the first photodetector PD1 and the second photodetector PD2. The second local oscillator component interferes with the second reference component after π / 2 phase modulation at the beam splitter BS3, and the quadrature component of the reference pulse is measured by the balanced homodyne detector. The first local oscillator component and the second local oscillator component generated by the unequal arm interferometer module of the next local oscillator light pulse respectively interfere with the first signal component and the second signal component at the beam splitter BS3 to generate the in-phase component and the quadrature component of the signal pulse respectively. Therefore, the output result of the balanced homodyne detector is the in-phase component and the quadrature component of the reference pulse, and the in-phase component and the quadrature component of the signal pulse that appear alternately in sequence, so that the phase of the reference pulse and the signal pulse can be obtained. The phase of the signal pulse is corrected by the phase of the reference pulse to obtain the encoding phase of the signal pulse, that is, decoding is realized, and a decoding sequence is obtained. Since the reference pulse and the signal pulse have experienced the same path, the phase changes of the optical path to the two are exactly the same, but the phase difference between the two can still remain stable. Therefore, the influence of decoherence during signal transmission can be greatly reduced by phase correction of the reference pulse.

[0089] The coding 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.

[0090] It can be seen from the various embodiments of the present invention that the present invention proposes a phase-coded laser radar based on a reference pulse, which transmits a reference pulse and a signal pulse to the target, and passes the local oscillator light and the echo signal through the same unequal-arm interferometer, and uses a homodyne detector to detect the in-phase component and the orthogonal component of the reference pulse and the signal pulse. By correcting the measurement result of the signal pulse with the phase measurement result of the reference pulse, the influence of the decoherence effect can be greatly reduced because the signal light and the reference light have experienced the same path. In addition, the use of a homodyne detector can realize the detection of the in-phase component and the orthogonal component, reducing the complexity of the system.

Claims

1. A phase-coded laser radar based on reference pulses, 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 a light pulse with a period of 2T; The first beam splitter BS1 and the second beam splitter BS2 form a first unequal-arm interferometer for generating emission light pulses and local oscillator light pulses with a period of T emitted from two output ports of the second beam splitter BS2; A first phase modulator PM1 is used to perform 0 or π phase encoding on the even pulses of the transmitted light pulses as signal pulses and the odd pulses as reference pulses; A fiber amplifier, used to amplify reference pulses and signal pulses; A transmitting telescope is used to expand the amplified reference pulse and signal pulse and illuminate the target; a receiving telescope for receiving an echo signal reflected from a target; An unequal-arm interferometer module, used to make each pulse in the echo signal generate two sub-pulses with a time difference t; and for causing the local oscillator light pulse to generate a first local oscillator component and a second local oscillator component with a time difference t; The second phase modulator PM2 is used to modulate the phase of the second local oscillator component to π / 2; A third beam splitter BS3 is used to make the first local oscillator component and the second local oscillator component interfere with the two sub-pulses of the echo signal respectively; Two photoelectric detectors form a balanced homodyne detector through signal difference, which is used to alternately measure the in-phase component and the orthogonal component of the reference pulse, and the in-phase component and the orthogonal component of the signal pulse in sequence.

2. The phase-coded laser radar based on reference pulse according to claim 1, It is characterized in that The unequal-arm interferometer module comprises a first polarization beam splitter PBS1, a second polarization beam splitter PBS2, a fourth beam splitter BS4 and a fifth beam splitter BS5. The two output ports of the fourth beam splitter BS4 and the two output ports of the fifth beam splitter BS5 are respectively connected through optical fibers of unequal lengths to form a second unequal-arm interferometer; The input port of the fourth beam splitter BS4 is connected to the input port of the first polarization beam splitter PBS1 after 90° polarization rotation; The input port of the fifth beam splitter BS5 is connected to the input port of the second polarization beam splitter PBS2; Two output ports of the first polarization beam splitter PBS1 are connected to the receiving telescope and the second phase modulator PM2 respectively; Two output ports of the second polarization beam splitter PBS2 are connected to one output port of the second beam splitter BS2 and one input port of the third beam splitter BS3 respectively.

3. The phase-coded laser radar based on reference pulse according to claim 1, It is characterized in that The unequal-arm interferometer module comprises a polarizer POL, a first circulator CIR1, a second circulator CIR2, a fourth beam splitter BS4 and a fifth beam splitter BS5. The two output ports of the fourth beam splitter BS4 and the two output ports of the fifth beam splitter BS5 are respectively connected through optical fibers of unequal lengths to form a second unequal-arm interferometer; The first port, the second port and the third port of the first circulator CIR1 are respectively connected to the output port of the polarizer POL, the input port of the fourth beam splitter BS4 and the input port of the second phase modulator PM2; The first port, the second port and the third port of the second circulator CIR2 are respectively connected to an output port of the second beam splitter BS2, an input port of the fifth beam splitter BS5 and an input port of the third beam splitter BS3; The input port of the polarizer POL is connected to the receiving telescope.

4. The phase-coded laser radar based on reference pulse according to claim 1, It is characterized in that The unequal-arm interferometer module comprises a polarizer POL, a fourth beam splitter BS4 and a fifth beam splitter BS5. The two output ports of the fourth beam splitter BS4 and the two output ports of the fifth beam splitter BS5 are respectively connected through optical fibers of unequal lengths to form a second unequal-arm interferometer; Two input ports of the fourth beam splitter BS4 are connected to the output port of the polarizer POL and the input port of the second phase modulator PM2 respectively; Two input ports of the fifth beam splitter BS5 are respectively connected to an output port of the second beam splitter BS2 and an input port of the third beam splitter BS3; The input port of the polarizer POL is connected to the receiving telescope.

5. The phase-coded laser radar based on reference pulse according to claim 2, 3 or 4, It is characterized in that The time difference between the two sub-pulses is t=T / 2.

6. The phase-coded laser radar based on reference pulse according to claim 2, 3 or 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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