Phase modulation continuous wave distance measurement method and system based on vernier effect

Abstract

The invention discloses a vernier effect-based phase modulation continuous wave distance measurement method and system. The vernier effect is utilized to enhance the distance measurement capability of phase modulation continuous waves. The method comprises the following steps: selecting two pseudo-random sequences of which the lengths are prime numbers for phase modulation; splicing the two sequences into a modulation sequence, and modulating the laser signal; transmitting a modulation signal to a measured target and receiving an echo; and processing echo signals, respectively measuring time delay by using two sequences, calculating normalized time delay in combination with a code length, solving actual time delay by using the Chinese remainder theorem, and further determining a target distance. The system comprises a laser, a beam splitter, a phase modulator, a signal generator, an acousto-optic frequency shifter, a transmitting / receiving device, a beam combiner, a photoelectric detector and a signal processing module, and realizes high-precision distance measurement. The vernier effect is utilized, the unambiguous measurement distance is effectively increased, the measurement speed is improved, and meanwhile the system complexity is reduced. By combining a precise signal processing algorithm, the actual distance between the measured target and the measuring device can be accurately and quickly calculated, and the method is suitable for high-precision and long-distance distance measurement requirements and has wide application prospects.

Description

Technical Field

[0001] The present invention relates to the field of laser radar technology, and in particular to a phase-modulated continuous wave ranging method and system based on vernier effect. Background Art

[0002] Continuous wave laser radar uses continuous laser signals for detection, and its working state is that the time domain power is basically constant, avoiding the influence of excessive peak power in pulse ranging on the performance of optical devices. Continuous wave laser radar ranging methods mainly include phase-type continuous wave ranging, frequency-modulated continuous wave ranging (Frequency-modulated continuous wave, FMCW) and phase-modulated continuous wave ranging (Phase-modulated continuous wave, PMCW). Invention CN105629258B proposes a phase-modulated continuous wave ranging method based on pseudo-random code phase modulation, which has strong anti-interference ability, but the maximum measurement unambiguous distance in this ranging method is proportional to the modulation period. It will be limited by the maximum measurement distance ambiguity within a certain coding period. When measuring a longer distance, a relatively long modulation period is required, so a single measurement requires a longer measurement time, which limits its practical application in the autonomous driving industry.

[0003] In view of the above limitations, it is particularly important to develop a phase-modulated continuous wave ranging method that can quickly complete the measurement and ensure the maximum unambiguous measurement distance. This requires not only solving the ambiguity problem in distance measurement, but also improving the measurement efficiency to meet the urgent needs of high-tech fields such as autonomous driving for high-precision and high-speed ranging technology. Summary of the invention

[0004] The technical problem to be solved by the present invention is the contradiction between the phase encoding length and the maximum unambiguous measurement distance. A method using a shorter phase encoding length to achieve a longer unambiguous measurement distance is proposed, thereby taking into account the requirements between the measurement rate and the measurement distance. In order to solve the above technical problems, a continuous wave laser ranging method based on the cursor effect and pseudo-random code phase modulation is proposed. Based on the original pseudo-random code phase modulation continuous wave ranging method, this method introduces a variety of pseudo-random sequences with different periods to measure the distance of targets that exceed the traditional maximum unambiguous measurement distance. By comprehensively processing the ranging results of these sequences, the actual distance can be accurately calculated, breaking the limitation that the maximum unambiguous measurement distance is directly related to the modulation period under a single phase code modulation, so that while keeping the encoding period relatively short, the maximum unambiguous measurement distance is significantly improved.

[0005] The technical solution of the present invention is as follows:

[0006] On the one hand, the present invention provides a phase modulation continuous wave ranging method based on vernier effect, which is characterized in that it includes the following steps:

[0007] S1. Select two m sequences of different lengths as pseudo-random codes, where the m sequence is the longest linear feedback shift register sequence, the lengths M and N of the two m sequences are mutually prime, and M and N are both expressed as 2 k -1, k is a positive integer;

[0008] S2. splicing the two m sequences into a modulation sequence for phase modulation of the laser signal;

[0009] S3. transmitting a phase-modulated laser signal to the target to be measured, the actual distance of which is greater than the maximum unambiguous measurement distance when the two selected m-sequences are measured separately, and then receiving an echo signal reflected from the target to be measured;

[0010] S4. Process the received echo signal, use two m-sequences to measure the echo signal delays τ1 and τ2, and calculate the delays according to the code length T c The normalized echo signal delays B1 and B2 are calculated, and then the actual delay τ0 is obtained to determine the actual distance between the measured target and the measuring device.

[0011] Further, the step S4 calculates the actual distance L of the measured target, and the specific steps are as follows:

[0012] S4.1 transfers the binary digital signals corresponding to the code elements of two m sequences of different lengths from the baseband to the intermediate frequency f, and then cross-correlates them with the codes of one period in the echo signal respectively. According to the known code length T c The two time delays τ1 and τ2 obtained by cross-correlation are used to calculate the normalized echo signal delay, that is, the normalized echo signal delay B1 = τ1 / T c = r + B m and B2 = τ2 / T c =s+B m , where r and s are non-negative integers less than the length of two m sequence codes, B m is the normalized residual delay, and B m =T m / T c , 0≤T m <T c is a residual delay less than one code length;

[0013] S4.2 The time delay of the measured target τ0=τ1+pMT c =τ2+qNT c, M and N are the number of bits of the code element in two m sequences of different lengths, p and q are non-negative integers, and the normalized delay of the target under test is defined as B0 = τ0 / T c , where T c is the duration of a single code element, and then τ 1、 Substituting τ2 into the equation, the normalized delay of the target can be expressed as: B0 = B int +B m , where B int is the integer part of the normalized delay B0, B int =r+pM=s+qN,B m is the fractional part of the normalized delay B0;

[0014] S4.3 According to the Chinese remainder theorem, solve the normalized delay integer part B int ;

[0015] S4.4 According to the normalized delay integer part B int , normalized residual delay B m And the normalized delay B0, the actual delay τ0 and actual distance L of the measured target are calculated, the formula is as follows:

[0016] τ0=B0T c

[0017] L=cτ0 / 2

[0018] Where c is the speed of light

[0019] Further, the method further comprises the following steps:

[0020] - providing a laser for emitting a single-frequency laser, wherein the line width of the laser ensures that the distance of the object to be measured is much smaller than the coherence length of the laser;

[0021] - providing a beam splitter to split the laser into an emission branch and a detection branch;

[0022] - In the transmitting branch, a binary code sequence generated by a signal generator is used to drive a phase modulator to perform phase modulation on an optical signal, and a fixed frequency shift f is applied to the modulated optical signal through an acousto-optic frequency shifter, and then the optical signal carrying the phase modulation information is transmitted to the target to generate an echo light through a transmitting device;

[0023] - On the detection branch, a beam combiner is used to combine the split local optical signal with the echo light received by the receiving device, and then photoelectric conversion is performed through a photoelectric detector.

[0024] On the other hand, the present invention also provides a phase modulation continuous wave ranging system based on the vernier effect, which is characterized in that it includes:

[0025] A laser for emitting a single-frequency laser whose line width ensures that the distance of the object to be measured is much smaller than the coherence length of the laser;

[0026] A beam splitter, used to split the laser light emitted by the laser into an emission branch and a detection branch;

[0027] A phase modulator, arranged on the transmitting branch, is used to perform phase modulation on the laser according to the binary code sequence generated by the signal generator so as to load it onto the laser signal;

[0028] A signal generator is used to generate a binary code sequence formed by splicing two m-sequences of different lengths front and back, and provide a synchronization signal;

[0029] an acousto-optic frequency shifter, arranged on the transmitting branch, for applying a fixed frequency shift to the modulated laser;

[0030] A transmitting device, used for transmitting an optical signal carrying phase modulation information toward a target to be measured;

[0031] A receiving device, used for receiving the echo light of the measured target;

[0032] A beam combiner, used for combining the local light on the detection branch and the echo light received by the receiving device;

[0033] A photodetector, used to convert the combined optical signal into an electrical signal;

[0034] The signal processing module is used to process the electrical signal output by the photodetector, and calculate the integer part B of the normalized delay according to the Chinese remainder theorem based on the delay results measured by the two m-sequences, namely τ1 and τ2. int , combined with the known residual B m , and then find the actual distance of the target.

[0035] Furthermore, the binary code sequence generated by the signal generator consists of two code elements whose numbers are mutually prime and can be expressed as 2 k -1 form of m sequence spliced ​​front and back.

[0036] Furthermore, it also includes a calibration device for calibrating the optical path between the transmitting device and the receiving device to improve the ranging accuracy.

[0037] The core of the present invention is based on the vernier effect. By using two m-sequences of different lengths to measure the same object, the regularity difference is combined with the Chinese remainder theorem to greatly expand the unambiguous ranging length. Compared with the single m-sequence PMCW ranging solution with the same unambiguous ranging length, the sequence length required by the present invention is shorter.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] Compared with the continuous wave ranging method based on pseudo-random code phase modulation proposed in invention CN105629258B, the present invention utilizes the vernier effect and uses the splicing of two or more short sequences to replace a long sequence to achieve the same unambiguous ranging length, thereby improving the measurement speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a schematic diagram of the principle of the novel phase modulation continuous wave ranging method based on the vernier effect of the present invention, wherein sequence 1 and sequence 2 respectively obtain time delay signal 1 and time delay signal 2 after detecting the same target object.

[0041] Figure 2 It is a system structure diagram of the novel phase modulation continuous wave ranging method based on the vernier effect of the present invention.

[0042] In the figure: 1-laser, 2-beam splitter, 3-phase modulator, 4-signal generator, 5-acoustic-optic frequency shifter, 6-transmitter, 7-receiver, 8-beam combiner, 9-photodetector, 10-signal processing module. DETAILED DESCRIPTION

[0043] The present invention will be further described below in conjunction with the accompanying drawings and examples, but the protection scope of the present invention shall not be limited thereto. The embodiments of the present invention include but are not limited to the following examples.

[0044] This embodiment is based on a phase modulated continuous wave (PMCW) ranging system and uses a pseudo-random code for phase modulation. The m-sequence (i.e., the longest linear feedback shift register sequence) is used as a modulation symbol sequence. The m-sequence is a pseudo-random sequence with excellent autocorrelation characteristics and orthogonality, and each code length corresponds to a unique binary sequence.

[0045] In this embodiment, two groups of m-sequences of different lengths (sequence 1 and sequence 2) are spliced ​​to form a modulation sequence to measure the distance of the same target. The time delay results measured by these two sequences, combined with the Chinese remainder theorem, can be used to calculate the actual distance of the target, thereby greatly extending the unambiguous ranging length.

[0046] Sequence 1 is M bits, total duration T1 = MT c , sequence 2 is N bits, total duration T2 = NT c . The sequence lengths M and N are both positive integers, prime to each other, and can be expressed as 2 k-1, where k is the number of bits of the m-sequence, taking any positive integer. For example, M = 15 (corresponding to k = 4) and N = 7 (corresponding to k = 3), the total coding time length is (M + N)T c = 22T c . The unambiguous measurement distance of a single m-sequence is equal to the distance corresponding to the coding length. Taking sequence 1 as an example, it is

[0047]

[0048] When measuring a target beyond the unambiguous measurement distance of a single m-sequence, this method utilizes the relationship between the time delays (τ1 and τ2) measured by two sets of m-sequences respectively and their actual time delay (τ0) with the measured target, and finally solves the actual distance of the target. Specifically, it includes:

[0049] τ0 = τ1 + pMT c = τ2 + qNT c

[0050] where τ0 is the actual time delay corresponding to the measured target, τ1 < MT c 、τ2 < NT c are the time delays measured by two m-sequences respectively, and p, q are non-negative integers.

[0051] The time delays τ1, τ2 can be further written as:

[0052] τ1 = rT c + T m

[0053] τ2 = sT c + T m

[0054] where r < M, s < N are non-negative integers, 0 ≤ T m < T c is the residual time delay less than a single code length. Since τ1, τ2, T c are all known, so r, s, T m can also be calculated.

[0055] Substituting the expressions of τ1, τ2 into τ0, we can get:

[0056] τ0 = rT c + pMT c + T m = sT c + qNT c + T m

[0057] Dividing both sides of the above equation by the code length T c , we get:

[0058] B0 = r + pM + B m = s + qN + B m

[0059] Wherein, the normalized time delay B0 of the target to be measured is defined as B0 = τ0 / T c (positive real number), the normalized residual time delay B m = T m / T c (positive real number less than 1). Denote the integer part of the normalized time delay B0 as B int (= r + pM = s + qN). Since B m is known (because T m and T c are known), so only B int needs to be obtained, and the total normalized time delay B0 can be obtained, and then the actual distance of the target can be calculated.

[0060] When the sequence lengths M and N are relatively prime to each other, according to the Chinese Remainder Theorem, we have:

[0061] B int = ruN + svM + wNM

[0062] In the formula, w is an integer to be determined, and u, v are the inverses of M, N for the modulo operation (taking the remainder) with respect to each other, that is, the smallest positive integers satisfying the following formulas:

[0063] uN = 1 (mod M)

[0064] vM = 1 (mod N)

[0065] For given M and N, the values of u and v are determined. For example, for M = 15 (= 2 4 -1) and N = 7 (= 2 3 -1), we have u = 28 and v = 1. Substitute u, v into the B int expression, and select an appropriate w such that 0 ≤ B int < MN. Finally, B0 = B int + B m can be used to obtain the total normalized time delay, and then the actual distance of the target to be measured can be obtained.

[0066] Compared with using a single m-sequence as the measurement sequence, this method has significant advantages. First, it greatly shortens the required sequence length, thus reducing the coding time and measurement time. For example, in the case of M = 15 and N = 7, this method only requires a sequence length of 22 bits, while the single m-sequence scheme requires a sequence length of 127 bits. Second, as the unambiguous measurement distance increases, the difference in the required sequence lengths between this method and the single m-sequence scheme increases exponentially, further highlighting the advantages of this method.

[0067] Example 2:

[0068] In this example, three m-sequences with different lengths (Sequence 1, Sequence 2, and Sequence 3) are concatenated to form a modulation sequence for ranging the same target. Based on the time delay results measured by these two sequences and the Chinese Remainder Theorem, the actual distance of the target can be calculated, thus greatly expanding the unambiguous ranging length.

[0069] Sequence 1 has M bits, and the total duration T1 = MT c , Sequence 2 has N bits, and the total duration T2 = NT c , Sequence 3 has Q bits, and the total duration T3 = QT C . Among them, the sequence lengths M, N, and Q are all positive integers, are relatively prime to each other, and can all be expressed as 2 k -1, where k is the number of bits of the m-sequence and takes any positive integer. The unambiguous measurement distance of a single m-sequence is equal to the distance corresponding to the coding length. Taking Sequence 1 as an example, it is

[0070]

[0071] When measuring a target beyond the unambiguous measurement distance of a single m-sequence, this method uses the time delays (τ1, τ2, and τ3) measured by three m-sequences respectively and their relationships with the actual time delay (τ0) of the target to be measured, and finally solves the actual distance of the target. Specifically, it includes:

[0072] τ0 = τ1 + pMT c = τ2 + qNT c = τ3 + zQT c

[0073] Among them, τ0 is the actual time delay corresponding to the target to be measured, τ1 < MT c , τ2 < NT c , τ3 < QT c are the time delays measured by three m-sequences respectively, and p, q, and z are non-negative integers.

[0074] The time delays τ1, τ2, and τ3 can be further written as:

[0075] τ1 = rT c + T m

[0076] τ2 = sT c + T m

[0077] τ3 = yT c + T m

[0078] where r < M, s < N, y < Q are non-negative integers, 0 ≤ Tm <T c is a residual delay less than a single code length. c are all known, so r, s, y, T m It is also calculable.

[0079] Substituting the expressions of τ1, τ2, and τ3 into τ0, we can obtain:

[0080] τ0=rT c +pMT c +T m =sT c +qNT c +T m =yT c +ZQT c +T m

[0081] Divide both sides of the above equation by the code length T c ,get:

[0082] B0=r+pM+B m =s+qN+B m =y+zQ+B m

[0083] Among them, the normalized delay of the target under test is defined as B0 = τ0 / T c (positive real number), normalized residual delay B m =T m / T c (a positive real number less than 1). The integer part of the normalized delay B0 is recorded as B int (=r+pM=s+qN=y+zQ). m is known (because T m and T c So we only need to find B int , we can get the total normalized delay B0, and then find the actual distance of the target.

[0084] When the sequence lengths M, N and Q are mutually prime, according to the Chinese remainder theorem, we can get:

[0085] B int =rt1NQ+st2MQ+yt3MN+wMNQ

[0086] Where w is an undetermined integer, t1, t2, and t3 are the inverse elements of the modulo operation (remainder) of the product of two of M, N, and Q, that is, the smallest positive integer that satisfies the following formula:

[0087] t1NQ=1(mod M)

[0088] t2MQ ≡ 1 (mod N)

[0089] t3MN ≡ 1 (mod Q)

[0090] For the given M, N, and Q, the values of t1, t2, and t3 are determined. For example, for M = 31 (= 2 5 - 1), N = 15 (= 2 4 - 1), and Q = 7 (= 2 3 - 1), there are t1 = 13, t2 = 13, and t3 = 5. Substitute t1, t2, and t3 into the B int expression, and select an appropriate w such that 0 ≤ B int < MNQ. Finally, B0 = B int + B m to obtain the total normalized time delay, and then the actual distance of the measured target can be obtained.

[0091] Compared with using a single m - sequence as the measurement sequence, this method has significant advantages. First, it greatly shortens the required sequence length, thus reducing the coding time and measurement time. For example, in the case of M = 31, N = 15, and Q = 7, this method only requires a sequence length of 53 bits, while the single m - sequence scheme requires a sequence length of 4095 bits. Second, as the unambiguous measurement distance increases, the difference in the required sequence lengths between this method and the single m - sequence scheme increases exponentially, further highlighting the advantages of this method.

[0092] The working principle of the present invention:

[0093] For the convenience of description, the symbols used are explained as follows:

[0094]

[0095] As Figure 1 shown, a novel phase - modulated continuous - wave ranging system based on the cursor effect. It includes: a laser, a beam splitter, a phase modulator, a signal generator, an acousto - optic frequency shifter, a transmitting device, a receiving device, a beam combiner, a photodetector, and a signal processing module;

[0096] The laser emits laser light, which is split into a transmitting branch and a detecting branch by the beam splitter. The transmitting branch sequentially passes through the phase modulator, the acousto - optic frequency shifter, and the transmitting device along the optical transmission direction. The signal generator generates a binary coding sequence of 01 with a certain length to drive the phase modulator to load phase modulation on the optical signal passing through it, and provides another synchronous signal to the signal processing module to calibrate time. The acousto - optic frequency shifter applies a fixed frequency shift f to the optical signal passing through it. The transmitting device emits the optical signal carrying the phase - modulation information towards the measured target and generates a reflected light wave;

[0097] On the detection branch, the optical signal after passing through the beam splitter is combined with the echo light received by the receiving device in the beam combiner, input to the photoelectric detector for photoelectric conversion, and finally processed by the signal processing module;

[0098] The laser outputs single-frequency laser, and the line width of the laser should ensure that the distance of the measured object is much smaller than the coherence length of the laser;

[0099] (The following examples are all based on two m-sequence codewords of different lengths) The coding sequence generated by the signal generator is composed of two m-sequences of different codeword lengths spliced ​​together. The two sequences are sequence 1, sequence length M, and sequence 2, sequence length N. The sequence lengths M and N meet the conditions: positive integers, prime to each other, and can both be expressed as 2 k -1, k is the number of bits of the m sequence, which can be any positive integer. The m sequence is a pseudo-random sequence with good autocorrelation characteristics and orthogonality, and one sequence length corresponds to a unique binary sequence;

[0100] The phase modulator converts the binary sequence generated by the signal generator into a binary phase modulation, for example, 0 corresponds to 0 rad phase shift and 1 corresponds to π rad phase shift;

[0101] The acousto-optic frequency shifter applies a frequency shift f so that after the local light on the detection branch and the echo light are combined, the electrical signal generated by the beat frequency in the photoelectric detector is located at an intermediate frequency f, which can eliminate the noise interference at the baseband in the detection system;

[0102] The signal processing module processes the beat frequency signal including the following steps:

[0103] 1) Move the signal at the intermediate frequency f to the baseband;

[0104] 2) The baseband signal is a series of high and low level sequences, which are converted into 01 binary digital signals according to the coding corresponding to the phase modulation and the time length of a single code element. During the processing, the relevant algorithms in digital signal processing can be used to suppress noise and DC fluctuations to avoid bit errors;

[0105] 3) Use the codes of two m sequences (i.e., sequence 1 and sequence 2) to perform cross-correlation with the code of one period (i.e., the length is equal to the length of sequence 1 plus the length of sequence 2) in the echo signal. Based on the cross-correlation principle and the synchronization signal given by the signal generator, calculate the signal delay. Sequence 1 calculates the normalized echo signal delay r+B m , Sequence 2 calculates the normalized echo signal delay s+B m The delay for a single code length T c After normalization, r and s are non-negative integers less than the code length of sequence 1 and sequence 2 respectively, and the normalized residual delay Bm =T m / T c is a positive real number less than 1, 0≤T m <T c is a residual delay less than one code length;

[0106] 4) Actual normalized echo signal delay B0 = r + pM + B m =s+qN+B m , p and q are non-negative integers. Fractional part B m is known, we only need to find its integer part B int =r+pM=s+qN. According to the Chinese remainder theorem, we have B int =ruN+svM+wNM, where w is an undetermined integer, and u and v are the inverse elements of the modulo operation (remainder) of M and N. For a given M and N, the values ​​of u and v are fixed. For example, for M=15 (=2 4 -1) and N=7(=2 3 -1), we have u=28 and v=1. Substitute u and v into B int Expression, and select a suitable w so that 0≤B int <MN;

[0107] 5) Total normalized delay B0 = B int +B m , the total delay τ0=B0T c , the actual distance of the measured target L = cτ0 / 2;

[0108] The m-sequence is not the only choice, and other sequences with good autocorrelation and orthogonality can be selected, requiring that the sequence lengths of the two spliced ​​sequences are prime numbers to each other;

[0109] The two groups of sequences described are not the only options. Multiple groups of sequences can be selected and the cursor effect between the multiple groups of sequences can be used to achieve the extension of the unambiguous ranging length. The sequence lengths of the multiple groups of sequences are required to be prime numbers to each other and have good autocorrelation characteristics and orthogonality, that is, when the sequence is autocorrelated with itself, the signal is the strongest, and when it is cross-correlated with other sequences, the signal is as weak as possible.

[0110] In this embodiment, the laser is a 1550nm single-mode distributed feedback DFB laser, the phase modulator is a lithium niobate high-speed electro-optic phase modulator, and the photodetector is a PIN photodiode with an analog bandwidth greater than 10 GHz.

Claims

1. A phase modulated continuous wave ranging method based on vernier effect, characterized in that: The following steps are involved: S1. Select two m sequences of different lengths as pseudo-random codes, where the m sequence is the longest linear feedback shift register sequence, the lengths M and N of the two m sequences are mutually prime, and M and N are both expressed as 2 k -1, k is a positive integer; S2. splicing the two m sequences into a modulation sequence for phase modulation of the laser signal; S3. transmitting a phase-modulated laser signal to the target to be measured, the actual distance of which is greater than the maximum unambiguous measurement distance when the two selected m-sequences are measured separately, and then receiving an echo signal reflected from the target to be measured; S4. Process the received echo signal, use two m-sequences to measure the echo signal delays τ1 and τ2, and calculate the delays according to the code length T c The normalized echo signal delays B1 and B2 are calculated, and then the actual delay τ0 is obtained to determine the actual distance between the measured target and the measuring device.

2. The phase modulated continuous wave ranging system based on vernier effect according to claim 1, characterized in that: The step S4 calculates the actual distance L of the measured target, and the specific steps are as follows: S4.1 transfers the binary digital signals corresponding to the code elements of two m sequences of different lengths from the baseband to the intermediate frequency f, and then cross-correlates them with the codes of one period in the echo signal respectively. According to the known code length T c The two time delays τ1 and τ2 obtained by cross-correlation are used to calculate the normalized echo signal delay, that is, the normalized echo signal delay B1 = τ1 / T c = r + B m and B2 = τ2 / T c =s+B m , where r and s are non-negative integers less than the length of two m sequence codes, B m is the normalized residual delay, and B m =T m / T c , 0≤T m <T c is a residual delay less than one code length; S4.2 The time delay of the measured target τ0=τ1+pMT c =τ2+qNT c , M and N are the number of bits of the code element in two m sequences of different lengths, p and q are non-negative integers, and the normalized delay of the target under test is defined as B0 = τ0 / T c , where T c is the duration of a single code element, and then τ 1、 Substituting τ2 into the equation, the normalized delay of the target can be expressed as: B0 = B int +B m , where B int is the integer part of the normalized delay B0, B int =r+pM=s+qN,B m is the fractional part of the normalized delay B0; S4.3 According to the Chinese remainder theorem, solve the normalized delay integer part B int ; S4.4 According to the normalized delay integer part B int、 Normalized residual delay B m And the normalized delay B0, the actual delay τ0 and actual distance L of the measured target are calculated, the formula is as follows: τ0=B0T c L=cτ0 / 2 Where c is the speed of light.

3. The phase modulated continuous wave ranging system based on vernier effect according to claim 1 or 2, characterized in that: The following steps are also included: - providing a laser for emitting a single-frequency laser, wherein the line width of the laser ensures that the distance of the object to be measured is much smaller than the coherence length of the laser; - providing a beam splitter to split the laser into an emission branch and a detection branch; - In the transmitting branch, a binary code sequence generated by a signal generator is used to drive a phase modulator to perform phase modulation on an optical signal, and a fixed frequency shift f is applied to the modulated optical signal through an acousto-optic frequency shifter, and then the optical signal carrying the phase modulation information is transmitted to the target to generate an echo light through a transmitting device; - On the detection branch, a beam combiner is used to combine the split local optical signal with the echo light received by the receiving device, and then photoelectric conversion is performed through a photoelectric detector.

4. A phase modulated continuous wave ranging system based on vernier effect, characterized in that: include: A laser for emitting a single-frequency laser whose line width ensures that the distance of the object to be measured is much smaller than the coherence length of the laser; A beam splitter, used to split the laser light emitted by the laser into an emission branch and a detection branch; A phase modulator, arranged on the transmitting branch, is used to perform phase modulation on the laser according to the binary code sequence generated by the signal generator so as to load it onto the laser signal; A signal generator is used to generate a binary code sequence formed by splicing two m-sequences of different lengths front and back, and provide a synchronization signal; an acousto-optic frequency shifter, arranged on the transmitting branch, for applying a fixed frequency shift to the modulated laser; A transmitting device, used for transmitting an optical signal carrying phase modulation information toward a target to be measured; A receiving device, used for receiving the echo light of the measured target; A beam combiner, used for combining the local light on the detection branch and the echo light received by the receiving device; A photodetector, used to convert the combined optical signal into an electrical signal; The signal processing module is used to process the electrical signal output by the photodetector, and calculate the integer part B of the normalized delay according to the Chinese remainder theorem based on the delay results measured by the two m-sequences, namely τ1 and τ2. int , combined with the known residual B m , and then find the actual distance of the target.

5. The phase modulated continuous wave ranging system based on vernier effect according to claim 4, characterized in that: The binary code sequence generated by the signal generator consists of two code elements whose numbers are mutually prime and can be expressed as 2 k -1 form of m sequence spliced ​​front and back.

6. The phase modulated continuous wave ranging system based on vernier effect according to claim 6, characterized in that: It also includes a calibration device for calibrating the optical path between the transmitting device and the receiving device to improve the ranging accuracy.

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