Femtosecond optical comb large-size precision absolute distance measurement system in complex environment

Abstract

The invention discloses a femtosecond optical comb large-size precision absolute distance measurement system in a complex environment. Comprising a source module, a beam splitter, a third dichroic mirror, a fundamental frequency femtosecond optical comb reference detector, a frequency doubling femtosecond optical comb reference detector, a fourth dichroic mirror, a frequency doubling femtosecond optical comb measurement detector, a fundamental frequency femtosecond optical comb measurement detector, a phase discriminator, a ranging zero point mirror and a corner reflector. The source module comprises an atomic clock, a femtosecond optical comb, an optical fiber beam splitter, a signal generator, an electro-optical modulator, a lens, a frequency multiplication module, a first collimation beam expander, a second collimation beam expander, a first dichroic mirror and a second dichroic mirror. According to the scheme, the defects that in the prior art, the measurement range is insufficient, complex industrial sites are difficult to adapt, and the real-time performance is poor are overcome, and a new way is provided for breaking through the technical bottleneck of large-range, high-precision, dead-zone-free, rapid and real-time measurement in a complex environment; and a technical support is provided for engineering application of a femtosecond optical comb precision distance measurement technology and development of a subsequent measurement prototype.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of precise optical measurement and detection, and particularly relates to a femtosecond optical comb large-size precise absolute distance measurement system in a complex environment. BACKGROUND

[0002] In recent years, with the rapid development of aerospace and high-end intelligent manufacturing fields, large-size precise measurement applications represented by precise formation flight and large equipment precise manufacturing have increasingly high requirements for distance measurement technology. Femtosecond optical comb has been widely concerned in the field of precise distance measurement due to its excellent time-frequency characteristics and measurement traceability, and it has built a high-precision transfer from a microwave frequency reference to an optical frequency reference, providing strong traceability for distance measurement.

[0003] At present, the research on large-size high-precision absolute distance measurement technology based on femtosecond optical comb is mostly concentrated in the laboratory, and few consider the measurement problem in complex environments such as outdoors and industrial manufacturing sites. In the process of promoting the industrial application of femtosecond optical comb large-size absolute distance measurement technology, there are still defects in the expansion of non-ambiguous distance and real-time correction of air refractive index in the whole path in a complex environment, which cannot meet the demand of industrial sites for large-range, high-precision real-time measurement. SUMMARY

[0004] The technical problem of the application is to overcome the shortcomings of the prior art, provide a femtosecond optical comb large-size precise absolute distance measurement system in a complex environment, and provide a new way to break through the technical bottleneck of large-range, high-precision, non-dead-zone, fast real-time measurement in a complex environment. It provides technical support for the engineering application of femtosecond optical comb precise distance measurement technology in large equipment precise manufacturing, satellite precise formation, and the development of subsequent measurement prototypes.

[0005] In order to solve the above technical problems, the application discloses a femtosecond optical comb large-size precise absolute distance measurement system in a complex environment, comprising: a source module, a beam splitter, a third dichroic mirror, a fundamental frequency femtosecond optical comb reference detector, a frequency-doubled femtosecond optical comb reference detector, a fourth dichroic mirror, a frequency-doubled femtosecond optical comb measurement detector, a fundamental frequency femtosecond optical comb measurement detector, a phase discriminator, a distance zero mirror and an angle reflector.

[0006] The combined beam output by the source module is split into reference light and measurement light by the wideband beam splitter;

[0007] The reference light is split into frequency-doubled femtosecond optical comb A2 and fundamental frequency femtosecond optical comb B2 by the third dichroic mirror, and enters the frequency-doubled femtosecond optical comb reference detector and the fundamental frequency femtosecond optical comb reference detector respectively, and is used as a local reference signal;

[0008] The measurement light is transmitted to the distance to be measured D through the reference zero mirror, returned to the original path by the corner reflector, reflected by the wideband beam splitter, and then incident to the fourth dichroic mirror, and the frequency-doubled femtosecond optical comb A3 and the fundamental frequency femtosecond optical comb B3 are obtained by the fourth dichroic mirror, and then the two combs are respectively input into the frequency-doubled femtosecond optical comb measurement detector and the fundamental frequency femtosecond optical comb measurement detector;

[0009] The four frequency measurement signals obtained by the photoelectric conversion of the fundamental frequency femtosecond optical comb reference detector, the frequency-doubled femtosecond optical comb reference detector, the frequency-doubled femtosecond optical comb measurement detector and the fundamental frequency femtosecond optical comb measurement detector are simultaneously input into the phase discriminator, and the value of D is output after the processing and calculation of the phase discriminator, so as to realize the accurate measurement of the distance to be measured.

[0010] In the above-mentioned femtosecond optical comb large-size precise absolute distance measurement system in a complex environment, the source module comprises an atomic clock, a femtosecond optical comb, a fiber beam splitter, a signal generator, an electro-optical modulator, a lens, a frequency doubling module, a first collimating and expanding mirror, a second collimating and expanding mirror, a first dichroic mirror and a second dichroic mirror.

[0011] The atomic clock serves as a reference frequency reference and outputs two reference signals; one reference signal is used as a clock reference source of a servo control module to lock the repetition frequency of the femtosecond optical comb, and the other reference signal is used to synchronize the signal generator to output a high-stability radio frequency modulation signal with a frequency of f m and an amplitude of V m , which drives the fiber electro-optical modulator.

[0012] The femtosecond laser with a repetition frequency of f r emitted by the femtosecond optical comb is divided into two paths by the fiber beam splitter; one path of the femtosecond laser directly passes through the lens to focus and then enters the frequency doubling module to obtain the frequency-doubled femtosecond optical comb A1; the other path of the femtosecond laser interacts with the electro-optical modulator to generate the fundamental frequency femtosecond optical comb B1 with intensity modulation, thereby expanding the non-ambiguous distance.

[0013] The frequency-doubled femtosecond optical comb A1 is first compressed in divergence angle by the first collimating and expanding mirror to ensure long-distance transmission, and then reflected by the second dichroic mirror to the first dichroic mirror.

[0014] The fundamental frequency femtosecond optical comb B1 is first compressed in divergence angle by the second collimating and expanding mirror to ensure long-distance transmission, and then transmitted by the first dichroic mirror to combine with the frequency-doubled femtosecond optical comb A1 reflected by the second dichroic mirror, thereby outputting the combined light.

[0015] In the above-mentioned femtosecond optical comb large-size precise absolute distance measurement system in a complex environment, the electro-optical modulator is used for intensity modulation of the femtosecond optical comb with a stable repetition frequency, and a plurality of frequency measurement signals are obtained by intermodal beating to perform combined wavelength distance measurement, thereby completing the femtosecond optical comb precise distance measurement and demodulation to obtain long-distance high-precision interstellar distance information.

[0016] In the femtosecond optical comb large-size precise absolute distance measurement system in the above complex environment, the first collimating and expanding mirror, the second collimating and expanding mirror, the fiber beam splitter and the lens constitute a coaxial optical system for transmitting and receiving, which is used for ensuring the quality of the long-distance transmission light beam and high-efficiency transmitting and receiving.

[0017] In the femtosecond optical comb large-size precise absolute distance measurement system in the above complex environment, the frequency doubling module is used for realizing high-efficiency frequency doubling to obtain a frequency-doubled femtosecond optical comb, which realizes real-time self-correction of the refractive index together with the fundamental frequency femtosecond optical comb.

[0018] In the femtosecond optical comb large-size precise absolute distance measurement system in the above complex environment, the phase discriminator is used for signal processing, sampling and high-precision phase discrimination of the photoelectric converted laser beams of the transmitted and received fundamental frequency femtosecond optical comb and frequency-doubled femtosecond optical comb, and fusion processing of the multi-measuring scale signals to obtain the accurate value of the to-be-measured distance after demisting.

[0019] In the femtosecond optical comb large-size precise absolute distance measurement system in the above complex environment, the solving process of the to-be-measured distance D is as follows:

[0020] The fundamental frequency femtosecond optical comb and the frequency-doubled femtosecond optical comb are of dual wavelengths, and the fundamental frequency femtosecond optical comb demisting precise optical distance D1 and the frequency-doubled femtosecond optical comb demisting precise optical distance D2 are obtained by solving.

[0021] The coefficient A is calculated by using the dual-wavelength dispersion equation;

[0022] The value of the to-be-measured distance D is determined by the following formula (1):

[0023] D=D1-A·(D2-D1)··· (1).

[0024] In the femtosecond optical comb large-size precise absolute distance measurement system in the above complex environment, D1 is obtained by solving in the following manner:

[0025] Based on the fast Fourier transform FFT, the first repetition frequency sideband signal f r -f m , the second repetition frequency sideband signal f r +f m , and the high-order harmonic signal Nf r corresponding to each other, the reference-measurement signal phase difference Then:

[0026]

[0027] Wherein, N is a positive integer greater than 1, c represents the speed of light, Λ - represents the first coarse measuring scale, Λ + represents the second coarse measuring scale, and Λ N represents the fine measuring scale.

[0028] Λ - , Λ + , Λ N , Λ - , Λ + , Λ N , Λ

[0029]

[0030]

[0031] D coarse = M - · Λ - + D - = M + · Λ + + D + ... (4)

[0032] wherein D coarse represents a rough distance, M - represents an integer part of the first rough scale Λ - , M + represents an integer part of the second rough scale Λ + , M - , M + are non-negative integers;

[0033] If D + - D - ≥ 0, then M + = M - , substituting into the above equation (4) can be obtained:

[0034] M - = round[(D + - D - ) / (Λ - - Λ + )]... (5)

[0035] wherein round[] represents rounding off to the nearest integer;

[0036] If D + - D - < 0, then M + = M - + 1, substituting into the above equation (4) can be obtained:

[0037] M - = round[(D + - D - + Λ + ) / (Λ - - Λ + ​)]··· (6)

[0038] The solved M - is substituted into the above formula (4) to obtain the value of D coarse .

[0039] According to the value of D coarse solved, the centering operation algorithm is used to obtain the value K of the integer part of the high harmonic precision measurement ruler of the fundamental frequency femtosecond optical comb:

[0040] K = floor[(D coarse + 1 / 2·Λ N -D N ) / Λ N ]···(7)

[0041] Wherein, floor[] represents rounding down;

[0042] Then, we have:

[0043] D1 = K·Λ N +D N ···(8).

[0044] In the above femtosecond optical comb large-size precision absolute distance measurement system in a complex environment, D2 is solved by the following method:

[0045] The value of D coarse solved by the fundamental frequency femtosecond optical comb is used to solve the ambiguity of the high harmonic signal Nf r precision measurement distance of the frequency-doubled femtosecond optical comb; assuming that the reference-measurement signal phase difference of the high harmonic signal of the frequency-doubled femtosecond optical comb is , then the corresponding precision measurement distance D′ N is:

[0046]

[0047] Then, the value K′ of the integer part of the high harmonic precision measurement ruler of the frequency-doubled femtosecond optical comb is:

[0048] K′ = floor[(D coarse + 1 / 2·Λ N -D′ N ) / Λ N ]··· (10)

[0049] Then, D2 is:

[0050] D2 = K′·Λ N +D′ N ··· (11).

[0051] In the above femtosecond optical comb large-size precision absolute distance measurement system in a complex environment, the two-wavelength dispersion equation is represented as follows:

[0052] A = (n1-1) / (n2-n1)··· (12)

[0053] Wherein, n1 represents the refractive index corresponding to the fundamental femtosecond optical comb, n2 represents the refractive index corresponding to the frequency-doubled femtosecond optical comb.

[0054] The present application has the following advantages:

[0055] The present application discloses a kind of femtosecond optical comb large size precision absolute ranging system under complex environment, adopts dual-wavelength femtosecond optical comb intensity modulation wavelength synthesis method, different ruler phase information is obtained based on the high-precision synchronous phase discrimination of fast Fourier transform (FFT) multiple rulers combination to be used for wavelength synthesis ranging, can overcome the delay defect of laser interference ranging existing breakage connection, solve the problem of the present femtosecond optical comb ranging technology measurement precision, measurement range and measurement speed;Combination femtosecond optical comb and dual-wavelength simultaneous ranging, solve the real-time self-modification problem of refractive index under complex environment;With the advantages of high ranging accuracy, long range, adapt to complex industrial field, good real-time performance etc. BRIEF DESCRIPTION OF DRAWINGS

[0056] Figure 1 It is the structure diagram of a kind of femtosecond optical comb large size precision absolute ranging system under complex environment in the embodiment of the present application. DETAILED DESCRIPTION

[0057] To make the purpose, technical scheme and advantages of the present application more clear, the following will be further detailed description to the disclosed embodiment of the present application in conjunction with drawings.

[0058] One of the core ideas of the present application is that, as described in the background, current femtosecond comb-based large-size high-precision absolute ranging technology research is mostly concentrated in the laboratory, and few consider the measurement problem in complex environments such as outdoor and industrial manufacturing sites. In the process of promoting the industrial application of femtosecond comb large-size absolute ranging technology, there are still defects in the expansion of non-ambiguous distance and real-time correction of full-path air refractive index in complex environments, which cannot meet the needs of complex industrial sites for large-scale, high-precision real-time measurement. Based on this, the present application provides a femtosecond comb large-size precise absolute ranging system in complex environments to overcome the problems of insufficient measurement range, difficulty in adapting to complex industrial sites, and poor real-time performance of existing high-precision laser ranging technology. The femtosecond comb large-size precise absolute ranging system in complex environments mainly consists of three parts: a femtosecond comb modulation system, an optical system, and a circuit system. Among them, the femtosecond comb modulation system is used to provide a high-stable femtosecond comb modulation light source; the optical system is used to collimate and expand the laser beam emitted by the femtosecond comb modulation system and to receive the laser beam reflected by the cooperative target after transmission; the circuit system is used to process and sample the emitted and received base frequency and frequency-doubled femtosecond comb electric conversion signals to obtain ranging signals, and to fuse the base frequency and frequency-doubled multi-measuring ruler signals to obtain real-time precise ranging information. Further, the femtosecond comb modulation system uses an electro-optical modulator to intensity-modulate a frequency-stable femtosecond comb, and simultaneously acquires a suitable measuring ruler for wavelength synthesis ranging to obtain long-distance high-precision interstellar distance information. The optical system uses a transceiver coaxial collimating and expanding light path to ensure that the laser transmits over a long distance with a small divergence angle, and uses a dichroic mirror and a beam splitter to combine and split the base frequency and frequency-doubled femtosecond combs, realizing the emission of dual-wavelength laser beams to the cooperative target in the same light path. The circuit system receives and processes the emitted and received laser signals of the femtosecond comb modulation system and the optical system, completes high-precision phase discrimination and wavelength synthesis ranging of multi-measuring ruler signals, and realizes real-time deambiguating of high-precision distance.

[0059] Reference Figure 1In the embodiment, the femtosecond optical comb large-size precise absolute distance measurement system in the complex environment comprises a source module, a beam splitter 12, a third dichroic mirror 13, a fundamental frequency femtosecond optical comb reference detector 14, a frequency-doubled femtosecond optical comb reference detector 15, a fourth dichroic mirror 16, a frequency-doubled femtosecond optical comb measurement detector 17, a fundamental frequency femtosecond optical comb measurement detector 18, a phase discriminator 19, a distance zero mirror 20 and an angle reflector 21. The source module comprises an atomic clock 1, a femtosecond optical comb 2, a fiber beam splitter 3, a signal generator 4, an electro-optical modulator 5, a lens 6, a frequency-doubled module 7, a first collimating beam expander 8, a second collimating beam expander 9, a first dichroic mirror 10 and a second dichroic mirror 11. The combined light output by the source module is split into reference light and measurement light by the broadband beam splitter 12: the main atomic clock 1 of the source module is used as a reference frequency reference, and two reference signals are output; one reference signal is used as a clock reference source of a servo control module to lock the repetition frequency of the femtosecond optical comb 2, and the other reference signal is used to synchronize a high-stability radio frequency modulation signal with a frequency of f m and an amplitude of V m output by the signal generator 4 to drive the fiber electro-optical modulator 5. The femtosecond laser with a repetition frequency of f r emitted by the femtosecond optical comb 2 is split into two paths by the fiber beam splitter 3; one path of the femtosecond laser directly passes through the lens 6 to be focused into the frequency-doubled module 7, and the frequency-doubled femtosecond optical comb A1 is obtained after the frequency-doubled module 7; the other path of the femtosecond laser passes through the electro-optical modulator 5 to generate the intensity-modulated fundamental frequency femtosecond optical comb B1, thereby expanding the non-ambiguous distance. The frequency-doubled femtosecond optical comb A1 is first compressed in divergence angle by the first collimating beam expander 8 to ensure long-distance transmission, and then reflected by the second dichroic mirror 11 to the first dichroic mirror 10. The fundamental frequency femtosecond optical comb B1 is first compressed in divergence angle by the second collimating beam expander 9 to ensure long-distance transmission, and then transmitted through the first dichroic mirror 10 to be combined with the frequency-doubled femtosecond optical comb A1 reflected by the second dichroic mirror 11, thereby outputting the combined light. The reference light is split into the frequency-doubled femtosecond optical comb A2 and the fundamental frequency femtosecond optical comb B2 by the third dichroic mirror 13, and is respectively input into the frequency-doubled femtosecond optical comb reference detector 15 and the fundamental frequency femtosecond optical comb reference detector 14 to be used as a local reference signal. The measurement light is transmitted through the distance to be measured D by the reference zero mirror 20, and then returned by the angle reflector 21, and then reflected by the broadband beam splitter 12 to be incident on the fourth dichroic mirror 16, thereby being split into the frequency-doubled femtosecond optical comb A3 and the fundamental frequency femtosecond optical comb B3, which are respectively input into the frequency-doubled femtosecond optical comb measurement detector 17 and the fundamental frequency femtosecond optical comb measurement detector 18. The four paths of the signals generated by photoelectric conversion of the fundamental frequency femtosecond optical comb reference detector 14, the frequency-doubled femtosecond optical comb reference detector 15, the frequency-doubled femtosecond optical comb measurement detector 17 and the fundamental frequency femtosecond optical comb measurement detector 18 are simultaneously input into the phase discriminator 19 after intermodal beat frequency conversion, and the value of D is output after processing and solving by the phase discriminator 19, thereby realizing accurate measurement of the distance to be measured.

[0060] In the embodiment, the atomic clock 1 is used to provide high-precision time-frequency reference for the femtosecond optical comb 2 and the signal generator 4; the femtosecond optical comb 2 is used to provide a high-stable femtosecond optical comb light source for large-range precision ranging; the signal generator 4 is used to provide a low-frequency sinusoidal modulation driving signal for the electro-optical modulator 5; the electro-optical modulator 5 is used to modulate the intensity of the repetition frequency stabilized femtosecond optical comb 2, to obtain a plurality of frequency measuring ruler signals through inter-mode beat frequency to perform combined wavelength method ranging, to complete femtosecond optical comb precision measuring ruler distance demodulation, and to obtain long-distance high-precision inter-satellite distance information. The frequency doubling module 7 is used to realize high-efficiency frequency doubling to obtain a frequency-doubled (780 nm) femtosecond optical comb, which is used together with the fundamental frequency femtosecond optical comb (1560 nm) to realize real-time self-correction of double-wavelength refractive index. The first collimating and beam expanding mirror 8, the second collimating and beam expanding mirror 9, the fiber beam splitter 3, and the lens 6 constitute a transceiver coaxial optical system, which is used to ensure the quality of long-distance transmission light beams and high-efficiency transceiving. In the embodiment, the phase detector 19 is used to perform signal processing, sampling, and high-precision phase discrimination on the photoelectric converted laser beams of the transmitted and received fundamental frequency femtosecond optical comb and the frequency-doubled femtosecond optical comb, and to perform fusion processing on the multiple measuring ruler signals to obtain the accurate value of the demodulated distance to be measured.

[0061] In the embodiment, the solving process of the distance to be measured D is as follows:

[0062] S1, the fundamental frequency femtosecond optical comb and the frequency-doubled femtosecond optical comb are double wavelengths, and the precision measured optical distance D1 after demodulation of the fundamental frequency femtosecond optical comb and the precision measured optical distance D2 after demodulation of the frequency-doubled femtosecond optical comb are obtained.

[0063] In the embodiment, D1 can be obtained by the following method:

[0064] Based on the fast Fourier transform FFT, the first repetition frequency sideband signal f r -f m , the second repetition frequency sideband signal f r +f m , and the high-order harmonic signal Nf r are obtained. Then, the following equation is obtained:

[0065]

[0066] Wherein, N is a positive integer greater than 1, c represents the speed of light, Λ - represents the first coarse measuring ruler, Λ + represents the second coarse measuring ruler, and Λ N represents the precision measuring ruler.

[0067] The non-fuzzy distance NAR(Λ - , Λ + , and Λ N is obtained. - , Λ+ , Λ N Distance value D - , D + , D N are respectively:

[0068]

[0069] The above distance values ignore the influence of air refractive index and are expressed as optical distance.

[0070] The distance coarse measurement is completed by two first-order sidebands of the frequency signal.

[0071] Sideband signal f r -f m , f r +f m Measure the same distance, there are:

[0072] D coarse =M - ·Λ - +D - =M + ·Λ + +D + ... (4)

[0073] Wherein, D coarse represents the coarse measurement distance, M - represents the integer part of the first coarse measurement ruler Λ - , M + represents the integer part of the second coarse measurement ruler Λ + , M - , M + are non-negative integers.

[0074] If D + -D - ≥0, then M + =M - , substituting the above formula (4) can be obtained:

[0075] M - =round[(D + -D - ) / (Λ - -Λ + )]... (5)

[0076] Wherein, round[] represents rounding to the nearest integer.

[0077] On the contrary, if D + -D - <0, then M + =M - +1, substituting the above formula (4) can be obtained:

[0078] M - = round[(D + -D - +Λ + ) / (Λ - -Λ + )]··· (6)

[0079] The solved M - is brought into the above formula (4), and the value of D coarse is obtained.

[0080] Further, according to the value of D coarse solved, the value of the integer part of the high harmonic precision ruler of the fundamental femtosecond optical comb K is obtained by using the rounding algorithm:

[0081] K = floor[(D coarse +1 / 2·Λ N -D N ) / Λ N ]··· (7)

[0082] Wherein, floor[ ] represents rounding down.

[0083] Then:

[0084] D1 = K·Λ N +D N ··· (8)

[0085] Further, D2 can be solved by the following way:

[0086] The value of D coarse solved by the fundamental femtosecond optical comb is used to solve the ambiguity of the high harmonic precision distance of the frequency-doubled femtosecond optical comb Nf r ; assuming that the reference-measurement signal phase difference of the high harmonic signal of the frequency-doubled femtosecond optical comb is , then the corresponding precision distance D′ N is:

[0087]

[0088] Then, the value of the integer part of the high harmonic precision ruler of the frequency-doubled femtosecond optical comb K′ is:

[0089] K′ = floor[(D coarse +1 / 2·Λ N -D′ N ) / Λ N ]··· (10)

[0090] Then, D2 is:

[0091] D2 = K′·ΛN +D' N ··· (11)

[0092] S2, the coefficient A is calculated by using the dual-wavelength dispersion equation.

[0093] In the embodiment, the dual-wavelength dispersion equation is expressed as follows:

[0094] A = (n1-1) / (n2-n1)··· (12)

[0095] Wherein, n1 represents the refractive index corresponding to the fundamental femtosecond optical comb, and n2 represents the refractive index corresponding to the frequency-doubled femtosecond optical comb.

[0096] S3, the value of the distance to be measured D is determined:

[0097] D = D1-A·(D2-D1)··· (1)

[0098] In the embodiment, since the coefficient A is not sensitive to environmental factors and is independent of the initial environmental factors, it can be approximately considered that A is a constant only related to the wavelength. Therefore, only by using the dual-wavelength dispersion equation and the Ciddor formula, the coefficient A is calculated based on the initial temperature, humidity, pressure, CO2 content and other parameters, and the two optical distances D1 and D2 obtained by the dual-wavelength of the fundamental femtosecond optical comb and the frequency-doubled femtosecond optical comb, the accurate measurement of the measured distance can be realized without real-time accurate measurement of the air refractive index.

[0099] In application, first, the appropriate modulation amplitude and modulation frequency are set for the electro-optic modulator, the phase detector carries out multi-scale synchronous phase detection based on fast Fourier transform (FFT) on the obtained fundamental femtosecond optical comb modulation photoelectric detection signal and the frequency-doubled femtosecond optical comb photoelectric detection signal, and the dual-wavelength ranging of the femtosecond optical comb and the frequency-doubled femtosecond optical comb is completed. Thus, the optical distance obtained by the fundamental femtosecond optical comb is D1. Similarly, the ranging of the frequency-doubled femtosecond optical comb can be studied, and the ranging result D1 of the fundamental femtosecond optical comb is used as the coarse measurement distance to complete the ranging result demodulation of the frequency-doubled femtosecond optical comb, and the optical distance value D2 measured by the frequency-doubled femtosecond optical comb is obtained. Due to the dispersion, the refractive index of laser of different wavelengths in the air is different, so the measured optical distance is different. Assuming that the measured distance is D, D1 and D2 are the optical distances measured by the two wavelengths of 1560 nm and 780 nm, the measured distance D can be expressed as D = D1-A·(D2-D1), A = (n1-1) / (n2-n1), the coefficient A is not sensitive to environmental factors and is independent of the initial environmental factors, and the coefficient A can be approximately considered to be related to the wavelength only. Finally, only by using the dual-wavelength dispersion equation to calculate the coefficient A, and combining the two optical distance information obtained by the dual-wavelength, the accurate measurement of the measured distance can be realized without real-time accurate measurement of the air refractive index.

[0100] In summary, the femtosecond optical comb large-size precise absolute distance measurement system in a complex environment disclosed in the application adopts a dual-wavelength femtosecond optical comb intensity modulation wavelength synthesis method, acquires different ruler phase information based on a high-precision synchronous phase discrimination of a fast Fourier transform (FFT) multi-ruler combination to perform wavelength synthesis distance measurement, can overcome the light interruption and connection delay defects of laser interference distance measurement, solves the problems of measurement precision, measurement range and measurement speed of the femtosecond optical comb distance measurement technology, and solves the real-time self-correction problem of the refractive index in a complex environment by combining the femtosecond optical comb and dual-wavelength simultaneous distance measurement, and has the advantages of high distance measurement precision, long distance measurement range, adaptation to complex industrial sites, good real-time performance and the like.

[0101] On the basis of the above-mentioned embodiment, the application further discloses a femtosecond optical comb large-size precise absolute distance measurement method in a complex environment based on the above-mentioned system, comprising:

[0102] S1, emitting a fundamental frequency femtosecond optical comb beam and a frequency-doubled femtosecond optical comb beam to a cooperative target, the cooperative target reflecting the laser beams and returning along the original path, and then processing the laser beams by a phase discrimination meter, and obtaining a coarse distance D measured by the fundamental frequency femtosecond optical comb based on a wavelength synthesis method phase distance measurement of a multi-ruler FFT. coarse .

[0103] S2, the coarse distance D measured by the fundamental frequency femtosecond optical comb coarse is fused with a high-order harmonic precision ruler thereof through a centering operation to obtain a precise optical distance after demodulation, and the precise optical distance after demodulation is fused with a high-order harmonic precision ruler of the frequency-doubled femtosecond optical comb to obtain a precise optical distance D1 after demodulation of the fundamental frequency femtosecond optical comb.

[0104] S3, the coarse distance D measured by the fundamental frequency femtosecond optical comb coarse is fused with a high-order harmonic ruler distance measurement result of the frequency-doubled femtosecond optical comb through a centering operation to obtain a precise optical distance D2 after demodulation of the frequency-doubled femtosecond optical comb; the initial environmental parameters (temperature, humidity, pressure, CO2 content and the like) obtained are brought into a Ciddor refractive index formula to calculate a refractive index n1 corresponding to the fundamental frequency femtosecond optical comb and a refractive index n2 corresponding to the frequency-doubled femtosecond optical comb, and then a coefficient A=(n1-1) / (n2-n1) is determined based on a dual-wavelength dispersion equation.

[0105] S4, fusing D1 and D2 to obtain D=D1-A·(D2-D1).

[0106] For the method embodiment, since it corresponds to the system embodiment, the description is relatively simple, and the related parts are described in the system embodiment part.

[0107] Although the present application has been disclosed with reference to the preferred embodiments, it is not intended to limit the present application to the preferred embodiments. Any person skilled in the art, without departing from the spirit and scope of the present application, can make possible changes and modifications to the technical solutions of the present application by using the disclosed methods and technical contents. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present application, without departing from the technical solutions of the present application, shall fall within the protection scope of the technical solutions of the present application.

[0108] The contents not described in detail in the specification of the present application belong to the known technology of the person skilled in the art.

Claims

1. A femtosecond optical comb large-size precise absolute distance measuring system in a complex environment, characterized in that, It comprises: a source module, a beam splitter (12), a third dichroic mirror (13), a fundamental frequency femtosecond optical comb reference detector (14), a frequency-doubled femtosecond optical comb reference detector (15), a fourth dichroic mirror (16), a frequency-doubled femtosecond optical comb measurement detector (17), a fundamental frequency femtosecond optical comb measurement detector (18), a phase detector (19), a ranging zero point mirror (20) and an angle reflector (21); The combined light output by the source module is split into reference light and measurement light by the wideband beam splitter (12); The reference light is split into frequency-doubled femtosecond optical comb A2 and fundamental frequency femtosecond optical comb B2 by the third dichroic mirror (13), and enters the frequency-doubled femtosecond optical comb reference detector (15) and the fundamental frequency femtosecond optical comb reference detector (14) respectively, serving as a local reference signal; The measurement light is transmitted by the reference zero point mirror (20) to be measured distance D, and then returned by the angle reflector (21) by the original route, and then reflected by the wideband beam splitter (12) and incident to the fourth dichroic mirror (16), and split into frequency-doubled femtosecond optical comb A3 and fundamental frequency femtosecond optical comb B3 by the fourth dichroic mirror (16), and enters the frequency-doubled femtosecond optical comb measurement detector (17) and the fundamental frequency femtosecond optical comb measurement detector (18) respectively; The four light signals converted by the fundamental frequency femtosecond optical comb reference detector (14), the frequency-doubled femtosecond optical comb reference detector (15), the frequency-doubled femtosecond optical comb measurement detector (17) and the fundamental frequency femtosecond optical comb measurement detector (18) are simultaneously input into the phase detector (19) after inter-mode beat frequency conversion, and the value of D is output after processing and solving by the phase detector (19), realizing accurate measurement of the distance to be measured.

2. The femtosecond optical comb large-size precise absolute distance measurement system in a complex environment according to claim 1, characterized in that, The source module comprises: an atomic clock (1), a femtosecond optical comb (2), a fiber beam splitter (3), a signal generator (4), an electro-optical modulator (5), a lens (6), a frequency doubling module (7), a first collimating and expanding mirror (8), a second collimating and expanding mirror (9), a first dichroic mirror (10) and a second dichroic mirror (11); The atomic clock (1) outputs two reference signals as a reference frequency benchmark. One reference signal is used as a clock reference source of a servo control module to lock the repetition frequency of a femtosecond optical comb (2), and the other reference signal is used to synchronize a signal generator (4) to output a high-stability radio frequency modulation signal with a frequency of f m and an amplitude of V m , which drives a fiber electro-optical modulator (5). The repetition rate of the femtosecond optical comb (2) is f r The femtosecond laser is split into two paths by the optical fiber beam splitter (3); one path of the femtosecond laser directly passes through the lens (6) to be focused and then enters the frequency doubling module (7), and the frequency doubling module (7) obtains the frequency-doubled femtosecond optical comb A1; the other path of the femtosecond laser interacts with the electro-optical modulator (5) to generate the intensity-modulated fundamental frequency femtosecond optical comb B1, and the non-blurring distance is expanded; The frequency-doubled femtosecond optical comb A1 is first compressed and diverged by the first collimating and expanding mirror (8) to ensure long-distance transmission, and then reflected by the second dichroic mirror (11) to the first dichroic mirror (10); The fundamental frequency femtosecond optical comb B1 is first compressed and diverged by the second collimating and expanding mirror (9) to ensure long-distance transmission, and then transmitted by the first dichroic mirror (10) and combined with the frequency-doubled femtosecond optical comb A1 reflected by the second dichroic mirror (11), outputting the combined light.

3. The femtosecond optical comb large-size precise absolute distance measurement system in a complex environment according to claim 2, characterized in that, The electro-optical modulator (5) is used for intensity modulation of the frequency-stable femtosecond optical comb (2), and a plurality of frequency measurement scale signals are obtained by inter-mode beat frequency to synthesize wavelength method ranging, and the femtosecond optical comb is de-muddled to measure the distance to obtain long-distance high-precision inter-satellite distance information.

4. The femtosecond optical comb large-size precise absolute distance measurement system in a complex environment according to claim 2, characterized in that, The first collimating and expanding mirror (8), the second collimating and expanding mirror (9), the fiber beam splitter (3) and the lens (6) constitute a coaxial optical system for receiving and transmitting, which is used for ensuring the quality of long-distance transmission light and high-efficiency receiving and transmitting.

5. The femtosecond optical comb large-size precise absolute distance measurement system in a complex environment according to claim 2, characterized in that, The frequency doubling module (7) is used for realizing high-efficiency frequency doubling to obtain a frequency-doubled femtosecond optical comb, which together with the fundamental frequency femtosecond optical comb realizes real-time self-correction of double-wavelength refractive index.

6. The femtosecond optical comb large-size precise absolute distance measurement system in a complex environment according to claim 2, characterized in that, The phase-detecting meter (19) is used for signal processing, sampling and high-precision phase discrimination of the emitted and received base frequency femto optical comb and frequency-doubled femto optical comb photoelectric conversion laser beams, and fusion processing of multiple measuring scale signals to obtain the accurate value of the demodulated distance to be measured.

7. The femtosecond optical comb large-size precise absolute distance measurement system in a complex environment according to claim 6, characterized in that, The calculation process of the distance to be measured D is as follows: The base frequency femto optical comb and the frequency-doubled femto optical comb are double wavelengths, and the base frequency femto optical comb demodulated accurate optical distance D1 and the frequency-doubled femto optical comb demodulated accurate optical distance D2 are obtained by calculation; The coefficient A is obtained by calculation using a double-wavelength dispersion equation; The value of the distance to be measured D is determined by the following formula (1): D=D1-A·(D2-D1)···(1).

8. The femtosecond optical comb large-size precise absolute distance measurement system in a complex environment according to claim 7, characterized in that, D1 is obtained by calculation in the following manner: Based on fast Fourier transform FFT, the first repetition frequency sideband signal f of the base frequency femtosecond optical comb conversion is obtained r -f m , the second repetition frequency sideband signal f r +f m , the high harmonic signal Nf r The respective reference-measurement signal phase difference Then, where N is a positive integer greater than 1, c represents the speed of light, Λ - represents a first coarse measurement scale, Λ + represents a second coarse measurement scale, Λ N represents a fine measurement scale; Λ - Λ + Λ N The distance values D - D + D N respectively are: Then, D coarse = M - · Λ - + D - = M + · Λ + + D + ...... (4) where D coarse represents a rough distance, M - represents an integer part of the first rough scale Λ - , M + represents an integer part of the second rough scale Λ + , M - , M + are non-negative integers; If D + - D - ≥ 0, then M + = M - , substituting into the above equation (4) gives: M - = round[(D + -D - ) / (Λ - -Λ + )] ··· (5) Wherein, round[] represents rounding off; If D + -D - <0, then M + = M - +1, substituting into the above equation (4) gives: M - = round[(D + -D - +Λ + ) / (Λ - -Λ + )]···(6) The value of D is obtained by substituting the solved M - into the above equation (4). coarse ​ According to the value of D coarse , the integer part of the value of the high harmonic precision measurement scale of the fundamental frequency femtosecond optical comb K is obtained by using the centering operation algorithm. K = floor[(D coarse + 1 / 2 · Λ N - D N ) / Λ N ]... (7) Wherein, floor[] represents rounding down; Then, D1 = K Λ N + D N ... (8).

9. The femtosecond optical comb large-size precise absolute distance measurement system in a complex environment according to claim 8, characterized in that, D2 is obtained by calculation in the following manner: The value of D obtained by solving the fundamental frequency femtosecond optical comb coarse , the high harmonic signal Nf r of the frequency-doubled femtosecond optical comb, is used to solve the ambiguity of the precise distance measurement; assuming that the reference-measurement signal phase difference of the high harmonic signal of the frequency-doubled femtosecond optical comb is , then the corresponding precise distance D′ N is: Then, the value of the integer part of the frequency-doubled femto optical comb high-order harmonic accurate measuring scale K' is: K' = floor[(D coarse + 1 / 2 · Λ N - D' N ) / Λ N ]... (10) Then, D2 is: D2= K' - Λ N + D' N (11).

10. The femtosecond optical comb large-size precise absolute distance measuring system in complex environment according to claim 9, characterized in that, The double-wavelength dispersion equation is as follows: A=(n1-1) / (n2-n1)···(12) Wherein, n1 represents the refractive index corresponding to the base frequency femto optical comb, and n2 represents the refractive index corresponding to the frequency-doubled femto optical comb.

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