Research On The Signal Acquisition And Phase Solution For Dual-Comb Multi-Wavelength Interferometric Laser Ranging

Laser tracker can realize ultra-precise three-dimensional coordinate positioning,which plays an indispensable and crucial role in the development of cutting-edge aerospace equipment and scientific experimental equipment.Among them,the measurement accuracy of target absolute distance is the core parameter that limits the accuracy of three-dimensional coordinate positioning.For example,the assembly manufacturing of large aircraft and super large accelerators require the precision to reach micron level,and can realize online rapid measurement.Traditional modulated wave ranging method or laser interferometric displacement measurement method based on continuous phase measurement is generally used in existing laser trackers.The accuracy of the former is limited,and the latter can not be used in complex scenes because of the loss of distance information after the light is cut off.With the birth of optical frequency comb,laser absolute ranging technology has been developed rapidly.At present,the multi-wavelength interferometry method based on dual-comb can achieve the absolute measurement accuracy at the micron level,but the data resolution rate is only at the Hz level,or the offline data processing,which cannot meet the requirements of online,fast and high-precision measurement at the same time.Aiming at the above requirements,this paper focuses on the signal acquisition and phase solution technology of dual-comb multi-wavelength interferometric ranging,and designs and implements a signal acquisition and phase solution scheme that can simultaneously provide the characteristics of online,fast and high-precision.So the following research works are carried out in this paper:The traditional digital phase-locked amplification phase measurement technology can only accurately measure the phase of the single-frequency signal,and it is difficult to extract the phase information of the frequency ranging of multiple comb teeth in the interference signal of dual-comb simultaneously.By analyzing the frequency spectrum characteristics of dual-comb interference signals and the principle of orthogonal digital phase-locked amplification and measurement,it is found that the frequency signals of each comb tooth are difficult to be eliminated by the classical low-pass filter in the phase-locked amplification process,and the residual frequency spectrum of comb tooth leads to a large phase measurement error.In this regard,a dual-comb multi frequency synchronous phase measurement method based on comb CIC low-pass filter is proposed.By using the equal interval comb band stop characteristics of CIC filter,the comb spectrum except direct flow is greatly suppressed,so as to ensure the effective extraction of single target ranging spectrum.The error model of the signal processing is established,and the core index requirements of the signal acquisition and processing board card are analyzed and determined.In view of the actual signal obtained by dual-comb interference in this paper,there is a large phase measurement error in the phase solution results of the frequency signal of each comb tooth.By analyzing the relationship between the input signal strength and the successive approximation inverse tangent method（CORDIC algorithm）,it is determined that the key problem is that the signal amplitude limits the phase measurement accuracy.However,the existing hardware amplification circuit will introduce harmonic distortion,resulting in new phase measurement error.So the self-gain amplifier module of weak signal is designed and realized by the method of software amplification.According to the intensity of input signal,the module can be automatically amplified to different degrees,so as to realize the high-precision solution of phase information contained in the weak comb signal.The existing dual-comb multi-wavelength interferometric ranging system uses off-line data processing method,it is difficult to measure the target online and quickly.Firstly,a dual-channel board to collect and process high-speed signal for dual-optical comb multi-wavelength interferometry ranging application is designed and implemented.On the basis of the function design,the power integrity and signal integrity are analyzed by cadence software,and the key parameters of the board are optimized.The high-precision signal acquisition at 99MHz high-speed sampling frequency is realized.Secondly,the user interface of the signal acquisition and processing system is designed and implemented in the Labview software development environment,and the display and high-speed storage of measurement results are realized by using the"synchronous control technology-queue"method.On the basis of the above research works,a double optical frequency comb multi-wavelength interferometer ranging signal acquisition and phase solution software and hardware system is implemented,and its core indicators are tested.The results show that:the phase measurement error is less than±0.025°when input single signal intensity is 1.3V_p-p comb frequency;under the condition that a single signal intensity is only 20m V_p-p,the signal acquisition and phase solution system with the self-gain amplifier module can realize the correct calculation of the phase information contained in the low intensity comb signal,and the phase measurement error is less than±0.030°in the short-term and one-hour long-term test results,and the phase resolution can reach0.020°;under the simulated input of actual interference signals,the signal acquisition and phase solution system with the self-gain amplifier module can realize the synchronous extraction of the phase information contained in the frequency of multiple target comb teeth,and the phase measurement errors are all less than±0.030°.All the above test results meet the requirement of±0.060°phase measurement error.