FPGA Implementation Of Ultrashort Laser Pulse Envelope Reconstruction And Its Application In Precision Ranging

A femtosecond laser pulse is a laser pulse having a pulse width of the order of femtoseconds,also referred to as an ultrashort laser pulse.In recent years,femtosecond lasers have been widely used in the field of distance measurement.High update rate femtosecond laser ranging is suitable for applications such as lidar,satellite formation flying,and space-based synthetic aperture imaging,which rely on high precision and high real-time distance measurement.In small-size and low-power scenarios such as microsatellite platforms,femtosecond laser ranging systems are moving toward integration and miniaturization.At the same time,with the increase of the laser pulse frequency,the data processing platform of the ranging system is put forward higher requirements.For the integrated femtosecond laser ranging system,this paper designs and implements an FPGA-based hardware data processing platform,and combines the quasi-Newton algorithm to realize ultrashort laser pulse envelope reconstruction,which extracts the pulse flight time interval more accurately and improves the system accuracy and real-time performance.The design divides the hardware data processing platform into seven functional modules according to the femtosecond laser ranging principle,including phase-locked loop module,dynamic threshold filtering module,pulse envelope reconstruction module,repetition frequency measurement module,ranging result calculation module,Kalman filter module and communication interface module.The hardware implementation method of ultrashort laser pulse envelope reconstruction is mainly studied in this paper.The hardware architecture of the pulse envelope reconstruction module is built based on the Gaussian function fitting algorithm.This paper proposes two hardware architectures for ultrashort laser pulse envelope reconstruction FPGA implementation,hardware architecture based on Caruana algorithm and its improved algorithm,and hardware architecture based on BFGS quasi-Newton algorithm.The hardware architecture based on Caruana algorithm and its improved algorithm has low computational complexity and fast calculation speed,which is easy to implement on the hardware platform,but at the cost of precision loss and low versatility.The hardware architecture based on BFGS quasi-Newton algorithm has small precision loss and good versatility,and can be used for different pulse function models,but the computational complexity is high.The BFGS hardware architecture design is optimized by parallel computing,pipeline technology and approximate computing technology,which effectively improves the BFGS hardware architecture in terms of computing speed.The above hardware design is implemented on an FPGA development board by Xilinx's EDA tool Vivado.The hardware design has a maximum operating frequency of 250 MHz.Using the hardware data processing platform designed in this paper,the integrated dual-optical comb femtosecond laser absolute distance measurement system can achieve absolute distance measurement of micrometer precision within a few tens of meters,and the update rate of the ranging result reaches 2 KHz.The hardware architecture based on the BFGS quasi-Newton algorithm has less precision loss.Compared with the hardware architecture based on Caruana algorithm,the precision loss is reduced by 63.63%.While the accuracy of the distance data is improved,the requirements of high real-time measurement of the precision ranging system are met.