Research On Frequency Capture Technology Of Pulsed Laser PLL

Compared with the traditional communication technology,coherent optical communication technology has the advantages of high sensitivity,long transmission distance and fast transmission of massive data.If pulse laser modulation is used in coherent detection,the peak power of the signal laser will be greater,which will increase the receiving sensitivity of the receiver and greatly improve the detection distance.Pulse laser PLL is the key technology of pulse coherent detection technology.It can realize the phase locking between the continuous local oscillator laser and the pulse signal laser.In recent years,it has become a hot spot in the research of coherent optical communication technology.Based on the wide-band and low delay PLL,the frequency acquisition technology of PLL is studied in this paper.It is hoped to realize the fast frequency acquisition of PLL and reduce the initial frequency difference to the fast capture band of PLL,so as to realize the phase locking.The main content of this paper is divided into the following four parts:(1)This paper introduces the research background of optical PLL technology,compares the advantages and disadvantages of pulse coherent detection and traditional coherent detection technology,and summarizes the research status of optical PLL at home and abroad.(2)This paper briefly introduces and theoretically analyzes several typical structures of optical PLL,then introduces the principle of Doppler effect,analyzes the influence of Doppler frequency shift on the frequency acquisition process of optical PLL,and compares four kinds of auxiliary frequency acquisition technology schemes,and concludes that the digital frequency discrimination auxiliary frequency acquisition technology is in the aspects of frequency acquisition accuracy,acquisition range,automation,etc Advantages.(3)Based on the auxiliary frequency acquisition technology of frequency discriminator,the possibility of frequency measurement of pulse frequency difference signal by digital frequency discriminator based on FFT is analyzed,and the structure of digital frequency discriminator and frequency controller which can effectively stack frequency discriminator voltage and loop signal are designed.The FPGA processing control unit and digital to analog conversion unit are developed.The digital frequency discriminator is composed of the clock generating unit and the signal acquisition unit.The FPGA chip of the FPGA processing control unit is programmed.The FPGA chip is divided into four modules,which are ADC control module,threshold detection and data deceleration module,FFT module and spectrum information filtering module.The signal acquisition unit is completed Function configuration,acquisition and deceleration of pulse difference frequency signal data,FFT operation,frequency value calculation and other functions.(4)Finally,the pulse laser phase-locked loop,the digital frequency discriminator and the frequency controller are connected to form a closed loop.The frequency acquisition experiment of the pulse laser phase-locked loop is carried out.The experimental results show that the auxiliary frequency acquisition system can realize the frequency of the pulse laser phase-locked loop Rate capture reduces the initial frequency difference of the loop to less than 1MHz.At this time,the PLL can quickly phase lock and complete the phase lock.Experimental results show that the auxiliary frequency acquisition system can capture ± 100 MHz pulse difference frequency signal in 100 ms.