Research On Wide-band Low-delay Optical Phase-locked Loop

Wideband laser phase-locked technology is mainly applied to homodyne laser coherent detection.Because the reflected laser of target is weak and interfered by space light(such as sunlight,space scattering light,artificial light source),it is difficult to detect and track in long distance.By means of wide-band laser phase-locking technology,the frequency and phase lock of echo pulse laser and local laser can be achieved,thus homodyne coherent detection of weak pulse laser echo signal can be realized.At the same time,the attention and research of laser phase-locked technology at home and abroad in recent years,In recent years,it has promoted the application of optical phase-locked technology in coherent optical communication,microwave photonics,coherent terahertz photonics and so on.In this paper,the broadband and low-delay phase-locked loop is studied,considering the bandwidth and delay of the loop.In the design and development of the loop,by miniaturizing the loop components and shortening the length of loop path,the broadband of the phase-locked loop is improved and the delay is reduced.This paper first introduces the application background of laser phase-locked loop,and the research progress and development direction of laser phase-locked loop at home and abroad are analyzed.At present,optical phase-locked technology is usually used in continuous laser.In order to realize pulse laser phase-locked loop,a wide-band laser phase-locked loop scheme is proposed in this paper.and the basic principle of balanced phase-locked loop is analyzed by using the structure of balanced phase-locked loop.At the same time,the main components of laser phase-locked loop include 90 °optical mixer,loop filter and wide-band tunable laser.The phase-locked loop model of pulse laser is established and analyzed by using linear phase model.The loop capture band and capture time are theoretically analyzed and simulated.By reducing the loop delay and increasing the frequency modulation bandwidth,the loop capture band can reach 120 MHz.At the same time,by reasonably selecting the loop gain,the phase-locked phase can be completed at the rising edge of the pulse.The smaller the initial frequency difference is,the shorter the acquisition time is,the better the recovery effect of pulse waveform is.The laser phase-locked loop model was built by Simulink,and the loop capture time was simulated,and theoretical analysis was made on the thermal noise,bulk noise,intensity noise,phase-locked precision and phase-locked laser power of the phase-locked loop.This article further has completed the design of laser phase-locked loop(PLL),has designed the overall structure of the laser phase-locked loop(PLL),and designed the whole optical path of the laser phase-locked loop mechanical structure,at the same time have already completed the 90° hybrid,balanced photodetector and loop filter in laser phase-locked loop,the performance simulation analysis was carried on.The experimental platform of laser phase-locked loop was set up,and the designed active loop filter and passive loop filter were applied respectively to realize the laser phase locking.The loop delay is only 1.2 ns and the loop bandwidth is up to 40 MHz.