Research On Tunable Diode Lasers Of Frequency Modulated Continuous Wave Lidar

Frequency Modulated Continuous Wave (FMCW) lidar technology is a largeabsolute distance measurement technology, with the characteristics of largemeasurement range, high range accuracy, large range resolution. It have significantapplications in the aerospace, ship building industry, heavy machinery and otherfields. Chirped laser is directly related to the overall performance of FMCW lidarsystem. Littman external cavity semiconductor lasers and three sections DBRsemiconductor laser are separately proposed and theoretical simulation for themFirst we designed the structure of Littman external cavity semiconductor laser,and it can theoretically be tuned to any wavelength. We analyzed wavelength tuningnonlinearity of the laser, in the vicinity of the wavelength1550nm, tunable lasersbrought less than nonlinear wavelength error of0.09nm in tuning range of57.64nm.According to principles of equivalent simplified three mirrors model to a two mirrorsmode, by which we analyzed the laser threshold gain and phase conditions. Whenreflectance of the diode facet near external cavity was lower10-4, the cavity mode ofexternal cavity mode didn’t affect threshold and phase condition largely. Analyzedthe laser wavelength changes caused by the temperature change, the stability wasdetermined primarily by the gain chip, laser plate, grating temperature stability.Numerical calculations showed that the external cavity laser collimation requirementwas in0.01°or less. Finally we completed the overall design of the laser.We simulated properties of the external cavity semiconductor laser. Consideredthat continuous tuning range was related pivot point position error, the results showshaft positions allowed only have error in a narrow region in. Considered Lorentzdiode laser gain spectrum and limited linewidth of antireflection (AR) coating, thelaser tuning range was simulated. The smaller AR coating reflection coefficient wasand the greater the bandwidth was, the greater the laser tuning range was. Withexternal cavity laser rate equations, the laser power characteristics were simulated.When the wavelength is constant, the laser power and current changes linearly. Whenthe laser was tuned, the power shows ups and downs. Linewidth of external cavitylaser external cavity laser calculations indicate that the linewidth can be achieved1KHz.For three sections DBR semiconductor laser we studied the tuning rules.Introducing the transfer matrix theory, calculated the transfer matrix forms of some of the basic optical structures. Using the transfer matrix method, reflection spectrumsof the FP etalon, Bragg grating and sampled grating reflection was simulated. Weanalyzed the DBR laser tuning theory. Using transfer matrix, we investigated lasingwavelength tunings by current injecting separately in phase section and Bragggrating section of the DBR lasers. Further we studied tuning of two sectionssimultaneously.