Study On Characteristics Of The Vertical Cavity Surface Emitting Laser Based On The Liquid Crystal Microcavity

Vertical Cavity Surface Emitting Laser?VCSEL?is a semiconductor laser widely used in optical communication,gas detection,and 3D sensing.It has a low threshold current,is easy to integrate in two dimensions,and has a high modulation rate.Advantage.In order to improve the reliability and stability of the system,a tunable inner cavity liquid crystal tunable VCSEL with an oscillation wavelength around 900-940 nm is designed in this paper.Based on the finite-difference time-domain method,the distribution of the light field in the device is simulated,and the resonant wavelength of the laser under various liquid crystal thickness and refractive index is obtained.The physical characteristics of the structure to obtain a wide range of wavelength tuning and polarization stable output are analyzed.The simulation result of the designed wavelength tuning range of the liquid crystal tunable laser reaches 42.4 nm,and the polarization and simulation analysis are performed experimentally.The main research work is as follows:1.Structural design work: liquid crystal microcavity structure design,including highcontrast grating and liquid crystal layer,and half VCSEL device structure design,including power area,DBR,resonant cavity,etc.Based on the rigorous coupled wave theory was designed using a liquid crystal as a low refractive index materials Si/SiO₂ composite high contrast grating as VCSEL mirror on the inner cavity of the liquid crystal tunable VCSEL,when 940 nm TM polarized incident,broadband is obtained by optimization of the parameters???=256 nm?high reflectance?R > 99%?and the stability of polarization grating structure,meet at the top of the vertical cavity surface emitting laser cavity surface mirror requirements.Based on the transfer matrix method and time-domain finite element difference method,the reflectivity of DBR is calculated,and the DBR logarithm,material refractive index contrast and growth sequence are discussed respectively.When the material is Al_0.9Ga_0.1As / Al_0.1Ga_0.9As and the logarithm is 25 pairs,the reflectivity of the structure is over 99%,and the bandwidth is over 150 nm Based on Fermi golden rule,using PICS3 D software for simulating a source area,and using the method of control variables get 940 nm material gain maximum quantum well structure parameters of well width of 0.007 microns,the base width of 0.1 microns In_0.17Ga_0.83As/Al_0.3Ga_0.7As quantum well,in the 940 nm peak gain 4771.2 cm-1;2.Study on tuning and polarization characteristics: The optical field distribution of the resonant cavity is calculated by the FDTD method,and the optimal liquid crystal thickness is obtained through optimization.In a period,the tuning range of the liquid crystal becomes larger as the thickness of the liquid crystal increases.When the thickness of the liquid crystal microcavity is 2002 nm,the device has the largest tuning range.When the refractive index of the liquid crystal changes from 1.65 to 1.5,the resonance wavelength changes from 936.9 nm to 894.5 nm,centered at 915.7 nm,and the tuning range is 42.4 nm.By calculating the threshold gain of the device under different cavity length conditions,it can be found that the device has obvious differences in different incident polarized light.At a thickness of 2002 nm,the liquid crystal achieves polarization stable output during the change of the refractive index from 1.7 to 1.55.A liquid crystal cell was prepared through experiments to test the birefringence of liquid crystals against polarized light.