Design And Simulation Of Ultra-narrow Linewidth Vertical Cavity Surface Emitting Laser Based On Guided Mode Resonant Coupling Cavity

There are many advantages of vertical cavity surface emitting lasers(VCSELs),such as low threshold current,single longitudinal mode lasing,good mode stability,and easy coupling with fiber.It makes VCSEL widely used in optical communication,optical interconnection,optical computing,medical care and so on.Therefore,high-performance VCSELs with high modulation rate,high output power,low dissipation,and good temperature characteristics are studied and reported widely.Especially,with the continuous development of high-tech fields such as atomic clock,atomic gyro and optical pump magnetometer,the high beam quality VCSEL with ultra-narrow linewidth and single-polarized has become a research hotspot.In this paper,based on the guided-mode resonant coupling cavity of subwavelength grating,it is integrated with the vertical cavity surface-emitting laser.Based on the characteristics of the guided mode resonant coupling cavity,such as high reflectivity and narrow linewidth,a narrow linewidth vertical cavity surface emitting laser based on guided mode resonant coupling cavity is proposed.The main research work of this paper is summarized as follows:1.Firstly,according to the physical mechanism of vertical cavity surface emitting laser,the basic structure and principle of VCSEL were studied.According to the linewidth formula,the factors affecting the linewidth of the laser were analyzed,including the cold cavity linewidth of the laser,the linewidth enhancement factor and the laser gain.The conditions of sub-wavelength grating resonance were studied by the basic principle of guided mode resonance.Then the relationship between reflection phase and reflection linewidth and the effect of the phase change of each layer structure were analyzed.Finally,the relationship between the phase of the light wave in the VCSEL resonator and the phase of the light wave in the guided mode resonant cavity was obtained.2.The guided mode resonant coupling cavity was simulated by COMSOL Multiphysics software based on finite element analysis.The structure of the guided mode resonant coupling cavity was designed and its reflection characteristics were analyzed.The structure parameters(grating period,grating thickness,spacer thickness,etc.)of the cavity were scanned and simulated,then the influence of the structural parameters on the reflection phase and the linewidth of the reflection spectrum wasstudied.Finally,by optimizing the components of each structural parameter,a guided-mode resonant coupling cavity device with an ultra-narrow linewidth of 2 pm was obtained.It is necessary to compare the influence of different materials on the reflection characteristics of the device,and the influence of the error of each structural parameter size on the performance was simulated.The results show that the grating period and the waveguided thickness have a great influence on the central wavelength.,and the other structural parameters have little influence on the central wavelength and the reflection linewidth within the process error range.3.The research and design of VCSEL based on guide mode resonant coupling cavity were carried out.By adjusting the structural parameters such as the grating period and cladding layer thickness,the phase position of the optical wave in the cavity is shifted,then the guided mode resonant coupling cavity and the VCSEL resonant cavity are coupled to each other.Finally,a 795 nm narrow linewidth VCSEL is obtained.It is two orders of magnitude smaller than the full width at half maximum(FWHM)of the conventional VCSEL cavity reflection spectrum.According to the linewidth formula,reflection spectrum FWHM of the VCSEL cavity has a great influence on the VCSEL excitation linewidth.By changing the structural parameters of the guided mode resonant coupling cavity,the precise selection of the wavelength is enhanced,and a VCSEL with a narrower linewidth is obtained.The linewidth of the VCSEL is on the order of kHz,which is more than three orders of magnitude lower than conventional lasers.When the power is 10 mW and FWHM is 7pm,the VCSEL linewidth reaches 21.67 kHz.