Design and investigation of stable polarization tunable VCSEL with intercavity subwavelength grating

We have designed and investigated a stable polarization microelectromechanical system (MEMS)-tunable vertical-cavity surface-emitting lasers (VCSELs) at wavelength around 980 nm with an inter-cavity subwavelength grating (ISWG). An ISWG is etched on the top of the “Half-VCSEL” consisting of the active semiconductor and the bottom mirror to select the polarization mode during the whole tuning range. The rigorous coupled wave analysis (RCWA) had be used to design and optimize the parameters of the ISWG including index, thickness, period and duty cycle to achieve a high reflectance for the desire polarization and a lower reflectance for the other polarization. Then we calculated the total reflectance of ISWG, air gap and top DBR using transmission matrix method. By designing the parameters of ISWG, we can ensure that the fundamental mode has a higher reflectance, or lower threshold current than the other modes. After calculation, we have gotten the parameters as follows. The index of the ISWG and the substrate is 3.58; thickness is 300nm; period is 500 nm; duty cycle is 0.5. The reflectance of ISWG is 0.985 for the TM polarization and 0.382 for TE polarization. The total reflectance of the whole structure is 0.995 for TM polarization and 0.902 for TE polarization in the tuning range. The difference of the reflectance between two polarization modes can select the polarization mode of lasing. This structure can achieve a tuning range of 30nm for TM single polarization.