Controlling polarization of vertical-cavity surface-emitting lasers using amorphous silicon subwavelength transmission gratings

Control of the polarization of vertical-cavity surface-emitting lasers (VCSELs) using a 240-nm-thick amorphous silicon subwavelength transmission grating (SWTG) is demonstrated. The grating, which has a strong polarization dependent reflectance and transmittance, was placed in front of the output window of a VCSEL. It was found that the SWTG can fix the VCSEL’s polarization in the direction perpendicular to the grating fingers, switch polarization directions, enhance the polarization ratio from 20:1 to over 200:1, and decrease the threshold current. Integration of these gratings into the VCSEL structure is discussed.