Fabrication and performance of thin amorphous Si subwavelength transmission grating for controlling vertical cavity surface emitting laser polarization

Amorphous Si subwavelength transmission gratings (SWTGs) with a thickness of 240 nm and a period ranging from 50 to 900 nm were fabricated on a fused silica substrate using electron beam lithography, lift-off, and reactive ion etching. At certain grating periods, the SWTGs exhibit polarization dependent reflectance and transmittance due to the polarization dependent coupling of the eigenmodes inside the grating. By putting the SWTG in front of the output window of a vertical cavity surface emitting laser (VCSEL), a polarization dependent optical feedback can be achieved. Using this feedback, we demonstrated the locking, switching, and enhancement of the VCSEL's polarization. A polarization ratio as high as 200:1 was achieved.