Subwavelength transmission gratings for polarization separation in the infrared

Subwavelength gratings exhibit attractive polarizing properties and have promising applications in communication, optical information processing, holography, and displays. The fabrication of subwavelength binary gratings for operation as polarizing beam splitters (PBS) at a wavelength of 1550 nm is presented. A simplified modal method was used for the design as well as to predict the efficiencies of the polarization components in each order. Electron beam lithography has been employed for patterning subwavelength grating structures on polymethyl methacrylate (PMMA) resist. The fixed beam moving stage patterning mode is used for patterning gratings with a period of 936 nm and width of 374 nm. The exposure and developing parameters are optimized to realize the grating with the designed feature sizes on PMMA resist. Gratings patterned using the optimized exposure and development parameters match well with the design, except for the height. The performance of the fabricated PBS grating has been evaluated by optical testing. The experimental results match well with the predictions.