High contrast long-period waveguide gratings on silicon-on-insulator (SOI) substrates

We report the practicality of fabricating the long-period waveguide gratings (LPWGs) on silicon-on-insulator (SOI) substrates with amorphous silicon (a-Si) layer incorporated as a cladding layer. Specifically, the devices are etched and patterned on SOI wafer via an anisotropic wet etching technique, while the a-Si is deposited using plasma-enhanced chemical vapor deposition (PECVD) system. The experimental results later confirm that the LPWG devices resonate within a wavelength range between 1563 and 1580nm and the LPWG waveguide with a width of 8µm has delivered a dip contrast as high as 30 dB and the FWHM as narrow as 1.76nm, as the input light is polarized as transverse electric (TE) wave. With the transverse magnetic (TM) polarized wave provided as an input, the LPWG waveguide with the width of 10µm yields a dip contrast as high as 14.5 dB and its FWHM measured is as narrow as 1.32nm.