Long-period waveguide gratings with amorphous silicon cladding layer on silicon-on-insulator substrates realized by anisotropic wet etching

Long-period waveguide gratings (LPWGs) are designed and fabricated on silicon-on-insulator (SOI) substrates with an amorphous silicon (a-Si) layer incorporated as the cladding layer. Specifically, ridge waveguides are etched and patterned on SOI wafers via anisotropic wet etching and a-Si is deposited using a plasma-enhanced chemical vapor deposition (PECVD) system. The experimental results confirm that the resonant wavelengths of LPWG devices are within the range of 1563-1580 nm and that an LPWG ridge waveguide of 8 µm wide yields a dip contrast as high as 29.5 dB and an FWHM as narrow as 1.76 nm when the input light is transverse-electric (TE)-polarized. As for the transverse-magnetic (TM)-polarized input light, an LPWG waveguide of 10 µm width yields a dip contrast as high as 14.5 dB and a measured FWHM as narrow as 1.32 nm.