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.

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