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We report the fabrication and characterization of the P-P À -N optical waveguide modulators fabricated on silicon-on-insulator (SOI) substrate. The modulation scheme was achieved via the carrier injection, or plasma dispersion effect. The corresponding P and N regions were defined in both types of SOI substrates (P-type SOI and highly resistive N-type SOI substrates with respective resistivities of $ 7 {10 cm and $ 7000 {10000 cm) using the spin-on-dopant (SOD) technique conducted at 900 -1000 C in a nitrogen ambient. The resultant dopant concentrations and diffusion depths were found to be critically dependent on the diffusion time/temperature and the resistivity of SOI substrate used. For the modulators fabricated with various waveguide widths and electrode lengths, the corresponding modulation index was enhanced in response to an increase in the electrode (or modulation) length and/or a decrease in waveguide width. The highest modulation index of $4:15% was successfully achieved for a silicon P-P À -N waveguide modulator with 5-mm-wide waveguide and 7-mm-long modulation electrode.

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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