We fabricated various microscopic optical devices using photonic crystal slab and Si-wire waveguides and demonstrated their fundamental characteristics. We demonstrated a channel-dropping filter with a photonic crystal slab point-defect optical cavity. Wavelength resolution of less than 1.5 nm and signal dropping efficiency of more than 90 % were obtained for a 20-μm-square device. We also demonstrated an optical add/drop multiplexer with Bragg grating reflectors made from Si-wire waveguides. Its dropping wavelength bandwidth was less than 2 nm, and the center wavelength of the dropped optical signal could be tuned by thermo-optic control using a microheater formed on the Bragg reflector. Using Si-wire waveguide, we also demonstrated thermo-optic switches by forming a micro heater on a branch of a Mach-Zehnder interferometer constructed from the waveguides. In this switching operation, we observed an extinction ratio of more than 30 dB, switching power of less than 100 mW, and switching response speed of less than 100 μs using a 1 × 2 optical switch with an 85 × 30 μm2 footprint. Using the 1 × 2 optical switch elements, we also fabricated a compact 1 × 4 optical switch and demonstrated its fundamental operation.