Micro-photonic devices with Si-wire waveguides were demonstrated for use in photonic networks. An optical ring resonator with the waveguides which has extremely small ring radius realized large free-spectral range. An optical add/drop multiplexer which is as small as 700-µm-long attained 7 nm wavelength tuning range with micro-heaters formed on the device. 1 × 4, 1 × 8 and 4 × 4 optical switches were also demonstrated with extremely compact sizes.