We demonstrate two types of nonlinear optical functions enhanced in silicon photonic wire waveguides. One is a wavelength conversion based on a four-wave mixing effect. Internal conversion efficiency was around-10 dB when a CW-operated 160-mW pump was applied. Another is a cross absorption modulation based on a non-degenerated two-photon absorption. Modulation depth was about 50% when a pump power was 300 mW. Efficiencies of these functions can be improved by suppressing free-carrier absorption effect. For this purpose, we have tried two practical methods: carrier extraction using PIN structures and recombination enhancement using lattice defects.