US Patent 7088747 Variable wavelength light source

When a piezoelectric element 3 applies an external force to a plastic photonic crystal, the photonic crystal deforms, and accordingly, the photonic band gap easily changes. When the photonic band gap changes, transmission of light with a specific wavelength is limited. Therefore, light with a desired wavelength is outputted from the photonic crystal 2 upon sufficient tuning, and extracted to the outside through an output window 6. In the present invention, a plastic photonic crystal 2 which can achieve sufficient wavelength tuning although it is small is used, and elements are unitized, so that the entire wavelength tunable light source unit is downsized.