Patent ID: 7019901

Claim:
A wavelength periodical filter, comprising: a polarization beam splitting unit splitting input light into different polarized light beams, that each follows a different optical path; a phase controller arranged in one of the optical paths of light beams which are split by said splitting unit a phase bias unit having an optical axis inclined 45 degrees toward the polarized light beams of the input light; and a resonating unit, wherein: said resonating unit comprises a semi-transparent mirror unit having different reflectances for different polarization states, wherein the phase bias unit and the semitransparent mirror separate the polarized light beams into groups of light waves, each group comprising at least two orthogonal polarization components and polarization planes of the split polarized light beams make a +45 and −45 degrees toward the optical axis of said phase bias unit, respectively, making part of light pass through, and reflecting part of the light, a total reflection mirror unit reflecting input light 100%, and a polarized wave rotating unit, which is arranged between said semi-transparent mirror unit and said total reflection mirror unit, multiple-reflecting the polarized waves of the light between said semi-transparent mirror unit and said total reflection mirror unit while rotating the polarized waves 90 degrees each time the light shuttles between said semi-transparent mirror unit and said total reflection mirror unit; and the input light is output from said polarization beam splitting unit after being output from said resonating unit, and made to inversely travel a path.