Patent ID: 7289733

Claim:
An optical apparatus comprising: an optical filter configured to transmit a light signal at a selected wavelength; a first lens and a second lens, each of the lenses situated on one side of the optical filter, wherein the first lens receives a light beam including signals respectively at a plurality of wavelengths including the selected wavelength and couples the light beam to the optical filter that passes a substantial portion of the signal at the selected wavelength to the second lens; a reflective element receiving a reflected light beam from the optical filter, the reflected light beam including the signals at the wavelengths other than the selected wavelength and a residual signal at the selected wavelength, wherein the reflective element is so positioned that the reflective element is impinged upon by the reflected light beam and reflects the reflected light beam back to the optical filter such that the residual signal at the selected wavelength is further reduced by the optical filter.