Abstract: A low-cost compact optical attenuator structure has an input port and an output port for optical signals arranged side by side; a reflecting member arranged to face both ports to reverse light from the input side on an optical path folded 180°; a birefringence crystal splits incident light into two polarization components, a converging lens converges the incident light, a fixed Faraday rotator having a variable rotation angle arranged in that order in the optical path. The partial reflecting member that transmits a portion of incident light to the rear side thereof, an optical sensor at the rear side of the reflecting member, optical guide means guide only the transmitted light from the input port side to the optical sensor, and optical detection signals of the optical sensor are used as optical input monitoring signals.

Abstract: A first separating/combining birefringent element 10, first and second optical-path controlling birefringent elements 11, 12, and a second separating/combining birefringent element 13 are spaced apart. Between the first separating/combining birefringent element and the first optical-path controlling birefringent element, a first polarization rotating means 14 is arranged for changing a polarization direction from an orthogonal relationship to a parallel relationship, or from a parallel relationship to an orthogonal relationship. Also, between the second optical-path controlling birefringent element and the second separating/combining birefringent element, a second polarization rotating means 17 is arranged.

Abstract: A low-cost compact optical attenuator having a simple structure is constructed from an input port and an output port for optical signals arranged side by side; a reflecting member arranged to face both of the ports to reverse light from the input side on an optical path folded 180°; a birefringence crystal which splits incident light into two polarization components, a converging lens which converges the incident light, a fixed Faraday rotator having a fixed rotation angle, and a variable Faraday rotator having a variable rotation angle arranged in that order in the optical path; wherein the reflecting member is a partial reflecting member that transmits a portion of the incident light to the rear side thereof, an optical sensor is provided at the rear side of the reflecting member, optical guide means are provided to guide only the transmitted light from the input port side to the optical sensor, and optical detection signals of the optical sensor are used as optical input monitoring signals.

Abstract: A variable optical gain equalizer in accordance with one embodiment of the present invention comprises a variable branching ratio beam splitter having a variable polarization rotator, the variable branching ratio beam splitter branching an input light beam into two light beams at an arbitrary power ratio, through control of the rotation angle of the polarization direction by the variable polarization rotator; an optical filter presenting different filter characteristics to the two branched output light beams; and a polarization coupler for polarization coupling the two light beams that have passed through the optical filter, wherein the rotation angle of the polarization direction is controlled by the variable polarization rotator so as to vary the spectra of the output light beams.

Abstract: Arranged, with spacing, are a first separating/combining birefringent element 10, first and second optical-path controlling birefringent elements 11, 12, and a second separating/combining birefringent element 13. Between the first separating/combining birefringent element and the first optical-path controlling birefringent element, is arranged first polarization rotating means 14 for changing a polarization direction from an orthogonal to a parallel or from a parallel to an orthogonal. Also, between the second optical-path controlling birefringent element and the second separating/combining birefringent element, is arranged second polarization rotating means 17. The first and second optical-path controlling birefringent elements are oppositely arranged symmetric in optical axis about an arrangement center thereof, between which is arranged a ½-wavelength plate for rotating 90 degrees a polarization direction of a light on a central optical path, thereby structuring an optical circulator.

Abstract: A beam shutter is provided which comprises a plane-parallel birefringent element for separation arranged to separate input light beams having orthogonal polarization directions on the same optical path; a plane-parallel birefringent element for synthesis arranged to synthesize light beams having orthogonal polarization directions on different optical paths, for output; the birefringent element for separation and the birefringent element for synthesis being disposed in a spaced apart relationship; and polarization rotating means having a variable Faraday rotator, the polarization rotating means interposed between the birefringent element for separation and the birefringent element for synthesis, for magneto-optically controlling the polarization directions; wherein transmission and interruption of output light beams are controlled by switching the polarization directions by means of the variable Faraday rotator.

Abstract: An optical circulator comprises a first birefringent element for separation and synthesis; a first polarization rotation block; a circulator function block; a second polarization rotation block; and a second birefringent element for separation and synthesis; the circulator function block includes a first birefringent element for optical path control; a second birefringent element for optical path control which shifts the optical paths depending on the polarization directions and which has twice the optical path shifting amount of the first birefringent element for optical path control; and a ¼ wave plate and a reflector allowing light beams along peripheral optical paths to bypass and acting on only light beams along central optical paths.

Abstract: A beam shutter is provided which comprises a plane-parallel birefringent element for separation arranged to separate input light beams having orthogonal polarization directions on the same optical path; a plane-parallel birefringent element for synthesis arranged to synthesize light beams having orthogonal polarization directions on different optical paths, for output; the birefringent element for separation and the birefringent element for synthesis being disposed in a spaced apart relationship; and polarization rotating means having a variable Faraday rotator, the polarization rotating means interposed between the birefringent element for separation and the birefringent element for synthesis, for magneto-optically controlling the polarization directions; wherein transmission and interruption of output light beams are controlled by switching the polarization directions by means of the variable Faraday rotator.

Abstract: A variable optical gain equalizer in accordance with one embodiment of the present invention comprises a variable branching ratio beam splitter having a variable polarization rotator, the variable branching ratio beam splitter branching an input light beam into two light beams at an arbitrary power ratio, through control of the rotation angle of the polarization direction by the variable polarization rotator; an optical filter presenting different filter characteristics to the two branched output light beams; and a polarization coupler for polarization coupling the two light beams that have passed through the optical filter, wherein the rotation angle of the polarization direction is controlled by the variable polarization rotator so as to vary the spectra of the output light beams.