Patent ID: 7142362

Claim:
An optical attenuator, comprising: an input port and an output port for optical signals arranged side by side; a reflecting member arranged to face both of said 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 said optical path; wherein said 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 said reflecting member, optical guide means are provided to guide only the transmitted light from said input port side to said optical sensor, and optical detection signals of said optical sensor are used as optical input power monitoring signals.