Abstract: Faraday rotators each have a Faraday element which rotates light and a magnetic field generator for applying a magnetic field to the Faraday element. A wavelength plate is disposed between the Faraday rotators and it retards the light. A polarizer transmits, of the light, light having a predetermined plane of polarization which has been rotated by the Faraday rotators and retarded by the wavelength plate. An optical receiver receives the light transmitted by the polarizer and outputs a light receiving signal which corresponds to the amount of light received. A signal generator outputs a control signal for polarizing the light to be measured into at least four polarization states to the magnetic field generator. A signal processor determines Stokes parameters which indicate the polarization state of the light to be measured based on the four polarization states, and the light receiving signal corresponding to each of the four polarization states.

Abstract: A multi-wavelength light source apparatus includes a tunable light source, optical intensity modulator, optical coupler, annular optical delay circuit, and optical gate device. The tunable light source successively changes and outputs a plurality of output lights different in wavelength from one another. The optical intensity modulator outputs a modulated signal light obtained by modulating an amplitude of the output light outputted from the tunable light source over a predetermined time. The optical coupler is optically connected to the optical intensity modulator, and receives the light outputted from the optical intensity modulator. The annular optical delay circuit is optically connected to the optical coupler, and delays a part of the output light outputted from the optical intensity modulator over a time longer than the predetermined time.

Abstract: Faraday rotators each have a Faraday element which rotates light and a magnetic field generator for applying a magnetic field to the Faraday element. A wavelength plate is disposed between the Faraday rotators and it retards the light. A polarizer transmits, of the light, light having a predetermined plane of polarization which has been rotated by the Faraday rotators and retarded by the wavelength plate. An optical receiver receives the light transmitted by the polarizer and outputs a light receiving signal which corresponds to the amount of light received. A signal generator outputs a control signal for polarizing the light to be measured into at least four polarization states to the magnetic field generator. A signal processor determines Stokes parameters which indicate the polarization state of the light to be measured based on the four polarization states, and the light receiving signal corresponding to each of the four polarization states.

Abstract: A laser light source apparatus includes a compound cavity and an optical gain medium. The compound cavity includes first, second, and third optical reflection members disposed along the optical axis. The first optical reflection member has a light wavelength selectivity. At least one of the first to third optical reflection members can change its own position on an optical axis in relation to the other reflection members. Two of the first to third optical reflection members are provided opposite to each other with the optical gain medium inserted therebetween, thereby forming a laser light source. The other one optical reflection member is provided so as to form a light path for feeding laser light emitted from the laser light source back to the laser light source.

Abstract: A tunable laser source apparatus includes an external cavity. The external cavity includes a semiconductor laser and a diffraction section. At least one laser output end facet of the semiconductor laser is covered with an AR coating. The diffraction section includes a first reflector and a diffraction grating, and has wavelength selectivity with which light emerging from the end facet of the semiconductor laser which is covered with the AR coating is received, and light having a predetermined wavelength is selected and reflected toward the semiconductor laser. The semiconductor laser further includes an angle detection section and a control section. The angle detection section detects the angle defined by the optical path of the light emerging from the semiconductor laser and the optical path of the diffracted light reflected by the diffraction section.