Abstract: An open-close valve unit includes a block body, a first open-close valve, and a second open-close valve. The block body includes a first main flow path and a second main flow path. The first main flow path has a first opening and a second opening. The second main flow path has a third opening and a fourth opening. The first open-close valve includes a first valve body movable to open and close the first main flow path. The second open-close valve includes a second valve body movable to open and close the second main flow path. The first open-close valve is in an open state when in an energized state. When the first open-close valve is in the energized state, the second open-close valve is in a de-energized state, and placed in an open state by a dynamic pressure of the fluid flowing in the second main flow path.

Abstract: An optical angle modulator includes: a first unit configured to generate first angle-modulated light and second angle-modulated light by performing angle modulation on continuous light using an electrical signal; and a second unit configured to generate third angle-modulated light by causing partially degenerate four-wave mixing of the first and second angle-modulated lights. A frequency band of the first angle-modulated light and a frequency band of the second angle-modulated light are different, and an angle of the second angle-modulated light decreases due to the electrical signal while an angle of the first angle-modulated light is increasing due to the electrical signal, and the angle of the second angle-modulated light increases due to the electrical signal while the angle of the first angle-modulated light is decreasing due to the electrical signal.

Abstract: An optical transmitter configured to transmit an optical signal to a photodiode includes: an angle modulator configured to perform angle modulation with respect to a transmission signal; and an optical tone signal generator configured to generate an optical tone signal, and the optical transmitter transmits an optical signal that includes a single sideband signal corresponding to an angle modulated transmission electrical signal and the optical tone signal that is disposed on a higher frequency side or a lower frequency side of a frequency band of the single sideband signal.

Abstract: An optical receiver includes: a first combiner configured to output first combined light by combining local light of first polarization and signal light of second polarization; a converter configured to convert the first combined light to a first electric signal; a converter configured to covert a component of the first combined light that has passed through a first polarizer to a second electric signal; a converter configured to convert a component of the first combined light that has passed through a wave plate and a polarizer to a third electric signal; a divider configured to output a fourth electric signal and a fifth electric signal by branching the first electric signal; subtractors configured to subtract the fourth electric signal from the second electric signal and the fifth electric signal from the third electric signal.

Abstract: An optical transmission system in which a transmitting station and a plurality of receiving stations are connected via an optical splitter, wherein the transmitting station includes: a controller configured to determine whether to perform intensity modulation or phase modulation on optical signals based on information on transmission distances to the receiving stations and modulation bands; an intensity modulator configured to perform intensity modulation on an optical signal; and a phase modulator configured to perform phase modulation on an optical signal, and wherein one of an intensity modulation signal and a phase modulation signal is transmitted from the transmitting station to each of the receiving stations.

Abstract: An optical receiver includes: a first combiner configured to output first combined light by combining local light of first polarization and signal light of second polarization; a converter configured to convert the first combined light to a first electric signal; a converter configured to covert a component of the first combined light that has passed through a first polarizer to a second electric signal; a converter configured to convert a component of the first combined light that has passed through a wave plate and a polarizer to a third electric signal; a divider configured to output a fourth electric signal and a fifth electric signal by branching the first electric signal; subtractors configured to subtract the fourth electric signal from the second electric signal and the fifth electric signal from the third electric signal.

Abstract: A polarization tracking device that tracks polarization fluctuation of light using a Stokes vector, includes: an updating unit configured to express a fluctuation amount of the Stokes vector on a Poincare sphere in an xy plane perpendicular to a travelling direction of a light wave using a first and a second angles, the first angle being an angle between a direction of an electric field of the light wave and y axis, and the second angle being a phase difference between a component of the optical electric field in a direction of the y axis and a component of the optical electric field in a direction of an x axis; and an application unit configured to rotate the Stokes vector using an inverse polarization rotation matrix expressed with the first and the second angles.

Abstract: An optical transmission system in which a transmitting station and a plurality of receiving stations are connected via an optical splitter, wherein the transmitting station includes: a controller configured to determine whether to perform intensity modulation or phase modulation on optical signals based on information on transmission distances to the receiving stations and modulation bands; an intensity modulator configured to perform intensity modulation on an optical signal; and a phase modulator configured to perform phase modulation on an optical signal, and wherein one of an intensity modulation signal and a phase modulation signal is transmitted from the transmitting station to each of the receiving stations.

Abstract: A polarization tracking device that tracks polarization fluctuation of light using a Stokes vector, includes: an updating unit configured to express a fluctuation amount of the Stokes vector on a Poincare sphere in an xy plane perpendicular to a travelling direction of a light, wave using a first and a second angles, the first angle being an angle between a direction of an electric field of the light wave and y axis, and the second angle being a phase difference between a component of the optical electric field in a direction of the y axis and a component of the optical electric field in a direction of an x axis; and an application unit configured to rotate the Stokes vector using an inverse polarization rotation matrix expressed with the first and the second angles.