A quantum communications system includes a first quantum repeater and a second quantum repeater each positioned at a repeater node and each having a first quantum memory and a second quantum memory. A first channel switch is optically coupled to the first quantum repeater and a second channel switch is optically coupled to the second quantum repeater. Further, a first sub-channel extends between and optically couples the first channel switch and the first quantum memory of the first quantum repeater, a second sub-channel extends between and optically couples the first channel switch and the first quantum memory of the second quantum repeater, a third sub-channel extends between and optically couples the second channel switch and the second quantum memory of the first quantum repeater, and a fourth sub -channel extends between and optically couples the second channel switch and the second quantum memory of the second quantum repeater.

A quantum communications system includes a first quantum repeater and a second quantum repeater each positioned at a repeater node and each having a first quantum memory and a second quantum memory. A first channel switch is optically coupled to the first quantum repeater and a second channel switch is optically coupled to the second quantum repeater. Further, a first sub-channel extends between and optically couples the first channel switch and the first quantum memory of the first quantum repeater, a second sub-channel extends between and optically couples the first channel switch and the first quantum memory of the second quantum repeater, a third sub-channel extends between and optically couples the second channel switch and the second quantum memory of the first quantum repeater, and a fourth sub -channel extends between and optically couples the second channel switch and the second quantum memory of the second quantum repeater.

An object to provide a submarine optical transmission apparatus capable of efficiently housing optical components and electric components. A submarine optical transmission apparatus includes a case, an electric component housing unit, and an optical component housing unit. The electric component housing unit and the optical component housing unit can house either or both of an optical component and an electric component and are stacked in a Z-direction. The case can house the electric component housing unit and the optical component housing unit that are stacked, and a longitudinal direction thereof is an X-direction.

An optical system, comprising: an emitter configured to output a first optical signal along a first optical path to an interference unit and to output a second optical signal along a second optical path to the interference unit, the interference unit being configured to interfere the first and second optical signals, wherein the coherence length of the optical signal is longer than the path difference between first and second optical paths, and there is a path difference between the first and second paths of at least 1 km.

An optical system, comprising: an emitter configured to output a first optical signal along a first optical path to an interference unit and to output a second optical signal along a second optical path to the interference unit, the interference unit being configured to interfere the first and second optical signals, wherein the coherence length of the optical signal is longer than the path difference between first and second optical paths, and there is a path difference between the first and second paths of at least 1 km.

Embodiments relate to a local free space optical (FSO) terminal that transmits and receives optical beams. The FSO terminal includes a fore optic, an optical relay system, and an actuator system. The fore optic focuses a receive (Rx) beam to a Rx spot on a focal plane of the fore optic. The focal plane also includes a Tx spot formed by a transmit (Tx) optical beam, however the Rx and Tx spots are laterally separated at the focal plane. The optical relay system creates a conjugate spot for the Rx or Tx spot so that the Rx and Tx fibers may be axially separated. Due to the axial separation, the actuator system can adjust a lateral separation of the Rx and Tx fibers to account for point ahead of the local FSO communication terminal.

Embodiments relate to a local free space optical (FSO) terminal that transmits and receives optical beams. The FSO terminal includes a fore optic, an optical relay system, and an actuator system. The fore optic focuses a receive (Rx) beam to a Rx spot on a focal plane of the fore optic. The focal plane also includes a Tx spot formed by a transmit (Tx) optical beam, however the Rx and Tx spots are laterally separated at the focal plane. The optical relay system creates a conjugate spot for the Rx or Tx spot so that the Rx and Tx fibers may be axially separated. Due to the axial separation, the actuator system can adjust a lateral separation of the Rx and Tx fibers to account for point ahead of the local FSO communication terminal.

A wavelength conversion device includes: a first wavelength conversion circuit that wavelength-converts, by passing first multiplex light obtained by multiplexing an optical signal of a first wavelength band from each transmitter through an inside of a wavelength conversion medium by using excitation light, the first multiplex light into second multiplex light in a second wavelength band different from the first wavelength band; and a first generation circuit that generates a first control signal that controls each transmitter to shift a signal wavelength of each optical signal in the first multiplex light before wavelength conversion according to a subsequent part to which the second multiplex light after wavelength conversion in the first wavelength conversion circuit is input, and transmits the first control signal to each transmitter.

An optical system, comprising: an emitter configured to output a first optical signal along a first optical path to an interference unit and to output a second optical signal along a second optical path to the interference unit, the interference unit being configured to interfere the first and second optical signals, wherein the coherence length of the optical signal is longer than the path difference between first and second optical paths, and there is a path difference between the first and second paths of at least 1 km.

An optical system, comprising: an emitter configured to output a first optical signal along a first optical path to an interference unit and to output a second optical signal along a second optical path to the interference unit, the interference unit being configured to interfere the first and second optical signals, wherein the coherence length of the optical signal is longer than the path difference between first and second optical paths, and there is a path difference between the first and second paths of at least 1 km.