According to embodiments of the present disclosure, apparatus is provided for protecting an optical link arranged to carry upstream optical signals and downstream optical signals. The apparatus comprises a first detector arranged to selectively detect a downstream optical signal received at a second port having a first wavelength and a second detector arranged to selectively detect a downstream optical signal received at the second port having a second wavelength different from the first wavelength. The apparatus further comprises control circuitry arranged to cause a protection switch to selectively couple a third port to the second port instead of to the first port based on the detecting by the first detector and the second detector. Also provided is a second apparatus for protecting the optical link. The second apparatus comprises a bypass element arranged to selectively direct at least a portion of an upstream optical signal at the first wavelength, received at a fourth port, such that a downstream optical signal at the first wavelength is transmitted from a fifth port.

Systems and methods describe synchronizing optical protection switching with an Optical Protection Switch (OPS) including a splitter on a transmit side to both a first fiber path and a second fiber path and a receive switch and monitoring port on a receive side with the receive switch set to only one of the first fiber path and the second fiber path. A method includes, responsive to detection of a fault on the first fiber path, generating a link Forward Defect Indication (FDI) and transmitting the link FDI over a messaging channel downstream; and utilizing the link FDI to generate an Optical Protection Switch Indicator (OPSI) status used by the OPS to cause a switch of the receive switch to the second fiber path.

Systems and methods describe synchronizing optical protection switching with an Optical Protection Switch (OPS) including a splitter on a transmit side to both a first fiber path and a second fiber path and a receive switch and monitoring port on a receive side with the receive switch set to only one of the first fiber path and the second fiber path. A method includes, responsive to detection of a fault on the first fiber path, generating a link Forward Defect Indication (FDI) and transmitting the link FDI over a messaging channel downstream; and utilizing the link FDI to generate an Optical Protection Switch Indicator (OPSI) status used by the OPS to cause a switch of the receive switch to the second fiber path.

According to the present invention, there is provided apparatus for providing protection of an optical link. The apparatus comprises a first port for coupling to the optical link and a second port for coupling to a further optical link. The apparatus further comprises a third port configured to receive an upstream optical signal to be transmitted over the optical link, and to output a downstream optical signal received over the optical link. The apparatus further comprises protection switching apparatus operable to selectively couple the third port to the first port or to the second port. The apparatus further comprises modifying apparatus configured to modify the upstream optical signal, received at the third port, before it is output from the first port, such that the switching upstream optical signal has a distinctive physical characteristic. The apparatus further comprises detecting apparatus, coupled between the first port and the third port, configured to receive a portion of an incoming optical signal, received at the first port, and to selectively detect the presence of the upstream optical signal or the downstream optical signal in the portion of the incoming signal based on the distinctive physical characteristic. The apparatus further comprises control circuitry configured to provide a control signal to the protection switching apparatus based on an output from the detecting apparatus.

Example embodiments of the present invention relate to an optical node comprising of at least two degrees, a plurality of directionless add/drop ports, a plurality of primary WDM transmitters and receivers, and at least one protection WDM transmitter and receiver, wherein the at least one protection WDM transmitter and receiver can transmit and receive in place of any of the plurality of primary WDM transmitters and receivers.

Example embodiments of the present invention relate to an optical node comprising of at least two degrees, a plurality of directionless add/drop ports, a plurality of primary WDM transmitters and receivers, and at least one protection WDM transmitter and receiver, wherein the at least one protection WDM transmitter and receiver can transmit and receive in place of any of the plurality of primary WDM transmitters and receivers.

A system includes an optical transmitter and an optical receiver. The optical transmitter includes a first comb light source, a second comb light source, an optical switch configured to selectively switch either the first comb light source or the second comb light source through to an output of the optical switch, and optical modulators configured to apply differential phase modulation, to channels associated with the switched first comb light source or with the second comb light source, to generate modulated light output signals. The optical receiver includes coherent receivers configured to receive the modulated light output signals from the optical transmitter, and detect and process the received, modulated light output signals to generate corresponding digital signals. The optical receiver further includes a digital signal processor configured to apply forward error correction to the digital signals to generate forward error corrected digital signals.

A system includes an optical transmitter and an optical receiver. The optical transmitter includes a first comb light source, a second comb light source, an optical switch configured to selectively switch either the first comb light source or the second comb light source through to an output of the optical switch, and optical modulators configured to apply differential phase modulation, to channels associated with the switched first comb light source or with the second comb light source, to generate modulated light output signals. The optical receiver includes coherent receivers configured to receive the modulated light output signals from the optical transmitter, and detect and process the received, modulated light output signals to generate corresponding digital signals. The optical receiver further includes a digital signal processor configured to apply forward error correction to the digital signals to generate forward error corrected digital signals.

The present application discloses a data secrecy method for a submarine cable system with a failure and a submarine cable system. The method includes: determining a first disaster tolerance set in response to that a failure occurs to a first branch; and replacing a target optical signal in a first optical signal with a virtual optical signal. The first branch is any branch in the submarine cable system. The first disaster tolerance set includes at least one wavelength used for optical signals for transfer from a first terminal station to the first branch. The first optical signal is an optical signal output from the first terminal station. The target optical signal includes optical signals corresponding to the respective wavelengths in the first disaster tolerance set. The virtual optical signal is an optical signal that does not carry data content.