An optical transmission system includes: a terminal station device that transmits a wavelength multiplexed optical signal resulting from multiplexing an optical signal and dummy light; and an optical add-drop multiplexer that receives respective wavelength multiplexed optical signals transmitted from a plurality of the terminal station devices and performs add-drop processing on the wavelength multiplexed optical signals. The dummy light has a wavelength arrangement in which adjacent wavelengths are arranged with equal spacing, and the wavelength arrangement of the dummy light differs between the terminal station devices.

This disclosure describes C and L band optical communications module link extender, and related systems and methods. An example method may include receiving, by a dense wave division multiplexer (DWDM) at a headend, one or more optical data signals over a C band and an L band. The example method may also include combining the one or more optical data signals. The example method may also include outputting the combined one or more optical data signals to a first WDM at the headend. The example method may also include separating, by the first WDM, the combined one or more optical data signals into a C band signal and an L band signal. The example method may also include outputting the C band signal to a first amplifier at the headend and the L band signal to a second amplifier at the headend. The example method may also include amplifying, by the first amplifier, the C band signal. The example method may also include outputting the amplified C band signal to a coexistence filter. The example method may also include amplifying, by the second amplifier, the L band signal. The example method may also include outputting the amplified L band signal to the coexistence filter. The example method may also include outputting, by the coexistence filter, the amplified C band signal and the amplified L band signal to an optical switch. The example method may also include outputting, by the optical switch, an egress optical data signal to a first fiber.

An optical amplification system includes: three or more nodes; a multi-core fiber having a plurality of cores, the multi-core fiber being used in at least a partial segment of the connection between the nodes; an amplification light input unit configured to input amplification light to a core of the plurality of cores of the multi-core fiber; an amplification unit configured to amplify communication light transmitted through at least one core of the plurality of cores of the multi-core fiber using the amplification light, the amplification unit being provided in the nodes or between the nodes; and an amplification light coupling unit configured to couple the amplification light input by the amplification light input unit to the amplification unit.

An optical amplification system includes: three or more nodes; a multi-core fiber having a plurality of cores, the multi-core fiber being used in at least a partial segment of the connection between the nodes; an amplification light input unit configured to input amplification light to a core of the plurality of cores of the multi-core fiber; an amplification unit configured to amplify communication light transmitted through at least one core of the plurality of cores of the multi-core fiber using the amplification light, the amplification unit being provided in the nodes or between the nodes; and an amplification light coupling unit configured to couple the amplification light input by the amplification light input unit to the amplification unit.

An undersea repeater includes: a case housing therein a plurality of subunits; a plurality of optical amplifiers each being included as the subunit and having an amplifier that amplifies, based on excitation light, optical power of input signal light and outputs the amplified light; and an excitation light source that is included as the subunit, generates the excitation light, and outputs the split excitation light to each of the optical amplification units.

An undersea repeater includes: a case housing therein a plurality of subunits; a plurality of optical amplifiers each being included as the subunit and having an amplifier that amplifies, based on excitation light, optical power of input signal light and outputs the amplified light; and an excitation light source that is included as the subunit, generates the excitation light, and outputs the split excitation light to each of the optical amplification units.

An optical transmission system includes: a terminal station device that transmits a wavelength multiplexed optical signal resulting from multiplexing an optical signal and dummy light; and an optical add-drop multiplexer that receives respective wavelength multiplexed optical signals transmitted from a plurality of the terminal station devices and performs add-drop processing on the wavelength multiplexed optical signals. The dummy light has a wavelength arrangement in which adjacent wavelengths are arranged with equal spacing, and the wavelength arrangement of the dummy light differs between the terminal station devices.

An optical transmission system includes: a terminal station device that transmits a wavelength multiplexed optical signal resulting from multiplexing an optical signal and dummy light; and an optical add-drop multiplexer that receives respective wavelength multiplexed optical signals transmitted from a plurality of the terminal station devices and performs add-drop processing on the wavelength multiplexed optical signals. The dummy light has a wavelength arrangement in which adjacent wavelengths are arranged with equal spacing, and the wavelength arrangement of the dummy light differs between the terminal station devices.

The present invention is directed to techniques and systems for extension of unrepeatered submarine fiber links to provide an increase in reach of unrepeatered fiber transmission. Both single channel unrepeatered systems and multiple channel unrepeatered systems can be used. The multiple channel unrepeatered systems can further employ nonlinearity compensation. The present invention is also directed to methods of signal transmission using the unrepeatered systems.

A method of controlling an optical amplifying system that processes an optical signal with the PAM4 mode is disclosed. The optical amplifying system includes a variable optical attenuator (VOA) and a semiconductor optical amplifier (SOA). The VOA attenuates the optical signal such that a maximum optical power thereof corresponding to one of the physical levels of the PAM4 signal becomes equal to a preset optical level for which the SOA may be linearly operable. The SOA may amplify the thus attenuated optical signal with a fixed optical gain.