Optical amplifier apparatus and method

An in-line optical amplifier module comprising:

• a first optical amplifier apparatus comprising:
• an input for receiving an incoming optical signal comprising an optical supervisory channel, OSC, signal and a plurality of service channel signals at channel wavelengths of a wavelength division multiplexing, WDM, channel wavelength grid;
• an output for outputting an outgoing optical signal;
• an optical amplifier having an input, an output and an operating bandwidth that includes the WDM channel wavelength grid;
• a first optical drop filter provided upstream of the optical amplifier input, the first optical drop filter configured to drop from an incoming optical signal an out-of-band, OOB, OSC signal at a wavelength outside the optical amplifier operating bandwidth;
• a second optical drop filter provided downstream of the optical amplifier output, the second optical drop filter configured to drop from an incoming optical signal an in-band, IB, OSC signal at a wavelength within the optical amplifier operating bandwidth;
• an OSC signal output configured to output the OSC signal dropped from the first optical drop filter or the second optical drop filter;
• an OSC signal input configured to receive an outgoing OOB OSC or IB OSC signal;
• and
• an optical add filter provided upstream of the output, the optical add filter configured to add an outgoing OOB OSC or IB OSC signal to a plurality of service channel signals at channel wavelengths of the WDM channel wavelength grid to form the outgoing optical signal,
• wherein the input is configured to receive a first incoming optical signal from a first direction and the output is configured to output a first outgoing optical second in a second direction, different to the first direction;
• and
• a second optical amplifier apparatus comprising:
• an input for receiving an incoming optical signal comprising an optical supervisory channel, OSC, signal and a plurality of service channel signals at channel wavelengths of a wavelength division multiplexing, WDM, channel wavelength grid;
• an output for outputting an outgoing optical signal;
• an optical amplifier having an input, an output and an operating bandwidth that includes the WDM channel wavelength grid;
• a first optical drop filter provided upstream of the optical amplifier input, the first optical drop filter configured to drop from an incoming optical signal an out-of-band, OOB, OSC signal at a wavelength outside the optical amplifier operating bandwidth;
• a second optical drop filter provided downstream of the optical amplifier output, the second optical drop filter configured to drop from an incoming optical signal an in-band, IB, OSC signal at a wavelength within the optical amplifier operating bandwidth;
• an OSC signal output configured to output the OSC signal dropped from the first optical drop filter or the second optical drop filter;
• an OSC signal input configured to receive an outgoing OOB OSC or IB OSC signal;
• and
• an optical add filter provided upstream of the output, the optical add filter configured to add an outgoing OOB OSC or IB OSC signal to a plurality of service channel signals at channel wavelengths of the WDM channel wavelength grid to form the outgoing optical signal,
• wherein the input is configured to receive a second incoming optical signal from the second direction and the output is configured to output a second outgoing optical second in the first direction.

A method at a communications network node, the method comprising steps of

• receiving an incoming optical signal comprising an optical supervisory channel, OSC, signal and a plurality of service channel signals at channel wavelengths of a WDM channel wavelength grid;
• dropping from an incoming optical signal an out-of-band, OOB, OSC signal, if any, at a wavelength outside an optical amplifier operating bandwidth that includes the WDM channel wavelength grid;
• amplifying ones of said signals of the incoming optical signal at wavelengths within the optical amplifier operating bandwidth;
• after said amplifying, dropping from the incoming optical signal an in-band, IB, OSC signal, if any, at a wavelength within the optical amplifier operating bandwidth;
• outputting the dropped OOB OSC or IB OSC signal;
• receiving an outgoing OOB OSC or IB OSC signal;
• and
• after the amplifying, adding the outgoing OOB OSC or IB OSC signal to a plurality of service channel signals at channel wavelengths of the WDM channel wavelength grid to form an outgoing optical signal.