System and method for controlling noise figure

An optical amplifier including an amplifier stage comprising:

• an input operable to receive a plurality of wavelength signals;
• an output operable to communicate at least some of the plurality of wavelength signals;
• wherein the amplifier stage has associated with it a noise figure having a shape varying as a function of wavelength;
• and
• means for approximately maintaining an intended shape of the noise figure as wavelength signals are added or dropped from the plurality of wavelength signals based at least in part on a signal power of one or more of the plurality of wavelength signals at the input to the amplifier stage.

An optical amplifier operable to amplify a plurality of optical wavelength signals at least in part through Raman amplification, the amplifier including an amplifier stage comprising:

• an input operable to receive a plurality of wavelength signals;
• a pump assembly operable to generate one or more pump signals operable to interact with one or more of the plurality of wavelength signals over a gain medium to cause Raman amplification of the one or more wavelength signals;
• and
• control circuitry operable to generate a control signal based at least in part on a signal proportional to a signal power of one or more of the plurality of wavelength signals at an input to the gain medium of the amplifier stage;
• wherein the amplifier is operable to adjust the power of at least one of the one or more pump signals in response to the control signal, the adjustment of the power of the at least one pump signal approximately maintaining an intended shape of a noise figure associated with wavelength signals being amplified.

A method of amplifying a plurality of wavelength signals, comprising:

• amplifying a plurality of wavelength signals;
• adding wavelength signals to or dropping wavelength signals from the plurality of wavelength signals, wherein adding or dropping wavelength signals causes a change in a shape of a noise figure associated with the plurality of wavelength signals;
• and
• selectively controlling the shape of the noise figure to obtain an intended shape of the noise figure as wavelength signals are added or dropped from the plurality of wavelength signals.

An optical communication system operable to facilitate communication of multiple signal wavelengths, the system comprising:

• one or more transmitters operable to generate alone or collectively a plurality of signal wavelengths;
• a multiplexer operable to combine the plurality of signal wavelengths into a single multiple wavelength signal for transmission over a transmission medium;
• and
• a plurality of optic amplifiers operable to receive the plurality of signal wavelengths, at least one of the optical amplifiers including an amplifier stage comprising:
• a gain medium operable to amplify the multiple wavelength signal through interaction with one or more pump signals, the amplification occurring prior to, during, or after the multiple wavelength signal's transmission over the transmission medium;
• wherein a power of at least one of the one or more pump signals is operable to be selectively adjusted in response to a change in a signal power of the plurality of wavelength signals at an input to the gain medium of the amplifier stage, the adjustment in pump power approximately maintaining an intended shape of a noise figure of the amplifier during operation of the amplifier.

An optical amplifier operable to amplify a plurality of optical wavelength signals at least in part through Raman amplification, the amplifier including an amplifier stage comprising:

• an input operable to receive a plurality of optical signal wavelengths comprising at least a shorter optical signal wavelength and a longer optical signal wavelength;
• a pump assembly operable to generate a plurality of pump signals operable to interact with one or more of the plurality of optical signal wavelengths over a gain medium to cause Raman amplification of the one or more optical signal wavelengths, wherein the plurality of pump signals comprise at least a shorter wavelength pump signal and a longer wavelength pump signal;
• and
• a control module operable to generate a control signal based at least in part on a power of one or more of the plurality of optical signal wavelengths;
• wherein the control signal is operable to be applied to adjust a power of at least the longer wavelength pump signal to obtain an improvement in a noise figure at the shorter optical signal wavelength and a degradation of a noise figure at the longer optical signal wavelength compared to a noise figure that would exist at those wavelengths without adjusting the pump power.

A method of amplifying optical signals, comprising:

• introducing to a gain medium one or more pump signals comprising a shorter wavelength pump signal and a longer wavelength pump signal, and a multiple wavelength signal comprising a shorter wavelength optical signal and a longer wavelength optical signal;
• detecting a change in power of one or more of the multiple wavelength signals;
• and
• selectively adjusting, based at least in part on the change in power of the one or more of the multiple wavelength signals, a power of at least the longer wavelength pump signal;
• wherein the adjustment to the power of at least the longer wavelength pump signal results in an improvement in an optical noise figure associated with the shorter optical signal wavelength and a degradation of a noise figure at the longer optical signal wavelength compared to a noise figure that would exist at those wavelengths without adjusting the pump power.

A multiple stage Raman amplifier operable to amplify a plurality of optical wavelength signals, the amplifier comprising:

• a first Raman stage operable to receive a plurality of optical signal wavelengths comprising at least a shorter optical signal wavelength and a longer optical signal wavelength;
• a second Raman stage operable to receive at least a majority of the plurality of optical signal wavelengths after those wavelengths have passed through the first Raman stage;
• a pump assembly operable to generate a plurality of pump signals operable to interact with one or more of the plurality of optical signal wavelengths within the first Raman stage, wherein the plurality of pump signals comprise at least a shorter wavelength pump signal and a longer wavelength pump signal;
• and
• a control module operable to generate a control signal based at least in part on a power of one or more of the plurality of optical signal wavelengths;
• wherein the control signal is operable to be applied to adjust a power of one or more of the shorter wavelength pump signal and the longer wavelength pump signal to obtain an improvement in a noise figure at the shorter optical signal wavelength compared to a noise figure that would exist at those wavelengths without adjusting the pump power.

A method of amplifying optical signals, comprising:

• receiving at a gain medium of a first Raman amplifier stage one or more pump signals comprising a shorter wavelength pump signal and a longer wavelength pump signal, and a multiple wavelength signal comprising a shorter wavelength optical signal and a longer wavelength optical signal;
• receiving at least a majority of the wavelengths of the multiple wavelength optical signal at a second Raman amplifier stage after those wavelengths have passed through the first Raman amplifier stage;
• detecting a change in power of one or more of the multiple wavelength signals;
• and
• selectively adjusting, based at least in part on the change in power of the one or more of the multiple wavelength signals, a power of at least one of the shorter wavelength pump signal and the longer wavelength pump signal;
• wherein the adjustment to the power of at least one of the shorter wavelength pump signal and the longer wavelength pump signal results in an improvement in an optical noise figure associated with the shorter optical signal wavelength compared to a noise figure that would exist at those wavelength without adjusting the pump power.