Low-noise Raman amplifier

A method for low-noise amplification of optical signals, comprising:

• receiving, at a first stage of an amplifier, an input optical signal;
• passing all wavelengths of the input optical signal through a first optical filter in a first propagation direction over a gain medium, the first optical filter reflecting first wavelengths above a first threshold wavelength received by the first optical filter over the gain medium in a direction opposite the first propagation direction;
• generating a first pump light at a first Rama pump using a first Fabry Perot laser;
• tuning, using a first temperature controller, the first Fabry Perot laser to shift a wavelength at which the first pump light is centered toward a wavelength lower than the first threshold wavelength;
• injecting the first pump light from the first Raman pump onto the gain medium for transmission in the first propagation direction;
• providing, over the gain medium, a first combined optical signal including all wavelengths of the input optical signal and the first pump light to a second stage of the amplifier;
• receiving, at the second stage of the amplifier, the first combined optical signal;
• passing all wavelengths of the first combined optical signal, including the first pump light, through the second optical filter in the first propagation direction over the gain medium, the second optical filter reflecting second wavelengths above a second threshold wavelength received by the second optical filter over the gain medium in a direction opposite the first propagation direction, the second threshold wavelength being lower than the first threshold wavelength;
• generating a second pump light at the second Raman pump using a second Fabry Perot laser;
• tuning, using a second temperature controller, the second Fabry Perot laser to shift a wavelength at which the second pump light is centered toward a wavelength lower than the second threshold wavelength;
• injecting the second pump light from the second Raman pump onto the gain medium for transmission in the first propagation direction;
• and
• outputting a second combined optical signal including all wavelengths of the first combined optical signal and the second pump light.

An optical system for low-noise amplification of optical signals, comprising:

• a transmitter configured to transmit an input optical signal;
• and
• a low-noise Raman amplifier, comprising:
• a gain medium;
• and
• a plurality of amplifier stages, including:
• a first amplifier stage configured to receive the input optical signal and to output a first combined optical signal, the first amplifier stage comprising:
• a first optical filter configured to pass all wavelengths of the input optical signal through the first optical filter in a first propagation direction over the gain medium and to reflect first wavelengths above a first threshold wavelength received by the first optical filter over the gain medium in a direction opposite the first propagation direction;
• and
• a first Raman pump configured to inject a first pump light onto the gain medium for transmission in the first propagation direction, the first pump light being centered at a wavelength lower than the first threshold wavelength, the first Raman pump comprising a first Fabry Perot laser configured to generate the first pump light, and comprising a first temperature controller configured to tune the first Fabry Perot laser to shift the wavelength at which the first pump light is centered toward the wavelength lower than the first threshold wavelength;
• and
• one or more additional amplifier stages, each additional amplifier stage being configured to receive a combined optical signal from a previous amplifier stage and to output a respective combined optical signal, and each additional amplifier stage comprising:
• a respective optical filter configured to pass all wavelengths of the received combined optical signal through the respective optical filter in the first propagation direction over the gain medium and to reflect respective wavelengths above a respective threshold wavelength received by the respective optical filter over the gain medium in a direction opposite the first propagation direction, the respective threshold wavelength being lower than a threshold wavelength at the previous amplifier stage;
• and
• a respective Raman pump configured to inject a respective pump light onto the gain medium for transmission in the first propagation direction, the respective pump light being centered at a wavelength lower than the respective threshold wavelength, the respective Raman pump at each of the additional amplifier stages comprising a respective Fabry Perot laser configured to generate the respective pump light, and comprising a respective temperature controller configured to tune the respective Fabry Perot laser to shift the wavelength at which the respective pump light is centered toward the wavelength lower than the respective threshold wavelength;
• wherein the first combined optical signal includes all wavelengths of the input optical signal and the first pump light and, for each of the additional amplifier stages, the respective combined optical signal output by the additional amplifier stage includes all wavelengths of the received combined signal and the respective pump light.