Optical compensation for dispersion-induced power fading in optical transmission of double-sideband signals

A device, comprising:

• an optical input port, receiving an input optical signal at an optical carrier frequency that is modulated to have a first modulation sideband and a second modulation sideband at different modulation frequencies;
• a first optical path and a second optical path coupled to said input port to receive a first portion of said input optical signal as a first optical signal and a second portion of said input optical signal as a second optical signal, respectively, wherein said first and said second optical paths have different path lengths to produce a relative phase shift of about π/2;
• an optical output port coupled to said first and said second optical paths to receive and combine said first and said second optical signals to produce an output optical signal;
• an optical dispersion element configured to produce different delays in optical signals at different wavelengths and coupled to interact with at least one of said first and said second optical signals to produce a difference of about π between a sum of phases of said first and said second modulation sidebands relative to a phase of the optical carrier at said carrier frequency in said first optical signal, and a sum of phases of said first and said second modulation sidebands relative to a phase of the optical carrier at said carrier frequency in said second optical signal, at said output optical port;
• and
• a polarization element coupled to at least one of said first and said second optical paths and operable to make a polarization of said first optical signal substantially orthogonal to a polarization of said second optical signal at said optical output port.

A system, comprising:

• a fiber network;
• and
• at least one power fading compensator disposed in an optical link in said fiber network to compensate for a distance-dependent power fading in an optical signal at an optical carrier frequency that is modulated to have a first modulation sideband and a second modulation sideband,
• wherein said power fading compensator includes:
• a first optical path having an input terminal and an output terminal, said input terminal receiving a first portion of said optical signal;
• a second optical path having an input terminal and an output terminal that are coupled to said input and said output terminals of said first optical path, respectively, wherein said second optical path receives a second portion of said optical signal;
• and
• an optical dispersion element configured to produce different delays in optical signals at different wavelengths and coupled to at least one of said first and said second optical paths to produce a difference of about π between a sum of phases of said first and said second modulation sidebands relative to a phase of the optical carrier at said carrier frequency in said first portion, and a sum of phases of said first and said second modulation sidebands relative to a phase of the optical carrier at said carrier frequency in said second portion.