Optical transmission system using optical signal processing in terminals for improved system performance

Abstract

An optical communication system configured to operate with optical signals at lower signal to noise ratios than previously contemplated. The communication system includes a receiver having an optical pre-processor coupled between a demultiplexer and a detector. The optical pre-processor includes either an optical polarization section having a polarization rotator and an optical polarizer, a phase modulation section that includes a phase modulator and a dispersion element and a clock recovery circuit, or an amplitude modulation section that includes an amplitude modulator clock recovery circuit and a spectral shaping filter. A method of communication includes transmitting an optical signal into the system and receiving the signal at a reduced signal-to-noise ratio through a transmission media, demultiplexing the optical transmission signal into a first optical signal, and pre-processing the first optical signal to form a first pre-processed signal by either rotating a polarization of the first optical signal, compressing a pulse in the first optical signal, or modulating an amplitude of a pulse in the first optical signal. The method then detects the first pre-processed signal to form an electrical signal. A reference signal-to-noise ratio is defined as a signal-to-noise ratio of a received signal that would produce a predetermined bit error rate in the electrical signal if the signal-to-noise ratio were to be determined with the pre-processing step omitted. The reduced signal-to-noise ratio is less than the reference signal-to-noise ratio, and a bit error rate in the electrical signal is less than the predetermined bit error rate when the step of transmitting transmits at the reduced signal-to-noise ratio.