METHOD AND APPARATUS FOR IMPROVING SPECTRAL EFFICIENCY IN WAVELENGTH DIVISION MULTIPLEXED TRANSMISSION SYSTEMS

摘要

A method and apparatus is provided for transmitting an optical signal. The method includes the step of generating an optical signal that includes a plurality of optical channels, which are sequentially numbered from 1 to N from lowest to highest wavelength. A state-of-polarization of predetermined odd-numbered channels is oriented t o be substantially orthogonal to a state of polarization of predetermined even-numbered channels by directing the predetermined odd- numbered channels and the predetermined even-numbered channels through orthogonally polarizing inputs of a polarization coupler. T he odd-numbered channels and the even-numbered channels may be directed through first and second wavelength combiners, respectively, prior to orienting their states of polarization. The orthogonal relationship between the states of polarization of odd and even-numbered channels advantageously limits the four-wave mixing products that can be generated in the optical transmitter and the optical transmissio n path to which it is typically coupled.