Single Sideband Up-Down Converter for Sub-Octave Bandwidth Transmission of Low Frequency Signals

摘要

A system for transporting a plurality of relatively low-frequency information signals over an optical fiber can include a plurality of transmitters. Each transmitter receives one of the relatively low-frequency information signals as an input, processes the input signal, and outputs an up-shifted (i.e. relatively high frequency) signal that has a suppressed sideband to reduce transmission power requirements. Sideband suppression is accomplished using a technique in which a first component of the input signal is shifted in phase by 180 degrees and summed with a second, in-phase signal component. The signals output from the transmitters are then frequency stacked and the resulting signal is converted to an optical signal for transmission over an optical fiber. The up-shifted signals output from the transmitters have frequencies within a single sub-octave frequency band to reduce the adverse effects of composite second order distortions that can occur during optical transport of the information signals.

主权项

1. A system for processing an input signal having a frequency, f0, to produce an upshifted signal having a suppressed sideband for transmission over an optical fiber, said system comprising:
a quadrature hybrid coupler receiving the input signal and outputting a first signal in phase with the input signal at a first coupler output and a second signal 90° out of phase with the input signal at a second coupler output; a local oscillator (LO) subsystem producing a first LO signal having frequency, f1, with f1>f0 and in phase with the input signal and a second (LO) signal having frequency, f1 and 90° out of phase with the first LO signal; a first mixer downstream of the first coupler output, the first mixer receiving the first LO signal and outputting a first mixed signal; a second mixer downstream of the second coupler output, the second mixer receiving the second LO signal and outputting a second mixed signal; and a summer downstream of the first mixer and second mixer for producing an upshifted, sideband suppressed signal for transmission over an optical fiber.