Patent ID: 7187870

Claim:
A device, comprising: an input port to receive an input optical beam at an optical carrier frequency; a first optical path coupled to the input port to receive a first portion of the input optical signal and comprising a first optical resonator locked in frequency to be resonant at the optical carrier frequency to transmit light at the optical carrier frequency through the first optical path; a second optical path coupled to the input port to receive a second portion of the input optical signal and comprising a second optical resonator, which is tunable to be in resonance with light at a selected optical frequency different from the optical carrier frequency, to transmit light at the selected optical frequency through the second optical path; an output port coupled to the first and second optical paths to combine transmitted light from the first and second optical paths to produce an output optical beam; and an optical detector to convert the output optical beam into a detector output carrying a signal at a frequency that is a difference between the optical carrier frequency and the selected optical frequency.