Accurate cancellation (to milliHertz levels) of optical phase noise due to vibration or insertion phase in fiber-transmitted light

Abstract

A single-mode optical fiber is a convenient and efficient transmission medium for optical signal. However, the optical insertion phase written on the light field by the fiber is very sensitive to the surrounding environment, such as temperature or acoustic pressure. This phase-noise modulation tends to corrupt the original delta-looking Hz-level optical spectrum by broadening it toward the kilohertz domain. Here we describe a simple and effective technique for accurate cancellation of such induced phase noise, thus allowing fiber-based optical signal transmission in very demanding high-precision frequency-based applications where optical phase noise is critical the system is based on double-pass heterodyne measurement and digital phase division by two to obtain the correction signal for the phase compensating AOM. The underlying physical principle is the fact that an optical fiber path ordinarily possesses an excellent degree of linearity and reciprocity, such that two counterpropagating signals can experience the sam phase perturbations. Overall, the fiber's kilohertz level of broadening is reduced to sub-millihertz domain by our correction.