The Influence Of Optical Fiber Phase Noise On Transmission Of Narrow-Linewidth Laser And The Technique Of Phase Noise Cancellation

Narrow-linewidth lasers have many important applications,such as high-precision laser spectroscopy,measurement of fundamental constant,tests of special relativity etc.Furthermore,they serve as one of the most important parts in optical clocks,which have potential to be future frequency standards.When a narrow-linewidth laser is transferred through optical fiber,the optical phase of the light in the fiber is extremely sensitive to environmental perturbations like pressure, temperature,etc.As a result,the light's phase is suffered from a random phase modulation that introduces phase noise,and the linewidth of the light after transferred is broadened.In this paper,we study the mechanism of fiber-induced phase noise,the effect of phase noise on transmission of narrow-linewidth laser and the basic principle for eliminating fiber-induced phase noise.The basic theory of phase noise is firstly introduced.Then the research on the principle and experiment scheme of fiber phase noise cancellation are investigated.Finally the fiber phase noise cancellation is experimentally performed.Using a 1064 nm Nd:YAG laser as the light source,a double-pass set-up for fiber-induced phase noise detection has been built with a 300 meters single-mode optical fiber.The fiber-induced phase noise is eliminated by using an acousto-optic modulator to make phase compensation.A beat notes between fiber input and output light are obtained with and without active noise cancellation.The frequency spectrum of the beat note are compared and analyzed.The results show that the linewidth of the beat note is broadened to kilohertz level after laser passes through 300-metre fiber without active phase noise cancellation.As active phase noise cancellation is applied,the linewidth of the beat note reduces to millihertz level,which means the additional linewidth induced by fiber phase noise can be eliminated to millihertz level.It proves that the active phase noise cancellation can effectively cancel the fiber-induced phase noise.