New method for residual amplitude modulation control in fibered optical experiments

Abstract

When locking the frequency of a laser to an optical cavity resonance, the residual amplitude modulation (RAM), which accompanies the phase modulation necessary to build the error signal, is a major limitation to the frequency stability. We show that the popular method demonstrated by Wong and Hall to cancel this effect, and based on the measurment of the RAM using an auxiliary detector, is not suitable in the case of optical setups including birefringent elements and polarization dependent losses, such as guided-wave optical systems. We propose and demonstrate a new method, using a single photodetector, to generate the two error signals and demonstrate its usefulness in the case of fibered systems.