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, based on the measurement of the RAM using an auxiliary detector, is limited in the case of optical setups exhibiting polarization dependent losses and an imperfect polarizer at the modulator output, 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.
Highlights
Laser frequency stabilization is mandatory for many applications, including optical gyroscopes [1,2], gravitational wave detection [3], spectroscopy [4], refractometry [5], etc
The beam is supposed to propagate through several components that can be described by their Jones matrices that take into account their polarization dependent losses (PDL) and their birefringences [26,27,28,29]
The laser light at λ = 1550 nm is phase modulated at ωmod/2π = 70 kHz by the integrated optics LiNbO3 PM and propagates in a polarization maintaining fiber (PMF) followed by a polarisation maintaining 50:50 coupler C
Summary
Laser frequency stabilization is mandatory for many applications, including optical gyroscopes [1,2], gravitational wave detection [3], spectroscopy [4], refractometry [5], etc. The aim of the present paper is 1) to analyze the influence of the birefringence of the fibered components on the evolution of the RAM along the light path, and in particular between the detector that monitors the RAM and the resonator on which the laser frequency is locked and 2) to develop a new method for RAM control that makes use of the detector that provides the frequency locking signal to monitor the effect of the RAM on the frequency locking itself.
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