Method for servocontrolling an optical device comprising a laser and a cavity, making it possible to compensate for an amplitude modulation introduced by a phase modulator

Abstract

A method for the servo control of an optical device includes a cavity exhibiting resonance around a center frequency ƒ, a laser and a phase modulator, the method being designed to servo-control the cavity to the laser or vice versa and to compensate for an amplitude modulation introduced by the phase modulator, the method comprising, inter alia, the following steps: A. varying a difference δν between the optical frequency of the laser radiation and the center frequency, such that the optical frequency scans the resonance, the difference being controlled by a parameter of an element of the device, and for each difference δνi. modulating, at a modulation frequency ƒ, a phase of the laser radiation, through a modulation phase φ, with the phase modulator, ii. injecting the phase-modulated radiation into the cavity, iii. using a photodiode to detect radiation reflected or transmitted by the cavity and generating an electrical signal (St, Sr) representative of the intensity of the detected radiation, iv. demodulating the electrical signal at the modulation frequency ƒby synchronously generating a first demodulated signal and a second demodulated signal representative of the demodulated electrical signal, respectively at a first demodulation phase φand at a second modulation phase φφ≈φk, where k∈[0; 2π] is different from the first phase, and by filtering the first and the second signal so as to retain only a DC component of the first demodulated signal Vϵ, called error signaland of the second demodulated signal Vϵ, called error signal