Nonlinear modification of the laser noise power spectrum induced by frequency-shifted optical feedback

Abstract

In this article, we study the non-linear coupling between the stationary (i.e. the beating modulation signal) and transient (i.e. the laser quantum noise) dynamics of a laser subjected to frequency shifted optical feedback. We show how the noise power spectrum and more specifically the relaxation oscillation frequency of the laser are modified under different optical feedback condition. Specifically we study the influence of (i) the amount of light returning to the laser cavity and (ii) the initial detuning between the frequency shift and intrinsic relaxation frequency. The present work shows how the relaxation frequency is related to the strength of the beating signal and the shape of the noise power spectrum gives an image of the Transfer Modulation Function (i.e. of the amplification gain) of the nonlinear-laser dynamics.The theoretical predictions, confirmed by numerical resolutions, are in good agreements with the experimental data.

Analysis and Application of Point Scanning and Full-Field Optical Techniques in Vibration Detection

“…The images on the left column show that the frequency distance between the two maxima (located symmetrically on both side of the carrier frequency) decreases. Also, in it can be noted that the amplitude of the maximum located on the right side of the carrier frequency increases (77).…”

“…In Figure A induced by the modification of the carrier amplitude (77). The images on the left column show that the frequency distance between the two maxima (located symmetrically on both side of the carrier frequency) decreases.…”

“…The strong feedback situation is also characterized by a strong modification of the RF signal power spectrum of the laser (75,76). In particular, the relaxation oscillations frequency can decrease, jointly with a modification of the shape of the noise power spectrum of the laser in the radio frequency (RF) range (77).…”

“…In this situation, the noise power spectrum of the laser in RF range, with and without optical feedback, is unchanged. The RF noise power spectrum is an image of the modulation transfer function (gain) of the laser dynamics (77). The knowledge of this gain is of paramount importance to extract without bias the vibration measurements from the laser dynamics of a reinjected laser, as will be discussed in the following section.…”

“…When the feedback is weak (R e = 10 − 9), it can be noted from plot a) in Figure A.1 that the gain adjusted on the noise power spectrum exhibits only one resonance (linear). On the other hand, when the feedback is strong (R e = 10 −7 ), the gain, which becomes non-linear, exhibits two resonances symmetrically located on both side of the carrier frequency (plot b) (77).…”