The hypothesis of the moving comb in frequency shifted feedback lasers

Abstract

International audienceThe use of frequency-shifted feedback (FSF) lasers in optical metrology is based on a unique coherence property: the appearance of beats in the noise spectrum at the output of a two-beam interferometer, whose frequencies vary linearly with the path delay of the interferometer. A description of the output of a FSF laser as a moving comb of optical frequencies is generally admitted to explain these specific coherence properties. Here starting from the model of a passive FSF cavity seeded by spontaneous emission we give a rigorous description of the time-spectrum properties of FSF lasers and show that the moving comb exists only in the limit of small frequency shift

Heterodyne beatings between frequency-shifted feedback lasers

“…To interpret the appearance of these beatings at the simplest level (i.e., neglecting the influence of the laser gain medium responsible for possible additional dynamic effects like self-pulsing), the FSF laser field has been first described by a moving comb: in the time-angular-frequency t; ω representation, the FSF laser field consists of a succession of parallel slanted lines, separated by 2π∕Δ and 2π∕τ r along the time and angular-frequency axes, respectively, where τ r is the cavity round-trip time and Δ is the angular-frequency shift per cavity round trip [3]. Recently it has been shown that, in the general case, the timefrequency representation of the FSF laser field is not a moving comb, but rather is a more complicated 2πperiodic moving function of ωτ r − Δt with the same periodicities [4]. In the following, this description is referred as the generalized moving comb (GMC).…”

“…Practical consequences for telemetry are finally discussed. The passive cavity model is useful to explain simply the coherence properties of FSF lasers [4,7,8]. Recall that the electric field at the output of the passive cavity seeded by spontaneous emission satisfies the relation Et ξt Re iΔtψ Et − τ r , where ξt is the electric field of the seeding (spontaneous emission in the cavity mode), R is the reflectivity of the cavity mirror, and ψ is an additional phase term characterizing the phase of the RF wave driving the AOM.…”

Ranging with frequency-shifted feedback lasers: from $$\upmu$$ μ m-range accuracy to MHz-range measurement rate

“…Further detailed analysis of FSF-laser properties and some new applications was presented by the Grenoble group [32,33,34,35,36,37,38]. …”

Broadband modeless cw quantum-dot semiconductor laser: design and coherence properties

“…The light left in the 0th order leaves the cavity as output. We calculated the transfert function of the FSF passive cavity 13 we built to check that the optical cavity indeed exhibit a continuum spectrum.…”