Statistical properties of frequency shifted feedback lasers

Abstract

International audienceWe evidence experimentally the statistical properties of frequency shifted feedback (FSF) lasers through measurements of the homodyne beat signal and interferometric autocorrelation of a dye FSF laser at the output of a Michelson interferometer. The FSF laser is found to show thermal fluctuations and photon bunching. Moreover whereas the degree of first-order coherence vanishes beyond the coherence length of the FSF source, the degree of second-order coherence exhibits periodic revivals far beyond the coherence length, with a period equal to the cavity roundtrip time. Our observations are in good agreement with the theoretical treatment of Yatsenko et al. [L.P. Yatsenko, B.W. Shore, K. Bergmann, Opt. Comm. 236 (2004) 183] and validate the description of the output field of a FSF laser by a broadband cyclostationary thermal field

The hypothesis of the moving comb in frequency shifted feedback lasers

“…The passive cavity model (PC) involves a ring-like optical cavity closed on the first order of diffraction of an acousto-optics (AO) modulator. For more consistence we adopt the notations used in [20] and [23]. The AO modulator is driven at angular frequency ∆: each time a photon makes a roundtrip in the cavity it experiences a frequency shift equal to ∆/2π.…”

Heterodyne beatings between frequency-shifted feedback lasers

“…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.…”

“…2(a). When laser 2 is off, only laser 1 is detected by the photodiode and the usual peaks at the free spectral range (270 MHz) and a residual amplitude modulation at twice the AOM frequency (80 MHz) are recorded [8]. When laser 2 is on, one recovers the additional beatings between the two FSF lasers.…”

Coherence properties of modeless lasers

“…which shows the periodic nature of the light intensity of the FSF laser. This periodicity is therefore present in the g (2) function [6]. This property is not specific to modeless…”

“…Concerning the g (2) function, because of the short coherence time of our modeless laser (about 10 ps) we chose to perform second harmonic generation (SHG) at the output of the interferometer to measure the autocorrelation trace of the modeless laser, in the same way as the measurement of ultrashort pulses. We used a long interferometer where the path difference between both arms can exceed one cavity length, enabling to reach delays larger than the cavity roundtrip time τ r [6]. Figure 10.…”