Heterodyne beatings between frequency-shifted feedback lasers

Abstract

Frequency-shifted feedback (FSF) lasers are potential candidates for long distance telemetry due to the appearance of beatings in the noise spectrum at the output of a homodyne interferometer: the frequencies of these beatings vary linearly with the path delay. In this Letter we demonstrate that these beatings also occur in the heterodyne mixing of two identical, but distinct, FSF lasers. This phenomenon is explained by the passive cavity model and is exploited to characterize the time-spectrum properties of FSF lasers. Consequences on telemetry with FSF lasers are presented.

Generation of ultrahigh and tunable repetition rates in CW injection-seeded frequency-shifted feedback lasers

“…where φ = ω s τ c = 2π f s / f c . Note that E(t) appears as a Fourier series with phase terms quadratic in n: the same kind of expression was previously shown as playing a fundamental role in the time-spectrum description of modeless FSF lasers [9,10]. In the following it is shown that these quadratic phases play also a decisive role in the expression of the intensity at the output of the CW injection-seeded FSF laser.…”

“…When seeded only with spontaneous emission FSF lasers can exhibit different regimes, depending essentially on the influence of the gain dynamics and non-linear effects like cross-phase modulation . When the influence of the gain medium and possible non-linear effects are neglected as in the passive cavity model, the output optical field shows a modeless spectrum and consists, in the time-frequency representation, in a periodic function chirping with time [9,10]. In the case where the frequency shift per roundtrip is much smaller than the cavity free spectral range, the periodic function tends to a Dirac comb and the FSF laser field can be seen as a frequency comb chirping in the timefrequency plane [11].…”