Abstract
We show both theoretically and experimentally that frequency-shifted feedback (FSF) lasers seeded with a single frequency laser can generate Fourier transform-limited pulses with a repetition rate tunable and limited by the spectral bandwidth of the laser. We demonstrate experimentally in a FSF laser with a 150 GHz spectral bandwidth, the generation of 6 ps-duration pulses at repetition rates tunable over more than two orders of magnitude between 0.24 and 37 GHz, by steps of 80 MHz. A simple linear analytical model i.e. ignoring both dynamic and non-linear effects, is sufficient to account for the experimental results. This possibility opens new perspectives for various applications where lasers with ultra-high repetition rates are required, from THz generation to ultrafast data processing systems.
Highlights
Frequency shifted feedback (FSF) lasers have attracted a sustained attention during the last 25 years because of their counter-intuitive physical properties that have triggered a large amount of fundamental studies in laser dynamics [1] or optical coherence [2,3,4], and have found applications in very diverse areas: communications protocols [5], atomic physics [6], telemetry [7], profilometry [8] and sensing among others
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]
We provide a simple model based on the interference of the optical modes of the frequency comb generated at the output of the CW injection-seeded FSF laser, and attribute this behavior to the fact that the phase of the nth mode has a quadratic dependence with n
Summary
Frequency shifted feedback (FSF) lasers have attracted a sustained attention during the last 25 years because of their counter-intuitive physical properties that have triggered a large amount of fundamental studies in laser dynamics [1] or optical coherence [2,3,4], and have found applications in very diverse areas: communications protocols [5] , atomic physics [6], telemetry [7], profilometry [8] and sensing among others. 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]. On the contrary when the gain dynamics and non-linear effects cannot be neglected, various pulsing regimes have been reported in the literature so far [12], especially in fiber FSF lasers where the spatial confinement enhances the non-linear effects [13,14,15,16,17,18]
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