Pulse Doublets Generated by a Frequency-Shifting Loop Containing an Electro-Optic Amplitude Modulator

Abstract

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Analysis of frequency-shifting loops in integer and fractional Talbot conditions: electro-optic versus acousto-optic modulation

“…There is also an intriguing transition from sub-threshold operation, described here, and the laser operation above threshold where repetition rate multiplication has already been observed experimentally (the so-called rational harmonic mode-locking [16,17]). Besides, the AMcase was already investigated in [13], but the present analysis predicts the possibility of observing repetition rate multiplication, which needs further experimental efforts.…”

“…( 8) with modulation frequencies corresponding to the cases of Eqs. ( 12)- (13). We choose simulation parameters as follows: the fundamental loop frequency is = 10 MHz ( = 100 ns), the frequency shift is adjusted to = 10 + ( ′ ′ ⁄ ) .…”

“…After having revisited the AO-based FSL for which these results had already been observed, we now turn to dual-sideband EO cases, first in the amplitude-modulation (AM) scheme that was recently shown to lead to pulse doublets [13], and then in the phasemodulation (PM) regime.…”

“…Interestingly, two temporally separated solutions appear in one modulation period. According to this analysis, we may predict that the output of the amplitude-modulated loop in the time domain delivers a periodic series of pulse doublets [13]. Moreover, the output signal does not map the input spectrum anymore.…”

“…Besides the AO frequency-shifter, a phase modulator (PM) or an amplitude modulator (AM) can also provide frequency-shifted sidebands at each round-trip, with a potentially much higher bandwidth. In this respect, electro-optic (EO) modulators have been demonstrated to provide high repetition rates [12] or peculiar doublepulse [13] regimes. In addition to high modulation frequency and bandwidth, EO modulators are compact and easy to integrate with other fiber devices.…”