Abstract
Optically harmonic mode-locking of a semiconductor optical amplifier fiber laser (SOAFL) induced by backward injecting a dark-optical comb is demonstrated for the first time. The dark-optical comb with 60-ps pulsewidth is generated from a Mach-Zehnder modulator, which is driven by an electrical comb at a DC offset of 0.3Vn. Theoretical simulation indicates that the backward injection of dark-optical comb results in a narrow gain window of 60 ps within one modulating period, providing a cross-gainmodulation induced mode-locking in the SOAFL with a shortest pulsewidth of 15 ps at repetition frequency of 1 GHz. The mode-locked SOAFL pulsewidth can be slightly shortened to 10.8 ps with a 200m-long dispersion compensating fiber. After nonlinearly soliton compression in a 5km-long single mode fiber, the pulsewidth, linewidth and time-bandwidth product become 1.2 ps, 2.06 nm and 0.31, respectively.
Highlights
Backward optical injection is a novel technology to achieve mode-locking in semiconductor optical amplifier based fiber-ring lasers (SOAFLs) [1,2,3,4,5,6,7,8]
We demonstrate for the first time the comparison on optical harmonic mode-locking of a semiconductor optical amplifier fiber laser (SOAFL) via backward injection of optical comb-like bright and dark pulse-trains with a pulsewidth of 60 ps at repetition frequency of 1 GHz
The mode-locked SOAFL pulsewidth significantly shrinks from 68 ps to 15 ps at a repetition frequency of 1 GHz as the average power of the dark-optical comb increases from 1.3 to 4.5 mW, which is already the shortest pulsewidth ever reported in similar systems at repetition rate of 1 GHz
Summary
Backward optical injection is a novel technology to achieve mode-locking in semiconductor optical amplifier based fiber-ring lasers (SOAFLs) [1,2,3,4,5,6,7,8]. The backward optical injection induced periodical gain-depletion as well as cross-gain modulation (XGM) in a SOAFL has been experimentally demonstrated and theoretically discussed [4,5,6]. A 4.3-ps pulse was obtained by gain-depleting the SOAFL with a compressed laser diode pulse-train at repetition of 20 GHz [2]. We demonstrate for the first time the comparison on optical harmonic mode-locking of a SOAFL via backward injection of optical comb-like bright and dark pulse-trains (referred hereafter as bright- and dark-optical combs) with a pulsewidth of 60 ps at repetition frequency of 1 GHz. The differences in mode-locked pulsewidth and pulse shape between two opposite modulation schemes are interpreted, and the correlation between the gain-depletion time and mode-locking pulsewidth is discussed. To further shorten the SOAFL pulsewidth, the fiber-based linear dispersion compensation and nonlinear soliton compression techniques are reported
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