Sub-kHz RF linewidth of quantum-dash mode-locked laser by self-injection from symmetric dual-loop feedback and fiber delay

Abstract

Sub-kHz RF-linewidth was demonstrated in two-section quantum-dash mode-locked lasers emitting near 1550 nm and 20 GHz repetition-rate using symmetric dual-loop and fiber delay. Compared to free-running lasing, RF-linewidth and timing-jitter reduced by ~100x and ~10x.

Coherent Terabit Communications Using a Quantum-Dash Mode-Locked Laser and Self-Homodyne Detection

“…5(b). Recently, in a separate series of experiments, we achieved 0.97 kHz linewidth (instrument limited) and timing jitter 0.45 ps with both cavities resonant [17], confirming that balanced SDL produces effective stabilization, but only at a specific delay with tolerance ∼ 1 ps, a very stringent requirement in practice. 5 k H z R F L i n e w i d t h ( k H z ) D e l a y ( p s ) R F L i n e w i d t h b a l a n c e d S D L R F L i n e w i d t h u n b a l a n c e d S Next, we explored unbalanced SDL feedback, in which the power split between the two loops was varied.…”

“…The latter is usually determined by measuring the linewidth of the repetition-rate peak in the RF intensity fluctuation spectrum. Several techniques such as single-loop external optical feedback [4][5][6][7][8], coupled optoelectronic oscillators (OEOs) [9][10][11], hybrid mode-locking [12], injection-locking [13][14][15] and dual-loop feedback [16][17][18][19][20] have been proposed and demonstrated to improve this key parameter of mode-locked lasers (MLLs). Among feedback-based techniques, optoelectronic feedback requires optical-to-electrical conversion, while hybrid mode-locking requires high speed electrical modulation of the gain and/or absorber sections.…”

InAs/InP quantum-dash lasers

“…In another study, Sooudi et al [91] utilized double locking with simultaneous optical injection and optical feedback on QD-MLL and reported a reduction of two times in the bandwidth product and two orders of magnitude reduction in the RF linewidth. This work was followed by an implementation of dual-loop feedback in tandem with optical injection and optical fiber delay by Wei et al [92] on a 1.55 mm, 20 GHz InAs/InP DaWELL. As such, the RF linewidth and timing jitter were significantly reduced from 97.9 kHz to 4.27 ps, respectively in the case of free-running, to 972 Hz and 430 fs.…”

Optimum stabilization of self-mode-locked quantum dash lasers using dual optical feedback with improved tolerance against phase delay mismatch

“…This dual loop feedback configuration gives sub-kHz linewidth with 38 dB suppression in the fundamental side-mode. A number of experimental [18][19][20][21] and numerical investigations [22] have also been made of the dynamics of modelocked semiconductor lasers subject to dual loop feedback. We note that optimum performance of RF linewidth and timing jitter in dual loop feedback has been very sensitive to small phase adjustments, which limits operation to a narrow parameter space and makes optimum performance vulnerable to environmental change.…”