Shane O'Donoghue

RF Linewidth in Monolithic Passively Mode-Locked Semiconductor Laser

We have analyzed theoretically and experimentally the linewidth of the first harmonic of the photocurrent (radio-frequency (RF) linewidth) in monolithic passively mode-locked semiconductor lasers. Due to the absence of restoring force, the timing jitter is directly related to the RF linewidth, avoiding possible underestimations made with conventional methods of phase noise measurement. The RF linewidth is also analytically related to the pulse characteristics using Hauss model. The timing stability performance of a promising two-section quantum-dot laser is presented using RF linewidth measurements. Experimental evolution of the RF linewidth with power and pulsewidth is finally compared to the analytical expression.

Quantum-Dot Mode-Locked Lasers With Dual-Mode Optical Injection

Quantum-dot mode-locked lasers are injection-locked by coherent two-tone master sources. Spectral tuning, significantly improved time-bandwidth product, and low jitter are demonstrated without deterioration of the pulse properties.

Optical linewidth of a passively mode-locked semiconductor laser

We measured the optical linewidths of a passively mode-locked quantum dot laser and show that, in agreement with theoretical predictions, the modal linewidth exhibits a parabolic dependence with the mode optical frequency. The minimum linewidth follows a Schawlow-Townes behavior with a rebroadening at high power. In addition, the slope of the parabola is proportional to the RF linewidth of the laser and can therefore provide a direct measurement of the timing jitter. Such a measurement could be easily applied to mode-locked semiconductor lasers with a fast repetition rate where the RF linewidth cannot be directly measured.

Quantum-dot mode-locked lasers with optical injection

Modal optical linewidths of a passively mode-locked and optical injection locked quantum dot laser are studied. For the free-running case the modal linewidth is in the order of tens of MHz and demonstrates a parabolic dependence on the mode optical frequency. The slope of the parabola, as was predicted theoretically, is proportional to the radio-frequency (RF) linewidth, which provides a direct measurement of the timing jitter. With optical injection the slave laser optical spectrum becomes narrowed and tunable via the master wavelength. Frequency resolved Mach-Zehnder gating measurements performed to characterize slave laser pulses showed significantly improved pulse time-bandwidth product with optical injection. Measurements of the modal optical linewidths of the injected laser have shown phase locking of the slave laser modes to the master laser in the vicinity of the injection wavelength. However, far from this wavelength modal linewidth of the slave laser increases to greater than that of the free running case, leading to increase of the RF linewidth and timing jitter with single-tone injection.

Single and dual-mode injection locked quantum-dot mode-locked lasers

Quantum-dot mode-locked lasers are injection locked by single and two-tone master sources. Narrow linewidth, improved time-bandwidth product and wavelength control are demonstrated.

Linewidth narrowing and phase locking of quantum-dot mode-locked lasers employing single- and dual-mode injection locking

Optical pulse sources with narrow oscillation linewidth and optical phase-controllability are important as the signal and local light sources for high-speed coherent communication. Quantum-dot CW lasers have shown very stable optical injection locking characteristics, with no instabilities observed at low detuning [1]. This observation suggests that QD-MLL performance could be further improved and controlled though optical injection locking and in particular that dual mode injection for remote coherent receivers should be investigated for this medium [2]. In this paper we investigate in-band single- and dual-tone injection. We show tunability of the slave laser optical spectrum via the master wavelength, significant linewidth narrowing and phase locking of the injected QD-MLL to the master laser.

Optical mode lineshape and linewidth in passively mode-locked semiconductor laser

Contrary to solid state mode-locked lasers where technical noises (cavity length fluctuation and pump noise) are predominant, passively mode-locked semiconductor lasers are submitted to a large level of quantum noise originating from the spontaneous emission in the cavity. RF linewidth of passively mode-locked semiconductor laser has been the subject of recent experimental studies [1] showing that the repetition rate of the laser exhibits on a large frequency span a Lorentzian spectrum whose linewidth decreases with the inverse of the internal optical power, which shows that the repetition rate is dominated by quantum noise. Optical linewidth of longitudinal modes in actively mode-locked diode lasers has been shown experimental to be constant [2]. However, no experimental results have been reported for passive mode-locking.

Characterisation of a Low Jitter 2-ps Passively Mode-Locked Semiconductor Quantum-Dot Laser by RF Linewidth Study

In this paper, the authors discuss the application of this method to characterize a promising high repetition rate quantum-dots PMLL and determine the best conditions of operations.

Timing Jitter in Compact Passively Mode-Locked Quantum-Dot Lasers

Passively mode-locked quantum dot laser diodes emitting near 1300 nm have produced picosecond pulses with high peak power and low timing jitter at a range of repetition rates. These should be sufficiently compact and robust for use in portable pulsed optical or terahertz sources.

High Repetition Rate Monolithic Passively Mode-Locked Semiconductor Quantum-Dot Laser: Investigation of the Locking Regimes and the RF Linewidth

We investigate global mode-locked regimes of a passively mode-locked quantum-dot GaAs/InAs laser at 1300 nm. Detailed RF linewidth studies demonstrate the possibility of obtaining 1.9 ps pulses with a pulse-to-pulse timing jitter of 6.5 fs/cycle.