Natalia Rebrova

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.

Stabilization of a passively mode-locked laser by continuous wave optical injection

We investigate numerically and experimentally the properties of a passively mode locked quantum dot semiconductor laser under the influence of cw optical injection. We demonstrate that the waveform instability at high pumping for these devices can be overcome when one mode of the device is locked to the injected master laser and additionally show spectral narrowing and tunability. Experimental and numerical analyses demonstrate that the stable locking boundaries are similar to these obtained for optical injection in CW lasers.

Bistable regimes in an optically injected mode-locked laser

We study experimentally the dynamics of quantum-dot (QD) passively mode-locked semiconductor lasers under external optical injection. The lasers demonstrated multiple dynamical states, with bifurcation boundaries that depended upon the sign of detuning variation. The area of the hysteresis loops grew monotonically at small powers of optical injection and saturated at moderate powers. At high injection levels the hysteresis decreased and eventually disappeared.

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.

Mode-Locked Semiconductor Lasers with Optical Injection

We perform characterization of the pulse shape and noise properties of quantum dot passively mode-locked lasers (PMLLs). We propose a novel method to determine the RF linewidth and timing jitter, applicable to high repetition rate PMLLs, through the dependence of modal linewidth on the mode number. Complex electric field measurements show asymmetric pulses with parabolic phase close to threshold, with the appearance of waveform instabilities at higher currents. We demonstrate that the waveform instabilities can be overcome through optical injection-locking to the continues wave (CW) master laser, leading to time-bandwidth product (TBP) improvement, spectral narrowing, and spectral tunability. We discuss the benefits of single- and dual-tone master sources and demonstrate that dual-tone optical injection can additionally improve the noise properties of the slave laser with RF linewidth reduction below instrument limits (1 kHz) and integrated timing jitter values below 300 fs. Dual-tone injection allowed slave laser repetition rate control over a 25 MHz range with reduction of all modal optical linewidths to the master source linewidth, demonstrating phase-locking of all slave modes and coherence improvement.

Dynamics of couple mode-locked quantum dot semiconductor laser

Quantum-dot (QD) monolithic mode-locked laser diodes (MMLDs) have been the subject of much research interest in the last number of years, with excellent results obtained in terms of pulsewidth, repetition rate etc. We have recently demonstrated that time-bandwidth product can be improved using single mode optical injection and that dual tone injection additionally improves the timing jitter and the optical linewidth of each mode of the optical comb [1].

Quantum-dot mode-locked lasers with dual mode optical injection

Quantum-dot mode-locked lasers are injection-locked by coherent two-tone master sources. 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 (TBP) with optical injection. Measurements of the modal optical linewidths of the injected laser demonstrated phase locking of all the slave laser modes to the master laser, which improved significantly the device timing jitter. Integrated over a 20 kHz-80 MHz range timing jitter values of 210 fs were achieved for small injection powers, close to the best reported results for the hybrid mode-locking of similar QD-MLLs.

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.

Theoretical study of mode-locked lasers with nonlinear loop mirrors

We analyze the properties of a unidirectional class-A ring laser containing a nonlinear amplifying loop mirror (NALM). The NALM is a Sagnac interferometer consisting of an amplifier and a Kerr-type nonlinear element, and has a reflectivity that periodically varies with the intra-cavity power. To model the dynamics of these lasers, we use the approach based on Delay Differential Equations (DDEs) that has been successfully applied to describe the properties of passively mode-locked semiconductor lasers. The proposed model allows us to investigate mode locking operation in this laser. The analysis of this DDE model for mode-locked operation was performed numerically and analytically in the limit of large cavity round trip times. We demonstrate that mode-locked pulses are born though a modulational instability of the steady state solutions when the pseudo- continuous branch crosses the imaginary axis. These asymmetric pulses always co-exist with the stable laser-off solution. Hence, they can be viewed as temporal cavity solitons having similar properties with localized structures observed in bistable spatially-extended systems.