Lina Jaurigue

Timing jitter of passively-mode-locked semiconductor lasers subject to optical feedback: A semi-analytic approach

We propose a semi-analytical method of calculating the timing fluctuations in mode-locked semiconductor lasers and apply it to study the effect of delayed coherent optical feedback on pulse timing jitter in these lasers. The proposed method greatly reduces computation times and therefore allows for the investigation of the dependence of timing fluctuations over greater parameter domains. We show that resonant feedback leads to a reduction in the timing jitter and that a frequency-pulling region forms about the main resonances, within which a timing jitter reduction is observed. The width of these frequency-pulling regions increases linearly with short feedback delay times. We derive an analytic expression for the timing jitter, which predicts a monotonous decrease in the timing jitter for resonant feedback of increasing delay lengths, when timing jitter effects are fully separated from amplitude jitter effects. For long feedback cavities the decrease in timing jitter scales approximately as

Dynamics of a passively mode-locked semiconductor laser subject to dual-cavity optical feedback.

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Experimental demonstration of change of dynamical properties of a passively mode-locked semiconductor laser subject to dual optical feedback by dual full delay-range tuning.

with the increase of the feedback delay time

Passively mode-locked laser coupled to two external feedback cavities

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Multipulse dynamics of a passively mode-locked semiconductor laser with delayed optical feedback

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Timing jitter and repetition rate control of a passively mode-locked semiconductor laser by dual optical feedback

We study the influence of dual-cavity optical feedback on the emission dynamics and timing stability of a passively mode-locked semiconductor laser using a delay differential equation model and verify the timing stability results by an initial experiment. By bifurcation analysis in dependence of the feedback delay times and feedback strength bistability, quasiperiodic and chaotic dynamics, as well as fundamental mode-locking are investigated, yielding a comprehensive overview on the nonlinear emission dynamics arising due to dual-cavity optical feedback. Optimum self-locking ranges for improving the timing stability by dual-cavity optical feedback are identified. A timing jitter reduction and an increase of the repetition rate tuning range of up to a factor of three, compared with single-cavity feedback, are predicted for the parameter ranges investigated. Improved timing stability on short and long timescales is predicted for dual-cavity feedback through the suppression of noise-induced fluctuations. Based on the numerical predictions, experimentally, a maximum timing jitter reduction up to a factor of 180 is found, accompanied by a side-band reduction by a factor of 58 dB, when both feedback cavities are resonant.

Phase sensitivity of mode-locking with optical feedback

In this contribution we experimentally demonstrate the change and improvement of dynamical properties of a passively mode-locked semiconductor laser subject to optical feedback from two external cavities by coupling the feedback pulses back into the gain segment. Hereby, we tune the full delay-phase of the pulse-to-pulse period of both external cavities separately and demonstrate the change of the repetition rate, timing jitter, multi-pulse formation and side-band suppression for the first time for such a dual feedback configuration. In addition, we thereby confirm modeling predictions by achieving both a good qualitative and quantitative agreement of experimental and simulated results. Our findings suggest a path towards the realization of side-band free all-optical photonic oscillators based on mode-locked lasers.

Passively mode-locked lasers subject to optical feedback: The role of amplitude-phase coupling

We study the effects of dual feedback on a passively mode-locked semiconductor laser using a delay differential equation model. Timing jitter reduction is achieved provided that one of the feedback cavities is resonant with the laser cavity. Maximal jitter reduction occurs when both feedback cavities are resonant. As with single cavity feedback there is a locking range in the feedback delay length about the main resonances. When both feedback delay lengths are tuned appropriately within this locking range simultaneous timing jitter reduction and repetition rate tuning can be achieved, making it interesting for device applications.

Coherent pulse shaping in passively mode-locked semiconductor lasers

Passively mode-locked semiconductor lasers are compact, inexpensive sources of short light pulses of high repetition rates. In this work, we investigate the dynamics and bifurcations arising in such a device under the influence of time delayed optical feedback. This laser system is modelled by a system of delay differential equations, which includes delay terms associated with the laser cavity and feedback loop. We make use of specialised path continuation software for delay differential equations to analyse the regime of short feedback delays. Specifically, we consider how the dynamics and bifurcations depend on the pump current of the laser, the feedback strength, and the feedback delay time. We show that an important role is played by resonances between the mode-locking frequencies and the feedback delay time. We find feedback-induced harmonic mode locking and show that a mismatch between the fundamental frequency of the laser and that of the feedback cavity can lead to multi-pulse or quasiperiodic dynamics. The quasiperiodic dynamics exhibit a slow modulation, on the time scale of the gain recovery rate, which results from a beating with the frequency introduced in the associated torus bifurcations and leads to gain competition between multiple pulse trains within the laser cavity. Our results also have implications for the case of large feedback delay times, where a complete bifurcation analysis is not practical. Namely, for increasing delay, there is an ever-increasing degree of multistability between mode-locked solutions due to the frequency pulling effect.

Pulse train stability of passively mode-locked semiconductor lasers

Optical feedback stabilization is a powerful concept to improve the timing stability of passively mode-locked lasers. We first study experimentally the repetition rate and timing jitter behavior of a single-cavity optical feedback as a function of the microscopic delay length. By a dual-cavity optical feedback configuration, we then present experimental and numerical results on the repetition rate and timing jitter dependence on dual-cavity fine-delay. Simulations are performed by a delay differential equation model. We obtain an improvement in timing jitter and an increase in pulse repetition rate tuning range as compared to the laser without optical feedback.