A.G. Vladimirov

Dynamics of Fourier domain mode-locked lasers.

We analyze the dynamics of Fourier Domain Mode Locked lasers and show that the frequency-sweep asymmetry in the output originates from inherent field-matter nonlinearities, resulting in two regions: chaos and mode group stepping.

Dynamics of a short cavity swept source OCT laser

We investigate the behaviour of a short cavity swept source laser with an intra cavity swept filter both experimentally and theoretically. We characterise the behaviour of the device with real-time intensity measurements using a fast digital oscilloscope, showing several distinct regimes, most notably regions of mode-hopping, frequency sliding mode-locking and chaos. A delay differential equation model is proposed that shows close agreement with the experimental results. The model is also used to determine important quantities such as the minimum and maximum sweep speeds for the mode-locking regime. It is also shown that by varying the filter width the maximum sweep speed can be increased but at a cost of increasing the instantaneous linewidth. The consequent impacts on optical coherence tomography applications are analysed.

Effect of dynamical instability on timing jitter in passively mode-locked quantum-dot lasers

We study the effect of noise on the dynamics of passively mode-locked semiconductor lasers both experimentally and theoretically. A method combining analytical and numerical approaches for estimation of pulse timing jitter is proposed. We investigate how the presence of dynamical features such as wavelength bistability in a quantum-dot laser affects timing jitter.We study the effect of noise on the dynamics of passively mode-locked semiconductor lasers both experimentally and theoretically. A method combining analytical and numerical approaches for estimation of pulse timing jitter is proposed. We investigate how the presence of dynamical features such as wavelength bistability affects timing jitter.

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.

Delay differential models in multimode laser dynamics: taking chromatic dispersion into account

A set of differential equations with distributed delay is derived for modeling of multimode ring lasers with intracavity chromatic dispersion. Analytical stability analysis of continuous wave regimes is performed and it is demonstrated that sufficiently strong anomalous dispersion can destabilize these regimes.

Dynamics of Fourier Domain Mode Locked lasers

We describe and explain the dynamics in the output of a Fourier Domain Mode Locked laser (FDML) both experimentally and numerically using a delay equation model. The laser is formed using a semiconductor optical amplifier and a swept filter placed in a ring cavity. For FDML operation the filter is swept periodically with a period that matches the round trip time in the cavity [1] allowing an output that can be thought of as a train of highly chirped pulses with a fixed phase relationship between successive sweeps. In our experiment the cavity length was approximately 20 km and the filter width was approximately 75 pm. The intensity was analysed with a high frequency photodetector and a real-time oscilloscope with a 12 GHz acquisition bandwidth. We studied the laser output as a function of the detuning of the drive frequency of the filter away from the resonant frequency. There is a pronounced asymmetry in the output at the turning points of the filter sweep and our studies show that this asymmetry has a fundamental origin related to the field-matter interactions in the laser. We also show that the physics of the system can be understood in terms of a simpler system. By considering the FDML in a frame comoving with the filter, one can see that the high frequency operation should be identical to a static filter. By this reasoning, for a small positive detuning ε the “FDML + ε ” operation should be identical to that when the sweep rate is “Static + ε.” We show that this is borne out in the experiment. This could be very useful for understanding the system for very short cavity lengths beyond what is currently achievable for FDML swept sources.

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].

Distributed delay differential model of a multimode semiconductor laser

Mode-locking is a very efficient technique to generate short optical pulses with high repetition rates used in many applications. A conventional approach to model semiconductor mode-locked lasers is based on the use of the so-called traveling wave equations, a system of partial differential equations governing the space-time evolution of the amplitudes of counter-propagating waves and the carrier density in the semiconductor medium. On the other hand, simpler and efficient approach to model mode-locked lasers exploiting a system of delay differential equations (DDEs) was proposed in [1]. In particular, a modification of the DDE model was used to describe the dynamics of frequency swept Fourier domain mode-locked (FDML) [2] and sliding frequency mode-locked [3] lasers used in optical coherence tomography. However, despite of its considerable success in modelling the dynamics of mode-locked, frequency swept, as well as other types of multimode semiconductor lasers, the DDE model does not account for such important physical factor as non-resonant second order intracavity dispersion. In order to fill this gap, we have developed a new model of a multimode semiconductor laser that takes into account non-resonant chromatic dispersion. This model satisfies automatically the causality principle and, in addition to fixed delay, contains a distributed delay term with explicit analytical expression for the response function. The distributed DDE model can be reduced to an infinite chain of delay differential equations with a single fixed delay which can be truncated in the case when the non-resonant dispersion is sufficiently small.

Phase and frequency dynamics of Fourier domain mode locked OCT lasers

We analyse the dynamical behaviour of a Fourier domain mode locked laser experimentally and theoretically. Heterodyne measurements of laser dynamics allows some insight into the frequency behaviour of the laser which coupled with theoretical arguments from previous work allow for a clear interpretation of the observations. Direct simulations using a delay differential equation model in full FDML mode display excellent agreement with the experimental results.