S.P. Hegarty

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.

Distribution of residence times in bistable noisy systems with time-delayed feedback

We analyse theoretically and experimentally the residence time distribution of bistable systems in the presence of noise and time-delayed feedback. The feedback provides a memory mechanism for the system which leads to non-Markovian dynamics. We demonstrate and explain various non-exponential features of the residence time distribution using a two-state as well as a continuous model. The experimental results are based on a Schmitt Trigger where the feedback is provided by a computer generated delay loop and on a semiconductor laser with opto-electronic feedback.

High-power ultra-fast single- and multi-mode quantum dot lasers with superior beam profile

Universal self-organisation on surfaces of semiconductors upon deposition of a few non-lattice-matched monolayers using MOCVD or MBE lead to the formation of quantum dots. Their electronic and optical properties are closer to those of atoms than of solids. We have demonstrated for QD-lasers a record low transparency current density of 6A/cm2 per dot layer at 1.16 μm, high-power of 12W, an internal quantum efficiency of 98%, and an internal loss below 1.5 cm-1. Relaxation oscillations indicate the potential for cut-off frequencies larger than 10 GHz. GaAs-based QD-lasers emitting at 1.3 μm exhibit output power of 5 W and single transverse mode operation up to 300 mW. At 1.5 μm again an output power of 5 W has been obtained for first devices showing a transparency current of 700 A/cm2. Single mode lasers at 1.16 and 1.3 μm show no beam filamentation, reduced M2, sensitivity to optical feedback by 30 db and α-parameter as compared to quantum well lasers. Passive mode locking of 1.3 μm lasers up to 20 GHz is obtained. Thus GaAs-lasers can now replace InP-based ones at least in the range up to 1.3 µm, probably up to 1.55 μm.

Phase and frequency dynamics of a short cavity swept-source OCT laser

We analyse the dynamical behaviour of a short cavity OCT swept-source laser experimentally and theoretically. Mode-hopping, sliding frequency mode-locking and chaos are all observed during the laser sweep period. Hetero- dyne measurements of laser dynamics allows some insight into the behaviour of the laser, while interferometric techniques allow the full phase reconstruction of the laser electric field. A delay differential equation enables modelling of the laser output, and laser parameters can be altered to provide optimisation conditions for future laser designs.

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.

Phase evolution and instantaneous linewidth of a Fourier domain mode locked laser

An experimental and theoretical analysis of the dynamics of a Fourier domain mode locked laser, currently one of the fastest swept source lasers applied in optical coherence tomography, is performed. A novel time- resolved technique to measure the laser output electric field allows access to the phase dynamics of the laser and thus the coherence properties. A delay-differential equation model for the laser is used to analyse the system theoretically and via direct simulation. Numerical simulations of the laser output are in excellent agreement with experimentally measured data.

Differential refractive index in 1320 nm quantum-dot lasers

In this paper we resolve the separate contributions of resonant and non-resonant carrier populations to the differential index below threshold. We then apply this understanding to the explanation of index shifts above and below laser threshold as a function of device gain saturation.

Size dependence of selectively oxidized VCSEL transverse-mode structure

We report the spectral and modal properties of small (0.5- to 5-/spl mu/m current aperture) VCSELs and identify Joule heating as a dominant effect in the resonator properties of the smallest lasers. The lasers studied here were AlGaAs structures with semiconductor distributed Bragg reflectors (DBRs), where the selectively oxidized confinement layer is pulled back three mirror periods from each side of the active region to produce a lateral effective index difference of 0.05.