Analysis of self-pulsating three-section DBR lasers

The characteristics of a three-section distributed Bragg reflector laser showing self-pulsation have been analyzed using a large signal time-domain traveling-wave simulator. The device dynamic properties have been investigated in all their complexity and analyzed as functions of the linewidth enhancement factor and of the injected current in the active and in the phase control sections. The simulation results have clearly shown the fundamental role of four wave mixing on the laser characteristics (output power, spectrum, etc.) and have been quantitatively correlated with the few available theoretical and experimental results. The considered self-pulsation operation frequencies around 40 GHz are of interest for practical applications

Modeling passive mode-locking in InAs quantum dot lasers with tapered gain sections

We propose a computationally efficient approach for the simulation and design of index-guided quantum-dot (QD) passively mode-locked lasers with tapered gain section; the method is based on the combination of simulations based on a finite differ-ence beam-propagation-method and dynamic simulations of mode-locking via a multi-section delayed differential equation model. The impact of varying the taper full angle on the pulse duration and peak power is investigated; simulations show that a correct choice of this parameter enables the generation of sub-picosecond optical pulses with peak power exceeding 5

Semiconductor racetrack resonator coupled to an S‐bent waveguide: Influence of the coupling coefficients on the unidirectional operation

Semiconductor ring lasers have attracted remarkable interest as laser sources in photonic integrated circuits. They result in bidirectional laser owing to the rotation symmetry between the two counter-propagating modes of the ring cavity. This symmetry can be broken incorporating in a racetrack resonator an S-bend waveguide, which generates an unbalanced loss mechanism and a nonreciprocal gain between clockwise and counter-clockwise direction beams. The propagating field along the resonator in the undesirable direction is evanescently coupled to the S element in correspondence of two coupling regions and converted into the preferred one. In this work, we examined how the field coupling coefficients of the couplers impact the resonator unidirectionality. In numerical simulations, we changed the coupler gap distance and the coupler length of the directional couplers to scan the full range of variability of the coefficients. The simulated performances of the resonator are discussed in term of the extinction ratio between the clockwise and the counter-clockwise modes as well as the power truly circulated in the two directions of the resonator net of all losses. The finite-difference time-domain method within Synopsys RSoft© suite was used to simulate the evolution of the counterpropagating field along the racetrack

A Python Tool to Control and Virtualize Laser Diodes Characterization Benches

We present a Python tool for the control of the laboratory instruments (thermal electric control, power meter, optical spectrum analyzer) used for the characterization of semiconductor laser sources in the framework of master degree courses available at Politecnico di Torino. This software can be used to control real benches, acquiring and elaborating the measurement data, but it can also work offline emulating the behavior of instruments and laser sources, thus allowing the students to work in a completely virtualized environmen

Cavity optimization of 1.3um InAs/InGaAs quantum dot passively mode-locked lasers

Performance improving for monolithic two-section passively mode-locked (ML) quantum dot lasers has been systematically investigated using the Finite-Difference Traveling-Wave numerical model. Two approaches have been considered. For the first case, we changed simultaneously the length of the saturable absorber and the output facet reflectivity. We demonstrate that, by properly choosing these two parameters, a reduction of the pulse width from 3.4 ps to 1.1 ps and an increase the peak power 1 W to 1.6 W were obtained. For another case, we exchanged the optical power reflectivities at two end facets. We found that this approach can be used to further improve the ML stability for devices considered in the first approach where trailing edge instability is the main restrictio

Design and Analysis of Enhanced Modulation Response in Integrated Coupled Cavities DBR Lasers Using Photon-Photon Resonance

In the last few decades, various solutions have been proposed to increase the modulation bandwidth and, consequently, the transmission bit-rate of semiconductor lasers. In this manuscript, we discuss a design procedure for a recently proposed laser cavity realized with the monolithic integration of two distributed Bragg reflector (DBR) lasers allowing one to extend the modulation bandwidth. Such an extension is obtained introducing in the dynamic response a photon-photon resonance (PPR) at a frequency higher than the modulation bandwidth of the corresponding single-section laser. Design guidelines will be proposed, and dynamic small and large signal simulations results, calculated using a finite difference traveling wave (FDTW) numerical simulator, will be discussed to confirm the design results. The effectiveness of the design procedure is verified in a structure with PPR frequency at 35 GHz allowing one to obtain an open eye diagram for a non-return-to-zero (NRZ) digital signal up to 80 GHz . Furthermore, the investigation of the rich dynamics of this structure shows that with proper bias conditions, it is possible to obtain also a tunable self-pulsating signal in a frequency range related to the PPR design

Time Domain Traveling Wave analysis of the multimode dynamics of Quantum Dot Fabry-Perot Lasers

In this paper we investigate with numerical simulations the rich multi-mode dynamics of Quantum Dot Fabry-Perot Lasers. We have used a Time Domain Traveling Wave approach including the electron and hole carrier dynamics in the various Quantum Dot confined states, the inhomogeneous broadening of the complex gain spectrum, the polarization dynamics and the effect of the carrier-photon interaction in the cavity. The role of the various non-linear interaction mechanism on the broadening of optical spectrum of the Quantum Dot laser has been investigated and the main parameters responsible for the phase locking between the longitudinal modes have been identified. We show that in some cases it is possible obtaining pulses after simulating the propagation of the laser output field in a dispersive medium. Many of the obtained simulation results are in good agreement with the experiments reported in the iterature

Self-pulsing in single section ring lasers based on Quantum Dot materials: theory and simulations

We studied theoretically coherent phenomena in the multimode dynamics of single section semiconductor ring lasers with Quantum Dots (QDs) active region. In the unidirectional ring configuration our simulations show the occurrence of self-mode-locking in the system leading to ultra-short pulses (sub-picoseconds) with a THz repetition rate. As confirmed by the Linear Stability Analysis (LSA) of the Traveling Wave (TW) Solutions this phenomenon is triggered by the analogous of the Risken-Nummedal-Graham-Haken (RNGH) instability affecting the multimode dynamics of two-level lasers

FDTW Approach for Simulation of QD lasers and SOAs

We present a Finite Difference Travelling Wave (FDTW) approach for the simulation of InAs/GaAs quantum dot devices. Several examples of applications will be discussed starting from simple QD-SLDs structures up to passive single section and two section mode-locked lasers