Simulation of single quantum-well semiconductor optical amplifiers Cristiano M. Gallep, student member, and Evandro Conforti, senior member IEEE Departamento de Microonda e Óptica – Faculdade de Engenharia Elétrica e de Computação – Unicamp Abstract – A simple model for quantum well semiconductor optical amplifier simulation is presented. Carrier population transients in the separate confinement heterostructure and in the unconfined (above) and confined (inside) states of the quantum well are considered. Preliminary results for the particular single-well case and short cavity length (100µm) are presented. cavity. The non-linear dependence of the optical gain with the photon density is generally introduced by a gain compression factor. In practice, the dynamic response of bulk-type active cavity devices are limited by RC parasites, heating, carriers relaxation times and maximum power supported by the structure. In the peculiar case of QW structures, the carrier transport mechanisms are very important to the dynamic performance. In that way, the QW structural optimization should also be done considering the relationship of the well’s width and number; the barrier’s height and width; the composition types of SCH (separate confinement heterostructure); the amount of bi-axial forces in the crystalline media and the type and amount of doping in the active layers. Key words  optical switching, quantum well semiconductor optical amplifier modeling. I. INTRODUCTION The semiconductor optical amplifier (SOA) is a promising device for add-and-drop links and wavelength routing. In addition, the SOA can be employed as an optical switch due to its small size, wide bandwidth and the potential to be integrated with other electronic and optical devices [1]. Present day limitations of a SOA switch are the high price and limited isolation between WDM (wavelength division multiplex) channels [2]. However, angle-facet S-bend SOA switches can overcome the last limitation, providing a large optical extinction ratio (optical off-on ratio) of 70 dB with a fiber to fiber gain of 20 dB [3]. Modern SOA with active cavity based on quantum well structures can provide wide gain band, high saturation power, good small signal gain and fast gain recovery, factors that make this devices a promising tool for the accomplishment of totally optical processing sub- systems The quantum-well structure provides a significant reduction of the valence band carrier’s effective mass [4], allowing operation with lower threshold current, reduced Auger recombination, increased differential gain and modulation band. The largest attractiveness of those devices are its potentialities of high dynamic response operation, due to the barrier’s carrier reservoirs and carrier tunneling. Using an optimum design, gain recovery time less than 10 ps was obtained in MQW optical amplifiers [5]. In an QW structure, the optical field confinement in the active area is very small, due to its small dimensions (relatively to the light wavelength). In those case a high insertion loss (~95%) is expected. Even so, the material gain is 50% larger in relation to common devices, when the wells are under presence of bi- axial forces [6]. Due to the quantum process involved in the electronic carriers transport, gain restoring times of pico- seconds can be obtained. Computer simulation of numerical models for such devices is an important tool to the design of more complex systems and prediction of high speed optical data links performance. In this work, a simple and efficient model for quantum-well semiconductor optical amplifier (QW-SOA) is presented with some simulations results. The rate equations account to the carrier populations in the SCH region and in the states above (unconfined) and inside (confined in) the well. Also, a photon population equation are considered. The Auger-type is one of the predominant processes of non-radioactive recombination in optical fiber communications lasers, affecting its gain linearity and modulation response. This process involves four states of particles (three elétrons (e) and a hole (h), two e and and two h, etc.). The resultant e-h recombination energy is transferred to another carrier (an electron or hole), that becomes excited, achieving a higher energy state in the corresponding band [7]. This hot-carrier then relaxes again to the ground state, losing energy through vibrations in the crystalline structure (phonon). The Auger recombination can be reduced 10 times in QW structures, in relation to the conventional ones. Such a fact could be explained by the reduction, in comparison to structures of matched crystalline layer, of the carrier effective mass [8]. Even so, the Auger recombination is still one of the most serious problems in SQW-lasers (single-quantum well) with InGaAsP-InP structure, in spite of been its coefficient (C II. QW-SOA CHARACTERISTICS The high-speed semiconductor lasers dynamics have been conventionally modeled using a pair of coupled first-order linear differential equations, usually called rate equations. In that approach, one equation governs the electronic carrier density and other one governs the photon density inside the Cristiano M. Gallep (gallep@dmo.fee.unicamp.br) and Evandro Conforti (conforti@dmo.fee.unicamp.br). Tel.:19-7883796. This work is partially supported by FAPESP-CEPID, CAPES and MCT-Pronex. 0-7803-7065-1/01/$10.00 ©2001 IEEE 321 SBMO/IEEE MTT-S IMOC 2001 Proceedings