Angelina R. Totović

A Self-Consistent Numerical Method for Calculation of Steady-State Characteristics of Traveling-Wave and Reflective SOAs

This paper presents a detailed numerical model of reflective and traveling-wave semiconductor optical amplifiers (SOAs), based on a self-consistent iteration method. The method is fully transparent to the input parameters and provides stable and efficient convergence of all relevant SOA variables as long as the sufficient number of previous iterations is taken into account. The model accounts for the detailed spectral and carrier density dependence of the radiative recombination rate, material gain, refractive index, and confinement factor. The analysis of unstrained bulk and strained multi-quantum well polarization insensitive SOAs based on this model provides a deep and detailed insight into the device internal state, confirming that spectral and carrier density material dependencies critically influence the modeling results.

Numerical Study of the Small-Signal Modulation Bandwidth of Reflective and Traveling-Wave SOAs

We present a comprehensive numerical model for intrinsic small-signal modulation response of both reflective, and traveling-wave semiconductor optical amplifiers. We investigate the small-signal photon and carrier density spatial distribution, modulation response, and -3 dB bandwidth for uniform and lossless traveling-wave modulation current model. The analysis shows that the current model does not significantly affect the modulation response as long as the modulation frequency is within the bandwidth. One of the most important results of our analysis is the discovery of the bandwidth maximum in case of a reflective semiconductor optical amplifier operating with low to moderate input optical powers and high current densities. The bandwidth can be further improved by choosing the optimal amplifier length.

Switching of Bistable Injection-Locked Fabry–Pérot Laser by Frequency Detuning Variation

Theoretical study of switching of a bistable injection-locked Fabry-Pérot laser by frequency detuning variation is performed and presented. It has been found that the shortest switching time of the master laser, which allows for the slave laser to be successfully switched by frequency detuning variation, reaches the values of several picoseconds, and up to 200 ps. The disproportion of the slave laser switching times with respect to the switching direction is found (3 versus 0.3 ns), and techniques for its equalization, as well as for minimization of the slave laser total switching time, are presented and discussed. We found that the modest increase of the master laser switching time establishes the balance between the two directions of the slave laser switching, providing almost one order of magnitude improvement in comparison to the results achieved for the shortest possible master laser switching times.

An Efficient Semi-Analytical Method for Modeling of Traveling-Wave and Reflective SOAs

An efficient semi-analytical method is developed for fast and precise assessment of the steady-state gain characteristics of the semiconductor optical amplifiers. It relies on the analytical solution for the photon densities spatial distribution, starting with the rough estimation without the nonlinear gain suppression, and subsequent refinement of the results by inclusion of the suppression. Carrier density spatial distribution is approximated either by a constant, or a piecewise constant function. Compared with the simplified wideband numerical method, which excludes the photon density spectral dependence, the semi-analytical method requires considerably lower processing resources, and, depending on the model complexity, can be between one and two orders of magnitude faster, without significant sacrifice of the accuracy.

An analytical solution for stationary distribution of photon density in traveling-wave and reflective SOAs

In this paper, we analyze two semiconductor optical amplifier (SOA) structures, traveling-wave and reflective, with the active region made of the bulk material. The model is based on the stationary traveling-wave equations for forward and backward propagating photon densities of the signal and the amplified spontaneous emission, along with the stationary carrier rate equation. We start by introducing linear approximation of the carrier density spatial distribution, which enables us to find solutions for the photon densities in a closed analytical form. An analytical approach ensures a low computational resource occupation and an easy analysis of the parameters influencing the SOA?s response. The comparison of the analytical and numerical results shows high agreement for a wide range of the input optical powers and bias currents.

Comparison of switching times in optically bistable injection-locked semiconductor lasers

In this paper, on the basis of the derived analytical model, we analyze switching between stable states of the optically bistable injection-locked semiconductor Fabry–Perot laser. We investigate three different mechanisms of switching: injection power, frequency detuning and bias current variation, and compare switching times obtained for these switching mechanisms.

Modelling of carrier dynamics in multi-quantum well semiconductor optical amplifiers

We present an analysis of carrier dynamics in a multi-quantum well (MQW) semiconductor optical amplifier in the saturation and recovery regimes. The model is based on an analytical solution of rate equations for carriers in the bulk and bound states of MQWs. The analysis shows that in the saturation regime, the carrier dynamics in the well, as well as material gain, considerably depends on the ratio of the differential gain to the nonlinear gain suppression factor, while the transport effects and capture and escape of carriers affect it slightly. The carrier dynamics in the bulk is dependent more on the transport effects and on the capture and escape of carriers. In the recovery regime, the carrier dynamics depends strongly on the carrier lifetime and bias current.

Self-Seeded RSOA Fiber Cavity Laser and the Role of Rayleigh Backscattering—An Analytical Model

Reflective semiconductor optical amplifiers (RSOAs) in a fiber cavity are attractive self-seeding optical sources for wavelength division multiplexed (WDM) access networks. This paper presents an analytical model of this fiber cavity laser (FCL). The model accounts for the Rayleigh backscattering (RB) of the fiber cavity as a primary mechanism of optical feedback inside the FCL. Moreover, it also includes the reflectivity of the remote node mirror. The purpose of the model is to analytically estimate the threshold RSOA gain required for the FCL to lase, by taking into account the fiber cavity length, the related attenuation and the RB. The model is suitable to experimentally characterize the Rayleigh backscattering coefficient, once the threshold gain of RSOA-FCL is measured.

Injection-locked Fabry-Pérot laser diodes for all-optical flip-flops

In this paper we present a full-scale multimode rate equation model of an injection-locked Fabry-Pérot semiconductor laser, analyze its stability and present new stability map. We recognize the region of the dispersive bistability, and within this region, we propose two optical switching methods, which could be employed in the realization of an all-optical flip-flop. We analyze switching times and propose methods for switching time optimization.

Analytical Method for Calculation of the Photon Lifetime and External Coupling Coefficient in Index-Coupled Phase-Shifted DFB Lasers

An analytical expression for the photon lifetime in index-coupled distributed feedback laser is derived and studied at, and below, the threshold condition. It is shown that the photon lifetime considerably varies with the frequency detuning in the vicinity of the dominant laser mode. The increase in the structural parameters, such as grating coupling constant and length of the DFB structure, leads to the increase in both the photon lifetime and the magnitude of its variation due to frequency detuning, while the increase in material gain has the opposite effect. The spectral dependence of the photon lifetime has important implications on calculation of the external coupling coefficient of DFB lasers.