Jasna V. Crnjanski

Injection Power and Detuning-Dependent Bistability in Fabry–Perot Laser Diodes

In this paper, we investigate the range of injection power and frequency detuning for which bistability of the injection-locked semiconductor Fabry-Perot laser diode can be achieved and preserved. The analysis is based on a detailed model of the multimode rate equations and material gain. The stationary analysis shows that there is a region of the injection power and detuning for which the laser has three stationary states. However, the stability analysis shows that for a wide range of injection powers and detuning, the two of three stationary states are stable and provide bistability. One of these states is the result of injection locking, whereas the other is mainly a consequence of the interplay between injection-locked and unlocked modes. The difference of the side-mode-suppression ratio between the stable states is of the order of 20 dB and it can increase with detuning and decrease with mode order.

Tailoring the spectral response of add/drop single and multiple resonators in silicon-on-insulator

Channel dropping waveguide filters based on single and multiple resonators in silicon-on-insulator (SOI) technology are of great interest due to their compactness and high wavelength selectivity, which is a desirable feature for photonic modulators, detectors, and other optically integrated components in telecommunication systems, in particular for wavelength division multiplexing (WDM) systems. Particular advantage of these filters is that they are capable of producing relatively large free spectral range (FSR) as well as narrow 3-dB bandwidth of the filter resonances. Herein we report experimental results and discuss the possibility of designing mono-mode and (nearly) polarization independent SOI ring and racetrack resonators with the FSR in excess of 30 nm.

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.

Multivalued Stability Map of an Injection-Locked Semiconductor Laser

We present a novel and detailed analysis of the locking range and the stability map for side-mode injection-locked in-plane semiconductor multimode lasers. By including the usually neglected unlocked modes in our model, we predict a multivalued locking range and stability map for this type of lasers. We also explain and relate, the previously noticed slave laser bistability phenomenon with the multivalued character of the locking range and stability map, and experimentally validate our findings. Moreover, we find that the unstable operating region, commonly found in literature by stability analysis of the injection-locked mode alone, is actually much smaller.

Switching time in optically bistable injection-locked semiconductor lasers

Switching between states in a dispersive bistable injection-locked slave laser has been theoretically investigated. We show that the switching can be achieved by relatively small and short (≈10-50 ps) variation of the master laser injection power or frequency, which, besides the variation of the slave laser optical power, leads to significant variation of its photon phase (≈5π/6). By using an analytical model, we calculate the switching time dependence on the magnitude of the injection power and the frequency detuning variation.

Band structure and intersubband absorption in modulation-doped V-groove quantum wires

A self-consistent nonparabolic calculation of the band structure and intersubband absorption in a V-groove-quantum-wire are presented and analyzed with respect to doping concentration, geometry, and temperature. A comparison with a parabolic flatband model shows that both the self-consistency and the nonparabolicity considerably affect subband edges and the intersubband absorption which are studied when both effects are taken into account. The absorption spectra exhibit a prominent peak in the terahertz region (wavelength range λX=55−95 μm) for the polarization in the direction of the weak confinement (X), while for polarization in the direction of the strong confinement (Y), it shows two groups of peaks, one in a slightly lower wavelength range than for the X polarization, and the second for λY=8−13 μm. Technological parameters considered in our analysis can be used to tailor and adjust the absorption spectra for various applications in the terahertz spectral range.

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.

Application of coordinate transformation and finite differences method in numerical modeling of quantum dash band structure

In this paper we propose an efficient and simple method for the band structure calculation of semiconductor quantum dashes. The method combines a coordinate transformation (mapping) based on an analytical function and the finite differences method (FDM) for solving the single-band Schrodinger equation. We explore suitable coordinate transformations and propose those, which might simultaneously provide a satisfactory fit of the quantum dash heterointerface and creation of an appropriate computational domain which encloses the quantum dash structure. After mapping of the quantum dash and the rest of computational domain, the Schrodinger equation is solved by the FDM in the mapped space. For the proposed coordinate transformations, we investigate and analyze applicability, robustness and convergence of the method by varying the FDM grid density and size of the computational domain. We find that the method provides sufficient accuracy, stability and flexibility with respect to the size and shape of the quantum dash and above all, extreme simplicity, which is promising and essential for an extension of the method to the multiband Schrodinger equation case.

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.