We discuss numerical challenges in constructing and resolving spectral problems for photonic crystal surface-emitting lasers with large (up to several mm2) emission area. We show that finite difference schemes with moderate and large domain discretization steps provide sufficient accuracy of several major (lowest-threshold) modes of particular device designs.
Avalanche photodetectors (APDs) are a crucial technology for detection of weak optical signals. These devices operate on internal gain, meaning only the device currents, including the optical signal, are amplified [1] . This allows high performance APDs to maximize their signal-to-noise ratio as long as the excess noise due to the amplification process remains low. In this work, we investigate how slight geometric changes to a device design due to variabilities in the fabrication process can affect the performance of an APD. The performance metrics considered are gain, excess noise factor, and bandwidth.
In this paper, we investigated the degradation mechanisms that negatively affect the reliability of UV-C LEDs. In particular, we modeled the process that involves trap generation identified through experimental electrical characteristics and contact degradation by means of numerical TCAD simulations.
We present a theoretical study on the impact of alloy disorder on carrier transport and recombination rates in an (Al,Ga)N single quantum well based LED operating in the deep UV spectral range. Our calculations indicate that alloy fluctuations enable ‘percolative pathways’ which can result in improved carrier injection into the well, but may also increase carrier leakage from the well. Additionally, we find that alloy disorder induces carrier localization effects, a feature particularly noticeable for the holes. These localization effects can lead to locally increased carrier densities when compared to a virtual crystal approximation which neglects alloy disorder. We observe that both radiative and non-radiative recombination rates are increased. Our calculations also indicate that Auger-Meitner recombination increases faster than the radiative rate, based on a comparison with a virtual crystal approximation.
Broad-ridge laser diodes exhibit rich lateral mode dynamics in addition to longitudinal mode dynamics observed in narrow-ridge laser diodes. To simulate mode dynamics in these diodes, an effective mode interaction term is derived from the bandstructure and carrier scattering in the quantum well. The spatial dependency of pump current densities plays a crucial role in lateral mode dynamics, and thus, a Drift-Diffusion model is employed to calculate the current densities with an additional capturing term.
We study optical properties of an ARROW-VCSEL, in which the antiresonant effect is provided by an oxide island located inside the optical cavity and manufactured with a planar oxidation technique. We analyze the impact of a refractive antiresonant oxide island buried in a top VCSEL mirror on the lasing conditions of lateral modes of different orders. By using the Bessel Expansion Transfer Method—suited for axisymmetric structures—we show that this oxide island strongly influences all lateral modes. By merely altering its radius (which can be easily controlled through the time of the planar oxidation process), we can put different lateral modes into resonance or antiresonance states, strongly affecting their optical losses and profiles. This allows to tune the threshold currents for modes of different order and—with the use of the spatial hole burning effect—to find a single-mode operation conditions.
A comprehensive 1D optical multiscale model combining coherent as well as incoherent light transport with support for incoherent light scattering is presented. The model is based on a detailed-balance conforming formulation of dipole emission and an incoherent net-radiation model, extended to scattering interfaces in the optical layer stack where various models can be used to compute the scattering matrices. Given its unified framework treating emission and absorption, this model excellently lends itself to the analysis of photon recycling and luminescent coupling effects in solar cells and LEDs and can be easily coupled to a drift-diffusion model to further analyze the full opto-electronic behavior of the device.
This work presents a three-dimensional electromagnetic and heat-transfer multiphysics simulation approach for the design and optimization of photonic devices that integrate phase change materials (PCMs) for emerging photonic computing systems. Leveraging the multiphysics simulation, a PCM-based compact and low-loss phase shifter is designed with 24 µs latency for π phase shift and a maximum insertion loss of 0.3 dB/π when the PCM is in the crystalline state.
Resonant enhancement of light-matter interactions is broadly applicable across many device functionalities where reduced energy consumption and footprint are important figures of merit. The increased sensitivity of resonant devices, however, makes both design and fabrication challenging in terms of reliability and yield. Here, we propose a design approach and device architecture that enable devices that have rich and reconfigurable spectral responses.
Ion implantation for the electrical isolation of semiconductor lasers is a commonly applied technique for multi-quantum well (MQW) lasers, as well as for the deep electrical isolation for quantum cascade lasers. In this paper, we present in detail the theoretical simulations of ion implantation processes for deep electrical isolation of AlGaAs/GaAs quantum cascade and for vertical-cavity surface-emitting laser structures. It will be shown the planning steps for establishing the optimal conditions for the proton implantation processes, which led to the choice of the ion energy and type of masking layer. They employed the simulations of distributions of implanted protons and vacancies, formed after the irradiation into the semiconductors as GaAs, AlGaAs etc. and different types of masking layers. The profiles were calculated from the data simulated by the TRansport in Matter code. It will be presented the design process and verification of scheme for AlGaAs/GaAs quantum cascade and vertical-cavity surface-emitting laser structures.
A theoretical model for predicting the range performance of a monocular thermal imager (MTI) is developed in this work. System MTF for an MTI is derived and then detection, recognition and identification (DRI) ranges were calculated using Targeting Task Performance (TTP) model. Current mainstreamed as well as futuristic detector and micro-display pixel side lengths are considered in MTF analysis and DRI range calculations. DRI ranges are estimated to be improved when smaller detector and micro-display pixel side lengths are employed. Numerical simulations show that DRI ranges can reach 26.757, 5.95, 4.12 km for an MTI with detector and micro-display pixel side lengths of 5µm each.
In this work we present the electrical modeling of novel 845 nm vertical-cavity silicon-integrated lasers (VCSILs) for silicon photonics (SiPh). We tested the reliability of the devices by submitting them to high current stress, corresponding to ≈ 20xIth, to observe the degradation as a function of time. During the stress experiment, we monitored the electrical characteristics at regular intervals and we observed two separate degradation phenomena: the series resistance increment and the lowering of the turn-on voltage. Thanks to a Poisson-drift diffusion simulator we simulated the I-V characteristics and the band diagrams to interpret the degradation phenomena. The results of the simulations confirmed that the electrical degradation can be caused by the diffusion of compensation impurities originating from the p-contact layers. The same mechanism was also responsible of the optical degradation of the devices.
We propose a methodology to include thermal crosstalk effects in the modeling of neuromorphic photonic circuits. Through component-level simulations of device building blocks and thermal analysis, we are able to successfully account for thermal effects, as shown by a comparison with experimental measurements of a 3×3 programmable optical circuit.
We present an analytical simulation and thermal control scheme for a pitch-chirped Contra-Directional Coupler, able to achieve a 5-nm bandwidth-tunability range for a C-band reference channel at 1.55 µm. The proposed structure showcases central wavelength consistency in different bandwidth configurations, as well as high thermal-crosstalk resiliency.
We experimentally model a VCSEL-based optical transmitter for high speed intra data center interconnects using a convolutional neural network digital twin. The device is able to effectively reproduce the VCSEL linear and nonlinear distortions on PAM4 signals transmitted at 107.2 Gbps, thus enabling the optimization of nonlinear VCSEL-MMF digital pre-distorters.
A well-in-well structure is proposed in the multiple quantum well (MQW) based active region of the III-Nitride based light emitting diode (LED) in order to achieve tunable emission by varying the applied bias. It has been found that the composite rectangular well structure takes a complex triangular quantum well structure under applied bias and the energy of the n-th electronic level in the QW increases with increasing bias resulting in blue-shift of the emission wavelength with increasing bias. This principle enabled a simulation study that results in a colour tunable model for the III-N based LEDs. It has been found that around 2.7V of applied bias the LED emits in red (~636 nm) with an internal quantum efficiency (IQE) of ~30% whereas at 3.4-3.6V of applied voltage it emits at green (~556 nm) with a promising ~75% of IQE. Hence the proposed structure is promising for realizing colour tunable LED by varying the applied bias. As a result, all the required colours, i.e., RGB will be available on a single material (III-Nitrides) platform for display applications.
We theoretically study the direct gap and the band-edge wavefunctions’ localization of nonuniform disordered GaAsSb alloy by using empirical tight-binding simulations. We show that the nonuniformity decreases the direct gap value of the alloy while increases its statistical scattering, leading to a larger bandgap bowing compared to the ideal random alloy case. Moreover, the localization of the band-edge hole wavefunction is also enhanced due to the nonuniformity, while the band-edge electron does not experience similar effect.
In this work we investigate different architectures to realize a single-mode VCSEL array for high power applications. This is done by simulating a large active-area VCSEL with either a metallic or a grating-relief-based patterning at the outcoupling aperture. The investigated designs are compared, highlighting possible strategies to improve the fiber coupling by improving the far field (FF) profile. This contribution also presents a satisfactory match between the simulations and the FF experimental data obtained from the measurements of a VCSEL array structure.
Quantum cascade lasers (QCLs) in self-starting harmonic comb operation are highly attractive for applications in optical and quantum communication. Recently, harmonic mode-locking in QCLs has been reported in several experimental studies, which demands for a robust theoretical description. Here, we provide an extensive numerical study of a terahertz QCL active gain medium capable of self-starting harmonic mode-locking. Our theoretical characterization is divided into stationary carrier transport simulations based on the ensemble Monte Carlo method and dynamical simulations of the light-matter interaction based on multi-level Maxwell-Bloch equations. We investigate the influence of the chosen eigenstates basis on the gain spectrum and present self-consistent simulation results of stable harmonic comb operation with a mode spacing of four times the free spectral range.
We numerically study the self-detection scattering type near field optical microscopy (SD s-SNOM), a detectorless and high resolution technique exploited for the retrieval of the dielectric properties of a resonant material sample in the terahertz (THz) range. We derive an approximated method for the reconstruction of the dielectric function in the weak feedback regime, where the signal to noise ratio is expected to be higher than in the commonly used very weak feedback regime, reporting reasonable accuracy in the estimation of the phonon resonances for a supposed Cesium Bromide (CsBr) sample.
