In this work, we present the simulation and analysis of an oxide-confined Vertical-Cavity Surface-Emitting Laser (VCSEL) using the Finite Difference Frequency Domain (FDFD) microcavity model, integrated within the Crosslight’s PICS3D simulation package. By utilizing a full vectorial microcavity approach, both fundamental and higher-order optical modes are accurately captured, offering detailed insights into the effects of key structural parameters of the optical cavity. This study focuses on the impact of the oxide layer’s position and thickness on mode behavior, lasing mode selection, and threshold current in large-aperture VCSELs. The optimized VCSEL design achieves a threshold current of 0.7 mA and a far-field divergence angle of approximately 8°.
The design and analysis of the Photonic Crystal Vertical Cavity Surface Emitting Laser (PCVCSEL) device are discussed and simulated using the 3D Finite Difference Frequency Domain (FDFD) microcavity model, available in the PICS3D simulation package. The 3D full vectorial microcavity model provides an accurate analysis of complex 3D structures, offering insights into mode complexity and modal parameters. In this paper, we investigate the effect of the photonic crystal unit cell on both the lasing power and the far-field pattern. The simulation results demonstrate a lasing power of almost 5mW with a threshold current of 0.2mA.
Based on a drift-diffusion simulator, 2D modeling of perovskite/Si tandem solar cell with tunnel junction is presented in this work. Current matching is explored between the two sub-cells. It is demonstrated that the basic tandem cell can achieve conversion efficiency as high as 28.27% with open-circuit voltage and short-circuit current density as 2.04 V and 16.18 mA/cm2 , respectively. As approaches for cell design optimization, the results are also analyzed versus the thickness and the minority carrier recombination lifetime of the perovskite layer. Efforts to incorporate coating, to consider texture effect for the bottom Si cell as well as to look for alternative electron transport layer for the top junction are also performed, presented and discussed. Efficiency as high as 36.40% is further projected.
The performance of the oxide-confined surface relief (SR) structure vertical-cavity surface-emitting laser (VCSEL) is simulated and analyzed by using the Finite Difference Frequency Domain (FDFD) microcavity model available in the PICS3D simulation package. Using the full vectorial microcavity model enables an accurate analysis of both the dominant and higher order modes, thus more insight into the cavity structural parameters can be investigated. In this proceeding, the impact of the oxide layer and the SR layer on both the emitting laser as well as the far field characteristics is investigated. The simulated Surface Relief (SR) VCSEL shows a threshold current increase to 1.2mA compared to 1.0mA without the SR layer, and far field divergent angles decrease to almost 10°.
In this paper, the optical problem of the Vertical Cavity Surface Emitting Laser (VCSEL) is analyzed in details. Taking advantage of the VCSEL layer structure, Maxwell’s equation is discretized on uniform Yee grid, and the rigorous full vectorial Finite Difference Frequency Domain (FDFD) method was used to formulate and solve the complex eigenvalue problem. The full vectorial solver is well suited for the fundamental as well as the higher-order modes and includes different field polarization. The method is demonstrated for advanced VCSEL incorporating the surface reliefs and the oxide layer. In order to compare with the experimental structure, a superposition of the VCSEL modes is used to construct the Linearly Polarized (LP) mode.
In this work, two-dimensional modeling of planar junction AlInAs avalanche photodiodes is reported. Modeling results of dark/photo current, multiplication gain, breakdown voltage, -3dB bandwidth and gain-bandwidth product, and excess noise etc., are presented. The modeling results of multiplication gain and -3dB bandwidth are consistent with the reported experimental demonstration. Design optimization is also explored for high gain-bandwidth product for such AlInAs avalanche photodiodes.
Three-dimensional (3D) modeling is reported for CMOS active pixel image sensors particularly by comparing front surface and back-surface illumination. The opto-electronic responses are presented versus various power intensity and illumination wavelength. The optical efficiency and quantum efficiency from FDTD modeling are also presented. For appropriately designed sensor structure, it is shown that back-surface illumination pixel could achieve improved sensitivity within certain wavelength range. The presented results demonstrate a methodological and technical capability for 3D modeling optimization of complex CMOS image sensor.
Based on Crosslight APSYS, we have made 2D simulation of dual and triple junction solar cells based on CdZnTe and
CdTe material system on Si substrate with tunnel junctions. The basic physical quantities like band diagram, optical
absorption and generation for these solar cells, and external quantum efficiency for individual subcell junctions of triple
junction solar cells are obtained. Current matching analyses and multi-sun concentration simulation are also performed.
The modeling shows efficiency 28.85% (one sun AM1.5G) for CdZnTe/Si dual junction solar cells and efficiency
34.92% (one sun AM1.5G) and maximum 39.09% (multi-sun concentration around 500-700 suns) for CdZnTe/CdTe/Si
triple junction solar cells. The presented results indicate that the dual and triple junction solar cells with II-VI CdZnTe
and CdTe on Si can achieve efficiency comparable to those III-V based compound on Ge substrate.
KEYWORDS: Solar cells, Tandem solar cells, Transparent conductors, Copper indium gallium selenide, Absorption, Interfaces, Thin film solar cells, Molybdenum, Quantum efficiency, Solid modeling
Based on Crosslight APSYS, single junction ZnTe/CdSe, CdZnTe/CdSe and CIGS/CdS solar cells as well as
CdZnTe(CdSe)/CIGS tandem cells are modeled. Basic physical quantities like band diagrams, optical absorption and
generation are obtained. Quantum efficiency and I-V curves are presented. The results are discussed with respect to the
interface recombination velocity and the related material defect trap states for ZnTe/CdSe single junction solar cells and
the top TCO layer affinity for tandem cells. The projected efficiency obtained is 28% for one of the modeled twoterminal
tandem cells. The modeling results give possible clues for developing CdZnTe(CdSe)/CIGS tandem solar cells
with increased efficiency.
Based on Crosslight APSYS, thin film amorphous Si (a-Si:H)/microcrystalline (μc-Si) dual-junction (DJ) and a-
Si:H/amorphous SiGe:H (a-SiGe:H)/μc-Si triple-junction (TJ) solar cells are modeled. Basic physical quantities like
band diagrams, optical absorption and generation are obtained. Quantum efficiency and I-V curves for individual
junctions are presented for current matching analyses. The whole DJ and TJ cell I-V curves are also presented and the
results are discussed with respect to the top surface ZnO:Al TCO layer affinity. The interface texture effect is modeled
with FDTD (finite difference time domain) module and results for top junction are presented. The modeling results give
possible clues to achieve high efficiency for DJ and TJ thin film solar cells.
Based on Crosslight APSYS, two-dimensional simulations have been performed on Si-based solar cell devices especially
those with V-grooved surface texture. These Si-based solar cells include rear-contacted cells and passivated emitter, rear
totally diffused cells etc. The APSYS simulator is based on drift-diffusion theory with many advanced features. It can
enable an efficient computation across the whole solar spectra by taking into account the effects of multiple layer optical
interference and photon generation. The integrated ray-tracing module can compute optical absorption through the
complex texture surface with multiple antireflection coating layers. Basic physical quantities like band diagram, optical
absorption and generation can be demonstrated. The I-V characteristics with short-circuit current density and open-circuit
voltage agree with the published experimental results and enhanced cell efficiency is shown with the V-grooved
texture. The results are analyzed with respect to surface recombination, antireflection coating, bulk doping/resistivity and
lifetime etc. Modeling capabilities for polycrystalline silicon and amorphous silicon cells are also discussed.
Optical coherence tomography (OCT) is a powerful, noninvasive biomedical technique that uses low-coherence light sources to obtain in-depth scans of biological tissues. We report results obtained with three different sources emitting at 1570, 1330, and 810 nm, respectively. Attenuation and backscattering measurements are obtained with these sources for several in vitro biological tissues. From these measurements, we use a graphical method to make comparisons of the penetration depth and backscattering intensity of each wavelength for the studied samples. The influence of the coherence length of each source is also taken into account in order to make a more relevant comparison.
Optical Coherence Tomography is a powerful, noninvasive biomedical technique that uses low coherence light sources to obtain in-depth scans of biological tissues. In this study, we report results obtained with three different sources: a 60 nm bandwidth superluminescent diode with a 1570 nm emission wavelength, a high power broadband fiber source (up to 100 nm bandwidth around 1330 nm wavelength), and a Ti:Sapphire ultrashort-pulsed laser (810 nm emission wavelength and 100 nm maximum bandwidth). Along with enhancement of some details and discontinuities in heterogeneous tissues, characterization of samples using these three wavelengths allows for a more complete description of tissue optical properties, such as attenuation, backscattering, or penetration depth. We will present results obtained in vitro on several samples of biological tissues.
The characterization of material and structural properties is essential in the development of high-performance optoelectronics devices. The gain and spontaneous emission of semiconductor emitters are intrinsically related, and knowing one determines the other. In this paper, we report on a comparison between the measured and calculated spontaneous emission spectra of complex semiconductor structures that were developed in our laboratory. Transversely emitted spontaneous emission spectra over a wide range of carrier densities have been obtained for GRIN-SCH-MQW InxGa1-xAsyP1-y structures consisting of three tensile and three compressive wells. Information from these measurements and materials parameters were used to estimate carrier density for each well and subsequently used in the calculation of the emission spectra. The theoretical results were obtained by calculating the spontaneous emission rate for each well independently and then by summing over the six wells. We first calculate the band structure from a 6x6 Luttinger-Kohn Hamiltonian and find the spontaneous emission rate using the carrier density obtained from experimental measurements. A comparison between the Markovian (Lorentzian) and non-Markovian (Gaussian) line shape functions is established, considering the bandgap renormalization. We show that the Gaussian broadening function gives better agreement with the experimental data.
We use a quasi-three-dimensional numerical model combining finite
element calculations in the x - y plane and a longitudinal optical model for the design and the simulation of wide band superluminescent InGaAlAs/InP light emitting diodes (SLEDs). It is shown that by using an active region with a continuously varying composition, bulk devices can provide singlelobe spectra of more than 100 nm full-width-at-half-maximum (FWHM) and output powers of a few tens of mW. This is broader than multiple quantum-well (MQW) device singlelobe spectra which do not exceed ~70 nm FWHM in the same power range.
We study the use of multi-section distributed feedback (DFB) lasers with integrated external cavities for the optical generation of millimeter-wave signals. Using a longitudinally-dependent time-domain model, we obtain the spectral characteristics of three basic designs through FFT analysis of the steady-state response. We then compare the stability and tunability of these devices and show the superiority of gain-coupled lasers with integrated active feedback.
The degradation of the side-mode suppression ratio (SMSR) in an integrated DFB laser and semiconductor optical amplifier (SOA) cavity is investigated. A numerical model combining finite element calculations in the x-y plane and a longitudinal model based on the Green's function approach is used for that purpose. An expression is derived that expresses the degradation of the SMSR in the case of a perfectly AR-coated SOA facet. It is shown that the ASE backcoupling can have dramatic effects and degrade and SMSR of single-mode devices to unacceptable levels.
Gain crosstalk in semiconductor optical amplifiers (SOAs) developed for WDM networks has in the past been a limiting factor in SOA deployment. One recently-proposed solution is the gain-clamped SOA, where the amplifier gain is stabilized in a complex cross-cavity configuration. In this paper, we describe the design of conventional SOAs for low multi-channel gain crosstalk (GXT). Specifically, we compare alternatives for reducing crosstalk, including reductions in SOA length, current density, and the number of quantum wells. Numerical modeling shows the reduction in well number to have the largest impact; experimental result for a 4-well device show 2-channel GXT of -20 dB at a modulation frequency of 10 GHz, a fiber-coupled output power of +5 dBm (+2 dBm per channel), and a module gain of 15 dB.
The effects of using multiple electrodes to reduce longitudinal spatial hole burning (LSHB) in a complex-coupled distributed feedback (DFB) laser are investigated. Using a time-domain model, we show that LSHB can be compensated by injecting more current into the center of the device. We also find that differntial current injection has an effect on the threshold current and quantum efficiency of the DFB laser. Spectral characteristics are obtained by fast Fourier transform of the time-domain data and we show that inhomogeneous current injection can also have an effect on the laser linewidth.
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