This PDF file contains the front matter associated with SPIE Proceedings Volume 12880, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

In this manuscript, we employ a time-domain traveling-wave model with a coupled-mode theory to characterize the dynamic behavior of a mid-Infrared (MIR) Quantum Cascade Laser (QCL) in the Distributed-Feedback (DFB) configuration. Our investigation underscores the crucial influence of the linewidth enhancement factor (LEF) and spatial hole burning (SHB) on the single-mode behavior of DFB QCLs. Disregarding these factors leads to an overestimation of the range of pump currents granting single-mode emission and results in an inaccurate simulation of the multimodal dynamics of DFB QCLs. The numerical simulations presented in this work closely align with experimental observations, specifically focusing on a DFB QCL operating at a wavelength of 9.34 μm.

Fabry-Perot nanocavities are widely used in nanophotonic applications due to their exceptional electromagnetic properties and subwavelength dimensions. The spectral response of these nanocavities is primarily governed by the separation between the reflecting mirrors and the refractive index of the spacer material. In this study, we present dynamic control over the resonance wavelength of a Fabry-P´erot nanocavity by incorporating an n-type doped indium antimony (n-InSb) layer as a tunable semiconductor within the nanocavity spacer. To achieve dynamic tuning, we exploit the sizable nonlinear response of the plasma frequency of the n-InSb as a function of electron concentration. The accumulation of electrons by applied voltage within a sublayer of n-InSb in a metal-oxide-semiconductor-oxide-metal nano structure enables a variation in total phase delay of the Fabry-Perot nanocavity. This facilitates a maximum effective optical modulation of about 91% at reasonably low applied voltage. The study predicts a 95 nm blue shift in a visible frequency Fabry-Perot resonance. The study also provides details on the carrier dynamics of n-InSb at applied voltage on one or both metal surfaces.

This study introduces an innovative indium tin oxide (ITO) plasmon-based asymmetric Mach-Zehnder Interferometer (MZI) modulator, designed to tackle prevailing issues in photonic modulators. Emphasizing the modulator’s attributes, we offer low bias voltage, compactness, sufficient extinction ratio (ER), low insertion loss (IL), and low electrical resistance, paving the way for operational speeds up to multiple GHz. We meticulously examined material properties and modulator design to strike an optimized balance between ER and IL, adhering to the constraints of minor phase shifts. A 4.7 μm-long ITO-plasmon-based asymmetric MZI modulator was devised, incorporating a phase shift of 0.33π, an ER of 3 dB, an IL of 2.9 dB, and a speed of 108 GHz under the bias of ±3.5 V. The device length is judiciously selected considering high transmission difference, high ER, and low IL. Our asymmetric MZI modulator (41:59) results in 0.4 dB lower IL in comparison to the symmetric MZI modulator. In terms of modulation depth, an amplified oxide thickness can curtail the device’s capacitance, thereby augmenting the RC-limited device bandwidth. Concurrently, we propose a design protocol to attain tailored metrics such as modulation depth, speed, and losses that broaden the selection of active materials for engineering modulators with functionality-based performance. Notably, the modulator showcases remarkable switching speeds up to 100 GHz, a notably low energy consumption of 380 fJ/bit, and is adaptable to a multitude of material frameworks. This work marks a significant stride in the field of photonic modulators, opening new avenues for compact, high-performance, and energy-efficient modulating devices.

In this work, we present the design and analysis of fiber optic interferometric devices for its application in vibration detection, allowing to create an optical system based on interferometric interactions that can vary the sensitivity through external signals e.g., NLPs (noise-like pulses). The simulation of numerical schemes of the fiber optic interferometer using the MATLAB software is presented, which will allow the development of a first prototype of experimental model. Numerical implementations will be performed in MATLAB using Jones matrices to model the behavior of the fiber optic interferometer. This numerical analysis allows to develop a compact experimental model, capable of varying its transmission, sensitivity and FSR (free spectral range), being able to study the interferometric response to external vibrations and modifying the input parameters, such as power, polarization, and operation range. The input characteristics for the interferometric system can be generated by a fiber optic pulsed laser e.g., F8L (figure eight laser), which can vary its output temporarily, spectrally and in polarization. The complete analysis will allow to propose an all-fiber experimental scheme that is compact and portable compared to conventional interferometric arrays, as are works where arrays of hundreds of meters are implemented, based on the study of fiber optic resonators that improves vibration detection system sensitivity. Subsequently, the first tests were performed using MATLAB functions based on pattern recognition, filtering, and amplification of repetitive signals, which will be experimentally tested in the interferometer in a future work. Finally, potential future applications of this work include detection of vibration anomalies in structures and motors, as well as the detection of sound for integration in specialized medical devices to treat hearing problems.

Germanium-on-silicon (Ge-on-Si) single photon avalanche diodes (SPADs) operating in the short-wave infrared (SWIR) have various applications such as long-range eye-safe LIDAR, quantum imaging, and quantum key distribution. These SPADs offer compatibility with Si foundries and potential cost advantages over existing InGaAs/InP devices. However, cooling is necessary to reduce dark-count rates (DCR), which limits photon absorption at 1550 nm wavelength. To address this, we propose integrating a photonic crystal (PC) nano-hole array structure on the Ge absorber layer. While this technique has shown enhanced responsivity in linear Ge detectors, its potential in Ge-on-Si SPADs remains unexplored. Our simulations consider temperature dependence and the impact of electric-field hot-spots on dark count rates. Through these simulations, we have identified means of enhancing single-photon detection efficiency (SPDE) without adversely affecting DCR. We predict significant improvements in performance, including at least a 2.5x enhancement in absorption efficiency.

The proposed optical gas sensor is based on the principle of electromagnetically induced transparency (EMT), which is a quantum interference phenomenon that occurs when two closely spaced resonant modes interact with an intermediate level. In our design, we use plasmonic corrugated ring resonators that resonate in the mid-infrared (MIR) wavelength range, which is of particular interest because it contains the absorption resonance for several gas molecules such as methane, carbon dioxide, carbon monoxide, and acetone. We propose a slotted waveguide coupled with a slotted corrugated ring resonator, which is etched inside a doped silicon wafer on sapphire. Doped silicon is a better alternative to noble metals for plasmonic techniques in the MIR region. By optimizing the corrugated and ring to resonate at the same wavelength, we observe interesting phenomena such as Fano-resonance and EIT effects. The EIT effect causes the absence of resonant spectral lines at the same wavelength and the creation of two resonance lines at red-shifted and blue-shifted wavelengths. This effect is useful in gas sensing because it provides a sharp and narrow transmission peak that enables precise detection of gas molecules. In our paper, we provide details about the dimensions and materials used in our design. We demonstrate that our sensor achieves a small footprint, high sensitivity, and high Figure of merit. The small footprint makes our sensor suitable for integration into compact devices, while the high sensitivity and Figure of merit make it ideal for accurate and reliable gas sensing applications.

Utilizing Beam Propagation Method (BPM) simulations, this study examines the layer thickness tolerances of Local Evanescent Array Coupled (LEAC) biosensors to be fabricated in silicon photonics foundries using conventional processes targeting 1.55 μm devices. The simulations reveal that sensitivity increases with lower cladding thickness while decreasing with core thickness. Additionally, the study investigates the biosensor's response to bulk and thin biofilm layers, offering nuanced insights with practical implications, especially for nanoscale-bound biological samples. In contrast to earlier fabrication and characterization work on LEAC sensors employing thick silicon detectors at visible wavelengths, simulations conducted at the long wavelength process with germanium photodetectors show an intriguing resonance phenomenon between the core waveguide and photodetector. This resonance allows for higher absorption and thus shorter sensor length but also requires excessively tight tolerances on detector thickness. To address this challenge, structures have been explored to shift the resonance, enhancing tolerance to variations in germanium photodiode layer thickness.

Semiconductor optical amplifiers (SOAs) are key building blocks in photonics. Given the large interest in the use of SOAs for ultrashort pulse amplification, it is important to adequately model the SOA operation while including the nonlinear effects taking place in these components. To increase the SOA performance, it would also be useful to have an inverse model that calculates the required input pulse to obtain a targeted output. However, to the best of our knowledge, no inverse models have been developed so far that consider the many nonlinear effects critical for ultrashort pulses. Here, we introduce a generic inverse SOA model that calculates the required input pulse including its shape and phase to obtain a desired output and that takes into account the effects of band filling, carrier heating, spectral hole burning, two-photon absorption, and the associated free carrier absorption. Our model will enable a more efficient and well-targeted design of SOA-based photonic systems, while also allowing better performance control.

We propose mode-locked laser diodes (MLLDs) for their deployment in a low-cost and portable optical coherence tomography (OCT) system. OCT is an essential imaging technique used for medical diagnoses in dermatology, ophthalmology, and cardiology. Based on low-coherence interferometry, OCT directs infrared light through various layers of tissue, which is reflected onto a detector and resolved as an image. Generally, swept-source OCT (SS-OCT) systems perform better than grating based systems and time domain OCT but require expensive laser sources which are optically pumped, meaning they require an additional pump laser, limiting their deployment in clinics. To that end we propose MLLDs as an excellent candidate to realize, low-cost, compact, and portable SS-OCT enabled by their fast electronic tuning and electrically pumped, monolithic construction. We present simulated SS-OCT images using experimentally measured spectra from our InAs Quantum-Dot MLLDs and compare this to simulated data using a Thorlabs research-grade micromechanically tuned VCSEL (vertical cavity surface emitting lasers). Our first results to date suggest MLLDs could resolve features of 62.5 μm, which, compared with the off-the-shelf system, is approximately half the resolution. Further studies suggest that by examining electronic fine-tuning of the spectral linewidths and central wavelength, MLLDs may be highlighted as a key tool in realizing low-cost portable OCT at comparable quality to existing research-grade systems. Couple this with the current shift in practices to complex image analysis using machine learning methods, a handheld SS-OCT system could be realized as a low-cost, compact and versatile tool for clinicians.

This research focuses on strain-free GaSb/AlGaSb quantum dots (QDs) grown via local droplet etching (LDE) for their potential in quantum photonic applications. These QDs exhibit excitonic emission in the telecom S-band with a narrow ensemble emission linewidth. Through theoretical modeling in addition to previous photoluminescence experiments, the study investigates the electronic band structure, dipole transitions, and dimensions of the GaSb/AlGaSb QDs. Key findings include insights into the indirect-direct bandgap crossover based on QD dimensions and the comparison of dipole transitions with photoluminescence measurements. The results contribute to the practical integration of these QDs in quantum photonic devices and fiber optics-based quantum key distribution networks.

The digital alloy (DA) growth technique has been widely reported to implement band structure engineering for deterministic optical and electronic properties and to overcome growth limitations imposed by miscibility gaps. Random alloy (RA) InGaAs lattice-matched to InP with a bandgap of 0.74 eV is widely used as the absorption material for photodetectors in the short-wavelength infrared spectral range. In this work, the InGaAs is grown on InP substrates as digital alloy, short-period InAs/GaAs superlattices, with six monolayer periodic thickness to extend its cut-off wavelength. The effective extension of the absorption spectral range makes DA InGaAs a promising candidate for absorption at longer wavelengths than the cutoff of RA InGaAs, motivating the study of the optical characteristics of this material system. Variable-angle spectroscopic ellipsometry measurements were carried out for both DA and RA InGaAs samples from 193 nm to the cut-off wavelength. After the multi-layer model building, the optical constants were extracted via the Kramers-Kronig consistent B-Spline fitting method. The results can be used to design new optoelectronic devices. The absorption coefficient at 2 μm of six monolayer DA InGaAs was found to be 398 cm^-1. The extracted optical constants of RA InGaAs were compared with the published values, and a good agreement was obtained, corroborating the effectiveness of extracting optical constants via ellipsometry for the InGaAs material system. These optical constants are beneficial for the future utilization of DA InGaAs in optoelectronic devices with extended spectral response.

High-aspect-ratio micro- and nanostructures play a pivotal role across diverse technological domains, encompassing microelectronics processors, photovoltaic devices, and optoelectronics. The conventional methods of fabricating these structures often involve reactive-ion dry-etch processes utilizing ionized gases or wet chemical-based etching. Recently, the emergence of metal-assisted chemical etching (MacEtch) has showcased significant potential in enabling the creation of nanoscale features with exceptionally high aspect ratios. Nonetheless, the application of MacEtch to quaternary III−V and heteroepitaxial semiconductors remains relatively unexplored. This research introduces a novel approach named inverse-progression metal-assisted chemical etching (I-MacEtch) that centers around the utilization of a bimetallic catalyst, specifically focusing on the utilization of a bimetallic catalyst. This technique is employed to fabricate well-organized arrays of submicron pillars. The study elucidates that precise control over the vertical and lateral etch rate can be attained through the selection of a suitable metal adhesion layer, which improves the overall catalyst work function, thereby facilitating the streamlined fabrication of ordered arrays of InP submicron pillars possessing predefined aspect ratios.

The design of all-solid-state photonic crystals depends on the existence of wavelength-dependent bandgaps for transverse electric and transverse magnetic fields. We have used the effective index approximation for InP-based multilayer stack to simulate bands in 2D photonic crystals. We carried out dispersion bands simulations that yielded joint bandgaps and defect bands for hexagonal lattices of air holes with dielectric as background and honeycomb lattice of rods of dielectric with air as background. To make fabrication more practical, we also investigated the impact of replacing air in both designs with more rigid porous materials with slightly higher refractive index. 3D FDTD simulations for these designs show good confinement and low propagation losses in straight and curved waveguides.

This paper presents a theoretical investigation of the neuromorphic XOR operation utilizing a polarizationswitched high-speed photonic spiking neuron based on QD spin-VCSEL. The principles and working mechanism of the neuron are explored, emphasizing the role of pump components on the spike information processing. Temporal maps and time traces are used to illustrate the neuron’s behavior and dynamics. By employing the right discrimination levels on pump ellipticity, all four XOR patterns (’00’, ’01’, ’10’, and ’11’) are effectively processed by the neuron. The performance of the XOR operation is evaluated in terms of processing speed, utilizing a success rate based on spike firing above an intensity threshold. The processing speed can reach up to 4 Gb/s allowing future exciting routes for information processing in neuromorphic computing applications.

We propose a methodology to analyze a 3×3 Mach-Zenhder-based neuromorphic optical network used as a programmable logic gate. The investigated approach starts from the electromagnetic simulation of the integrated optical elements, then moves to the description of the thermal heaters including thermal cross-talk, and finally addresses the definition of the logical levels.

The upcoming optical telecommunication networks face a significant challenge due to a massive increase in internet traffic. To handle this, higher-capacity transmission schemes are being implemented. To increase the optical signal-to-noise ratios (OSNR), higher launch powers are used, which are limited by nonlinear distortions caused by the Kerr effect in the transmission fibers. Currently, expensive and power-hungry digital signal processing (DSP) solutions are used to tackle this problem. Our proposal offers an alternative solution using a neural network based on a photonic reservoir to address the nonlinear distortions in transmission links. This approach is potentially more cost-effective and consumes less energy. The photonic reservoir design is based on a four-port architecture incorporating multimode interferometers (MMIs), Mach-Zehnder-Interferometers (MZIs), and semiconductor optical amplifiers (SOAs). Inside the reservoir, the optical signals from past and current transmissions are mixed, providing the network with a memory-like capability. The training process focuses solely on driving the MZI and SOA arrays, resulting in accurate outcomes with reduced training time and energy consumption. We numerically demonstrate the mitigation of nonlinearities in high-order transmission links using a photonic reservoir. By comparing various configurations of the neural network (NN), we highlight the specific advantages of each implementation. Looking ahead, we aim to implement this approach using a photonic integrated circuit (PIC) to further enhance its practicality and efficiency.

Surface nanostructure organizational entropy and spectral antireflective functionality relations have been recently suggested. They result from correlations between the onset of spectral transmission enhancement and surface grouped-feature separation collective disorder. Random antireflective surface structures (rARSS) enhance transmission by effectively reducing the electromagnetic impedance between optical indices across a boundary. Effective-medium approximation emulates the “random” structure surface layer with homogeneous films, failing to predict the critical wavelength above which the enhancement effect is observed. It is not clear as to what qualifies the “randomness” of rARSS, other than conventional profilometry measurements. We fabricated various rARSS silica surface modifications and quantified their randomness through Shannon’s measure of nano-structural entropy. A surface organization state variable, granule population distributions, and spectral reflectivity suppression were related to disorder phase-transitions. Surface disorder parameter trends were compared to spectral measurements and simulations, to distinguish short-wavelength uncooperative nanostructure effects (bi-directional scatter) from cooperative effects (transmission enhancement.)

An increasing number of integrated photonic solutions find applications in the fields of biomedicine, manufacture, quantum computation and telecommunications. Size mismatch between optical fibers, light sources, photodetectors and photonic waveguides is usually significant, typically with the former having cross-sections on the orders of hundreds of micrometers or more and the latter a few micrometers or hundreds of nanometers. Efficiency in coupling light to and from photonic integrated circuits is an extremely important parameter since it influences device’s performance, affecting signal-to-noise ratio. Several approaches exist for light coupling, such as off-plane coupling with the assistance of grating couplers, on-plane/edge coupling with or without the assistance of tapers and adiabatic coupling. In this study we focus on grating couplers designed in amorphous silicon-on-insulator (SOI) platforms. Grating couplers are compact, can be tested at wafer-level, and do not require application specific fiber terminations, such as lenses and/or tapers. Two approaches in the optimization of grating couplers were explored, one based on a lithographic mask defined by the superposition of two different grating patterns, with different periods, having an offset to provide a random distribution of grating elements, and a technique based on the quadratic variation of the refractive index of the grating structure along its length. Results were obtained from 2D-FDTD simulations. Coupling efficiencies for the quasi-TE mode over -13 dB and -3 dB were obtained for the random and quadratic variations of the effective refractive index at a wavelength of 1550 nm, without bottom reflectors.

Power splitting is usually accomplished in photonic integrated circuits through multimode interference devices. A compact form of such structures is the multimode interference reflector, which enables efficient light manipulation and wavelength selection. Being able to precisely tune the output characteristics of multimode interference reflectors is of paramount importance for various applications in communication systems and signal processing. Conventional methods for output tuning often rely on complex design iterations and simulations, hindering their scalability and adaptability. This research explores a novel approach to tune multimode interference reflectors using deep neural networks. By leveraging the learning capabilities of neural networks, a framework to accurately model the intricate relationships between the input parameters and the output responses of multimode interference reflector devices is being explored. A representation of a matrix of inference reflectors is considered. Then, a dataset is generated from rigorous simulations to train a neural network to predict the multimode interference reflector configuration under diverse operating conditions. A Generative Adversarial Network (GAN) is being optimized to tune the reflection characteristics of multimode interference reflectors to meet desired specifications, such as signal routing requirements and power division ratio at the output. The proposed method will significantly reduce the design cycle time, offering a substantial advantage in rapid prototyping and deployment of multimode interference reflector based photonic circuits, and showcases the potential of using neural networks for tuning these devices, presenting a transformative and data-driven approach to optimize the performance of photonic integrated circuits.

Adiabatic mode evolution is an important concept in photonic devices and is utilized in several applications including spot size conversion, mode coupling between the two waveguides, and broadband power splitters/couplers. In such devices, the linear adiabatic tapers are not always the best choice in terms of the device footprint and hence the taper profile needs to be optimized to provide small footprint while ensuring adiabatic mode evolution. In many instances, the best taper profile can be quite complex, and a parametric design might require a lot of parameters to accurately define the taper profile. In such cases, the traditional optimization using parameter sweep can be challenging. Several techniques such as Fast Quasi Adiabatic (FAQUAD) dynamics and constant loss approach have been proposed in the literature for such optimization. We implement these techniques and conduct a brief comparison using two different integrated photonic components. We also briefly discuss the challenges associated with relying solely on the optimization algorithms (inverse design) without utilizing constraints associated with these techniques.

While the circular polarization of electromagnetic waves is well known from its poplar definition, its handedness is not uniquely defined, even with given phase convention, observer location and phase difference. For example a circular polarization Ex+jEz (j=sqrt(-1)) traveling along y axis has opposite handedness of the polarization to Ex+jEy traveling in z axis, counter-intuitively. This cannot be explained by the conventional definition, due to the lack of clarity of the definition. In general, when there are two orthogonally linearly-polarized plane waves, say E1 and E2, choice of the reference wave to be E1 or E2 and application of the phase difference to the other wave are ambiguous. This causes confusions and sometimes contradictory results at least in simulations. This paper suggests the necessary and sufficient conditions with the help of the propagation vector and magnetic fields to define uniquely the handedness of a circular or elliptical polarization and thus a desired handedness can be correctly injected in a simulation. The newly proposed triad is added to the conventional definition for easy determining the handedness. The unique handedness of a circular polarization is critical in design, simulation, quantification of polarization-sensitive nanophotonics devices where wave can travel in 4π space along any arbitrary direction.

Recent developments in thin-film fabrication and processing open up interesting possibilities for both established and emerging optics technologies. There, one of the key questions requiring more complete understanding is by how much one can improve the performance of thin-film devices by utilizing resonance effects and surface texturation. In this work, we report on our recent theoretical investigations around two aspects of this question: (1) how much the overall (=angle and energy-integrated) emission of extremely thin (~ 10 nm) layers can be enhanced through cavity effects, and (2) how much resonances effect the emission of moderately thin (> 100 nm) layers in a typical device interacting with free space (in this case an ultra-thin solar cell). Beginning with topic (1), we find that the total emission of active layers with thicknesses < 50 nm in particular can be boosted through resonant effects by placing them in a cavity. For topic (2), the results indicate that a radiative transfer approach (i.e., one not accounting for resonant effects) can give even quantitatively accurate predictions of the total emission of moderately thin layers in a thin-film device, as long as the reflectances of the device's outer boundaries are known, and the emitting layer is not very close to optical elements supporting direct evanescent coupling (such as metal mirrors). Finally, we demonstrate that extending the self-consistent radiative transfer-drift-diffusion approach for diffusive scattering presents an interesting tool to optimize thin-film devices even with textured surfaces.

The use of 3D Monte Carlo simulations for the study of an indirect time of flight (iToF) pixel revealed underlying information compared to conventional simulation tools. Experimental tendencies and results are systematically compared with results obtained numerically. During the sensor operation, iToF pixels reconstruct the depth information using an optical signal modulated in intensity at high operation frequencies of hundreds of MHz. A demodulation operation samples the photogenerated charges at different times in a single pixel. An efficient transfer is dependent of the charge carrier path in the pixel volume. Through the coupling of 3D Monte Carlo with a commercial Poisson solver and optical simulation tools, a complete and accurate simulation methodology was developed allowing the estimation of iToF main figures of merit such as demodulation contrast, parasitic light sensitivity and quantum efficiency. The method consists of generating a light impulse and studying the distribution and collection of each unitary charge in time through MC simulations. Detailed information can be obtained in the 3D volume of a pixel for the photogenerated carriers. The efficiency of charges transfer from the pixel volume to sensing nodes is given at the operation frequency by the demodulation contrast. The electrostatic potential barriers reducing the transfer efficiency can be easily identified and lost photogenerated carriers can be estimated. The prediction accuracy of Monte Carlo simulation is further improved through the coupling of photogeneration and electron mobility profiles extracted from optical simulation and drift-diffusion-based-technology computed-aided design tools respectively. A non optimized small pitch pixel was optimized thanks to these advanced multi-physics simulations.

This paper explores a groundbreaking Nonlinear Activation Function (NLAF) module for Optical Neural Networks (ONN), utilizing innovative micro-ring resonators (MRRs). These resonators, capable of generating whispering gallery modes within a single-mode hybrid silicon waveguide, offer tunability via temperature adjustments of phase-changed materials (PCM) on the MRR. This research delves into the nonlinear activation function of these resonators, showcasing their potential as optical neurons in ONNs. It particularly focuses on the temperature-dependent nonlinear response in various phase-changed materials (PCMs), such as MgF₂, CdGeP₂, and LiNbO₃, showcasing how temperature variation alters amorphous and crystalline structures on silicon, thereby impacting refractive index properties. This control leads to a sigmoidal response in transmission, representing the nonlinearity of the structure. We use the numerical analyses based on the Finite Difference Time Domain (FDTD) method to calculate the transmission of MgF₂ at 1336 nm and 1540 nm, CdGeP₂ at 1350 nm and 1560 nm, and LiNbO₃ at 1341.4 and 1547 nm, respectively at various temperatures. Adjusting the temperature from 20 to 300 degrees Celsius results in an average transmission change of 0.000065 for MgF₂, 0.0018 for CdGeP₂, and 0.0188 for LiNbO₃. This indicates a significant variance in the temperature sensitivity and optical transmission properties among these materials, highlighting their potential to satisfy the requisite optical nonlinearity for the NLAF in future all-photonic neural networks.

Ever-evolving imaging and low-to-single photon-count detection applications demand high-speed, efficient, and complementary metal oxide semiconductor (CMOS) compatible photodetectors. Due to the non-overlapping research and development in the CMOS logic and optoelectronic industry, holistic system optimization is lacking. We propose a PiN device design method addressing the speed-efficiency trade-off and enabling an independent optimization of both speed and absorption efficiency. We present a hybrid device structure combining lateral and vertical PiN architectures. We introduce a highly doped buried P⁺− region connecting the top P⁺− contact doping and separating the N⁺-contact doping by a critical width. The top P⁺− and N⁺− contacts are laterally separated by an i-layer for absorption. The use of a lateral i-layer enables a larger volume for efficient photon absorption, and the presence of a highly doped P⁺− region enables an efficient collection of slow-moving holes after the illumination is turned off. The critical i-layer width sandwiched between the buried P⁺− region and the N⁺− contact doping facilitates an efficient conduction path. We optimize the critical width (optimized width = 200 nm) for device capacitance and the admittance to maximize the response time (rise time, fall time, and full-width half maxima). The optimization is performed using ATLAS Silvaco technology computer-aided design software. The optimized device structure possesses 22 GHz 3 dB bandwidth (BW = 0.35/Fall-time) at 850 nm illumination wavelength as against 0.6-10 GHz 3 dB bandwidth range for conventional PiN devices. We also show that reducing the critical width to zero results in impact ionization drive avalanche phenomenon at ∼6 V applied bias, making these devices suitable for low-power and low-photon count detection. With a large absorber width, an optimized critical conduction path, and a low-bias trigger avalanche process, the proposed photodiodes result in high-speed, high-bandwidth, low-photon count detection, essential for state-of-the-art light detection and ranging systems and the single-photon detectors for quantum communications.

Lately, the need for multi-feature photodetectors has created a rigor among researchers and academicians to explore the light-matter interaction beyond carrier generation and photon detection. The introduction of surface plasmon structures or photon trapping structures for wavelength selective absorption enhancement has been widely exploited. Researchers are exploring meta-materials for polarization and Direction of Arrival (DoA) sensing. However, there still is an unmet need for an in-built DoA capability in a photodetector compatible with the complementary metal oxide semiconductor fabrication process. In this work, we propose an asymmetric surface structure-equipped photodetector capable of sensing the DoA of the photon in addition to standard photon detection. We present a detailed Finite Difference Time Domain Lumerical simulation-based surface structure design for precise detection of the incidence angle (θ) and angle of azimuth (Φ). The presence of the grated surface structures facilitates an asymmetric electromagnetic (EM) wave incidence and interaction and results in a change in the responsivity with the DoA. Using the detailed absorption profile simulated for a range of wavelengths, θ and Φ, and the function regression model, we have devised a framework to predict the DoA, i.e., θ and Φ. The proposed framework predicts the DoA accurately with an introduced signal-to-noise ratio (SNR) ≥160 dB and the predictions become indistinguishable for an SNR ≤100 dB. Such direction-sensitive photodetectors in combination with function regression models can revolutionize the field of object tracking in defense, indoor positioning in factories, wireless communication, and solar tracking.

Due to the instability of the conventional Hg_1-xCd_xTe alloy, the demand for barrier-based superlattice device structures for next-generation infrared photodetectors is rapidly growing. InAs_1-xSb_x, a Ga-free III–V ternary alloy, has the potential to show an advancement in the development of fourth-generation mid-wavelength infrared detectors. In this work, we develop an analytical, reliable simulation model to predict the dark current behavior of an nBn photodetector at various conditions and explain the physics of this new device structure to understand the operation of back-illuminated nBn photodetectors quantitatively. To provide the best possible performance, we consider InAs_1-xSb_x ternary alloy to design the absorber region due to its band gap tunability with Sb molar composition and favorable absorption characteristics. In order to complete the device design, InAsSb is used as a contact layer, and a lattice-matched, large-bandgap barrier layer of AlInAsSb is employed with the intent of minimizing diffusion current, depletion-region Shockley-Read-Hall (SRH) generation and leakage current in such devices. To construct the band structure of the considered heterostructure, we first determine the hole quasi-Fermi-level outside of the thermal equilibrium by solving the coupled equations for the electrostatic, carriers’ current continuity, and Poisson equations. Finally, we calculate the current-voltage characteristics to gain insight into the dominant mechanisms in the generation of dark current and demonstrate how the radiative and non-radiative processes affect the performance in relation to temperature and applied bias. In addition, we shed light on the performance of the considered photodetector by varying the depth of the contact and absorber regions. Our findings from the current device design show that the InAsSb/AlInAsSb-based nBn architecture may be a promising alternative for achieving high performance using a simplified device structure while circumventing issues related to the conventional material system, thereby serving as a basis for next-generation infrared detectors.

Variable angle spectroscopic ellipsometry (VASE) was used to determine the thicknesses of polymethyl methacrylate (PMMA) on Si before and after etching with two different etchants (CF₄ + O₂ and Argon). Once a complete optical model for a base PMMA on Si sample was created, it was applied to all etched samples to determine thicknesses. Despite some minor changes to the optical behavior of PMMA caused by the Ar etching, our ability to fit to observed interference peaks remained unaffected. This technique allows for nanometer accurate thickness measurements, which is an improvement from current thickness measurement methods such as stylus profilometry.

Transition metal dichalcogenides are being used extensively due to their 2-D nature, in spintronic and optoelectronic technologies. TMDs, specifically molybdenum disulfide (MoS₂) and tungsten disulfide (WS₂), have recently attracted considerable interest and extensive research has been dedicated to these materials, unveiling their immense potential for various applications such as catalysts, lubricants, lithium batteries, phototransistors, and nanoelectronics. Mo_xW_1−xS₂ alloys have been synthesized via experimental techniques to harness the properties of both materials. Bilayer TMDs exhibit properties such as tunable bandgap, higher exciton binding energy and interlayer interaction giving rise to new optical modes and excitonic resonances. In this work we study the utility of bilayer Mo_xW_1−xS₂ alloys through first principle computational techniques. We observe an indirect bandgap of around 1.49-1.55eV as we vary the composition of the alloy from 72% Mo to 22% Mo. This capability is significant as it allows researchers to precisely engineer the electronic and optical properties of the material to suit various device requirements. The out-of-plane absorption coefficient of the alloys shows a peak shift from 1.95eV to 2.55eV on increasing percentage of W in the alloy. This shift in the absorption spectrum indicates that the material can effectively absorb light of different wavelengths, thus enabling the design of TMD-based photodetectors with the capability to detect a broad range of wavelengths. This versatility in light absorption is of great importance for applications such as sensors, photovoltaics, optoelectronic devices, where the detection of specific wavelengths is crucial.

As the demand for scalable and complex on-chip nanophotonic devices with multi-wavelength and multi-mode optical functionalities increases, fast and efficient design algorithms have become an essential tool in silicon photonics. Although inverse design coupled with adjoint optimization has emerged as a powerful method to design such devices by requiring only two simulations in each iteration of the optimization process, these simulations still make up the vast majority of the necessary computations, and render the design of complex devices with large footprints computationally infeasible. Here, we present a substantial speed-up in the finite-difference frequency-domain (FDFD) simulations by introducing a factorization caching approach, and significantly reduce the computational requirements for device optimization. Specifically, we cache the symbolic and numerical factorizations of system matrices corresponding to discretized Maxwell’s equations, and re-use them throughout the entire optimization. Using this method, we reduce the majority of the computational operations in the FDFD simulations and drastically improve the simulation speeds. To demonstrate the resulting computational advantage compared to conventional FDFD methods, we show simulation speedups reaching as high as 8.5-fold in the design of broadband wavelength and mode multiplexers. These results present significant enhancements in the computational efficiency of inverse photonic design, and can greatly accelerate the use of machine-optimized devices in future photonic systems.

The merit function defines the permissible range of component variable values in optimizing lens systems. This ensures the optimization algorithm explores parameter variations within specified bounds, contributing to the generation of feasible designs. In this study, we introduce an approach to identify the optimization-sensitive surface parameters of a relay lens through the utilization of the multi-configuration composite feature. The parameter variations sensitivity is analyzed by employing the Zernike Standard Sag Surface as an add-on composite surface, with a perturbation pattern of spherical aberration irregularity across multiple configurations preceding each lens surface within the Zemax lens data editor. The primary performance degradation impact on surface parameters is identified by examining the image spot dimension charts. In light of the analysis results, rigorous constraints are imposed on the sensitive component. A suitable variable range is defined to establish practical limits, aiding the algorithm in searching for solutions within the feasible parameter space. This ensures optimized designs that are physically realizable and meet the specified performance criteria.

The current work shows a novel multilayer heterostructure with Stranski-Krastanov (S-K) quantum dots (QDs), which shows the relatively superior performance in terms of strain reduction and propagation, and optical emission. Here, 2.7 ML InAs/GaAs(Sb) multilayer S-K QDs heterostructures are grown by employing a solid-source Molecular Beam Epitaxy (MBE) system. The multilayer heterostructures consist of single, bi, and hepta-layer S-K QDs with an adaptation of novel growth strategy by estimation of overgrowth percentage. Such overgrowth percentage optimization and new growth strategy is able to grow uniform dots in reach layer from bottom to top layer and residual strain is reduced with the increasing QD layers. To maintain the similar overgrowth percentage (33%) throughout the heterostructures, monolayer coverage is maintained to be 2.5 ML from just next layer of bottom QDs layer to top for each multilayer heterostructures. The simulation is done by Nextnano software for all the heterostructures to analyse the strain propagation, and bandalignment in depth and all results exhibit that residual strain are almost constant after bi-layer with maximum blue-shift in ground-state emission peak. Low-temperature (19 K) Photoluminescence (PL) measurements are performed to investigate the optical properties of the heterostructures and ground state peaks are found at ~ 1084 nm, which confirms the uniform S-K QDs for all the heterostructures. However, lowest FWHM and highest absorptivity are obtained for hepta-layer heterostructures. Further, HRXRD peaks and corresponding values of strain confirm the enhancement of crystallinity and smooth interfaces with significant amount of reduction in strain for multilayer heterostructures.