This PDF file contains the front matter associated with SPIE Proceedings Volume 11274 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

In this paper, we present results from our theoretical and experimental exploration of tailoring the absorption spectrum of a type of metamaterial absorber through manipulating the symmetricity and uniformity of the metallic submicron particle array on the top layer. The absorber under study is a metal-insulator-metal (MIM) trilayer structure made up of a top layer of engineered metallic submicron particles, a middle insulator spacer layer and an opaque ground metal reflector layer. We first studied the structure with a top layer consisting of a uniform array of raindrop-shaped gold (Au) submicron disks. We designed the raindrop shape with a reflectional symmetry on the 45° line. We compared the spectrum generated with that of a similar structure but the top layer which is filled with uniformly arranged circular submicron discs. It has been well reported that an array of circular particles each with both reflectional and rotational symmetries usually generates a spectrum with one absorption spike. By changing the circular shape to raindrop shape, the MIM absorber has been predicted to generate two absorption peaks with significantly broadened absorption bandwidth. Subsequently, we found that even wider spectra could be achieved if the top layer is built with a periodic arrangement of the unit cells containing differently sized raindrop-shaped disks. This leads to a wider bandwidth of higher than 50% absorbance ranging from 2.80 μm to 3.90 μm.

A moving refractive index front can induce an indirect transition between states before or after the front. A linear Schrödinger equation can be used to describe the transition of a slowly varying signal envelope at the front. In waveguides with weak dispersion usually spatial evolution of the pulse temporal profile is tracked. However, we show that for waveguides with strong dispersion it is beneficial to track temporal evolution of the pulse spatial profile. Simulation examples close to the band edge of a photonic crystal waveguide are presented. We also compare the numerical results with the theoretical predictions from the phase continuity criterion.

We have numerically presents a perfect graphene metasurface based solar absorber in the frequency range from 100 THz to 1200 THz. The periodically arranged C-shaped in the 3x3 matrix above the graphene monolayer sheet helps to absorb incoming electromagnetic radiation and thus result in increasing absorption. The absorber gives broadband average absorption with 82.7% in infrared (280 THz to 380THz), 86.5% (430 THz to 770 THz) in the visible and 93% in ultraviolet (780 THz to 1000 THz) regions. The band of absorption varies from lower to higher in terahertz range and vice-versa by changing the parameters changes. This tunability makes the proposed based absorber to be used in optical sensors.

Infrared cameras are used in a wide variety of applications, from military to civilian. Cryogenically cooled IR cameras based on photon-detector arrays are many times more sensitive and faster than uncooled microbolometer thermal imagers.Ga-free InAs/InAsSb type 2 superlattice (T2SL) based devices have been recently fabricated and they showed a first realization of MWIR (Mid-Wave InfraRed) broadband detection up to 5μm. However the band parameters (band offsets, effect of strain, effective mass) of this material system have not been determined accurately, thus limiting the understanding and the prediction of the electronic properties of the devices. In this work we determined the relevant parameters via magnetoabsorption measurements performed on dedicated T2SL samples. Interband magneto-optical transitions lead to an accurate mapping of the Landau levels. The Landau level energies have been calculated using an 8 bands k.p model and the comparison with the experimental data provided a clear description of the T2SL band structure at low temperatures.

2D materials have a number of intriguing value proposition that could be harnessed for compact, tunable, high-performance optoelectronic devices when heterogeneously integrated in photonic circuits. Here I review our latest work including; (1) tunable TMD-based microring resonator with engineered critical-coupling condition, (2) a broadband graphene plasmon-slot photodetector (R=0.7A/W), (3) a 200mV bandgap-shifted strain-engineered absorption-enhanced MoTe2 photodetector (R=0.5A/W, low-dark-current <10nA@-1V), (4) a record-high responsivity (R=1.36A/W) slot-plasmon exciton-modulated MoTe2 photodetector, (5) a MoS2 electro-absorption modulator all enabled by our recently developed method of cross-contamination-free yet deterministic dry transfer 2D material ‘printer’ mimicking a 3D printer for enabling rapid prototyping. These devices are based co-integration of 2D materials into Silicon and SiN photonics, with the latter used for on-exciton modulation or exciton absorption.

The defect corrections to the polarization and dielectric functions of conduction electrons in a quantum well are first calculated. Following this, we derive the first two moment equations from the semi-classical Boltzmann transport theory and apply them to explore defect effects on magneto-transport of electrons. In addition, we obtain analytically momentum-relaxation time and mobility tensor of electrons by using the defect-corrected polarization function. Based on quantum-statistical theory, we further investigate the defect capture and charging dynamics by employing a hydrogen-like quantum-mechanics model for point defects and going beyond a short-range δ-function for their probability functions. Finally, both the capture and relaxation rates, as well as the density for captured electrons, are studied as functions of temperature, subband-electron density and different types of defects, which can be utilized for quantifying burst noise in transistors and blinking noise in photo-detectors.

Mott insulators are a class of strongly correlated materials with emergent properties important for modern electronics applications. The key property for application is the Electric Mott insulator to metal Transitions (EMT) whose proposed mechanism is related to the creation of hot electrons by electric field triggering an electronic avalanche after a time delay. This model suggests that the direct creation of hot carriers thanks to a laser pulse should drastically affect the EMT. We have tested this idea by performing pump-pump-probe experiments on single crystals of the Mott insulator GaTa4Se8, whereby electric and laser pulses simultaneously excite the crystal while electric probe monitors its conductivity. Our results show that the concomitant application of femtosecond laser pulse reduced the time delay of EMT by a factor up to. Measurements performed with different laser wavelengths and fluences support moreover that the EMT is driven by a hot carriers generation mechanism.

Photonic systems are candidates for next generation neural networks, promising to boost energy efficiency and speed via optical vector matrix multiplication. We will introduce the first scalable neural network integration strategy, demonstrating a network for 999 neurons in 0.36 mm^2.

Currently, multiple photonic reservoir computing systems show great promise for providing a practical yet powerful hardware substrate for neuromorphic computing. Among those, delay-based systems offer a simple technological route to implement photonic neuromorphic computation. Its operation boils down to a time-multiplexing with the delay length limiting the processing speed. As most optical setups end up to be bulky employing long fiber loops or free-space optics, the processing speeds are ranging from kSa/s to tens of MSa/s. Therefore, we focus on external cavities which are far shorter than what has been realized before in such experiments. We present experimental results of reservoir computing based on a semiconductor laser, operating in a single mode regime around 1550nm, with a 10.8cm delay line. Both are integrated on an active/passive InP photonic chip built on the Jeppix platform. Using 23 virtual nodes spaced 50 ps apart in the integrated delay section, we increase the processing speed to 0.87GSa/s. The computational performance is benchmarked on a forecasting task applied to chaotic time samples. Competitive performance is observed for injection currents above threshold, with higher pumps having lower prediction errors. The feedback strength can be controlled by electrically pumping integrated amplifiers within the delay section. Nevertheless, we find good performance even when these amplifiers are unpumped. To proof the relevance and necessity of the external cavity on the computational capacity, we have analysed linear and nonlinear memory tasks. We also propose several post-processing methods, which increase the performance without a penalty to speed.

We propose a physical alternative of software based approaches for advanced classification task by considering a photonic-based architecture implementing a recurrent neural network with up to 16,384 physical neurons. This architecture is realized with o↵-the-shelf components and can be scaled up to hundred thousand or millions of nodes while ensuring data-ecient training strategy thanks to the reservoir computing framework. We use this architecture to perform a challenging computer vision task: the classification of human actions from a video feed. For this task, we show for the first time that a physical architecture with a simple learning strategy, consisting of training one linear readout for each class, can achieve a >90% success rate in terms of classification accuracy. This rivals the deep-learning approaches in terms of level of performance and hence could pave the way towards novel paradigm for ecient real-time video processing at the physical layer using photonic systems.

While the data throughput of electronic processors is rather high (TFLOP range), the question arises whether optical neural networks (NN) enable a value proposition for zero-delay (real-time) processing? The answer might be ‘yes’, since once the network is trained, the time to perform an inference tasks is simply given by the time-of-flight of the photon through the processor’s NN. Here we discuss how the three functions of the perceptron (dot-product synaptic weighting, summation, and nonlinear thresholding) can be mapped onto a) optoelectronic [George et al. Opt.Exp. 2019], and b) all-optical hardware [Miscuglio et al. OMEx 2018]. The latter is realized via co-integration of phase-change-materials atop Silicon photonics. Once trained, the weights only require rare updating, thus saving power. Performance wise, such an integrated all-optical NN is capable of < fJ/MAC using experimental demonstrated pump-probe [Waldecker et al, Nat. Mat. 2015] with a delay per perceptron being ~ps.

We show that semiconductor Fano lasers strongly suppress dynamic instabilities induced by external optical feedback. A comparison with conventional Fabry-Perot lasers shows orders of magnitude improvement in feedback stability, and in many cases even total suppression of coherence collapse, due to a unique reduction of the characteristic relaxation oscillation frequency. The laser dynamics is analysed using a generalisation of the Lang-Kobayashi model for semiconductor lasers with external feedback.

We present simulation results showing the impact of a longitudinal linearly varying electrical contact width on intra-cavity intensity, carrier density and temperature distributions of broad-area lasers. In addition, the impact of index guiding trenches on these internal distributions is investigated. The simulations were performed using a time-dependent traveling wave model which takes all relevant physical effects into account. We show that a tapered contact area results in a reduced longitudinal intensity inhomogeneity as well as longitudinal spatial hole burning, at the cost of an increased temperature towards the front facet. Index guiding trenches were found to effectively prevent lateral intensity modulation as well as lateral carrier accumulation near the contact edges at the front facet.

The growth of reliable III-V quantum well (QW) lasers on silicon remains a challenge as yet unmastered due to the issue of carrier migration into dislocations. We have recently compared the functionality of quantum dots (QDs) and QWs in the presence of high dislocation densities using rate equation travelling-wave simulations, which were based on 10-μm large spatial steps, and thus only allowed the use of effective laser parameters to model the performance degradation resulting from dislocation-induced carrier loss. Here we increase the resolution to the sub-micrometer level to enable the spatially resolved simulation of individual dislocations placed along the longitudinal cavity direction in order to study the physical mechanisms behind the characteristics of monolithic 980 nm In(Ga)As/GaAs QW and 1.3 μm QD lasers on silicon. Our simulations point out the role of diffusion-assisted carrier loss, which enables carrier migration into defect states resulting in highly absorptive regions over several micrometers in QW structures, whereas QD active regions with their efficient carrier capture and hence naturally reduced diffusion length show a higher immunity to defects. An additional interesting finding not accessible in a lower-resolution approach is that areas of locally reduced gain need to be compensated for in dislocation-free regions, which may lead to increased gain compression effects in silicon-based QD lasers with limited modal gain.

The first results are presented, which showed general patterns explaining the influence of drift velocity saturation effects on the light-current curve for an example AlGaAs/InGaAs/GaAs laser heterostructure with an ultra-wide asymmetric waveguide emitting in the 1060 nm spectral range at ultrahigh pump currents (tens of kA/cm² ). The study carried out clearly shows the limitations of the simplest drift-diffusion models that take into account and do not take into account the saturation of the drift velocity. It is shown that when analyzing high-power semiconductor lasers at high pump currents, it is necessary to take into account the effect of heating of charge carriers in the waveguide by an electric field. The inclusion of an additional mechanism of internal optical loss obtained in the energy balance model made it possible to obtain a satisfactory agreement between the calculated light-current curves and the experimental ones.

In this paper we study, both experimentally and theoretically, the turn on transient dynamics observed in a long (20m) cavity laser. The laser consists of a ring cavity based on a single mode fiber with unidirectional propagation of light. The gain is provided by a semiconductor optical amplifier (SOA) centered around 1300nm and wavelength selection is provided by a tunable narrow transmission bandwidth Fabry-Perot filter. At high bias current and when the filter transmission sets the laser to operate in an anomalous dispersion regime, the laser exhibits only chaotic oscillations, while in a normal dispersion regime, the laser can exhibit stable operation. At a bias current close to the threshold the laser always exhibits multiple dropouts. In order to record the lasing build up dynamics, the bias current driven to the SOA is periodically switched from the off-state to a high current level. The lasing build up occurs at each roundtrip via a step-wise increase of the laser intensity. The laser intensity is widely oscillating during the first steps and approaches a stationary state after a large number of roundtrips. Recording of the phase evolution of the electric field during each step demonstrates the linewidth narrowing at each subsequent roundtrip. Theoretically, we describe the system by a set of delay differential equations and observe similar behavior. While typically a semiconductor laser exhibits relaxation oscillations before reaching the stable lasing regime, which is associated with class B lasers, our study shows that the long cavity laser demonstrates a different mechanism of lasing build up.

We report on our experimental and numerical demonstration of tunable four-wave mixing (FWM) in dispersion engineered microresonators. In this paper, we focus on the engineering of higher-order dispersion, which enables the generation of tunable parametric oscillation far from the pump light. It allows us to obtain a localized comb structure, which is known as a clustered frequency comb. The numerical simulation agrees well with the experimental demonstrations, which confirms that the top-down dispersion engineering of a microresonator allows us to obtain phase-matched parametric oscillation deterministically.

The scope of this paper is to demonstrate a fully working and compact photonic Physical Unclonable Function (PUF) device capable of operating in real life scenarios as an authentication mechanism and random number generator. For this purpose, an extensive experimental investigation of a Polymer Optical Fiber (POF) and a diffuser as PUF tokens is performed and the most significant properties are evaluated using the proper mathematical tools. Two different software algorithms, the Random Binary Method (RBM) and Singular Value Decomposition (SVD), were tested for optimized key extraction and error correction codes have been incorporated for enhancing key reproducibility. By taking into consideration the limitations and overall performance derived by the experimental evaluation of the system, the designing details towards the implementation of a miniaturized, energy efficient and low-cost device are extensively discussed. The performance of the final device is thoroughly evaluated, demonstrating a long-term stability of 1 week, an operating temperature range of 5⁰C, an exponentially large pool of unique Challenge-Response Pairs (CRPs), recovery after power failure and capability of generating NIST compliant true random numbers.

Optically injected quantum dot lasers display many unique nonlinear phenomena and, in particular, are excellent testbeds for excitable dynamics. We show that – in contrast to most systems – both Type I and Type II excitability can be found. We focus on the recent discovery of the Type II dynamics, which manifests as square wave excitability. The phenomenon arises via an optothermal instability that breaks a bistability and renders the system excitable. Numerical analysis of the system shows that the onset of the square wave regime has two potential origins: One via a bistability and the other via a canard explosion.

Epitaxially grown self-assembled quantum dots (QDs) are promising candidates for an efficient single-photon generation. In order to maximize the number of photons extracted from the device, QDs are frequently embedded into photonic structures such as micro-cavities. Once the QD is positioned inside an optical cavity, the Purcell effect ensures that light is emitted predominantly into the cavity mode. In this contribution, we demonstrate results of emission tuning of QDs inserted in micro-cavities. A sample containing an InAs/GaAs QDs embedded in a planar cavity based on Bragg reflectors has been integrated onto the PMN-PT piezo crystal. Subsequently, micro-cavities have been fabricated by electron-beam lithography and reactive ion etching. The application of external stress produces linear shifts of QDs emission which could be tuned into the resonance with fundamental cavity mode and allow enhancement of QD emission due to the Purcell effect.

The small-signal dynamic response of quantum dot (QD) lasers with asymmetric barrier layers (ABLs) is studied. The modulation bandwidth of this novel type of laser is shown to have a maximum as a function of the dc component of the pump current and parameters of the structure. This provides a clear path for optimizing the laser structure to enhance its bandwidth. The effect of non-instantaneous capture of electrons and holes into QDs on the modulation bandwidth is studied. The maximum bandwidth and the optimum dc injection current at which it is attained are calculated as functions of the capture cross-section. The optimum dc injection current is shown to be considerably lower in ABL QD lasers as compared to conventional QD lasers, i.e., the maximum bandwidth is easier to attain in ABL QD lasers.

Diffuse optical spectroscopy is a well-established methodology for noninvasive functional imaging of biological tissue. Intrinsic contrast is provided by optical absorbers including hemoglobin, water, and lipid, which provides physiologicallyrelevant information on tissue composition, metabolism, and structure. Frequency domain diffuse optical spectroscopy (FD-DOS), unlike continuous-wave DOS, provides measures of absolute absorption and scattering using phase-resolved intensity-modulated (>50 MHz) light and enables deeper and more accurate tissue characterization. However, the imaging depth and sensitivity of FD-DOS is almost always constrained by photodetector sensitivity. It has been recently demonstrated that by using highly sensitive silicon photomultiplier (SiPM) detectors, these limitations may be overcome. Though SiPMs are typically employed in photon-counting or pulsed time-domain measurement applications, they provide up to 30dB increase in signal to noise ratio and deeper tissue sensitivity, as compared to avalanche photodiodes in FDDOS. In this paper, we explore how fundamental SiPM characteristics affect the detection of FD-DOS signals. We develop simulations capable of evaluating and optimizing SiPM parameters (microcell size, microcell number, and recharge time constant) utilizing a Monte Carlo approach to SiPM response from modulated FD-DOS signals. The effects of these parameters are examined in relation to bandwidth and signal to noise ratio, thus providing a methodology for choosing the best SiPM for this unconventional application, and further improving FD-DOS performance.

Amorphous selenium is a unique wide-bandgap disordered material, that shows a deterministic single-carrier hole impact ionization process which results in a very low excess noise factor. A key feature of the avalanche phenomenon in amorphous selenium is that transport at high electric fields shifts to non-activated extended states and this necessitates the need to obtain microscopic access into the relaxation dynamics of non-equilibrium 'hot' holes in extended states. Another interesting aspect of elemental selenium is the similarity in short range order that exists across all allotropic forms. Thus, we employ an in-house ensemble Monte Carlo algorithm, in which we take into consideration scattering from acoustic and non-polar optical phonons to describe the general details of the extended-state hole-phonon interaction. The delocalized extended state transport in the amorphous phase is modeled using the band-transport lattice theory of its crystalline counterpart, trigonal selenium. The energy and phonon band structure along with the density of states and acoustic/optical deformation potentials for the crystalline phase was calculated using density functional theory and a parabolic approximation to the density of states function was used in the simulation. We validate our calculated drift mobility with experimental results in the perpendicular and parallel directions to the c-axis, in the unit cell for trigonal selenium. Moreover, in the direction perpendicular to the c-axis we show that acoustic and non-polar optical phonons are able to maintain a stable hole-energy distribution as long as the electric field is lower than the critical value of 650 kV/cm. Beyond a certain critical electric field, holes in selenium can get 'hot' and gain energy at a faster rate than they loose to the lattice.

High quantum-efficiency photodiodes support responsivity-critical applications including sensing, metrology, communication and computation. Freedom Photonics has developed high speed, high quantum efficiency PIN photodiodes to fill these needs. In this talk, we report our most recent results on high quantum efficiency devices at wavelengths including 780 nm and 1550 nm. These results include spectral response, bandwidth, and dark current values for devices which are intended for linear-mode operation. These devices are designed to support high responsivity applications while maintaining high bandwidths.

Modeling of optoelectronic devices involves long and complex numerical simulations, usually performed with TCAD tools. Numerical simulations provide accurate results for a single device but are not feasible when dealing with a full circuit comprising several nodes. To solve this issue, we developed a novel approach to simulate optoelectronic devices in standard SPICE circuit simulators, thus avoiding using TCAD tools. The concept is based on a coarse meshing of the semiconductor whose nodes are interconnected with the so-called Generalized Lumped Devices. The Generalized Lumped Devices are four ports devices: two ports simulate real currents and voltages in the semiconductor while two additional ports simulate excess carrier density and gradient through the definition of equivalent currents and voltages. The model behind the Generalized Devices is physics based and can correctly simulate optical generation of excess carriers, drift-diffusion transport, bulk and surface recombination as well as capacitive effects, without the need to introduce fitting or empirical parameters. Moreover, since all inputs and outputs are electrical quantities, the model is fully SPICE-compatible and can be merged with SPICE netlists of circuits. In this work, we use the Generalized Devices approach to simulate a bipolar phototransistor and prove that we can predict the photocurrent versus the collector voltage, for different illumination intensities. The model accurately takes into account the optically-triggered current amplification in the phototransistor. Sentaurus TCAD numerical simulations are in agreement with the Generalized Devices approach. Finally, since the model is physics based, we could assess the impact of different semiconductor parameters, such as doping concentrations, lifetime, surface recombination velocity, on the output characteristics of the phototransistors, directly with SPICE circuit simulators.

During the primary steps of photosynthesis, the light-harvesting complexes capture sunlight and transfer the associated energy to reaction centers where charge are separated. Surprisingly, optical spectroscopy has recently revealed manifestations of quantum coherence in the ultrafast dynamics of these natural nanosystems, that would be controlled by the interaction between excitations and the surrounding protein motion. Inspired by the architecture of a natural reaction center, we have designed a generic molecular nanodevice, and simulated the time-dependent photocurrent induced by a femtosecond laser pulse. In this analogue, a time-dependent external voltage is applied to the device in the picosecond timescale via a gate, in order to mimic the effects of protein vibrations. The voltage characteristics are the parameters of this study. The numerical investigation we propose aims at unraveling the conditions in which this external control may increase the photocurrent inside the nanodevice. To this aim, we have developed a combined theoretical/numerical framework to describe and understand the quantum transport of energy and charges, from the nonequilibrium Green's function formalism. Our findings show that such an external control may be beneficial for the integrated (dc) current owing through the interface. Indeed, this external control enables to prevent the back tunneling oscillations of the timedependent photocurrent, which globally enhances the dc current. This exploratory work paves the way towards smart biologically-inspired optoelectronics.

In this work, we investigate the optical properties of different semi-conducting single wall CNTs (Sc-SWCNTs) using abintio simulations and the transfer matrix method (TMM). The simulated results are compared with spectroscopic experimental measurements as well. The real and imaginary parts of the refractive indices in near-infrared (NIR) from 1.2 up to 2.5 μm are calculated, and then used to feed multi-layered homogeneous thin-film utilizing the TMM to calculate the reflectivity, transmissivity, and absorptivity of the Sc-SWCNTs thin-films versus wavelength in the NIR region. The spectral reflectivity is measured using an integrating sphere that collects the overall reflections diffused into the different directions and then couple it to a NIR spectrometer. The measured reflectance spectra shows good agreement with the theoretical predictions. The results suggest that Sc-SWCNTs thin films are highly absorbing over the NIR range due to the distribution of various bandgaps of the CNTs with different diameters.

This Conference Presentation, “Dynamical chaos in silicon micro-cavity optomechanics for physically-enhanced information processing” was recorded at Photonics West OPTO 2020, held in San Francisco, California, USA.

In this paper, a novel method to generate optical frequency combs (OFCs) using nanoscale structures is explored. The growing demand for on-chip photonic processing dictates the need for multi-wavelength light sources, such as OFCs, that can be densely integrated with low processing power. Photonic crystal structues provide a viable method to generate all-optical modulation with sub-femto joule switching power and high density integration potential. This method of all-optical modulation is utilised here to generate an OFC from photonic crystal nanocavities and waveguides. Very- at-topped optical frequency combs with a small intensity variation can be generated based on theoretical predictions via detailed analysis of coupled mode theory for photonic crystal nanocavities and waveguides.

We have demonstrated the first plasmonic exceptional points (EPs) at subwavelength scale. The plasmonic EPs are based on the hybridization of detuned resonances in multilayered plasmonic crystals to reach a critical complex coupling rate between nanoantennas arrays, and, exhibit the dispersion of exceptional points around the non-Hermitian singularity and enhanced nanosensing was observed. The ability to drive plasmons to EPs lays the foundation to explore topological physics at small scales and to novel sensors and optoelectronic devices based on topological polaritonic effects

In this paper, a trench-based novel structure for high-sensitive surface plasmon resonance sensor (SPR), sensitivity enhancement has been observed and presented. The novel structure provides localization of a large fraction of the light energy inside a layer that is adjacent to the outer surface of a metal coating on the sensor. In this technique, a propagating surface plasmon gets confined typically by illuminating thin, multilayer metal films through the novel structure. The novel structure helps to extend more localization of the plasmonic field into the buffer medium where sensing has to occur. The trench-based SPR sensor has excellent optical properties, further enhanced the sensitivity compared with the conventional SPR. The change chemical parameter result directly gives the change in refractive indexes of sensing materials corresponds to change in radiation wavelength, reflectivity, phase for a specific incidence angle.

Surface Plasmon Resonance occurs when a polarized electromagnetic field strikes a metallic surface at the separation interface between metal and an insulator. This phenomenon is characterized by the conduction electrons resonant oscillation at the interface, resulting on propagating plasmon waves on the metallic surface. Since this wave is generated at the boundary between the metallic surface and the external medium, these structures are highly sensitive to alterations on the surrounding environment, namely the refractive index, and may be used in sensing structures. The large majority of these devices use noble metals, namely gold or silver, as the active material. These metals present low resistivity, which leads to low optical losses in the visible and near infrared spectrum ranges. Gold shows high environmental stability, which is essential for long-term operation, and silver’s lower stability can be overcome through the deposition of an alumina layer. However, their high cost is a limiting factor if the intended target is large scale manufacturing. In this work, we performed Finite Differences Time Domain simulations on a Surface Plasmon Resonance based sensing structure, considering cost-effective materials such as aluminium for the active metal and hydrogenated amorphous silicon for the waveguide supporting elements, and verified that these structures are able to detect refractive index variations of the surrounding environment at the 1550 μm operating wavelength. This sensing architecture has also been modelled with dispersive materials, losses included, to reflect as much as possible physical reality, revealing good performance capabilities when compared to similar noble metals based devices.

In this work we outline our multiscale approach for modeling electronic, optical and transport properties of III-N-based heterostructures and light emitting diodes (LEDs). We discuss our framework for connecting atomistic tight-binding theory and continuum-based calculations and how finite element and finite volume meshes are generated for this purpose. Utilizing this framework we present an initial comparison of the electronic structure of an (In,Ga)N quantum well carried out within tight-binding theory and a single band effective mass approximation. We show that for virtual crystal approximation studies, a very good agreement between tight-binding and effectivemass model results is achieved. However, for random alloy fluctuations noticeable deviations in the electronic ground and excited states are found when comparing the two methods. In addition to these electronic structure calculations, we present first LED device calculations, using a drift-diffusion model.

Recent advances in quantum circuits and hybrid quantum well systems have been enabled by leveraging the strong coupling regime in hybrid material heterostructures. Quanta of light-matter interactions are polaritons, the coupled modes of photons and a material excitation, such as plasmons, excitons, or phonons. Due to their short wavelength, polariton lasers operating via intersubband polariton transitions in cascaded quantum wells have shown great promise as terahertz and mid-infrared sources with low threshold energies, with phonon-polariton lasers having applications in nanostructure fabrication and inspection. Hexagonal boron nitride (hBN) has come to the forefront of metamaterial research due to its polar van der Waals crystal structure and two infrared active phonon modes exhibiting hyperbolicity. Because of the small lattice mismatch (less the 22% of the GaN lattice constant) between [0001] oriented wurtzite GaN and hBN, hBN has been used as a substrate and mechanical release layer for GaN and AlGaN with minimal damage to the crystalline quality. Intersubband phonon-polaritons have already been detected in GaN/graphene heterostructures and intersubband excitonpolaritons have been detected in GaN/AlN heterostructures; due to the similar nature of these materials, we believe hBN will be a suitable barrier material for gallium nitride wells. In this study, the conduction band structure of the aforementioned heterostructure will be calculated using a self-consistent Schrödinger-Poisson solver. Intersubband phonon-polariton transitions in a layered hBN/GaN lattice via and Finite Element Method (FEM) simulation of the reflectivity and polaritonic dispersion will be evaluated.

An approach is proposed to incorporate second-order nonlinear effects into finite-difference time-domain simulations, which allows dispersion to be included for all 18 elements of the second-order nonlinear susceptibility tensor. The developed approach is implemented to investigate optical rectification and difference frequency generation in a bulk LiNbO₃ crystal. This method allows for the generalized finite-difference time-domain investigation of second-order nonlinear effects.

Solid-state white light sources gain increasing interest due to their advanced characteristics compared to conventional lighting solutions. New design challenges are introduced in the remote phosphor set-up by the substitution of the efficiency-droop-limited LEDs with laser diodes (LDs) that exhibit peak efficiencies at much higher operating currents. Although laser-excited remote phosphor (LRP) systems have already been employed in some commercial applications, the bottleneck in their performance is identified in the down-conversion process within the phosphor material. The high intensity exciting laser beam in combination with the temperature-dependent properties of phosphors can lead to thermally induced instabilities in the system. For this reason, an opto-thermal simulation framework is developed to investigate the optical and thermal interdependencies and derive the LRPS optimization parameters. The optical analysis is performed with commercial ray-tracing software, where the optical heat losses are computed and subsequently used as the volume heat source in thermal analysis implemented by the finite element method (F.E.M.). The question now arises as to how to properly model the phosphor material in such a simulation scheme. The LED experience has produced a variety of phosphors for lighting applications, most commonly powders in some appropriate resin matrix, which are treated simulation wise as bulk diffusers. As the low thermal conductivity of resins is deemed critical for their use in LRPS, recent research focuses on resin free materials such as glass phosphors, single crystals, polycrystalline dense ceramics, etc. The different modeling approaches of such solutions are investigated here as the scattering properties and surface topology of the samples can vary.

Electrically tunable optical metasurfaces based on Liquid Crystal (LC) offer fast switching speed, low cost, and mature technological development, making it highly desirable for these applications. However, to date, all electrically tunable metasurfaces are designed at a single phase using physical intuition, without controlling the alternate phase and thus leading to limited switching efficiencies (~30 %) and small angular steering (15 degrees). Here, we use adjoint-based “inverse design” (equivalent to “backpropagation” in deep learning) to discover tunable metasurfaces with state-of-the-art efficiency (>80 %) and wide-angle steering (144 degrees). Inverse design can efficiently compute sensitivities with respect to arbitrarily many geometrical degrees of freedom, and thus is very effective for optimizing complicated photonic devices.

Digital pulse modulation of strongly injection-locked whistle-geometry semiconductor ring lasers is investigated. Specifically, we address the problem of optical output signal distortion due to transient behavior of the laser in response to picosecond input pulses of injection current. Pulse modulation of a 2-μm-diameter strongly injection-locked whistlegeometry ring laser with up to 50 GHz repetition rate and substantially suppressed transient emission tails is demonstrated in numerical modeling for a sequence of triangular injection current pulses of picosecond duration.

The spectral linewidth of quantum cascade lasers (QCL) is a few megahertz, while the intrinsic linewidth is only a few hundred hertz. This work proposes to employ strong optical feedback to narrow the linewidth of QCLs without any phase control. It is found that strong optical feedback always reduces the linewidth for any feedback phase. In addition, we experimentally show that the spectral linewidth of the measured QCL is reduced from 7.6 MHz down to 107 kHz by optical feedback with a feedback ratio of -3.8 dB. The corresponding frequency noise below 100 kHz Fourier frequency is reduced by about 40 dB.

In this paper we review our recent progress on high performance mode locked InAs quantum dot lasers that are directly grown on CMOS compatible silicon substrates by solid-source molecular beam epitaxy. Different mode locking configurations are designed and fabricated. The lasers operate within the O-band wavelength range, showing pulsewidth down to 490 fs, RF linewidth down to 400 Hz, and pulse-to-pulse timing jitter down to 6 fs. When the laser is used as a comb source for wavelength division multiplexing transmission systems, 4.1 terabit per second transmission capacity was achieved. Self-mode locking is also investigated both experimentally and theoretically. The demonstrated performance makes those lasers promising light source candidates for future large-scale silicon electronic and photonic integrated circuits (EPICs) with multiple functionalities.

Ultra-narrow linewidth tunable hybrid integrated lasers are built from a combination of indium phosphide (InP) and silicon nitride-based TriPleX™. By combining the active functionality of InP with the ultra-low loss properties of the TriPleX™ platform narrow linewidth lasers in the C-band are realized. The InP platform is used for light generation and the TriPleX™ platform is used to define a long cavity with a wavelength-selective tunable filter. The TriPleX™ platform has the ability to adapt mode profiles over the chip and is extremely suitable for mode matching to the other platforms for hybrid integration. The tunable filter is based on a Vernier of micro-ring resonators to allow for single-mode operation, tunable by thermo-optic or stress-induced tuning. This work will show the operational principle and benefits of the hybrid lasers and the state of the art developments in the realization of these lasers. High optical powers ( <100 mW) are combined with narrow linewidth (< 1 kHz) spectral responses with tunability over a large (>100 nm) wavelength range and a low relative intensity (< -160 dB/Hz).

Photonic integration technologies allow for fabrication of on-chip laser sources and systems that provide functionalities for applications beyond telecommunications, such as sensing, healthcare, millimeter and terahertz generation and quantum technologies. New applications impose a different range of demands regarding performance of such semiconductor laser sources. All characteristics of the optical output signal, output power, wavelength tuning range and mechanism, long and short term stability as well as the energy footprint have to be considered. Monolithic integration technologies on indium phosphide substrates natively support an on-chip combination of active and passive functions that enable development of a new class semiconductor lasers with complex cavities. Such lasers can be tailored to achieve optimum performance with respect to a specific application. A number of single frequency, tunable laser sources in form of photonic integrated circuits for applications in gas sensing, optical coherence tomography, millimeter and terahertz generation and quantum applications have been developed at Eindhoven University of Technology. Ongoing research and development activities that address challenges related to addressable wavelength bands, wavelength tuning and stability imposed by specific applications are enabled by mature generic monolithic technology on indium phosphide. In parallel to those efforts, extensive research works towards expansion of accessible wavelength bands. Tunable and mode-locked leaser geometries and challenges related to unique performance expectations are presented.

The crystal is represented in the form of individual molecule sublattices. Within oscillation electronic model, a superconducting phase transition in an ABCD crystal is possible when the square plasma energy Φ² of the resulting molecular sublattices is equal (or larger) to the square plasma energy of the initial crystal.
Within the electron oscillation model, the parameters of the valence electron TGS crystal interaction — triglycine sulfate (NH₂CH₂COOH)₃H₂S0₄ were considered. For TGS, the parameters for phase transition temperatures at T₁ <10 K, T₂ = 110 K, T₃ = 322.05 K were calculated.

The results of calculations using the electron plasma model for TGS: M is the molecular mass, ρ is the mass density, s is the number of valence electrons, G is the glycine molecule NH₂CH₂COOH, Φ² = 830 ● ρ ● s / M ─ square plasma energy in eV²; q, v = z●β, β are interaction parameters, z is the number of formula units,
q = v●Φ² (TGS)/ΣΦ²─1, Φ² (TGS) ─ square plasma energy for TGS, ΣΦ² is the total square energy of the resulting molecules when the valence bonds are broken.

Φ² (TGS) = 830●1.69●122 / 323.3 = 529.32075471,
2●Φ² (O) = 2●354.9456 = 709.89.
0.5●Φ² (S) = 0.5●321.48069606 = 160.74034803,
Φ² (GH) = 543.55343762, 0.5●Φ² (G) = 533.02650859/2 = 266.513254295
Φ² (GH) + 0.5●Φ² (G) = 543.55343762 + 266.513254295 = 810.066691915

Energy balance criterion
Φ² (TGS) = 529.32075471 < Φ² (GH) + 0.5●Φ² (G) = 810.066691915,
Φ² (TGS) = 529.32075471 < 2●Φ² (O) = 709.8912,
Φ² (TGS) = 529.32075471 > 0.5●Φ² (S) = 0.5●321.48069606 = 160.74034803.

ΣΦ² = 709.8912 + 810.066691915 + 160.74034803 = 1680.698239945
q = 2●β●529.32075471 / 1680.698239945 ─ 1
From the equation T_c = 40.05687 q² ─ 234.44056 q + 191.51842 we calculate the parameters q, β for several temperatures: 322.15, 110, 6, 2.872413475, 0.

It can be assumed that the phase transition in TGS crystal at T₂ = 110 K is antiferroelectric. The coexistence or phase separation of the antiferroelectric and superconducting phases is possible. At T <150 K, the TGS crystal undergoes phase separation, leading to crystal destruction. Therefore, it is necessary to use a TGS crystal for detectors in the temperature range up to 200 K.

Our group is developing a guided-wave optical pressure sensor to detect minute pressure fluctuations occurring during tsunami formation. The sensor consists of a diaphragm as a pressure-sensitive structure and a semi-closed structure with a small hole under the diaphragm which provides a unique high-pass filter function. Cutoff frequency of the high-pass characteristic is an important factor to detect pressure fluctuations due to tsunami formation. In this study, investigations were carried out on frequency characteristics and cutoff frequencies, which vary according to the semiclosed structure dimensions and pressure vibration amplitude, by numerical simulations and experiments in order to further establish design details of the sensor

Using the knowledge that any gate can be built through different arrangements of micro-ring resonators, this paper proposes the all-optical design of XOR and XNOR logic gates. The gates structure thus consists of micro-ring resonators (MRR) paired with a constant source of light (COS). MRRs in these designs are utilized as modulators by tuning their resonant wavelengths. In this way, under no external disturbances, the rings are uncoupled by default. The proposed devices are CMOS-compatible meaning that they can be fabricated using the existing technologies. Also, to reduce the fabrication complexity of the proposed devices, thermo-optic modulation is employed as primary light modulating technique. The logic gates are tested at 25 kpbs. Device parameters are provided as well for manufacturing purposes. The study concludes with suggestions on design improvements and potential application of the optical gates.

The essential broadening of the beam at the corner is a constraint in the fabrication which can be avoided by using the concept of corner radius in using lithography by electron beam technique. In the present study, we investigated single corner plasmonic nanostructure to observe the effect of corner radius in the enhancement of electromagnetic field and resonance wavelength. We explored different geometries of plasmonic nanostructures using simulation technique. Herein we report numerical modelling of plasmonic nanostructures to determine the enhancement in intensity and its resonance wavelength as a novel application in chemical sensor based on surface-enhanced Raman spectroscopy (SERS). Intensity enhancement factor decreases with increase in corner radii at fixed gap and with increase in gap at fixed corner radii in case of plasmonic nanobowtie, square and pentagon nanostructures. We have studied a different plasmonic nanostructure with greater enhancement factor by having both the sharper corner and shorter gap in comparison with other nanostructures. Further, we noticed the gap size effect is higher in comparison with the effect of corner radii on enhancement factor. The electric field enhancement factor is higher at larger corner radii in the case of our proposed plasmonic nanostructure as compare to other plasmonic geometries. Moreover, the single corner plasmonic nanostructures has been modelled and their near-field optical properties of nano shells and nano spheres has been examined so as to optimize our simulation parameters and to test for convergence.

Structural, electronic and optical properties of WS₂/Black Phosphorene heterostructure have been explored using the abinitio simulation based on density functional theory (DFT). An interlayer separation of 3.1 Å at equilibrium is found for the optimized heterostructure with the lowest binding energy. This suggests strong van-der Waal (vdW) interconnections in the relaxed heterostructure. The electronic properties of the optimized heterostructure are studied by calculating the band structure and density of states (DOS) plots. Band structure calculation for the monolayer WS₂/Black Phosphorene heterostructure shows an indirect energy gap behaviour having value around 0.79 eV. To explore the optical characteristics of the relaxed heterostructure, Kubo-Greenwood formalism in a combination with DFT is used. The absorption coefficient, Dielectric constant and refractive index are calculated for the heterostructure. The absorption coefficient spectrum lies in the ultraviolet region for individual WS₂ monolayer and black phosphorene. While the relaxed heterostructure based on monolayer WS2/Black Phosphorene shows its absorption coefficient spectrum in both visible (~380-420 nm) and ultraviolet region. Redshift phenomena have been observed for the relaxed heterostructure. Other optical properties like refractive index and dielectric constant are also in accordance with the absorption coefficient. Further, Type II energy band alignment has been found for the relaxed heterostructure. These calculated results suggest its potential applications in the designing of novel optoelectronic devices.

Optimization of plasmonic nanostructures of Gold (Au) and Silver (Ag) nano-sphere and nano-shell dimers have been investigated by using the simulation technique. The convergence study has been carried for all the simulated nanodimer structures. Here, we explored nano-rod, nano-bowtie, and nano-pillar plasmonic nanostructures to study the effect of length, gap separation, height, and thickness on optimization of the structure. Further, the enhancement in the electric field and resonance wavelength have been evaluated. A decrement in the electric field with the increase in gap separation between Ag and Au nano-dimer structures has been observed. These calculated results show a relatively high enhancement in the case of Ag as compare to Au. An enhancement in the electric field and red shifting of the wavelength is observed with a decrease and increase in the height and length of the plasmonic nanostructures of Ag and Au respectively. However, a reduction in the enhancement of field has been observed with an increment in the thickness of hollow and bimetallic nano-dimer structures. Moreover, larger enhancement in the electric field has been observed in the case of hollow nano-rod as compared to the nano-bowtie shells and nano-pillar plasmonic structure. The enhancement peak in nano-shell dimer structure is lying in the infrared (IR) region while the solid and bi-metallic dimer nanostructures enhancement peak is in near IR region. These optimized plasmonic nanostructures suggest their potential applications in the designing of the modern devices for communication and detection of the hydrogen molecule.

Ab-initio density functional theory (DFT) in a combination with Kubo-Greenwood formalism-based simulations was performed to tailor the structural, electronic and optical properties of functionalized graphene. Halogen atoms (X= Fluorine, Chlorine, Bromine and Iodine) were used to functionalize both sides of the graphene sheet. Functionalization of graphene with fluorine (F) on both sides results in sp2 to the sp3 transformation of hybridization in carbon (C) atom. A band gap of 3.20 eV (direct gap) and 1.51 eV (indirect gap) have been observed when the F and chlorine (Cl) atoms were used to functionalize the graphene sheet respectively. While functionalization of the graphene sheet with bromine (Br) and iodine (I) changes the semi-metallic behavior of graphene to pure metal. The optical properties of functionalized graphene have been examined by calculating the absorption coefficient. Graphene sheet size dependence on the absorption coefficient for the functionalized graphene has been also investigated. Simulated results indicate that absorption coefficient decreases with increase in the size of the functionalized graphene sheet in case of X= F, Br, and I. While for the case of X= Cl, the absorption coefficient increases with increase in the size of the functionalized graphene sheet. The absorption coefficient for the case of X= F and Cl lies in the ultraviolet and visible region respectively. For the case of X= Br, and I, the absorption coefficient lies in all region (infrared, visible and ultraviolet) with the highest absorption coefficient as compared to X= F, and Cl.

This paper investigates the applicability of an intuitive wayfinding system in complex buildings using Visible Light Communication (VLC). Typical scenarios include: finding places, like a particular shop or office, guiding users across different floors, and through elevators and stairs. Data from the sender is encoded, modulated and converted into light signals emitted by the transmitters. Tetra-chromatic white sources are used providing a different data channel for each chip. At the receiver side, the modulated light signal, containing the ID and the 3D geographical position of the transmitter and wayfinding information, is received by a SiC photodetector with light filtering and demultiplexing properties. Since lighting and wireless data communication is combined, each luminaire for downlink transmission becomes a single cell, in which the optical access point (AP) is located in the ceiling and the mobile users are scattered across the overlap discs of each cell, underneath. The light signals emitted by the LEDs are interpreted directly by the receivers of the positioned users. Bidirectional communication is tested. The effect of the location of the Aps is evaluated and a 3D model for the cellular network is analyzed. In order to convert the floorplan to a 3D geometry, a tandem of layers in a orthogonal topology is tested, and a 3D localization design, demonstrated by a prototype implementation, is presented. Uplink transmission is implemented, and the 3D best route to navigate through venue is calculated. Buddy wayfinding services are also considered. The results showed that the dynamic VLC navigation system enables to determine the position of a mobile target inside the network, to infer the travel direction along the time, to interact with received information and to optimize the route towards a static or dynamic destination.

A laser operated nanocomposites for linear electrooptics modulators based on cadmium sulfide (CdS) nanoparticles synthesized by electrochemical anodizing method in the polyvinyl alcohol (PVA) solvent are realized. The basic components are CdS nanoparticles. The XRD data confirm that the wurtzite component content was varied within the 10 % to 27%. Varying PVA solvent the average sizes have been changed. The synthesized powders consist of nano-sized particles with sizes varying within 11 nm…14.5 nm. It is demonstrated an influence of PVA content on the grain sizes. The diameter of particles of CdS is enhanced with an increasing PVA content. The PVA causes a significant increase in the size of the particles. The photoinduced electrooptics has been performed using as a photoinducing 120 fs femtosecond laser at 1045 nm. The linear electrooptics was probed by He-Ne cw laser at 1150 nm. A correlation between the content of wurtzite CdS component and the output electrooptics is found. The maximal values are achieved for the 83.8 % of wurtzite CdS component. For other content of wurtzite CdS these values are less. This one reflect a fact of significant role of acentric crystallites in the observed dependences that may be used for the further search and design of the laser operated electrooptical materials in a future development of laser modulators and laser triggers. Additional important role is played by interfaces. The principal physical origin of the effect is caused by interfaces between the nanoparticles and structurally disordered background. The effect is completely irreversible and disappears after several seconds.

Novel glasses based on TeO₂-P₂O₅-ZnO-M_xO_y-PbF₂ doped by rare earths for laser operated optical anisotropy are proposed. We have discovered an increase of birefringence within coherent laser densities within the 200...500 MW/cm² power densities up to 5×10^-5. After it is enhanced more slowly and is saturated after 800 MW/cm². The glasses have been treated by two bicolour laser beams which propagated under the incident angles varying within the 22…25 degree for 45 degree light polarization. The photoinducing beam have been formed by the 10 ns Nd:YAG laser with 10 Hz frequency repetition. The set of polarizers, lenses and mirrors have been used for formation of the photo inducing laser beams with the desired parameters. The all investigated glasses in temperature interval within the 20°C up to 300°C show the same mechanism of electric charge transport. We have discovered that the glasses possess a high thermostability with the small exception for the first two cycles of heating-cooling and for all the glasses for the third and higher cycling. Addition of rare earth elements has not a huge influence on their stability. The maximal changes are observed for TiO₂ containing compounds, the middle one – for ZnO and the lowest for WO₃. The laser operation has been performed by simultaneous treatment by two bicolor coherent beams. The relaxation processes are equal to about several minutes. Here principal role play polarizabilities of the Ti ions which are maximal and the relatively higher atomic radiuses for Zn and W. The obtained glasses may be promising for laser stimulated fibers during transmission of optical information.

Photoconducting properties of heavily doped black silicon (BSi) fabricated by laser-chemical etching method have been investigated. BSi is used as a photoconductor in the study of carrier transport, photo response and minority carrier lifetime of the BSi material. It is found that the BSi is a good photoconductor with enhanced absorption in NIR from the density of states from the cone like spikes on 2 D surface. Metal contacts can be easily made by inserting metal stripes onto the BSi surface due to its high conductivity. Photocurrent spectra were measured under different voltages in the wavelength range 300 nm ~ 1300 nm. From the linear relationship between the photocurrent and the voltage, the minority carrier lifetime is determined to be about 171 μs for an electron density of 7x10¹⁷ cm^-3 , which is more than 17 times as long as that for n-type silicon. The experimental results demonstrates that the BSi is a suitable material for solar cells not only as absorber but also as conductor.

In this study, we present simulation studies of an intensity modulation technique to produce an optical pulse train. This technique used two optical phase modulators connected to a Fabry-Perot filter (with a free spectral range of 200 GHz and finesse of 500) connected in series to a fiber. Short RF pulses with a phase difference of 180 degrees induced the optical phase modulators. A digital phase shifter created a 180-degree phase difference between RF signals. In the simulation studies, the technique was investigated in a ring-cavity laser design model at the laser wavelength of 1300 nm. Optical pulses were obtained at a repetition rate of 100 MHz with a pulse width of about 600 ps. It was possible to change the optical pulse parameters by changing the bit sequence configuration and bit-rate of the digital phase shifter. With further improvement in effective control of rapid phase shift between RF signals, the technique can be used in active modelocking.

Interband cascade laser (ICL) is a power-efficient mid-infrared semiconductor laser source. Linewidth broadening factor (LBF) is a crucial parameter of semiconductor lasers. This work investigates the sub-threshold LBF of a continuous wave ICL operated at room temperature, using the Hakki-Paoli method. The carrier-induced gain variation of the ICL is extracted from the amplified spontaneous emission spectrum. The refractive index variation is determined by the optical wavelength change, and the thermal effect is carefully removed. It shows that the LBF of the ICL around the gain peak ranges from 1.1 to 1.4, depending on the operation wavelength.

Laparoscopic and endoscopic instruments for minimally invasive surgery are widely used and developed. Previously, author proposed an optical system for an endoscope operating in the long-wavelength IR spectral range [1] for thermal monitoring of biological tissue during surgery. The system is a sequence of germanium lenses. This paper discusses energy performance of the resulting system. The analysis of the long wave infrared range (LWIR) detectors is presented, absorption and throughput is evaluated. Signal-to-noise ratio of the resulting system is calculated.

In the case of an optical system using a solid lens, mechanical movement is required to vary the focus because it is focused only at a specific distance, and there are physical distance restriction when applied to various application. Liquid lens have the merit of changing the focal length because they can change the shape of the lens freely unlike the solid lens with fixed shape. But commercially available liquid lenses are basically aberrated compared to solid lens. Some attempts have been made to correct the aberration at a specific focal length by making the surface membrane of the liquid lens into a lens shape, but the aberration varies even if the focal length changes slightly. This paper proposes a system that pull the lens surface membrane vertically and horizontally by getting ideas from the lens and ciliary body of the human eye. As the ciliary body of the eye contracts and relaxes to adjust the thickness of the lens, the thickness of the lens surface film can be continuously changed while attracting the lens surface film. This allows control of aberration caused by changes in the focal length of the focus variable lens. In the proposed system, the hydraulic method is used to change the focal length of the lens. The surface of the lens is made of elastic material. Depending on the specific shape, the thickness of the lens surface can be changed and the aberration controlled.

To control the spectral and angular bandwidths with high diffraction efficiency, it is important to investigate the characteristics of volume phase (VP) gratings. The relationships between the characteristics and the refractive index distributions (RIDs) inside the recording material of VP gratings are focused on. In the previous work, continuously changeable graded types were investigated. In this work, the functions expressed as continuously changeable trapezoid types of RIDs are proposed. The characteristics of trapezoid-type and graded-type of RIDs which change continuously from a triangular type to a rectangular type are simulated and compared using the rigorous coupled wave analysis. It becomes clear that the same bandwidths can exist for the different types of RIDs with the same refractive index modulation. They are the trapezoid types and the graded types of RIDs. Theoretically the characteristics of a certain angulated trapezoid type can be considered to be the same as that of a certain rounded graded type of RID. It also becomes clear that there are some gratings whose thickness and bandwidths are the same for various trapezoid types of RIDs with the different refractive index modulation, and they are controlled. The tendency is the same as various graded types of RIDs.

We show theoretically that optical feedback can be used to phase lock the successive modes of multi-section frequency-swept source lasers as a means to increase the coherence length. The time-gated feedback technique can be applied to transfer the coherence between the subsequent modes to retain the coherence along the full sweep or to synchronise two independent swept sources. In analogy with CW lasers, we derive an Adler equation describing the locking conditions. When the constant feedback is applied, the laser can operate in a self-mixing, mode-locking or chaotic regime, depending on the sweeping speed. In order to verify the theoretical results, we have developed an experimental set up and performed initial measurements with optical feedback.

Surface plasmon resonance sensors have emerged has one of the most suitable approaches for biosensing. A common approach consists of exciting the plasmons at the interface between a functionalized metal film and a sample medium containing the analyte. The propagation of the surface plasmon is highly dependent on changes of the refractive index of the surrounding environment thus providing a mechanism for sensing. The typical interrogation schemes are based on scanning over the wavelength or the incident angle to search for the resonance condition. These solutions require additional motor-driven rotation stages, prisms or other bulky components, introducing complexity which prevents the fabrication of fully on-chip devices. This work reports a simulation study of an amorphous silicon waveguide structure consisting of an array of parallel surface plasmon interferometers with different propagation lengths, each one comprising a thin layer of gold embedded into a-Si:H waveguide. The surface plasmon modes at the end of the plasmonic structure can interfere constructively or destructively depending on the refractive index of the analyte and the interferometer’s length. The variation of the output intensity at the end of each element of the array provides a convenient interrogation scheme that is suitable for on-chip integration. In this paper we investigate this setup and analyze the output power at the end of the array as a function of the refractive index of the sampling medium. The setup is simulated and characterized by the eigenmode expansion method.

The design of the AlGaAs/InGaAs/GaAs laser heterostructure with an ultra-narrow waveguide was developed and studies on the generation of high-power laser pulses with high beam quality were carried out. The heterostructure design included a 100-nm-thick waveguide and an InGaAs quantum well for a lasing at 1060 nm. For the studies the mesa-stripe geometry single-mode lasers with a 5.1-μm-width contact were fabricated. The mesa-stripe geometry parameters were optimized using a 2D-simulation of waveguide properties, taking into account the spatial distribution of temperature and gain. As a result, the divergence was of 18.5 and 5 degrees in the growth direction and parallel to the heterostructure layers, respectively. Studies of the light-current characteristics in the range of pulse durations of 5–1000 ns showed that the peak power of 1.75 W was limited by the catastrophic optical damage. The dynamics is associated with modes of high-quality factor that approach their threshold conditions at high pumping level. A spectral line of these modes is redshifted relative to a fundamental one.

In this paper, we have investigated the bending losses that occur in an optical fiber, which results in loss of power and efficiency for highly sensitive applications. We have analyzed different power results on the bending of an optical fiber concerning the number of turns and the bending radius. The result analysis has done with both plastic and silica fibers on the mentioned parameters. The simulation result shows power loss in fiber when radius of curvature changed with fixed number of turns on fiber wrapping. The experimental results have presented with the effects of bending radius and wrapping turn on fiber. The observation of this analysis helps to develop modeling of plastic optical and silica fiber to draw sensing structure. This paper focuses on areas of medical, industrial applications where highly sensitive applications are required, and losses in transmission cannot be compromised.

This article is devoted to design hight-aperture optical systems, which is installed on unmanned aerial vehicles (UAV) for identification of damage to crops by adverse meteorological phenomena, detection of damage to crops by pests and diseases, monitoring of germination of grain, detection of the situation to which weeds are distributed, etc. A feature of such system is that the camera can take photographs of one area in different spectral ranges, which recognizes spectral signatures from objects and allows more detailed information in a shorter time for wide field of view with hight resolution. The searching and designing results of an optical system providing necessary characteristics are described.

The paper presents the analysis of the performance of the InAs/InAsSb superlattice barrier detector operated at 230 K and long-wavelengths infrared spectrum (LWIR). To determine the position of the electron miniband and the first heavy hole state in the superlattice, we have used a k·p. Having the position of the conduction band and valence band we have to determine a correct band alignment between the barrier and absorber layer – the barrier in the valence band must be sufficiently low to ensure the flow of optically generated holes. We have considered an AlSb material for barrier best aligned to LWIR InAs/InAsSb superlattice absorber.

GaSe_1-xS_x mixed crystals have recently drawn worldwide attention owing to their wide bandgap, which can be tuned by varying the ratio between Se and S. We have addressed the scarcity of comprehensive studies on its dynamic properties by investigating the photoluminescence (PL) and time-resolved photoluminescence (TRPL) of GaSe_1-xS_x (x = 0, 0.1, 0.2, 0.5) mixed crystals at different temperatures (14 – 300 K) using 404 nm excitation from a Ti:Sapphire laser. This paper aims to show that the PL spectra and the lifetime of GaSe_1-xS_x could be used to determine the stacking type and composition of the sample. Three Gaussian peaks were deconvoluted from the obtained PL spectrum and were attributed to excitons from the direct and indirect bandgaps. As the sulfur composition increases, the color of the emission changes and the PL spectra exhibits a blueshift. Selenium-rich samples, which have a ε-stacking, have an orange emission while sulfur-rich samples, which have a ε-β mixed stacking, have a yellow to green emission. TRPL results reveal that the lifetime becomes longer as the sulfur composition increases. The stacking type influences the separation and transfer of the carriers. Hence, sulfur-rich samples have a significantly longer lifetime than selenium-rich samples due to their β- stacking. As the temperature increases, the lifetime also becomes longer due to the increase of the non-radiative recombination rate, which plays a dominant role in the PL emission. These results are useful for the development of GaSe_1-xS_x-based optoelectronic devices in the red to the blue visible region.