This PDF file contains the front matter associated with SPIE Proceedings Volume 9742, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

We discuss some of the key issues to be addressed along the way to complement, and possibly to replace, the standard semiclassical Boltzmann picture with genuine quantum approaches for the simulation of carrier transport and recombination in GaN-based LEDs, with the goal of gradually removing the fitting parameters presently required by semiempirical "quantum corrections" and to better understand the processes responsible for the efficiency droop. As examples of augmented semiclassical models, we present a three-step description of trap-assisted tunneling, especially relevant below the optical turn-on, and a carrier-density-dependent estimate of the phonon-assisted capture rate from bulk states to quantum wells (QWs). Moving to genuine quantum models, we solve the semiconductor Bloch equations to calculate the gain/absorption spectra of AlGaN/GaN QWs, and we discuss our first simulations of spatially and energetically resolved currents across the active region of a single-QW LED based on the nonequilibrium Green’s function approach.

Noise performance of avalanche photodiodes in light detection is typically described by the excessive noise factor, taking into account only the increase of the variance of the output electron count distribution with respect to the input. This approach is attractive since the excessive noise factor, together with the avalanche gain, can easily be included into the signal-to-noise ratio expression of the complete detection chain. For low-light applications down to single-photon counting, that description is typically not sufficient since one is also interested in the higher moments of the output distribution. Analytical derivation of the output electron count distributions of avalanche photodiodes is typically possible only for very simple electric field profile approximations, which is often not a sufficient description of reality. This work presents a Monte Carlo simulator for numerical prediction of the output distribution that can be applied to any arbitrary electric field profile as well as any light absorption profile and therefore serve as a useful tool for device design and optimization. Comparison with the standard McIntyre theory is provided for a constant field profile showing good agreement. Furthermore, the presented method is used to predict the avalanche noise performance of the recently presented pinned avalanche photodiode pixel (PAPD) with the electric field profile extracted from a finite-element simulation. The pixel is aiming for improvements in high-speed and low-light level image detection in minimally-modified CMOS image sensor technology.

This paper presents a design and simulation of a novel high performance 3D-silicon photodetector for implementing in the low intensity light detection at room temperature (300K). The photodetector is modeled by inspiration of general MEMS fabrication to make a 3D- structure in the silicon substrate using a bulk micromachining process, and based on a complementary metal-oxide semiconductor (CMOS) technology. The design includes a vertical n⁺/p junction as an optical window for lateral illumination. The simulation is carried out using COMSOL Multiphysics relying on theoretical and physical concepts, and then, the assessment of the results is done by the numerical analysis with SILVACO (Atlas) device simulator. Light is regarded as a monochromatic beam with a wavelength of 633nm that is placed 1μm far from the optical window. The simulation is considered under the reverse bias dc voltage in the steadystate. We present photocurrent-voltage (Iph-V) characteristics under different light intensities (2… 10[mW/cm²]), and dark current-voltage (Id-V) characteristics. Comparative studies of sensitivity dependence on the dopant concentration in the substrate as an intrinsic region are accomplished utilizing two different p-type silicon substrates with 1×10¹⁵ [1/cm³] and 4×10¹² [1/cm³] doping concentration. Moreover, the sensitivity is evaluated with respect to the active substrate thickness. The simulated results confirmed that the high optical sensitivity of the photodetector with low dark current can be realized in this model.

Three-dimensional (3D) modeling is reported for CMOS active pixel image sensors particularly by comparing front surface and back-surface illumination. The opto-electronic responses are presented versus various power intensity and illumination wavelength. The optical efficiency and quantum efficiency from FDTD modeling are also presented. For appropriately designed sensor structure, it is shown that back-surface illumination pixel could achieve improved sensitivity within certain wavelength range. The presented results demonstrate a methodological and technical capability for 3D modeling optimization of complex CMOS image sensor.

This paper reports theoretical results which delineate a range of nonlinear dynamical behaviours which arise in nanolasers subject to external optical influences. Firstly attention will be given to the impact of external optical feedback on nanolasers. Secondly the dynamical behaviour of semiconductor nano-lasers under external optical injection will be treated. Finally consideration will be given to effects arising in nano-lasers subject to phase conjugate feedback.

High-speed generation of random bits has attracted much attention recently using chaotic dynamics in laser diodes subject to different perturbations. Extraction of randomness has been investigated from a chaotic laser using selfinjection from a grating with dispersion. While the optical feedback invokes chaos, the dispersion induces different delays to different frequency components to conceal the information of the feedback delay time. Experimentally, random bits were extracted using a laser under feedback from a grating. The undesirable time-delay signature (TDS) was reduced by about 10 times. So a continuously tunable sampling rate was allowed for random bit generation (RBG), where the overall output rate tunable across 3 orders of magnitude up to 100 Gbps was demonstrated. Numerically, the concealment of TDS is further investigated using a rate-equation model incorporating self-injection through an all-pass filter (APF), which is realized by coupling the feedback path to a lossless ring cavity. While the APF provides dispersion to suppress the TDS, the APF provides no frequency selectivity so that a large chaotic bandwidth is attained. For minimal TDS, the coupling ratio to the ring is optimized at 0.5. The round-trip time of the ring also needs to be sufficiently long for inducing dispersion in the chaotic light. With comparable performance in TDS suppression, the APF feedback can generate chaos with broader bandwidth than grating feedback. The results are applicable to generating random bits for digital systems with widely tunable rates.

Quantum dot lasers readily lase from multiple distinct energy states. We examine the influence of optical injection into the ground state (GS) when the free-running operation is the first second excited state (ES) only and demonstrate the existence of an injection-induced bistability between GS emission and ES emission. There is a consequent hysteresis loop in the lasing output. Experimental and numerical investigations are in excellent agreement.

The modulation response of an optically-injected gain lever semiconductor laser is studied and calculations show that a gain-lever laser operating under medium to strong optical injection provides a unique and robust configuration for ultra large bandwidth enhancement. Modulation bandwidths above nine times the relaxation oscillation frequency of the free-running laser can be reached using injection-locking conditions that are reasonable for practical applications. The impact of the gain compression on the modulation dynamic is discussed for the first time. This work is of prime importance for the development of directly-modulated broadband optical sources for high-speed operation at 40 Gbps and beyond.

We propose a novel rate equation model of an optically-injected semiconductor nanolaser based on an expression of the complex electric field including a novel spontaneous emission term. The latter takes into account the amplification of the zero-point energy of the field as well as the Purcell effect. The modulation response of the optically injection-locked nanolaser is studied for the first time using a small-signal analysis of the model. We then investigate the injection map of the nanolaser and study the 3-dB bandwidth of the nanolaser inside the locking region.

We present a study of various models for the mode-locked pulse dynamics in a vertical external-cavity surface emitting laser with a saturable absorber. The semiconductor Bloch equations are used to model microscopically the light-matter interaction and the carrier dynamics. Maxwell’s equations describe the pulse propagation. Scattering contributions due to higher order correlation effects are approximated using effective rates that are found from a comparison to solving the microscopic scattering equations on the second Born-Markov level. It is shown that the simulations result in the same mode-locked final state whether the system is initialized with a test pulse close to the final mode-locked pulse or the full field build-up from statistical noise is considered. The influence of the cavity design is studied. The longest pulses are found for a standard V-cavity while a linear cavity and a V-cavity with an high reflectivity mirror in the middle are shown to produce similar, much shorter pulses.

This communication presents a dynamic model of a multi-junction heterostructure that combines the functions of a fast current switch and a high-efficiency laser emitter. Approaches to designing a multi-junction heterostructure with faster switching (rise and decay times of about 1 ns) and higher peak current (>10 A) are considered. It is shown that an important role is played in the dynamics of the injection drive currents of the laser part by the modulation by excess carriers in the lightly doped base and collector regions of the N-p-N transistor part. As a result, a field domain is formed, which serves as a virtual emitter of electrons and holes via impact ionization.

With a use of electro-optic modulator based comb generator, ultra-wideband optical comb is stably and flexibly synthesized from a continuous-wave light. Larger modulation depth at a higher repetition rate would proportionally enhance bandwidth of the generated comb. Practically, however, achievable modulation depth is limited by available output power of microwave amplifiers. In addition, the repetition rate, i.e. comb spacing, is determined by system-side requirements. For example, frequency spacing of the generated comb should fit to the wavelength grid of optical fiber networks. Narrower frequency spacing is requested for photonic measurements assisted by advanced electrical signal processing based on low-speed electronics. In this paper, through numerical analysis, we propose and discuss configurations of serially cascaded Mach-Zehnder modulator-based flat comb generators, aiming for optical comb generation satisfying both higher bandwidth and narrower frequency spacing.

A novel, time-resolved interferometric technique is presented allowing the reconstruction of the complex electric field output of a fast frequency swept laser in a single-shot measurement. The power of the technique is demonstrated by examining a short cavity swept source designed for optical coherence tomography applications, with a spectral bandwidth of 18 THz. This novel analysis of the complete electric field reveals the modal structure and modal evolution of the device as well as providing a time-resolved real-time characterization of the optical spectrum, linewidth and coherence properties of a dynamic rapidly swept laser.

Bidirectional coupling of semiconductor lasers (SLs) through optical injection is a well established method to generate chaotic signals which, through their dynamics, may give rise to several applications from sensing to monitoring and from communication to security. Recent works have shown the capability of joint behavior or complete synchrony of mutually coupled networks of SLs. In these works, the coupling architecture, the operational conditions and the properties of the active elements determine the types of dynamics of the emitted optical signals, through which the network can potentially be synchronized. In this experimental work, a network of mutually coupled semiconductor lasers has been synchronized through chaotic optical signals that spectrally extend over 10GHz. The synchronization among the lasers that participate in the coupled network is affected, besides the structural and operational conditions, by the signals' bandwidth that circulates optically. Here we show that the synchronization performance of the detected signals when monitoring the network nodes through optoelectronic conversion is in direct dependence on the signal bandwidth. Smaller signal bandwidth at the GHz range may result in synchronization with cross-correlation values over 0.97 in most of the SL nodes, rejecting higher frequencies that are not optimally synchronized. Another source of improving the synchronization of the network that has been recorded in this experimental setup is by harnessing the de-synchronization events that are almost always apparent, especially when emitted signals include power dropouts.

Fields such as optical metrology and computational lithography require fast and efficient methods for solving the time-harmonic Maxwell's equation. Highly accurate geometrical modelling and numerical accuracy at low computational costs are a prerequisite for any simulation study of complex nano-structured photonic devices. We present a reduced basis method (RBM) for the time-harmonic electromagnetic scattering problem based on the hp-adaptive finite element solver JCMsuite capable of handling geometric and non-geometric parameter dependencies allowing for online evaluations in milliseconds. We apply the RBM to compute light-scattering at optical wavelengths of periodic arrays of fin field-effect transistors (FinFETs) where geometrical properties such as the width and height of the fin and gate can vary in a large range.

Optical isolators are important devices in photonic circuits. To reduce the unwanted reflection in a robust manner, several setups have been realized using nonreciprocal schemes. In this study, we show that the propagating modes in a strongly-guided chiral photonic crystal (no breaking of the reciprocity) are not backscattering-immune even though they are indeed insensitive to many types of scatters. Without the protection from the nonreciprocity, the backscattering occurs under certain circumstances. We present a perturbative method to calculate the backscattering of chiral photonic crystals in the presence of chiral/achiral scatters. The model is, essentially, a simplified analogy to the first–order Born approximation. Under reasonable assumptions based on the behaviors of chiral photonic modes, we obtained the expression of reflection coefficients which provides criteria for the prominent backscattering in such chiral structures. Numerical examinations using the finite-element method were also performed and the results agree well with the theoretical prediction. From both our theory and numerical calculations, we find that the amount of backscattering critically depends on the symmetry of scatter cross sections. Strong reflection takes place when the azimuthal Fourier components of scatter cross sections have an order l of 2. Chiral scatters without these Fourier components would not efficiently reflect the chiral photonic modes. In addition, for these chiral propagating modes, disturbances at the most significant parts of field profiles do not necessarily result in the most effective backscattering. The observation also reveals what types of scatters or defects should be avoided in one-way applications of chiral structures in order to minimize the backscattering.

We propose a Rayleigh-Sommerfeld based method for numerical calculation of multiple tilted apertures near and far field diffraction patterns. Method is based on iterative procedure of fast Fourier transform based circular convolution of the initial field complex amplitudes distribution and impulse response function modified in order to account aperture and observation planes mutual tilt. The method is computationally efficient and has good accordance with the results of experimental diffraction patterns and can be applied for analysis of spatial noises occurring in master oscillator power amplifier laser systems. The example of diffraction simulation for a Phobos-Ground laser rangefinder amplifier is demonstrated.

We describe a study of electro-absorption effects in high quality 1300nm InAs/GaAs quantum dot (QD) material grown by molecular beam epitaxy. The photocurrent spectra as a function of electric field is investigated and the quantum confined Stark shift of the QD states is compared to reports for various quantum well (QW) systems (GaAs/AlGaAs, InGaAs/GaAs, InGaAsP/InP). We show that the rate of shift of the QD absorption peak is smaller than that of the reported QW systems (~0.1 meV/kVcm-1 c.f. 0.15-0.2 meV/kVcm- 1) and that the QD ground-state absorption is comparatively insensitive to the applied electric field. We observe a strong QD absorption peak at all biases up to avalanche breakdown, which is not observed in previous reports for these QW systems.

Quantum information science relies on the feature of distant quantum entities (mostly "qubits") to form non-local states. A main challenge consists of generating such non-local entangled states between qubits. We exploit the fact that for coupled qubits, the eigenstates of the coupled system are usually highly entangled, and of different excitation energies. This allows to address the different entangled eigenstates by frequency-dependent control schemes.

In our proposal, we present such a control mechanism, and demonstrate how it can be used to create entanglement from a fully separable initial state. The mechanism of our choice is time-delayed quantum-coherent feedback. If a qubit occupation decays via the emission of a photon, one can store this photon for a delay time τ and couple the radiation back into the qubit afterwards. Through the choice of τ, one can set the phase of the feedback, which will then lead to either an increased or decreased qubit decay. Since this phase depends on sin(ωτ), this effect strongly depends on the qubit frequency ω. In particular, it can be used to separate different entangled states in a quantum network by enhancing the decay of all entangled eigenstates except one.

We discuss this protocol on the example of two coupled qubits, and analyze in detail its effectiveness depending on the feedback delay time τ.

Nanostructure is an effective solution for realizing optoelectronic devices with compact size and high performances simultaneously. This paper reports our research progress on integrated nanophotonic devices for optical interconnections. We proposed a parent-sub micro ring structure for optical add-drop multiplexer (OADM) with compact footprint, large free spectral range, and uniform channel spacing. All eight channels can be multiplexed and de-multiplexed with 2.6 dB drop loss, 0.36 nm bandwidth (>40 GHz), -20 dB channel crosstalk, and high thermal tuning efficiency of 0.15 nm/mW. A novel principle of optical switch was proposed and demonstrated based on the coupling of the defect modes in photonic crystal waveguide. Switching functionality with bandwidth up to 24 nm and extinction ratio in excess of 15 dB over the entire bandwidth was achieved, while the footprint was only 8 μm×17.6 μm. We proposed an optical orbital angular momentum (OAM) coding and decoding method to increase the data-carrying capacity of wireless optical interconnect. An integrated OAM emitter, where the topological charge can be continuously varied from -4 to 4 was realized. Also we studied ultrafast modulated nLED as the integrated light source for optical interconnections using a nanobeam cavity with stagger holes.

In this work we study Ge transistor structures grown on silicon substrate. We use photoluminescence to determine the band gap of Ge under tensile strain. The strain is induced by growing Ge on an InGaAs buffer layer with variable In content. The band energy levels are modeled using a 30 band k·p model based on first principles calculations. Photoluminescence measurements show a reasonable correspondence with calculated values of the band energies.

Greatly enhanced high-speed modulation performance has been recently predicted in numerical calculations for a novel injection-locking scheme involving a distributed Bragg reflector master laser monolithically integrated with a unidirectional whistle-geometry semiconductor micro ring laser. In this work, we confirm the unidirectionality of the whistle-geometry configuration through rigorous three-dimensional finite-difference time-domain (FDTD) simulation by showing a strong asymmetry in photon lifetimes between the two counter propagating modes. At the same time, we explain why this result does not violate the Helmholtz reciprocity principle.

Possessing both the high-speed characteristics of heterojunction bipolar transistors (HBTs) and enhanced radiative recombination of quantum wells (QWs), the light-emitting transistor (LET) which operates in the regime of spontaneous emissions has achieved up to 4.3 GHz modulation bandwidth. A 40 Gbit/s transmission rate can be even achieved using transistor laser (TL). The transistor laser provides not only the current modulation but also direct voltage-controlled modulation scheme of optical signals via Franz-Keldysh (FK) photon-assisted tunneling effect. In this work, the effect of FK absorption on the voltage modulation of TLs is investigated. In order to analyze the dynamics and optical responses of voltage modulation in TLs, the conventional rate equations relevant to diode lasers (DLs) are first modified to include the FK effect intuitively. The theoretical results of direct-current (DC) and small-signal alternating-current (AC) characteristics of optical responses are both investigated. While the DC characteristics look physical, the intrinsic optical response of TLs under the FK voltage modulation shows an AC enhancement with a 20 dB peak, which however is not observed in experiment. A complete model composed of the intrinsic optical transfer function and an electrical transfer function fed back by optical responses is proposed to explain the behaviors of voltage modulation in TLs. The abnormal AC peak disappears through this optoelectronic feedback. With the electrical response along with FK-included photon-carrier rate equations taken into account, the complete voltage-controlled optical modulation response of TLs is demonstrated.

We investigate an optomechanical system with an unstable steady state, which can be stabilized via Pyragas control. We will demonstrate this for low and high pump rates. The system contains a pumped cavity, where one mirror is movable. To obtain time delayed feedback, we feed back the cavity field with an external mirror. This way, we achieve a maximal cavity field in the low pumping regime, which also corresponds to a large displaced movable mirror.

During the past century the electromagnetic field momentum in material media has been under debate in the Abraham-Minkowski controversy as convincing arguments have been advanced in favor of both the Abraham and Minkowski forms of photon momentum. Here we study the photon momentum and optical forces in cavity structures in the cases of dynamical and steady state fields. In the description of the single-photon transmission process we use a field-kinetic one-photon theory. Our model suggests that in the medium photons couple with the induced atomic dipoles forming polariton quasiparticles with the Minkowski form momentum. The Abraham momentum can be associated to the electromagnetic field part of the coupled polariton state. The polariton with the Minkowski momentum is shown to obey the uniform center of mass of energy motion that has previously been interpreted to support only the Abraham momentum. When describing the steady state non-equilibrium field distributions we use the recently developed quantized fluctuational electrodynamics (QFED) formalism. While allowing detailed studies of light propagation and quantum field fluctuations in interfering structures, our methods also provide practical tools for modeling optical energy transfer and the formation of thermal balance in nanodevices as well as studying electromagnetic forces in optomechanical devices.

We report on possible consequences of alloying of GaAs with GaBi or InBi on band structure and material gain of quantum wells. Typical considered structure consists of 8nm wide GaAsBi quantum well on GaAs substrate. Our analysis is performed using 8-band and 14-band kp models. The obtained results indicate that for GaInAsBi/InP quantum well with 5% of Bi it might be possible to achieve emission wavelengths around 4 μm .

This work presents an investigation of room temperature ultra-fast carrier dynamics in a p-doped dash-in-a-well structure emitting at 1.5 μm using single colour heterodyne pump-probe spectroscopy. This technique enabled simultaneous access to the gain and refractive index dynamics in various operational conditions including both the absorption and gain regime. Comprehensive analysis of the timescales related to carrier relaxation and escape processes in addition to the ’dynamical’ linewidth enhancement factor are presented and compared with results obtained from similar un-doped materials. The direct influence of the p-doping on the carrier dynamics is also discussed.

In this paper, we examine recent theoretical investigations on 3D hybrid perovskites (HOP) that combine concepts developed for classical bulk solid-state physics and empirical simulations of their optoelectronic properties. In fact, the complexity of HOP calls for a coherent global view that combines usually disconnected concepts. For the pseudocubic high temperature reference perovskite structure that plays a central role for 3D HOP, we introduce a new tight-binding Hamiltonian, which specifically includes spin-orbit coupling. The resultant electronic band structure is compared to that obtained using state of the art density functional theory (DFT). Next, recent experimental investigations of excitonic properties in HOP will be revisited within the scope of theoretical concepts already well implemented in the field of conventional semiconductors. Last, possible plastic crystal and orientational glass behaviors of HOP will be discussed, building on Car-Parrinello molecular dynamics simulations.

In this paper, we propose a description of the Rashba-Dresselhaus effect in Hybrid Organic Perovskite (HOP). We show how the loss of the inversion symmetry leads to the loss of the spin degeneracy. An example of structure where both Rashba and Dresselhaus operate is illustrated with the formamidinium tin iodide CH(NH₂)₂SnI₃. The control of this effect is as well addressed by two examples. A first example concerns the control with the temperature and is demonstrated for the 2D HOP Bz₂PbCl₄ (Bz = benzylammonium). Then the control with an external field is established for the 3D HOP CH₃NH₃PbBr₃.

For long wave length infrared transmission, a surface plasmonic device, having the periodic subwavelength metal hole array on Si substrate, was fabricated using photo-lithography and electron beam evaporation. The maximum transmitted wavelength was adjustable arbitrarily as a function of the period hole arrays. The maximum transmittance was measured 70.3% at 15.4 μm with a plasmonic device composed of a pitch of 5 μm and hole arrays of 3 μm. When the hole size became larger than a half pitch of the hole array, the transmitted infrared spectrum was split into two peaks. The surface plasmon mode of the six degenerated (1,0) Ag/Si was split from three to five modes depending on the incident beam angle. The blue and red wavelength shifts were measured at the same time.

Nonlinearity enhanced by noble metallic nanoparticles provide novel light manipulation capabilities and innovative applications. Recently, we discovered a new nonlinear phenomenon on the scattering of metallic nanoparticles by continuous-wave (CW) lasers at the intensity around MW/cm² and applied to super-resolution microscopy that allowed spatial resolution of plasmonic nanostructures down to λ/8. However, its mechanism is still unknown. In this work, we elaborate the mechanism behind the nonlinear scattering of gold nanospheres. There are four possible candidates: intraband transition, interband transition, hot electron, and hot lattice. Each of them has a corresponding nonlinear refractive index (n²), which is related to temporal dependence of its light-matter interaction. We first measure the intensity dependence of nonlinear scattering to extract the effective n₂ value. We find out it has the closest n₂ value to hot lattice, which causes either the shift or weakening of the surface plasmon resonance (SPR). To further verify the mechanism, the nanospheres are heated up with both a hot plate and a CW laser, and the variation of single-particle SPR scattering spectra are measured. In both cases, more than 50% reduction of scattering is observed, when temperature rises a few tens of degrees or when illumination intensity reaches the order of 1MW/cm². Thus, we conclude the spectra variation by the two different heating source, as well as the nonlinear scattering are all due to hot lattice, and subsequent permittivity change with temperature. The innovative concept of hot lattice plasmonics not only opens up a new dimension for nonlinear plasmonics, but also predicts the potential of similar nonlinearity in other materials as long as their permittivity changes with temperature.

In this paper, we proposed highly efficient all-dielectric Huygens’ metasurfaces working at mid-IR frequencies. The meta-atom of the designed Huygens’ metasurface is a cubic dielectric resonator or its variety, which is made from PbTe that possesses a high refractive index of around 5 at mid-IR frequencies. By overlapping spectrally both the magnetic and electric dipole modes of the high-index dielectric resonators, a full phase coverage of 2π and an equal-magnitude transmission could be achieved, which are essential conditions for realizing a metasurface. Two Huygens’ metasurfaces for beam bending are designed with a phase change between two consecutive meta-atoms of π/4 and π/3, respectively. The simulation results agree well with the design theory.

In this paper, an effective quality-factor is analyzed for asymmetric Mach-Zehnder interferometer (AMZI) with ring resonator sensor. The device is designed with AMZI to interference with the optical input of the ring resonator based on silica semiconductor process. The design of device satisfy a critical resonance at out of phase condition through asymmetric power split ratio. According to operation principle of Mach-Zehnder interferometer, the critical resonance occurs when the power passing through asymmetric arm is in a range of ring resonator power variation. Our simulation shows that the Q-factor of the device is enhanced from 1161.9 to 5342.5 if a RR is coupled to an arm of AMZI.

An efficient sensitivity analysis approach for quantum nanostructures is proposed. The imaginary time propagation method (ITP) is utilized to solve the Time Dependent Schrödinger’s Equation (TDSE). Using this method, an extraction of all the modes and their sensitivity with respect to all the design parameters have been performed with minimal computational effort. The sensitivity analysis is performed using the Adjoint Variable Method (AVM) and results are comparable to those obtained using Central Finite Difference Method (CFD) applied directly on the response level.

The spatial discontinuity of physical parameters at an abrupt interface may increase numerical errors when solving partial differential equations. Rather than generating boundary-adapted meshes for objects with complicated geometry in the finite-element method, the subpixel smoothing (SPS) replaces discontinuous parameters inside square elements that are bisected by interfaces in, for example, the finite-difference (FD) method, with homogeneous counterparts and matches physical boundary conditions therein. In this work, we apply the idea of SPS to the eight-band effective-mass Luttinger-Kohn (LK) and Burt-Foreman (BF) Hamiltonians of semiconductor nanostructures. Two smoothing approaches are proposed. One stems from eliminations of the first-order perturbation in energy, and the other is an application of the Hellmann-Feynman (HF) theorem. We employ the FD method to numerically solve the eigenvalue problem corresponding to the multiband Schrodinger’s equation for circular quantum wires (QWRs). The eigen-energies and envelope (wave) functions for valence and conduction states in III-V circular QWRs are examined. We find that while the procedure of perturbation theory seems to have the better accuracy than that of HF theorem, the errors of both schemes are considerably lower than that without smoothing or with direct but unjustified averages of parameters. On the other hand, even in the presence of SPS, the numerical results for the LK Hamiltonian of nanostructures could still contain nonphysical spurious solutions with extremely localized states near heterostructure interfaces. The proper operator ordering embedded in the BF Hamiltonian mitigates this problem. The proposed approaches may improve numerical accuracies and reduce computational cost for the modeling of nanostructures in optoelectronic devices.

Thermal poling, a technique to introduce effective second-order nonlinearities in silica optical fibers, has found widespread applications in frequency conversion, electro-optic modulation, switching and polarization-entangled photon pair generation. Since its first demonstration around 25 years ago, studies into thermal poling were primarily based on anode-cathode electrode configurations. However, more recently, superior electrode configurations have been investigated that allow for robust and reliable thermally poled fibers with excellent second order nonlinear properties [1, 2]. Very recently, we experimentally demonstrated an electrostatic induction poling technique that creates a stable second-order nonlinearity in a twin-hole fiber without any direct physical contact to internal fiber electrodes whatsoever [3]. This innovative technique lifts a number of restrictions on the use of complex microstructured optical fibers (MOF) for poling, as it is no longer necessary to individually contact internal electrodes and presents a general methodology for selective liquid electrode filling of complex MOF geometries. In order to systematically implement these more advanced device embodiments, it is first necessary to develop comprehensive numerical models of the induction poling mechanism itself. To this end, we have developed two-dimensional (2D) simulations of space-charge region formation using COMSOL finite element analysis, by building on current numerical models [4].

III-V compound semiconductors seem to be the ideal materials for photovoltaic devices because they exhibit fast carrier velocity. III-V compound semiconductors, however, are unfavorable materials to be commercialized on large scale photovoltaic devices because of their high material cost. The textured surface shows the potential to increase the performance of solar cells because of the properties such as high absorption and longer light path length. These properties can overcome the disadvantage of the III-V compound semiconductors through thin thickness use when producing solar cells. In this study, we demonstrate that textured surfaces on InP formed by nano-sphere lithography and plasma etching process can enhance the absorption effectively in comparison with planar surface. The power conversion efficiency of InP solar cells using the textured InP and the aluminum doped zinc oxide was achieved up to 8%.

Due to the improved economic situation in the high technology sectors, work on the creation of industrial robots and special mobile robotic systems are resumed. Despite this, the robotic control systems mostly remained unchanged. Hence one can see all advantages and disadvantages of these systems. This is due to lack of funds, which could greatly facilitate the work of the operator, and in some cases, completely replace it. The paper is concerned with the complex machine vision of robotic system for monitoring of underground pipelines, which collects and analyzes up to 90% of the necessary information. Vision Systems are used to identify obstacles to the process of movement on a trajectory to determine their origin, dimensions and character. The object is illuminated in a structured light, TV camera records projected structure. Distortions of the structure uniquely determine the shape of the object in view of the camera. The reference illumination is synchronized with the camera. The main parameters of the system are the basic distance between the generator and the lights and the camera parallax angle (the angle between the optical axes of the projection unit and camera).

Compared with FBG, long period fiber gratings (LPFGs) have higher sensing sensitivity in many aspects. With the development of few-mode fiber (FMF), few mode long period fiber gratings (FM-LPFGs) has grasped a lot of research focus in recent years. The co-propagating coupling between a core mode and a cladding mode, or two different core modes, will bring different effects on the sensing characteristics of temperature, strain and refractive index. However, the coupling characteristics between core modes and cladding modes have been rarely reported in theory before. In this paper, based on the coupled-mode theory, we simulate the transmission spectrum of the FM-LPFGs by use of MATLAB and COMSOL software. Assuming that all the power is launched in a certain mode, we calculate the coupling coefficients and the transmission spectrums between the core modes (LP₀₁, LP₁₁, LP₂₁, and LP₀₂) and the cladding modes LP_lm (l=1) at 1550nm. In addition, we change some fiber parameters like grating period, refractive index modulation depth and cladding diameter to analyze their effect on the transmission spectrum. Based on the simulation, we fabricate some FM-LPFGs by the CO₂ laser, and use them in temperature sensing experiments. With the certain strain, we measured the temperature sensing sensitivity of the FM-LPFGs. The measured sensitivities of temperature is -43.98pm/°C.

Performances of any system for data processing based on acousto-optical technique are mainly determined by parameters of the acousto-optical cell (AOC) exploited within the schematic arrangement. Here, basic properties of the AOC, involved into a novel processor for precise optical spectrum analysis dedicated to modern astrophysical applications, are considered. Because potential applications of this processor will be focused on investigations in extra-galactic astronomy as well as studies of extra-solar planets, an advanced regime of the non-collinear two-phonon light scattering has been elaborated for spectrum analysis with significantly improved spectral resolution. Under similar uprated requirements, the AOC, based on that specific regime in the calomel (Hg₂Cl₂) crystal, had been chosen, and its parameters were analyzed theoretically and verified experimentally. Then, the adequate approach to estimating the frequency/spectral bandwidth and spectral resolution had been developed. The bandwidth was calculated and experimentally realized with the additionally involved tilt angle of light incidence, allowing variations for acoustic frequencies. The resolution was characterized taking into account its doubling peculiar to the nonlinear two-phonon mechanism of light scattering. Proof-of-principle experiments were performed with the calomel AOC of 52 mm optical aperture, providing ~94% efficiency in the transmitted light due to the slow-shear acoustic mode of finite amplitude (the acoustic power density ~150 mW/mm²) with the velocity of 0.347×105 cm/s at the radio-wave acoustic frequency ~71 MHz. As a result, we have obtained the spectral resolution <0.235 Å within the spectral bandwidth <290 Å that looks as the best one can mention at the moment in acousto-optics.

We report a novel method to manipulate the direction of a laser beam by controlling the thickness of a dielectric elastomer. The system is controlled by applying different voltages to multi-layers of dielectric elastomers without mechanical movement. We employed laser beams with different wavelengths to test the proposed system, and the experimental results showed that it has an excellent transmittance profile in the ultraviolet and visible wavelength bands, and that we achieved high-precision control in the micrometer range. The results show the feasibility of this technique for laser applications that require high positional accuracy, such as laser cutting, drilling machines, and 3D printing.

In general, thin-film coating process is widely applied on optical lens surface as anti-reflection function. In normal production process, at first lens is manufactured by molding, then anti-reflection is added by thin-film coating. In recent years, instead of thin-film coating, sub-wavelength structures adding on surface of molding die are widely studied and development to keep anti-reflection performance. As merits, applying sub-wavelength structure, coating process becomes unnecessary and it is possible to reduce man-hour costs. In addition to cost merit, these are some technical advantages on this study. Adhesion of coating depends on material of plastic, and it is impossible to apply anti-reflection function on arbitrary surface. Sub-wavelength structure can solve both problems. Manufacturing method of anti-reflection structure can be divided into two types mainly. One method is with the resist patterning, and the other is mask-less method that does not require patterning.

What we have developed is new mask-less method which is no need for resist patterning and possible to impart an anti-reflection structure to large area and curved lens surface, and can be expected to apply to various market segments. We report developed technique and characteristics of production lens.

We present numerical simulation of III-nitride monolithic multi-color LED covering full red-green-blue (RGB) color gamut. The RGB LED structure was grown at Ostendo Technologies Inc. and has been used in Ostendo proprietary Quantum Photonic Imager (QPI) device. Active region of our RGB LED incorporates specially designed intermediate carrier blocking layers (ICBLs) controlling transport of each type of carriers and subsequent carrier injection redistribution among the optically active quantum wells (QWs) with different emission wavelengths. ICBLs are proved to be essential elements of multi-color LED active region design requiring optimization both in material composition and doping level. Strong interdependence between ICBL parameters and active QW characteristics presents additional challenge to multi-color LED design. Combination of several effects was crucial for adequate simulation of RGB LED color control features. Standard drift-diffusion transport model has been appended with rate equations for dynamic QW-confined carrier populations which appear severely off-balanced from corresponding mobile carrier subsystems. QW overshoot and Auger-assisted QW depopulation were also included into the carrier kinetic model thus enhancing the non-equilibrium character of QW confined populations and supporting the mobile carrier transport across the MQW active region. For device simulation we use COMSOL-based program suit developed at Ostendo Technologies Inc.