Single quantum dots embedded in tapered nanowire waveguides have emerged as leading candidates for designing high efficiency single-photon and entangled photon sources, with efficiencies exceeding 90%. Here we have developed a bottom-up growth approach that allows for independent control of boththe quantum dot size, and position, as well as the nanowire shape. Importantly, by design, the single quantum dot is always found perfectly on the nanowire axis. By integrating a gold mirror at the base of a tapered nanowire waveguide we obtain a 20-fold enhancement in the single-photon flux in comparison to no waveguide. The 20-fold enhancement is accompanied by a shortening of the exciton lifetime as the quantum emitter couples to the fundamental waveguide mode with an increased rate. Finally, the optical quality of the emitter is drastically improved by removing the nanowire stacking faults in the vicinity of the quantum dot. As a result, we demonstrate very pure single-photon emission with a probability of multi-photon emission below 1%, and an emission line width that is reduced by at least an order of magnitude (<30 μeV) as compared to when stacking faults were present in the nanowire (as high as 10-100 per micron). The demonstrated brightness of our single-photon source (42 % efficiency), combined with the very pure single photon emission and high spectral purity is encouraging in development of future quantum technologies based on nanowires, such as interfacing remote quantum bits or constructing a secure quantum network.

We discuss the highly-efficient on-chip transmission of quantum light from an integrated source. Under optical excitation, single photons emitted from a semiconductor quantum dot are injected into the propagating mode of a coupled photonic crystal waveguide. In such a system, slow-light effects induce Purcell enhancement of the coupled emitter increasing significantly the single-photon emission rates. Our system exhibits a single-photon emission rate into the propagating mode of 19 MHz with 23% efficiency. The high emission rates together with the coherence properties of the emitted single photons demonstrate the suitability of these systems for on-chip quantum information processing using quantum optical circuits.

Photonic wires have recently demonstrated very attractive assets in the field of high-efficiency single photon sources. After presenting the basics of spontaneous emission control in photonic wires, we compare the two possible tapering strategies that can be applied to their output end so as to tailor their radiation diagram in the far-field. We highlight the novel “photonic trumpet” geometry, which provides a clean Gaussian beam, and is much less sensitive to fabrication imperfections than the more common needle-like taper geometry. S4Ps based on a single QD in a PW with integrated bottom mirror and tapered tip display jointly a record-high efficiency (0.75±0.1 photon per pulse) and excellent single photon purity. Beyond single photon sources, photonic wires and trumpets appear as a very attractive resource for solid-state quantum optics experiments.

Increased differential gain is typically realized through strain, quantum confinement, or p-type doping in the active region. These methods have been applied to quantum dots or dashes to raise the differential gain with limited success because the optical gain of these low dimensional systems saturates at modest values. Instead larger differential gain can be accessed at wavelengths blue-shifted from the gain peak and close to optical transparency using the threshold shift induced by optical injection. Using these approaches, greater than 50X improvement in the differential gain has been achieved in an injection-locked QDash FP laser compared to its free-running value.

Taking into account the carrier dynamics in the wetting layer, excited state and the ground state, the intensity modulation properties of an injection-locked quantum dot laser are studied theoretically through a semi-analytical approach. It is demonstrated that both high carrier capture and relaxation rates enhance the modulation bandwidth as well as the resonance-peak amplitude. Moreover, the pre-resonance dip arising under positive detuning can be eliminated as well, which is beneficial for further bandwidth enhancement. It is also found that a large capture time reduces both the resonance frequency and the damping factor while both are increased by a large relaxation time.

A novel method for modulation bandwidth enhancement is presented, involving strongly injection-locked whistle-geometry semiconductor ring laser modulated through photon lifetime. Advantages of photon-lifetime modulation over conventional injection-current modulation are confirmed through numerical modeling.

The direct laser modulation bandwidth can be extended substantially by introducing a supplementary photon-photon resonance (PPR) at a higher frequency than the carrier-photon resonance (CPR). The paper presents a modified rate equation model that takes into account the PPR by treating the longitudinal confinement factor as a dynamic variable. The conditions required for obtaining a strong PPR and an enhancement of the small-signal modulation bandwidth are analyzed and experimental results confirming the model are presented. Since the small-signal modulation bandwidth may not be indicative of the large-signal modulation capability, particularly in case of a small-signal modulation response with substantial variations across the bandwidth, we have also analyzed the influence of the PPR-enhanced small-signal modulation response shape on the large-signal modulation capability as well as the methods that can be employed to flatten the small-signal modulation transfer function between the CPR and PPR.

In this paper, performance of monolithic quantum dot passively mode-locked lasers over broad temperature excursions is characterized. It is shown that there is a linear dependence between absorber to gain length ratio and the characteristic temperature that a device transitions from ground-state to excited-state lasing when the saturable absorber is grounded. The pulse shape and optical spectrum characteristics are examined in detail around these transition regimes. Experimental operational maps have also been constructed showing the range of biasing conditions that produce stable mode-locking across a wide range of temperatures. A comparison is made between regions of mode-locking stability for two devices having the same absorber to gain length ratio, with varying ridge waveguide widths. Finally, gain and absorption characteristics are derived from measurements of amplified spontaneous emission, and a correlation between reduced values of unsaturated absorption and reduced time-bandwidth product is shown. Key features in the experimental operational maps and their respective significance on the operation and design of future devices is discussed.

A nonlinear delay differential equation model for passive mode-locking in semiconductor lasers, seeded with parameters extracted from the gain and loss spectra of a quantum dot laser, is employed to simulate and study the dynamical regimes of mode-locked operation of the device. The model parameter ranges corresponding to these regimes are then mapped to externally-controllable parameters such as gain current and absorber bias voltage. Using this approach, a map indicating the approximate regions corresponding to fundamental and harmonically mode locked operation is constructed as a function of gain current and absorber bias voltage. This is shown to be a highly useful method of getting a sense of the highest repetition rates achievable in principle with a simple, two-section device, and provides a guideline toward achieving higher repetition rates by simply adjusting external biasing conditions instantaneously while the device is in operation, as opposed to re-engineering the device with additional passive or saturable absorber sections. The general approach could potentially aid the development of numerical modeling techniques aimed at providing a systematic guideline geared toward developing microwave and RF photonic sources for THz applications.

Passively mode-locked fiber laser (MLFL) has been widely used in many applications, such as optical communication system, industrial production, information processing, laser weapons and medical equipment. And many efforts have been done for obtaining lasers with small size, simple structure and shorter pulses. In recent years, nonlinear polarization rotation (NPR) in semiconductor optical amplifier (SOA) has been studied and applied as a mode-locking mechanism. This kind of passively MLFL has faster operating speed and makes it easier to realize all-optical integration. In this paper, we had a thorough analysis of NPR effect in SOA. And we explained the principle of mode-locking by SOA and set up a numerical model for this mode-locking process. Besides we conducted a Matlab simulation of the mode-locking mechanism. We also analyzed results under different working conditions and several features of this mode-locking process are presented. Our simulation shows that: Firstly, initial pulse with the peak power exceeding certain threshold may be amplified and compressed, and stable mode-locking may be established. After about 25 round-trips, stable mode-locked pulse can be obtained which has peak power of 850mW and pulse-width of 780fs.Secondly, when the initial pulse-width is greater, narrowing process of pulse is sharper and it needs more round-trips to be stable. Lastly, the bias currents of SOA affect obviously the shape of mode-locked pulse and the mode-locked pulse with high peak power and narrow width can be obtained through adjusting reasonably the bias currents of SOA.

High efficiency dynamic holography at 1.55 microns is achieved on a broad-area InP based multiple quantum well devices. The quantum well cavity is sandwiched between a DBR and amorphous mirror, and consists of a number of wells. High energy pulsed writing beams at 1.06 microns generate free carrier gratings which are probed by a 1.55 micron tunable laser in a four wave mixing configuration. Diffraction efficiency into a single order of 30% has been achieved by contribution of a phase grating, mode pulling and asymmetric Fabry-Perot reflection.

One focus of the current research on light emitting diodes (LEDs) for lighting are nano structured devices which are expected to improve the efficiency and reduce the production costs. Structuring on the sub-micrometer scale increases the surface area with respect to the active volume so that surface effects have a large impact on the device performance. The physics of these devices is not fully transparent to characterization making an experimental analysis tedious. In this work we demonstrate the computational modelling of nano structured LEDs to complement the experiment. The implementation of the simulation model considers surface effects using a numerically accurate true area box method discretization. The derived surface models are applied to the self-consistent simulation of nano wire quantum disk light emitting diodes. By the computational study we demonstrate that the surface physical effects are critical for the performance of nano structured optoelectronic devices and that a low efficiency may be fully attributed to surface recombination.

The growing importance of In_0:18Al_0:82N stems from the fact that it can be grown lattice matched to GaN and for its potential applications in a large number of electronics and optoelectronics devices. In this work we employed a full band Monte-Carlo approach to study the carrier transport properties of this alloy. We have computed the temperature and doping dependent electron and hole mobilities and drift velocities. Furthermore, for both sets of transport coefficients we have developed a number of analytical expressions that can be easily incorporated in drift-diffusion type simulation codes.

Today’s advanced technology allows engineers to fabricate GaN LEDs with various heights, widths, shapes, and materials. Total internal reflection is a key factor in GaN LED design, because all light that is created inside the LED is lost unless it approaches the chip to air interface at an angle less than 23.58° with respect to the normal. The narrow range of angles at which light can successfully escape the chip is a result of the large difference in refractive indices between GaN and air. Adding a layer of ITO to the GaN reduces the difference in refractive indices between steps and increases the critical angle to 28.4°. Transmitting from ITO into epoxy reduces this difference in refractive indices again, bringing the critical angle to 47.9°. Because a higher critical angle should allow more light to escape the LED, we focus on enhancing light extraction efficiency of GaN LED's that utilize an ITO to epoxy interface using FDTD simulations. The simulation results show us that increasing the critical angle to 47.9° improves light extraction by 40%, proving that the critical angle does play a significant role in light extraction. From this initial result, we then compare light extraction efficiencies of ITO and GaN gratings over varied grating periods, and show that adding an Ag reflection layer improves overall efficiency. Finally, we show that the light extraction for LED's utilizing an Ag reflection layer is highly dependent on the sapphire substrate thickness.

Mie theory describes the scattering of electromagnetic waves on spheroidal particles whose diameter is comparable to the wavelength of the incident radiation. We have implemented a parallel algorithm using graphics adapters to calculate perpendicular and parallel polarized scattered waves, from which other scattering parameters can be derived. This facilitates parallel propagation of monochromatic electromagnetic waves in scattering media. We have shown that a parallelization can reduce computation time rigorously.

Internal back-and-forth propagation of photons within a light emitting diode (LED) will naturally tend towards a Lambertian intensity profile when surface texturing is sufficiently rough. Novel designs in light extraction efficiency (LEE) can therefore benefit by optimizing under this expectation. This paper develops a framework for calculating LEE from a planar LED structure with textured surface features under the assumption of Lambertian intensity within the substrate. The method can estimate the total LEE value when given a substrate width w, an attenuation constant α, and the transmittance function T(θ,Φ) through the top interface. We demonstrate our theory on a pyramidal surface texture over a GaSb substrate at 4.5 μm wavelength by computing the expected LEE as a function of w.

We discuss a novel finite element method-based technique for estimating accurate sensitivities of the desired response. Our technique utilizes the central adjoint variable method (CAVM) for estimating the response sensitivities. This approach features accuracy comparable to that of the central finite difference (CFD) approximation at the response level. Our approach uses a simple perturbation method to calculate the sensitivity of modal parameters of various waveguide structures with respect to the geometric and material parameters. No additional simulation is required to calculate the response and its sensitivity with respect to all the design parameters. The accuracy of our approach is illustrated by comparing the results with the second order accurate CFD applied on the response level. Our results show a very good agreement between the CAVM-based sensitivities and those obtained using the expensive central.

Conditions for obtaining slow/fast and backscattered light via nonlinear wave interactions in semiconductor lasers are investigated using numerical modeling of interacting waves. Feasibility of superluminal propagation induced by a strong driving wave is discussed.

Surface plasmons (SPs) have recently gained substantial attention due to their sub-wavelength localization and strong interactions in the near-field. Their unique properties are expected to be essential for the next-generation photonic nanodevices, for instance, to improve light extraction in light-emitting diodes (LEDs). We discuss and develop a rigorous and transparent method to model luminescence enhancement and absorption in grated multilayer structures. The method is based on Green's functions, obtained as a perturbative solution to Maxwell's equations, and the fluctuational electrodynamics description of the structures. The model provides an analytical alternative to numerical methods such as finite-element methods and gives insight beyond the numerical solutions, offering a direct means of studying emission and luminescence from the periodic structures. The model is applied to answer key fundamental questions regarding luminescence enhancement, absorption and reflection in realistic plasmonic GaN light-emitting diode (LED) structures. Two aspects are considered in particular: (1) modeling the reflectometry measurements of grated LED structures to explain and map the interference patterns observed experimentally by our collaborators, and (2) modeling the enhancement in plasmonic structures where the emission takes place in quantum wells in the vicinity of the metallic grating. The results clearly reveal e.g. the SP-related luminescence enhancement in InGaN quantum well structures incorporating periodic silver grating.

We propose an adjoint variable method (AVM) for efficient wideband sensitivity analysis of the dispersive plasmonic structures. Transmission Line Modeling (TLM) is exploited for calculation of the structure sensitivities. The theory is developed for general dispersive materials modeled by Drude or Lorentz model. Utilizing the dispersive AVM, sensitivities are calculated with respect to all the designable parameters regardless of their number using at most one extra simulation. This is significantly more efficient than the regular finite difference approaches whose computational overhead scales linearly with the number of design parameters. A Z-domain formulation is utilized to allow for the extension of the theory to a general material model. The theory has been successfully applied to a structure with teethshaped plasmonic resonator. The design variables are the shape parameters (widths and thicknesses) of these teeth. The results are compared to the accurate yet expensive finite difference approach and good agreement is achieved.

We propose two distinctive designs of metamaterials demonstrating antireflective properties in the optical and near infrared region and, simultaneously, a high reflectivity in the mid-infrared. Since the emissivity is related to the absorption of a material, our structures would then offer a high emissivity in the visible and near infrared. Beyond those wavelengths, the emissivity would be quite low. Usually, such systems find their applications in the field of thermophotovoltaics, where the goal is to convert radiation from the visible up to 2.5 microns into electrons, while limiting the emissivity for the larger wavelengths. A particular interest in the field of optoelectronics is found as well, especially for optical detection. Here, the major difficulty is to offer a metal thick enough to be considered as mirror across the electromagnetic radiation spectrum that possesses at the same time an anti-reflective character within a range of several microns. Thus, we have summoned the exceptional physical properties of the material patterning. Numerical analysis has been performed on commonly used metamaterial designs: a perforated metallic plate and a metallic cross grating. Through all these structures, we have demonstrated the various physical phenomena contributing to a reduction in the reflectivity in the optical and near infrared region. By showing realistic geometric parameters, the structures were not only designed to demonstrate a good optical response but were also meant to be feasible on large surfaces by lithographic methods such as micro contact printing or nano-imprint lithography.

Achieving a broadband antireflection property from material surfaces is one of the highest priorities for those who want to improve the efficiency of solar cells or the sensitivity of photo-detectors. To lower the reflectance of a surface, we have decided to study the optical response of a top-flat cone shaped silicon grating, based on previous work exploring pyramid gratings.

Through rigorous numerical methods, such as Finite Different Time Domain or Rigorous Coupled-Wave Analysis, we then designed several structures theoretically demonstrating an antireflective character within the middle infrared region. From the opto-geometrical parameters such as period, depth and shape of the pattern determined by numerical analysis, these structures have been fabricated using controlled slope plasma etching processes. Afterwards, optical characterizations of several samples were carried out. The reflectance of the grating in the near and middle infrared domains has been measured by Fourier Transform Infrared spectrometry and a comparison with numerical analysis has been made.

As expected, those structures offer a fair antireflective character in the region of interest. Further numerical investigations led to the fact that patterning the top of the cone could enlarge the antireflective domain to the visible region. Thus, as with the simple cone grating, a comparison of the numerical analysis with the experimental measurements is made. Finally, diffracted orders are studied and compared between both structures. Those orders are critical and must be limited as one wants to avoid crosstalk phenomena in imaging systems.

Surface Plasmon Resonance (SPR) is a wave phenomenon occurring at an interface between a dielectric and a metal. SPR has applications in label-free biodetection systems, where advances in microfabrication techniques are fostering the development of SPR-based labs-on-a-chip. This work presents a numerical analysis for the excitation of SPR using Kretschmann's configuration. With a SiO₂ prism, an Au metal layer, and water as the dielectric, the system is made to be compatible with a post-CMOS microfabrication process. The results obtained from both theory and software simulation show that for a light source at 633 nm, a 50 nm thick Au film is optimal, with the reflectivity falling to a minimum of ~2% at an angle of ~68.5°, due to maximum electromagnetic SPR coupling. Simulations with a Ti adhesion layer were also performed, showing a negative effect by increasing to ~17% the minimum reflectivity when SPR is achieved, thus reducing the dynamic range of the signal captured by the system's photodetector. SPR biosensors work by monitoring changes on the refractive index close to the SPR interface, these changes were simulated showing that a change of ~10^-4 RIU on the dielectric medium produces a ~0.01°change in the SPR angle. These results will facilitate the physical implementation of label-free biosensing platforms with a CMOS image sensor (CIS) photodetection stage.

We model conduction and free-carrier injection in laterally doped GaAs p-i-n diodes formed in one and twodimensional photonic crystal (PC) nanocavities. Finite element simulations show that the lateral geometry exhibits high electrical conductivity for a wide range of PC parameters and allows for precise control over current flow, enabling efficient carrier injection despite fast surface recombination. Thermal simulations indicate that the temperature increase during steady-state operation is only 3.3K in nanobeams and 0.29K in L3 defect nanocavities. The results affirm the suitability of lateral doping in PC devices and indicate criteria for further design optimization.

The semiconductor micropillar is attractive for cavity QED experiments. For strong coupling, the figure of merit is proportional to Q/√V, and a design combining a high Q and a low mode volume V is thus desired. However, for the standard submicron diameter design, poor mode matching between the cavity and the DBR Bloch mode limits the Q. We present a novel adiabatic design where Bloch-wave engineering is employed to improve the mode matching, allowing the demonstration of a record-high vacuum Rabi splitting of 85 μeV and a Q of 13600 for a 850 nm diameter micropillar.

Efficient coupling between a localized quantum emitter and a well defined optical channel represents a powerful route to realize single-photon sources and spin-photon interfaces. The tailored fiber-like photonic nanowire embedding a single quantum dot has recently demonstrated an appealing potential. However, the device requires a delicate, sharp needle-like taper with performance sensitive to minute geometrical details. To overcome this limitation we demonstrate the photonic trumpet, exploiting an opposite tapering strategy. The trumpet features a strongly Gaussian far-field emission. A first implementation of this strategy has lead to an ultra-bright single-photon source with a first-lens external efficiency of 0.75 ± 0.1 and a predicted coupling to a Gaussian beam of 0.61 ± 0.08.

High-power broad-area laser diodes often suffer from a widening of the lateral far-field with rising current injection. This effect is also referred to as thermal blooming, since self-heating is considered the main cause. The non-uniform temperature profile inside the waveguide leads to a lateral refractive index profile that enhances the index guiding of laser modes (thermal lens). This paper presents a self-consistent electro-thermal-optical simulation and analysis of the thermal blooming effect, including the non-uniform heat power distribution inside the laser as well as the non-uniform carrier and gain distributions inside the quantum wells. The calculated results are in good agreement with measurements. The simulations demonstrate that thermal blooming is not only caused by the rising order of lateral modes but also by the far field widening of each individual mode with increasing current.

A time-domain traveling wave algorithm is extended to investigate high-order quantum dot based laterally-coupled distributed feedback semiconductor lasers. The effect of radiation modes in laser performance is included via Streifer’s terms. We calculate the optical gain spectra based on a coupled set of rate equations and taking into account both inhomogeneous broadening due to dot size fluctuation and homogeneous broadening due to polarization dephasing. It was found that, for third-order quantum dot based laterally-coupled distributed feedback lasers; a stable single mode operation with high SMSR can be achieved by means of fine tuning of the grating duty cycle

A ridge-waveguide 1.55-μm semiconductor laser with a multiple-quantum-well carrier confinement structure was characterized from room temperature down to 10 K. The temperature dependence of important laser parameters, such as threshold current, series resistance, differential efficiency, and emission wavelength, extracted from standard L-I/I-V measurements, is reported. The applicability of the standard ideal-diode model of semiconductor laser at cryogenic temperatures is analyzed.

We report a first experimental observation of two-wavelength switching (2WS) and bistability with a 1310nm-Quantum Dot (QDot) Distributed Feedback (DFB) laser subject to external optical injection and operated in reflection. We experimentally demonstrate the switching of the emission wavelength of the QDot laser when an external optical signal is injected into one of the subsidiary longitudinally modes located in the longer wavelength side of the device’s lasing mode. Clockwise nonlinear switching and bistability are attained in all cases for both the emitting and the injected mode of the QDot laser as the injection strength is increased. Moreover, very high on-off contrast ratio is measured in the switching (and bistability) transition of the emission mode of the device. We have also analysed the switching properties of the 1310-QDot DFB laser as a function of the applied bias current and the initial wavelength detuning between the wavelengths of the external signal and that of the device’s injected mode. In general, wider bistable loops, higher on-off contrast ratio between output states and higher input power requirements for switching are observed as the applied bias and initial detuning are increased. This diversity of switching behaviors obtained with a 1310 QDot DFB laser under external optical injection, added to the theoretically superior properties of nanostructure lasers, offers exciting prospects for novel uses of these devices in all-optical logic and all-optical switching/routing applications in present and future optical telecommunication networks.

A predictive approach using 3D full-wave optical and electronic modeling of an organic bulk-heterojunction photovoltaic device (P3HT:PCBM) is presented. The optical part is modeled by solving 3D frequency domain Maxwells equations such that the scattering of subwavelength nanostructures can be modeled accurately. The electronic simulation which consists of solving the rate equations to account for the generation and recombination of polarons or charges, and the flow of electrons and holes are assumed to be drift-diffusion in nature. Here, nanoparticles with subwavelength sizes are added to the P3HT:PCBM photovoltaic device and the current-voltage behavior is predicted by the model.

The paper presents the optical power absorption simulation in a silicon solar cell utilizing single and double diffraction gratings at varying locations (depths) within the device. The solar cell under discussion consists of a rectangular top grating, P-type Si, N-type Si, a rectangular bottom grating, and a reflective material on the bottom. We use 3D finite differential time domain (FDTD) simulations to calculate the power at the solar cell PN interface at wavelengths ranging from 300nm to 1100nm. Throughout simulation, the structure of the gratings remains unchanged – only its location within the device varies, which is accomplished by varying the thickness of the P and N regions. The spectrum of incident solar light and the photo-responsivity of silicon are also took into account to obtain a total weighted power factor, allowing comparison between all simulated cases. We find an increase in weighted power absorption (compared to the non-grating case) ranging from 42% to 72% across all simulated grating locations. Overall, our simulations show that varying the location of the grating(s) changes the amount of power absorbed, and that certain device thicknesses correspond to increased power absorption and are preferred in the design.

In this paper, we have designed and optimized the metallic nano-structures on a conventional surface plasmon resonance (SPR) sensor which induce the localized surface plasmon resonance for an improved sensitivity. Designed SPR sensor was simulated with 3D Finite-difference time-domain method. The sensitivity is maximized to 130.9 degree/RIU when the thickness of film layer T_F is 30 nm while that of a conventional SPR sensor is less than 99.6 degree/RIU, and the reflectivity is minimized when T_F is 25 nm. The most appropriated diameter of particles is about 35 nm for high sensitivity.

The concentrated local electric field on a substrate surface is very helpful to enhance the signal for surface-enhanced Raman scattering (SERS) and surface plasmon resonance (SPR) techniques. In this research, the metallic nano-cylinder, the nano-hole, and nano-annular aperture structures on the glass have been simulated by the finite difference time domain method (FDTD) first to understand the localized surface plasmon resonance (LSP) of them. The simulations for different inner diameters, outer diameters and thickness of the gold film have been done and the better dimension and film thickness which can induce the largest electric field concentration have been chosen. We coated 2 nm and 5 nm thick chromium(Cr), and 50nm and 60nm thick gold(Au) films on SF2 glass substrate, respectively. The different nanoannular aperture structures were successfully patterned on them by using focus ion beam (FIB) to etching gold film surface. Using the OB Morph measurement to observe the structure caused by the SPR shifted. The transmission spectrometer has been adapted to measurement the substrate to observe the spectrum of them. Different concentrations of sodium chloride(NaCl) solutions also have been measured on the different substrates, and the shift of the transmission light wave peak was detected.

In the past, Faraday based optical polarimetry approaches have shown considerable potential for the measurement of optical activity with application towards the noninvasive measurement of physiological glucose concentration. To date, most reported closed-loop systems incorporate separate Faraday components for modulation and compensation requiring two optical crystals. These systems have demonstrated significant stability and sub-millidegree rotational sensitivities; however, the main drawbacks to this approach are the optical materials (e.g., terbium gallium garnet) can be quite expensive and often custom fabricated induction coils are required. In this investigation, we propose a new design for the Faraday components capable of achieving both modulation and compensation in a single crystal device. The design is more compact and is capable of achieving similar performance with low cost commercially available inductive components. To facilitate prototype optimization, our group has developed a finite element model (FEM) that can simulate various physical parameters such as geometry, inductance, and orientation with respect to the optical rod in order to minimize power consumption and size while maintaining appropriate field strength. Performance is comparable to existing nonintegrated approaches and is capable of achieving modulation depths < 1° under similar operating conditions while attaining sub-millidegree linear polarization sensitivity. There is also excellent correlation between the FEM and experimental prototype with operational performance shown to be within 1.8%. The use of FEM simulations allows for the analysis of a vast range of parameters before prototypes are fabricated and can facilitate custom designs as related to development time, anticipated performance, and cost reduction.

This research numerically calculated the optical absorption of gold nanoparticles (AuNP) in the presence of metallic (Au) and dielectric (Si) AFM probes, illuminated by a surface plasmon polaritons on an infinite gold substrate. Nanoscale probes localize and enhance the field between the apex of the tip and the particle. However, the absorption of the nanoparticle is not always enhanced; in fact, under a gold tip, the absorption is suppressed for a 50 nm diameter AuNP. After fitting the numerical absorption data with the equation of a driven damped harmonic oscillator (HO), it was found that the AFM tip modifies both the driving force (F₀), consisting of the free carrier charge (q) and the driving field (E), and the overall damping of the oscillator (β). The enhancement or suppression of absorption with different tips can be understood in terms of competition between β and F₀. Introducing the metallic tip increases β and decreases F₀, resulting in reduced absorption. Introducing the dielectric tip, although it increases β, it also increases F₀, resulting in overall absorption enhancement. Therefore, one most consider both β and F₀ to control the absorption of nanoparticles under Surface Plasmon Polaritons.

The theory of pure-collision and phonon-assisted Auger recombination mechanisms in bulk InGaN alloys is reviewed. The model is based on a Green function formalism and uses realistic electronic structures obtained by nonlocal empirical pseudopotential calculations and phonon spectral density functions determined from first-principles lattice dynamical cal- culations. The effect of phonons is formally included to the infinite order of perturbation theory by means of the spectral density function which contains summation over all possible phonon momenta. Auger transitions in quantum wells may significantly differ from their bulk counterpart since momentum conservations is lifted along the confining direction. A preliminary analysis indicate that direct Auger transitions in confined structures exhibit an enhancement with respect to the bulk case. The analysis is based on a full-zone description of the electronic structure in which confined and unbound states are represented as a superposition of bulk states of the underlying lattice, thus allowing a fair comparison between Auger coefficients in bulk and quantum wells.

We model carrier-density-dependent radiative and non-radiative recombination rates in an InGaN/GaN quantum well structure containing a V-pit and a threading dislocation. It is known that the threading dislocation acts as the nonradiative recombination center, leading to the reduction of carriers which can participate in the radiative recombination. On the other hand, the quantum well structure grown on the sidewalls of V-pit, formed by the strain relying on In/Ga contents and connected with threading dislocation directed along the polar direction, plays a role of energy barriers to prevent quantum well in-plane charge carriers from flowing to the non-radiative recombination center, i.e., the threading dislocation. Therefore, such V-pits can enhance the internal quantum efficiency in the InGaN/GaN quantum well light emitting diode (LED). However, the explicit model of the V-pit and the threading dislocation coupled to three dimensional electronic states has rarely been studied. We take into account those defects by including their potentials in a system Hamiltonian. It can describe the electronic states of in-plane quantum well, in which a V-pit and a threading dislocation are positioned. Here we show that charged carriers are more distributed away from the threading dislocation by having the V-pit, and it leads to the reduction of carrier losses to the non-radiative recombination and hence the enhancement of radiative recombination rate. Their effects on the recombination rates depend on injected carrier densities. We also discuss mid-gap defect states, which may be generated due to the threading dislocation and the V-pit.

Gallium nitride based light emitting diodes (LEDs) have established as powerful devices, that are well suited for general lighting. Despite the progress within the recent years the so-called “efficiency droop” is still a central issue of nitride-based LED research. Up to now, no widely accepted explanation is available for the reduction of the internal quantum efficiency with increasing injection current. We report on a novel mechanism contributing to efficiency droop, that combines two of the previously reported effects: Auger recombination and carrier leakage. A sophisticated Auger model, that takes account of the overlap of the wave functions, is extended to model the energy transfer towards the third involved carrier. This carrier is assumed to be expelled from the well and regenerated in the continuum carrier population, where it can contribute to carrier leakage. A physics-based simulation of a quantum well LED employing a semi-classical approach has been carried out to demonstrate the impact of this effect. Depending on the parametrization, the inclusion of Auger expulsion reduces the Auger coefficient up to 50% when compared to a standard Auger model, which could explain the discrepancy between calculated and experimentally extracted Auger coefficients.

We study a hybrid silicon organic high speed electro-optic phase shifter based on polymer infiltrated P-S-N (“S” refers to the slot) diode capacitor structure. This optical phase shift is realized based on index perturbation both inside the slot via Pockels nonlinearity and within the silicon ridges via the free carrier effect (carrier depletion). The combination of the polymer diode capacitor configuration with the low aspect ratio slot waveguide system leads to a promising method of constructing sub-THz speed optical modulators without sacrificing either modulation efficiency or energy consumption. By optimizing the waveguide geometry in terms of balancing effective index shift and device speed, at least 269 GHz bandwidth can be achieved with a high modulation efficiency of 5.5 V-cm when the diode capacitor is reverse biased by an external radio frequency (RF) voltage signal between the electrodes (optical propagation loss is acceptably low at 4.29 dB).

In recent years, emerging applications, such as diffuse optical imaging and spectroscopy (e.g., functional brain imaging and optical mammography), in which a wide dynamic range is crucial, have turned the interest towards Single-Photon Avalanche Diode (SPAD). In these fields, the use of a fast-gated SPAD has proven to be a successful technique to increase the measurement sensitivity of different orders of magnitude. However, an unknown background noise has been observed at high illumination during the gate-OFF time, thus setting a limit to the maximum increase of the dynamic range. In this paper we describe this noise in thin-junction silicon single-photon avalanche diode when a large amount of photons reaches the gated detector during the OFF time preceding the enabling time. This memory effect increases the background noise with respect to primary dark count rate similarly to a classical afterpulsing process, but differently it is not related to a previous avalanche ignition in the detector. We discovered that memory effect increases linearly with the power of light impinging on the detector and it has an exponential trend with time constants far different from those of afterpulsing and independently of the bias voltage applied to the junction. For these reasons, the memory effect is not due to the same trapping states of afterpulsing and must be described as a different process.

Optical and electronic devices for optoelectronic integrated circuits have been extensively studied, and now, more efforts for the conversion between optical and electrical signals are accordingly required. In this work, a silicon (Si)-compatible optically drivable III-V-on-Si metal-oxide-semiconductor field-effect transistor (MOSFET) is studied by simulation. The proposed optoelectronic device provides a strong interface between the optical and the electronic platforms as a key component of the optical interconnect. The optically driven MOSFET device is analogously analyzed into a photodetector and its complementary device, getting rid of receiver circuitry, which improves the integration density and simplifies the fabrication processes. To realize the optical switching with maximized photo-sensing region, a bottom gate is formed to modulate the channel, where germanium (Ge) and gallium arsenide (GaAs) are the active materials on Si platform. Both direct-current (DC) and alternating-current (AC) performances of an optimized device are evaluated.

The intensity modulation (IM) property of an optical injection-locked quantum cascade (QC) laser is theoretically investigated via a three-level rate equation model. The locking regime is obtained based on the local bifurcation theory. It is shown that the injection-locked QC laser exhibits a rather flat modulation response at zero detuning, whose bandwidth increases with the injection level. In contrast to interband lasers, both positive and negative detunings enhance the modulation bandwidth. Besides, a large linewidth enhancement factor (LEF) can increase the peak amplitude in the response. Moreover, it is found that no frequency dip occurs in the IM response of injection-locked QC lasers.

Accurate, reliable and fast numerical modeling methods are required to design the optimum radial refractive index profile for single and multimode fibers to give specific dispersion characteristics prior to or even obviating costly experimental work. Such profiles include graded index and multiple concentric cladding layers. In this paper, a new numerical method is introduced which enables the derivatives of the propagation coefficient to be calculated analytically up to the third order of a single mode or multimode weakly guiding optical fiber with an arbitrary radial refractive index profile. These quantities are required to determine the group delay, τ_g, chromatic dispersion, D, and dispersion slope of the fiber. The expansion of the modal fields in terms of Laguerre-Gauss polynomials in the Galerkin method offers certain benefits. In particular, due to simplicity of the basis functions it is possible to carry out further analytical work on the results such as repeated differentiation of the matrix equation resulting from the Galerkin method to define up to the third-order derivatives of the propagation coefficients with respect to wavelength. This avoids approximation errors inherent in numerical differentiation, giving better accuracy and, at the same time, significantly reduces the computation time. A computer program was developed to demonstrate the proposed method for single and multimode fibers with radially arbitrary refractive index profiles. The paper provides simulation results to validate the approach.

Prestressed concrete structure is getting more and more extensive application in architecture, hydraulic engineering and traffic engineering because of its significant advantages of crack later or not cracks completely. It is an internal stress concrete structure that a certain force relies on prestressing tendons. The effectivity of the prestressing tendon in concrete structure is directly related to the reliability, applicability and viability of the whole concrete structure. So it is a key program to apply accurate prestress to the prestressing tendon. According to the pressure sensing principle of the fiber Bragg grating (FBG), a circular plate diaphragm-based FBG sensor for high pressure electric oil pumps that is the pressure source device of the prestressed concrete structure was presented. To overcome the cross sensitivity of temperature and pressure, two FBGs were integrated in the sensor, one of the FBGs isolated from the pressure is used as temperature compensation grating, it is called temperature-FBG comparing to another FBG called pressure-FBG. The elastic diaphragm was chosen as the pressure sensing element whose distortion displace is proportional to the difference of the two sides’ pressure of the diaphragm. A certain stress is applied to the pressure-FBG which is stuck to the center of the diaphragm, and then the reflection wavelength of the pressure-FBG is inverse proportional to load of the diaphragm. The results indicated that the linearity is up to 99.99%, and the pressure sensitivity coefficient is 0.024nm/MPa within the measurement scope of 0-70MPa.

A polarization splitter (PS) based on a directional coupler (DC) composed of vertical multiple-slotted waveguide (MSW) and silicon nanowire is proposed and designed by using a modified three-dimensional full-vectorial beam propagation method (BPM). By utilizing the unique modal properties of the slot waveguide, the coupling of the DC in quasi-TE modes can be almost neglected, and only that in quasi-TM is considered, leading to a compact PS. Moreover, the MSW has the advantages of both strong field confinement and high birefringence, which improves the performance of the present device. The numerical results show that a PS with a length of 20.5μμm in the coupling region is achieved whose bandwidth is up to 22nm (ranged from 1.540 to 1.562μm) with the crosstalk lower than -20dB. In addition, the fabrication tolerances to the structural parameters are investigated in detail. And the evolution of the injected field along the propagation distance through the PS is also demonstrated.

In this study, the polarization effect in III-nitride based ultraviolet (UV) light-emitting diodes (LEDs) has been investigated theoretically. Some specific designs in active region are proposed to reduce the polarization effect and, hence, improve the device performance. Simulation results show that by utilizing properly designed quaternary AlInGaN material in active region, the hole injection efficiency can be enhanced due to the reduction of polarization mismatch between hetero-layers. On the other hand, the electron leakage is suppressed owing to that the effective potential height for electrons is increased. Therefore, the performance of UV LEDs is significantly improved by the polarization engineering in active region.

The authors propose a type of plasmonic ring laser which has the footprint smaller than previous published devices, showing the potential to be a single-mode ultra-compact light source. In this structure, CdS gain medium and Ag substrate are separated by an ultrathin MgF₂ layer. The short distance between high-index CdS material and silver makes photonic modes of CdS ring hybridize with surface plasmon plaritons (SPPs) of the Ag-MgF₂ interface, which leads to strong light confinement in this thin MgF₂ gap region. The surface plasmons of this structure carry high momentum, which leads to strong feedback at the ring boundary by total internal reflection forming whispering gallery like mode. Finite difference time domain (FDTD) method is used to calculate and optimize the plasmonic ring geometry. With a 15 nm thick MgF₂ layer, the ring’s outer and inner radius can be shrunk to 290 nm and 170 nm with quality factors of 70 at the resonant wavelength of 514 nm. We fix ring width and reduce MgF₂ thickness and ring radius to get better confinement. When MgF₂ thickness is 5 nm, the outer and inner radius are set as 310 nm and 190 nm respectively, Q factors can reach 93. Free spectral range (FSR) of the ring is around 45 nm, which shows a good ability to generate single mode signal during a large wavelength range. The circled and confined optical fields can significantly enhance light-matter interactions and getting high Purcell factors.

Several methods exist for modeling the Fresnel reflectance arising from arbitrary refractive index profiles. In many cases, the calculation can be done analytically; however, a numerical method must be employed for more complicated scenarios. The transmission matrix is an analytic method which is well suited for modeling reflection at abrupt interfaces. In this work, we develop a numerical approach, relying on the transmission matrix method, which can properly model the reflection and transmission properties of a continuously varying index profile. This approach has been applied to high power semiconductor lasers by modeling the built-in distributed feedback arising from the continuously mismatched wave impedance along the cavity length caused by a non-uniform temperature profile.

A novel polarization rotator with asymmetric optical waveguide based on plasmonics is proposed and analyzed for the first time. The polarization rotator using skewing effects at the slotted optical waveguide (SOW) with metal film was designed by 3D-FDTD method. A metal film on the waveguide acts to rapidly rotate the optical polarization, because the plasmonic characteristics of a metal film can induce the slow group velocity through the metal-clad optical waveguide. Here, the optical waveguide with a buffer layer is proposed to reduce the propagation loss. The polarization rotator length of 6 μm is among the shortest reported in the waveguide-type polarization rotators. The polarization conversion efficiency of 98.93 % is observed near 1550 nm along with a propagation loss of -0.43 dB. The proposed structure is smaller than previous polarization rotator with asymmetric optical waveguide and is more effective to control polarizations using by plasmonic effects.

Cavity length vs. inverse of slope efficiency technique is most widely used to extract the injection efficiency in semiconductor lasers which assumes that all the carriers occupy single energy level in the laser active region. However, QD lasers contain multiple higher lying energy levels in addition to the ground level and have significant carrier capture times which results in the occupation of these higher energy levels. In addition to the multiple energy levels, the density of states of each energy level is inhomogeneously broadened, which leads to the broadening of the gain spectrum as a whole. Inhomogeneous broadening is a result of the random size distribution of QDs grown by the self-assembled growth technique. In this work, we present the results of an above threshold multi-level rate equation model developed to understand the effect of inhomogeneous broadening on the measured low injection efficiencies of InAs-InGaAs based quantum-dot (QD) lasers operating at 1.3 μm.

In this note we extend the Differential Transfer Matrix Method (DTMM) for a second-order linear ordinary differential equation to the complex plane. This is achieved by separation of real and imaginary parts, and then forming a system of equations having a rank twice the size of the real-valued problem. The method discussed in this paper also successfully removes the problem of dealing with essential singularities, which was present in the earlier formulations. Then we simplify the result for real-valued problems and obtain a new set of basis functions, which may be used instead of the WKB solutions. These basis functions not only satisfy the initial conditions perfectly, but also, may approach the turning points without the divergent behavior, which is observed in WKB solutions. Finally, an analytical transformation in the form of a matrix exponential is presented for improving the accuracy of solutions.