This PDF file contains the front matter associated with SPIE Proceedings Volume 8980 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

Performance of III-N based solid-state lighting is to a large extent limited by current transport effects that are also expected to contribute to the efficiency droop in real devices. To enable studying the contributions of electron transport in drooping more accurately, we develop and study a coupled Monte Carlo–drift-diffusion (MCDD) method to model the details of electron current transport in III-N optoelectronic devices. In the MCDD method, electron and hole distributions are first simulated by solving the standard drift-diffusion (DD) equations. The hole density and recombination rate density obtained from solving the DD equations are used as inputs in the Monte Carlo (MC) simulation of the electron system. The MC simulation involves solving the Boltzmann transport equation for the electron gas to accurately describe electron transport. As a hybrid of the DD and MC methods, the MCDD represents a first-order correction for electron transport in III-N LEDs as compared to DD, predicting a significant hot electron population in the simulated multi-quantum well (MQW) LED device at strong injection.

Optical splitters are one of the fundamental and most necessary components in modern photonic devices. They are used for splitting, coupling and monitoring photonic systems. So far, most splitters were fabricated based on evanescent field coupling or Y-branch dividers for which high precision lithography alignment is needed. In this work, we have proposed a new type of splitter which works based on multimode bend loss and mode mismatch coupling. Since this device has a novel suspended multimode region, it could be functionalized to detect any type of molecule binding to the surface. We have developed a 3D FDTD model to simulate the device’s behavior. One of the most interesting features of this device is that they have a broadband response and the coupling ratio doesn’t change by wavelength and is constant. The main idea behind coupling mechanism in this splitter is the existence of a protrusion region in which the mode conversion occurs.

We propose a design methodology for systematic design of surface relief transmission gratings with optimized diffraction efficiency. The methodology is based on a gradient-based topology optimization formulation along with 2D frequency domain finite element simulations for TE and TM polarized plane waves. The goal of the optimization is to find a grating design that maximizes diffraction efficiency for the -1^st transmission order when illuminated by unpolarized plane waves. Results indicate that a surface relief transmission grating can be designed with a diffraction efficiency of more than 40% in a broadband range going from the ultraviolet region, through the visible region and into the near-infrared region.

In many experimentally realized applications, e.g. photonic crystals, solar cells and light-emitting diodes, nanophotonic systems are coupled to a thick substrate layer, which in certain cases has to be included as a part of the optical system. The finite element method (FEM) yields rigorous, high accuracy solutions of full 3D vectorial Maxwell's equations¹ and allows for great flexibility and accuracy in the geometrical modelling. Time-harmonic FEM solvers have been combined with Fourier methods in domain decomposition algorithms to compute coherent solutions of these coupled system.^{2, 3} The basic idea of a domain decomposition approach lies in a decomposition of the domain into smaller subdomains, separate calculations of the solutions and coupling of these solutions on adjacent subdomains. In experiments light sources are often not perfectly monochromatic and hence a comparision to simulation results might only be justified if the simulation results, which include interference patterns in the substrate, are spectrally averaged. In this contribution we present a scattering matrix domain decomposition algorithm for Maxwell's equations based on FEM. We study its convergence and advantages in the context of optical simulations of silicon thin film multi-junction solar cells. This allows for substrate lighttrapping to be included in optical simulations and leads to a more realistic estimation of light path enhancement factors in thin-film devices near the band edge.

Certain designs for frustrated total internal reflection fiber optic evanescent wave sensors (FTIR FOEWS) include the partial removal of cladding along a finite length of the fiber optic that acts as the sensing region. This paper presents a model for a FTIR FOEWS that has a thin, partial cladding in the sensing region. Since the thickness of the cladding in the sensing region is in the 1 μm range, while the propagating light is on the order of 850 nm, commonly used ray optic modeling techniques fail to properly simulate the thin film interference effects. In this study, a modification to the usual ray model is performed by including thin film optic analysis at the thin film sensing interface. The resulting hybrid ray/thin film model maintains the efficiency of previously reported models, but also adds the ability to fully model the partial cladding of the sensing region. The intensity and angular distributions of light from a Lambertian LED source onto the fiber input face is also derived to discuss the effects of launching conditions on the sensor performance. Investigation of a variety of meridional propagation ray distributions into the fiber are performed by varying the distance and angle of the point source to the fiber input face. Optimal cladding thicknesses, LED distance and tilt angle are studied and used to draw conclusions about FTIR FOEWS performance based on launching conditions.

We study nano-scale ITO top transmission gratings to improve light extraction efficiency (LEE). We use the finite difference time domain (FDTD) method to measure light extraction from a device with various grating structures and layer thicknesses. We simulate our device using a twodimensional model with top triangular-gratings in a crystal lattice arrangement described by grating cell period (Α), grating cell height (d), and grating cell width (w). We also define ITO layer thickness (L) as the layer between the p-type GaN and the ITO surface layers. Simulation models vary in grating period, grating width, and ITO layer thickness. Our simulations monitor the amount of light emitted from the top, bottom, and sides of the LED model. We calculate the total light extraction and determine which grating duty cycle maximizes LEE. We found that adding a nano-scale grating with optimum duty cycle can achieve 165.67% and 136.77% LEE improvement, respectively, for ITO layer thickness of 230nm and 78nm.

Semiconductor lasers often make use of external optical feedback, for various reasons, like single-mode selection, stabilization or linewidth narrowing. A draw-back of such method is that delayed feedback can easily lead to sustained relaxation oscillations (RO). The occurrence of the RO is sensitive to, among other things, the applied settings of the phase of the feedback light. It is known from early studies that the onset of ROs already occurs with weak feedback. However, the onset of ROs is shifted to higher feedback strengths under resonance conditions, i.e. when the product of RO-frequency and external delay time equals an integer. This finding was based upon certain numerical and analytical considerations, but no simple explanation was given. From a theoretical analysis based on the Lang and Kobayashi equations, the existence of RO-free bias-current intervals of substantial width will be demonstrated for realistic pumping values, irrespective of the feedback phase. It will be shown that for conventional semiconductor lasers with weak optical feedback under RO-resonance condition the laser with feedback behaves as if no feedback is present. Therefore, under these conditions the RO is damped, hence will be suppressed. This result is valid in the regime of sufficiently weak feedback, such that the RO frequency is not deviating significantly from its value in the solitary laser and is supported by calculations of the RIN spectrum.

A set of rate equations is derived describing the deterministic multi-mode dynamics of a semiconductor laser. Mutual interactions among the lasing modes, induced by high-frequency modulations of the carrier distribution, are described by carrier-inversion moments and lead to special spectral content of each spatial mode. The diffusion of carriers is shown to play an important role in determining the spectral properties of the field. The Bogatov effect of asymmetric gain suppression in semiconductor lasers will be derived. We will explicitly discuss the nontrivial relationship between the modes of the nonlinear cavity and the optical spectrum of the laser output and illustrate this for a two and three-mode laser.

Dynamics of the output of a semiconductor laser with frequency-shifted optical feedback system is systematically analyzed. Results from experimental studies using an 830 nm, QW, Fabry-Perot cavity, semiconductor laser are reported. The dynamics are mapped as a function of the level of frequency shifted feedback (FSF) and the injection current. The frequency shift of the optical feedback is the fundamental or a sub-harmonic of the external cavity frequency in the experiments. Multi-GHz-bandwidth real time data collection and analysis is used to investigate the temporal and spectral behaviour of the output power of the nonlinear system. The results are contrasted with those from conventional semiconductor laser with optical feedback systems. Three fundamentally different regimes of operation are identified for the FSF system corresponding to low, medium and high levels of FSF. The low and medium level FSF regimes are consistent with those found in the semiconductor with conventional optical feedback system. It is only when high levels of FSF are used that the output gives a noisy, near periodic output which is similar to the pulsed comb of mode output observed in analogous FSF laser systems using solid state gain media when the FSF is resonant.

Metal-cavity submonolayer (SML) quantum-dot (QD) microlasers are demonstrated at room temperature under continuous-wave electrical injection for 2-μm-radius devices and pulsed operation for 0.5-μm-radius devices. Compared to our previous quantum well devices, the superior optical properties of SML QDs provide the possibility for further size reduction. Size-dependent lasing characteristics are extracted from measurements to investigate the device physics for future size reduction. An optical cavity model using the transfer matrix and the effective index method including metal dispersion is developed and used for both the design and the experimental results analysis. The laser uses an active region consisting of three groups of SML QDs, and each group consists of 10 stacks of 0.5-monolayer InAs QD layers. The cylindrical microcavity is formed by hybrid metal-distributed Bragg reflectors (DBRs) mirrors with an optimized SiNx passivation layer on the sidewall to reduce the metal loss and to avoid the leakage current. The transverse optical modes are solved using the Maxwell equations, and the resonance condition is determined by roundtrip phase matching. Vertically-correlated QDs are modeled as quantum disks, and the wave functions and eigenenergies in both conduction and valance bands are solved from Schrodinger equation. Carrier-dependent material gain is calculated using Fermi’s golden rule and included in the model. The lasing wavelengths, quality factors, and confinement factors for cavity modes are the inputs for the rate-equation model, which predicts the light output power vs. current behavior and has shown excellent agreement with experiments. Size-dependent physical quantities such as leakage current and spontaneous emission coupling factor are extracted and investigated. Further size reduction using only four pairs of DBRs is proposed.

Tamm plasmons are interface modes formed at the boundary between a metallic layer and a dielectric Bragg mirror. They present advantages associated both to surface plasmons and to microcavities photonic modes. One of their striking properties is that they can be spatially confined by structuring only the metallic part of the structure, thus reducing the size of the mode and allowing various geometries without altering the optical properties of the active layer. These modes are very good candidates for optimizing the emission properties of semiconductor nanostructures. In particular, due to the relatively low damping and the versatility of the Tamm geometries, they open new perspective for the development of hybrid metal/semiconductor lasers. In this paper, we will show that a laser effect can be achieved in a bidimensional Tamm structure under pulsed optical pumping. We will also demonstrate that the mode can be spatially confined, and that this results in a reduction of the pump power at threshold.

Recent research on epsilon-near-zero (or index-near-zero) materials has revealed their promising applications in optoelectronics. We explore a novel waveguide structure, namely “epsilon-near-zero-slot waveguide”, by utilizing transparent conducting oxides as the active medium, which can be tuned between epsilon-near-zero and epsilon-farfrom- zero by accumulation carriers, resulting in sharp effective index change. We propose laser beam steering by taking advantage of this epsilon-near-zero-slot waveguide structure. With about 60°steering angle being achieved, this waveguide structure has the advantages of ultra high speed and compact dimension, as well as easy fabrication.

Ga doping of ZnO allows for generation of free electrons up to concentrations of about 10²¹ cm^-3 without significant deterioration of the crystal structure. In this way, a metallic dielectric function is formed with a negative-to-positive crossover of the real part tunable from mid infrared up to telecommunication wavelengths. The losses are at least one order of magnitude lower than for traditional metals. We demonstrate surface plasmon polaritons with dispersion relations that can be engineered in a unique way by utilizing epitaxial multi-layer structures of different doping level.

Ga-doped ZnO grown at 200 °C by pulsed-laser deposition in Ar ambient and annealed face-down on Zn foil at 500 °C in forming gas can attain near-record electrical characteristics for ZnO: resistivity ρ = 1.23 × 10^-4 Ω-cm, mobility μ_Hall = 34.1 cm²/V-s, and free-electron concentration n = 1.4 x 10²¹ cm^-3, leading to a plasmonic resonance wavelength λ_res = 1.05 μm. A value of λ_res near 1 μm is important because metal-based plasmonics are lossy in the IR region. Longer resonant wavelengths in ZnO, e.g., the telecommunication wavelengths λ_res = 1.3 and 1.55 μm, are then simply produced by furnace anneals in air. A relatively unexploited characterization tool for such materials is spectroscopic ellipsometry (SE). By harnessing the full potential of SE we demonstrate full-color maps of thickness d, concentration n_SE, and mobility μ_SE.

Conventional metals with high carrier concentrations have served to date as the materials of choice for plasmonic and metamaterial devices. However, typical metals are not well suited for near IR (NIR) plasmonic applications because their associated plasma frequencies correspond to the visible and ultraviolet regions of the spectrum. On the other hand, materials with lower plasma frequencies such as conducting oxides like ZnO and VO₂ are capable of more efficiently coupling the electromagnetic radiation for optical metamaterial and plasmonic applications in the NIR. Furthermore, unlike metals, the electrical transport properties of conductive oxides can be modulated intrinsically by doping or extrinsically by applying heat, light or an electrical bias, thus allowing tuning of their electro-optical behavior. At the Naval Research Laboratory (NRL), we have investigated the use of laser processing techniques for the deposition and processing of various types of conducting oxides, such as Al-doped ZnO and W-doped VO₂, which can be optimized over a wide range of optical/electrical properties. This paper will describe the laser deposition of these oxide films and their electrical and optical characterization in the NIR.

We have studied the performance of deep-UV avalanche photodetectors based on AlGaN alloys. We have evaluated the carrier multiplication gains and excess noise factors using a model based on recurrence equations and activated ionization coefficients derived from a full-band Monte Carlo model. We find that for devices with Al_0.4Ga_0.6N the excess noise factor increases linearly with the gain. When Al_0.6Ga_0.4N is used, the excess noise factor is significantly reduced. Finally, from the analysis of the possible device configurations, electric field distribution and its magnitude, we find that the fabrication of these devices will be challenging and alternative approaches should be considered.

Water splitting under illumination with a GaN/InGaN planar and nano wire structure is modeled using a drift diffusion approach. The main features of the experiment such as current density without biasing and current saturation effects are explained by the simulation. The electrolyte where ionic transport occurs is modeled as material with diffusion coefficients matching ionic diffusivity experiments. The simulation allows design and analysis of GaN based nano structures and their water photo electrolysis efficiency.

We present a comparison among GaN/AlGaN, GaN/InAlGaN, and GaAs/AlGaAs quantum cascade structures based on a Monte Carlo study of carrier dynamics, to highlight the improvements offered by nitride latticematched structures. We take into account the interactions of electrons with other electrons as well as LO-phonons. The results obtained from the Monte Carlo simulations are used to calculate the population inversion of each structure to determine its temperature dependence. This study shows that the nitride-based structures offer significantly improved high-temperature performance compared to the GaAs device, including the possibility of room-temperature operation. Furthermore, by virtue of its lattice-matched nature, the GaN/InAlGaN materials system can potentially enable the high-quality growth of thick quantum cascade structures without plastic relaxation, as a way to overcome the structural issues that have so far hindered the development of these devices with nitride semiconductors.

The slope sensitivity of an active ring laser gyro can be improved by decreasing the group index and the wavelength without having to increase the size of the ring. The nonlinear interaction between a strong driving wave and a probe wave (which is in the spectral vicinity of the driving wave) results in modification of group index of the probe wave. The reduced group index can be used to improve slope sensitivity (scale factor) of a ring laser gyro. By using an InGaN-based multiple quantum well (MQW) semiconductor laser the sensitivity can be further improved, because the lasing wavelength is shorter and the nonlinear interactions between the modes in this material system are also stronger when compared with GaAs-, InGaAs-, and InGaAsP-based laser systems. The finite element method is used to model a realistic InGaN/GaN quantum well waveguide structure. The induced dispersion is calculated and variation of the group index is obtained by the numerical modeling. The spectral position of the critically anomalous dispersion point is shown in wide range of driving wave intensity.

We present analytical, numerical and experimental results about the unidirectional behaviour of semiconductor ring or disk lasers in which the coupling from the clockwise (CW) mode to the counterclockwise (CCW) mode is different from the coupling from the counterclockwise to the clockwise mode. The theoretical and numerical results show different regimes, depending on the gain suppression in the active layer. At very low power, the ratio of the powers of the CW and CCW modes depends mainly on the ratio of the coupling constants, while at high power gain suppression is dominant and the ratio of the powers depends on the ratio of the gain suppression and the weakest coupling coefficient. Our analytical expressions for the unidirectionality are in excellent agreement with numerical results obtained using coupled rate equations. Some experimental results are given for a microdisk laser coupled to a bus waveguide, on one side of which an almost 100% reflecting Bragg grating is designed.

The simulation of the lasing behavior of semiconductor quantum well structures with accurate description of transport phenomena and optical propagation poses great challenges when complex epitaxial layers are coupled with optical cavities in the transverse direction that are more complex than the well know Fabry-Pérot and distributed feedbackreflector based resonators. In this work, we present an approximate approach for the simulation of an electricallypumped III-V strained quantum well laser with coupled concentric racetrack resonators. The electrical, thermal and optical behavior of an epitaxial stack with at least one quantum well is obtained from a physics based simulator for a reduced dimensionality problem, and this solution is coupled with the cold cavity analysis of the resonator using either finite difference time domain simulation or coupled-mode analysis. The effects of gain and charge transport on the active resonator are then taken into account as a perturbation and the approximate solution derived. Comparison with actual devices based on InGaAlAs/InGaAs/InP and InGaSb/AlGaAsSb/GaSb shows reasonable agreement. The concentric racetrack resonator exhibits complex dispersive behavior, with possible applications in sensing, nonlinear phenomena and optical signal processing.

We perform two analyses on temperature effects in Metal-Clad Subwavelength Semiconductor Lasers (MCSELs). Firstly, we analyze the temperature dependence of the threshold gain in the infinite waveguide approximation. We show that the dielectric layer of the semiconductor-dielectric-metal composite waveguide (CWG) becomes increasingly important as temperature increases. However, we further show that the optimal geometry of the CWG is nearly invariant with the temperature. Secondly, we relax the infinite waveguide assumption with the fully 3D finite element method, and analyze the temperature dependence of the spontaneous emission factor, β. We identify a cavity geometry that mitigates detuning between the dominant cavity mode and emission spectra. Ignoring coupling to freespace modes, we explain that the modified cavity may lead to a MCSEL with large β (~0.5) for all temperatures.

We analyzed two approaches to calculate band structure and optical gain in GaInNAs/GaAs quantum well structures based on 10-band and 8-band kp models. The obtained results are discussed in the context of importance of conduction band nonparabolicity. We also briefly report on the influence of hydrostatic pressure on optical gain in this system.

The unique properties of surface plasmons (SPs) are expected to provide a great improvement of light extraction in light-emitting diodes (LEDs). Surface plasmon modes are characterized by a high local density of states, and if scattered by gratings, significantly high emission enhancement is achievable. We investigate the physical role of SPs in improving light extraction from GaN quantum-well (QW) light-emitting structures incorporating metallic grating, by using first-principle theory based on Maxwell's equations and fluctuational electrodynamics. We demonstrate how careful nano-engineering, specifically by choosing the right nano-grating period, can reduce absorption losses and provide optimal enhancement; in the investigated test geometries, light extraction is increased by a factor of four, with the plasmonic losses being reduced from ~ 90% to below ~ 60% thanks to the metallic grating. While the results confirm a strong enhancement and reduction in the plasmonic losses, the overall losses still represent a significant obstacle for plasmonic-enhanced emission. With further optimization of the structure, the grating shapes and the materials, a much larger enhancement and lower losses are expected to be possible.

In this paper, we propose a surface plasmon resonance (SPR) sensor with metallic nano-particles, which is based on the Kretschmann configuration for reflective-type measurement with enhanced sensitivity. The proposed structure is analyzed and compared with a conventional Kretschmann configuration by using 3D finite-difference time-domain method. The proposed structure is composed of semi-spherical nano-particles and a thin cladding layer. The evanescent field on the metallic structure is enhanced by the factor of 2.7, where the diameter of nano-particles, fill factor, and thickness of cladding film layer T_F are 30 nm, 50 %, and 40 nm, respectively. On the other hand, the enhancement of the evanescent field in the conventional SPR sensor is 1.7 for the same TF. Because of the enhanced evanescent field, the sensitivity of our proposed sensor is maximized to 137.1 degree/RIU while that of a conventional SPR sensor is 99.6 degree/RIU.

We report a theoretical study of the enhancement of Goos-Hänchen (GH) effect in a prism-waveguide coupling system with magneto-optic materials, including dielectric waveguide (Prism/Air/Ce:YIG/SiO₂) and plasmonic waveguide (Prism/Au/Ce:YIG/SiO₂) structures. Giant GH shift is observed in both waveguides. By applying opposite magnetic field across the CeYIG layer, a variation of the GH shift, namely MOGH (magneto-optical Goos-Hänchen effect) is observed. Compared to the reflectivity and Goos-Hänchen effects of the structures, the MOGH effect shows higher sensitivity for index variations, therefore is very promising for chemical or biomedical index sensors. The device performance as a function of layer dimension, material refractive index and magneto-optical properties are simulated and discussed in detail. It is observed that coupling layer, MO layer thickness and prism index plays an important role in the plasmonic waveguide to control MOGH effect.

We explore tunable plasmonic metamaterials for electro-optic modulator applications based on ITO-based multilayer structures. Two different structures are investigated, and modulation depth up to 38.8% can be achieved. Preliminary results are presented for the real time response of an ITO/electrolyte gel/doped Si modulator. Furthermore, another modulator configuration is investigated by substituting electrolyte gel by high-k dielectric material (HfO₂).

A p-i-n solar cell is best suited for strong absorbers with poor collection capabilities. However, the absorption naturally decreases at photon energies close to the electronic bandgap of the semiconductor. We hypothesized that a quasi-periodic surface textures in the role of diffraction gratings at the back contact can efficiently scatter light increasing the optical path length inside the absorber layer. The effect of quasi-periodic corrugated backing metallic contact of various types was studied theoretically. To help optimizing the design of the quasi periodic grating the corresponding canonical problem was considered. The absorption of light was calculated using the rigorous coupled-wave approach. The n- and i-layers consist of isotropic nonhomogeneous multilayered semiconductor.

The frequency chirp characteristics of an optically injection-locked quantum cascade laser are theoretically investigated. The key parameter chirp-to-power ratio (CPR) is analytically derived from a full rate equation model. The CPR value can be efficiently reduced by increasing optical injection strength, especially at modulation frequencies less than 10 GHz. In contrast to interband lasers, both positive and negative frequency detuning increase the CPR. Since the frequency detuning is also predicted to enhance the intensity modulation response, a trade-off is required in the optical injection to simultaneously obtain a large modulation bandwidth and low frequency chirp.

Greatly enhanced high-speed modulation performance has been recently predicted in numerical calculations for a novel injection-locking scheme involving a DBR or DFB master laser monolithically integrated with a unidirectional semiconductor microring laser. In this work, we investigate the effect of light backscattering between the two counterpropagating modes on high-speed modulation performance of strongly injection-locked unidirectional semiconductor microring lasers.

There are basically five nonlinear phenomena that occur in the optical fiber which limits the power or distort the signal in the data transmission. One of the most important is the phenomenon called Stimulated Brillouin Scattering (SBS) as it only requires relatively low pump power for affecting signal power in single and multiwavelength transmission in DWDM systems, for instance. There are numerous studies of this phenomenon that deal with power threshold determination which represents the limit on the transmit power but many of them are very complex and not very clear. In this work we propose a simple algorithm for the analysis and simulation of Brillouin power threshold by choosing a set-point. The results are obtained via solving the proposed set of coupled differential equations which then are compared to experimental results for Brillouin and Rayleigh scattering and forward power, i.e. residual pump.

Dense wavelength division multiplexing (DWDM) metropolitan networks are currently being extensively deployed with distances ranging from a couple of ten’s kilometers to several hundred kilometers. 40 DWDM channels are commonly used; each of them is carrying today Ethernet or Fiber Channel traffics ranging from 1 to 10 Gb/s. This type of network requires achromatic components, for which the provider can fix the operating wavelength in order to have the same type of components in the consumer’s home. The DWDM sources could be based on a tunable laser source or on a selfseeded- reflective semiconductor optical amplifier (RSOA) as recently proposed. In this last case, the RSOA is coupled to a mirror, located at a few kilometers in a central office. A frequency filter fixes the wavelength. The RSOA is then directly modulated at a few GHz. However even if a 100 GHz-wide filter is used, a much narrower slot of wavelengths is selected on the “red” side of the transmission window of the filter. This communication gives from a Green function approach the modal structure of an RSOA coupled to a long cavity with strong optical feedback and explains how such coupled structure is operating.

Frequency chirp simulations based on rate equation analysis are performed for strongly injection-locked ring lasers for applications in optical communication and rf photonics. Different scenarios are explored and compared, including weak injection of a single ring laser, strong injection of a single ring laser, and strong injection of cascaded ring lasers. Together with previously published results, these simulations confirm that the novel whistle-geometry ring laser scheme can provide, especially when modulation signal is applied to both ring lasers in the cascaded arrangement, a greatly improved performance in terms of modulation response and frequency chirp, and more flexibility in the design of ultrahigh speed transmitters.

Massless Dirac electrons in graphene and surface states of topological insulators have peculiar optical properties and strong coupling to light. Surface plasmons in these materials may provide an attractive alternative to noble-metal plasmons due to their tighter confinement, peculiar dispersion, and longer propagation distance. We present theoretical studies of the difference frequency generation (DFG) of terahertz surface plasmon modes supported by two-dimensional layers of massless Dirac electrons, which includes monolayer graphene and surface states in topological insulators. Our results demonstrate strong enhancement of the DFG efficiency near the plasmon resonance and the feasibility of phase-matched nonlinear generation of plasmons over a broad range of frequencies.

Synergizing graphene on silicon based nanostructures is pivotal in advancing nano-electronic device technology. A combination of molecular dynamics and density functional theory has been used to predict the electronic energy band structure and photo-emission spectrum for graphene-Si system with silicon as a substrate for graphene. The equilibrium geometry of the system after energy minimization is obtained from molecular dynamics simulations. For the stable geometry obtained, density functional theory calculations are employed to determine the energy band structure and dielectric constant of the system. Further the work function of the system which is a direct consequence of photoemission spectrum is calculated from the energy band structure using random phase approximations.

We demonstrate greatly enhanced light absorption by monolayer graphene over a broad spectral range, from visible to near infrared, based on attenuated total reflection (ATR). The designed structure consists of two dielectric media and monolayer graphene between them. Up to 42.7% light absorption has been achieved by this structure. Moreover, when applying electrolyte gel, electric double layers are formed at the graphene-gel interface, which leads to the change of graphene’s electrical properties as well as optical properties. As a result, light absorption of graphene can be manually modulated. This design may help build electro-optic modulators for applications in communications, sensing and spectroscopy.

Due to the promises of ultrahigh speed computation realized in the optical domain, great interest towards alloptical integrated systems has been shown. A great number of different types of optical logic gates have been proposed during the last years and the optical diode effect based on photonic crystal is of crucial importance in optical logic gates and computing integrated optical systems. The diode effect can be achieved by breaking the spatial inversion symmetry by various ways. Many different linear passive structures that exhibits optical isolation and unidirectional transmission behavior have been proposed, which exploit the properties of point defects, mode conversion and filtering, chirped structures or heterojunction slabs (two different 2D Photonic Crystals structures). Further improvements of these structures are here proposed and enhanced unidirectional behavior was achieved by optimization of the originally proposed structures where good optical isolation has been achieved. The results were obtained by efficient numerical simulations and it is shown that these devices are good candidates for building blocks of integrated optical systems.

We show that the concept of supersymmetry (SUSY) can be utilized as a versatile tool to design integrated optical structures with desirable eigenmode spectra. Our approach relies on the intriguing ability of SUSY transformations to systematically construct a “superpartner” structure that shares all of its propagation constants with the original waveguide. This approach can be employed to any given one-dimensional refractive index landscapes and establishes perfect global phase matching condition between an, in principle, arbitrarily large number of guided modes, while separating the fundamental mode of the original waveguide. In doing so, SUSY transformations also relate the field distributions of the paired modes, in turn allowing for mode conversion with unity efficiency. Here, the concept of supersymmetry is illustrated through several examples of one-dimensional waveguides. These include the step-index (slab) waveguide as well as parabolic and exponential index profiles. In all cases the superpartner can be obtained analytically. The unique properties of coupled superpartner arrangements make them an ideal platform for integrated mode filtering and multiplexing applications. The key idea behind this is that global phase matching allows each mode from the original waveguide to interact freely with the neighboring guides, while the fundamental mode remains isolated. Here, this whole set of modes can be simultaneously manipulated, attenuated/amplified, or passed through to higher-order SUSY arrangements.

For advanced photonics networks all kind of optical devices are being developed with the aim of routing high speed optical signals. The multimode interference MMI principle is becoming important because these devices have a simple configuration, compactness and are suitable for integration. MMI couplers based on subwavelength periodical gratings and silicon nanowires are here analyzed based the coupled-mode formulation. Several geometrical configurations were analyzed as a function of the operating wavelength, by varying the width/radius, the period, the segment length (dutycycle) and the nanowires radius. It was observed that for some specific configurations a wavelength independent behavior can be obtained.

Recent advances in optical waveguides have brought long-awaited technologies closer to practical realization. Although the concept of a single-mode (SM) waveguide has been around for a while, SM condition usually posed very stringent conditions in fabrication for small waveguides. Researchers have developed low loss silicon nitride (Si3N4) at 1550nm wavelength, the developments in specific application have down converted to 1310nm (O-band) so they do not have to compete with internet data for bandwidth and could share the existing optical fiber infrastructure. However, wavelengthdemultiplexer technology at this band is not readily commercial available. Custom-made O-band optical devices for wavelength-demultiplexing have typical losses. Such high losses deplete more than 75% of the already-scarce photons. We studied Si3N4 channel waveguide with ultra-thin slab for (SM) condition at 1310nm wavelength using finite element method (FEM) and 3-D imaginary beam propagation method (IDBPM). We have shown that SM condition is possible for ultra-thin slab with wide waveguide width; such condition can ease the constraint of photolithography, allowing deposition of thin Si3N4 layer to be accomplished in minutes. Studies show that for ultra-thin layer, for example, at 60nm, we can achieve a wide range of widths that fulfilled the SM condition, ranging from 2μm to 5μm. SM condition becomes more stringent when the Si3N4 layer increases. Substrate losses are estimated at 0.001 dB/cm, 0.003 dB/cm, and 0.1 dB/cm for slab height at 100nm, 80nm, and 60nm respectively.

We investigate theoretically the slowdown of optical pulses due to quantum-coherence effects in InGaAs-based quantum dots and quantum dot molecules. Simple models for the electronic structure of quantum dots and, in particular, quantum-dot molecules are described and calibrated using numerical simulations. It is shown how these models can be used to design optimized quantum-dot molecules for quantum coherence applications. The wave functions and energies obtained from the optimizations are used as input for a microscopic calculation of the quantum-dot material dynamics including carrier scattering and polarization dephasing. The achievable group velocity slowdown in quantum-coherence V schemes consisting of quantum-dot molecule states is shown to be substantially higher than what is achievable from similar transitions in typical InGaAs-based single quantum dots.

Monte Carlo markovian models of a dual-mode semiconductor laser with quantum well (QW) or quantum dot (QD) active regions are proposed. Accounting for carriers and photons as particles that may exchange energy in the course of time allows an ab initio description of laser dynamics such as the mode competition and intrinsic laser noise. We used these models to evaluate the stability of the dual-mode regime when laser characteristics are varied: mode gains and losses, non-radiative recombination rates, intraband relaxation time, capture time in QD, transfer of excitation between QD via the wetting layer. . . As a major result, a possible steady-sate dualmode regime is predicted for specially designed QD semiconductor lasers thereby acting as a CW microwave or terahertz-beating source whereas it does not occur for QW lasers.

Nondegenerate four-wave mixing (NDFWM) in semiconductor gain media is a promising source for wavelength conversion in the wavelength division multiplexed (WDM) systems and for fiber dispersion compensation in long distance fiber links. In contrast to bulk and quantum well (QW) semiconductors, the quantum dot (QD) gain medium is favorable for enhancing the performance of the FWM because of the wide gain spectrum, large nonlinear effect as well as ultrafast carrier dynamics. Especially, the destructive interference can be eliminated due to the reduced linewidth enhancement factor (LEF) for obtaining high efficiency in the wavelength up-conversion. This work reports the NDFWM generation in a dual-mode injection-locked QD Fabry-Perot (FP) laser. The device has a wide gain spectrum with a full width at half maximum of 81 nm, and a peak net modal gain of 14.4 cm^-1. The laser exhibits two lasing peaks induced by Rabi oscillation, which provides the possibility for efficient FWM generation. Employing the dual-mode injection-locking scheme, an efficient NDFWM is achieved up to a detuning range of 1.7 THz with a weak injection ratio of 0.44. The highest measured values for both the normalized conversion efficiency (NCE) and the side-mode suppression ratio (SMSR) with respect to the converted signal respectively are -17 dB and 20.3 dB at the detuning 110 GHz.

We theoretically investigate the sub-Poissonian light generation in a cavity quantum electrodynamics system of a single quantum dot coupled a bimodal nanocavity. It is shown in a recent work [Arka Majumdar et.al, Phys. Rev. Lett. 108, 183601 (2012)] that the system can generate strongly sub-Poissonian light when one of the cavity modes is driven coherently and resonantly. We study the two-mode coherent driving regime of the coupled system. The effect of additional cavity mode driving on the statistic characteristics of photon emission is presented by evaluating the zero-delay second-order correlation function g²(0). We interpret the optimization of sub-Poissonian feature by regulating the ratio between driving strengths of two cavity modes and observe that g²(0) can be reduced up to several orders of magnitude (g²(0))<10^-4), comparing with one-mode driving system (g²(0)~0.1), indicating ultra-strongly sub-Poissonian light generation.

Simulation of III-nitride color-coded multiple quantum well (MQW) LED structures was performed using as an experimental benchmark dichromatic semipolar LEDs grown in Ga-polar and N-polar crystallographic orientations (Y. Kawaguchi et.al, APL 100, 231110, 2012). Different QW depths in the color-coded LEDs and opposite interface polarization charges in Ga-polar and N-polar structures provide different conditions for carrier transport across the LED active regions. Combination of several effects was crucial for adequate reproduction of the emission spectra experimentally observed in color-coded structures with violet-aquamarine and aquamarine-violet active region layouts. A standard drift-diffusion transport model wascompleted with rate equations for nonequilibrium QW populations and several high-energy transport features, including the effects of QW carrier overshoot and Auger-assisted QW depopulation. COMSOL-based Optoelectronic Device Modeling Software (ODMS) developed at Ostendo Technologies Inc. was utilized for device simulation.

Optical pulse generation and compression have been numerically studied in anomalous dispersion decreasing fibers (DDF). We show that evolution of modulation instability observed with chirped wave packets in tapered fibers produces the mechanism for generation of ultra-short pulses with high repetition rates. The role of modulation instability and Raman self-scattering has been also discussed. The simulations show that pulse chirping enhances self-Raman scattering at early stages of pulse propagation and improves compression of the generated pulses. It is also shown that the presence of amplitude and frequency modulation of the seed wave provide essential impact on the pulse train formation. The new method for increasing the pulse train repetition rate through frequency modulation of the seed wave has been proposed.

Rigorous optical simulations are an important tool in optimizing scattering properties of nano-photonic devices and are used, for example, in solar cell optimization. The finite element method (FEM) yields rigorous, timeharmonic, high accuracy solutions of the full 3D vectorial Maxwell's equations1 and furthermore allows for great flexibility and accuracy in the geometrical modeling of these often complex shaped 3D nano-structures. A major drawback of frequency domain methods is the limitation of single frequency evaluations. For example the accurate computation of the short circuit current density of an amorphous silicon/micro-crystalline multi-junction thin film solar cell may require the solution of Maxwell's equations for over a hundred different wavelengths if an equidistant sampling strategy is employed. Also in optical metrology, wavelength scans are frequently used to reconstruct unknown geometrical and material properties of optical systems numerically from measured scatterometric data. In our contribution we present several adaptive numerical integration and sampling routines and study their efficiency in the context of the determination of generation rate profiles of solar cells. We show that these strategies lead to a reduction in the computational effort without loss of accuracy. We discuss the employment of tangential information in a Hermite interpolation scheme to achieve similar accuracy on coarser grids. We explore the usability of these strategies for scatterometry and solar cell simulations.

This work addresses a versatile modeling of complex photonic integrated circuits (PICs) including optical and electrical sub-elements. We introduce a new family of electrical elements, together with a novel electronic-photonic co-design, that complements current capabilities of photonic circuit simulators. This is illustrated with the modeling of complex electric circuits contained in photonic devices. Simulations of the interaction between electrical and optical parts allow the analysis of unwanted effects such as reflections due to impedance mismatching, as well as the optimization of the PIC as a whole. We illustrate the functionalities of our approach through application examples. As a use case, we present a model of the electrical driver for a monolithically-integrated InP transmitter developed in frame of the European research project MIRTHE and the analysis of the driver and the EA-Modulator interplay.

Electrons and holes in type-II nanostructures are spatially separated. Therefore, both the radiative and nonradiative recombination rates are reduced. Although the photon conversion efficiency is hence decreased, the lowered nonradiative recombination such as Auger process benefits photovoltaic applications. Furthermore, if generated carriers can be rapidly removed from nanostructures through quasi-bound states, the photon absorption may be designed and enhanced regardless of the concern on nonradiative mechanisms. Here, we model the bound-tocontinuum absorption of type-II nanostructures in the presence of tunneling using the density-matrix formalism and convert it into a radiation problem in the multiband space with band mixing. An effective source is derived from the eight-band momentum operator, and the corresponding field is expressed in terms of the source and retarded Green’s function of the eight-band Luttinger-Kohn Hamiltonian. On the other hand, the response is actually calculated without the Green’s function. Perfectly-matched layers in the multiband space are introduced to model the effect of quasi-bound states in open regions. In this way, the interplay between photon absorption and tunneling is fully taken into account. We present both the transverse-electric and transverse-magnetic absorption spectra of type-II GaAs _0:65Sb_0:35/GaAs coupled quantum wells. The corresponding lineshape broadening near the resonant energy can be divided into two parts. One comes from various incoherent relaxation mechanisms, and another well-fitted by the Fano resonance originates from the coherent tunneling. For a 2-nm potential barrier, the tunneling times of metastable states in nanostructures are around 20 fs, and their degrees of mixing to the continuum are high.

The aim of this paper is to describe the design and simulation of an optical waveguide for its potential integration with an optical source based on silicon rich oxide (SRO), on a silicon substrate. SRO deposited by Low Pressure Chemical Vapor Deposition (LPCVD) has emission of light in the visible range, and then our goal is to integrate this optical source with an appropriate optical waveguide. In this sense, we describe the methodology followed for the design of the optical waveguide able to transmit light emitted in the wavelength range from 400 to 800 nm. Due to its optical properties and compatibility with silicon technology the core material selected for the waveguide is silicon nitride (Si₃N₄), surrounded by silicon oxide (SiO₂). The optimal dimensions and geometry that reduces losses and confine the light into the core zone are obtained by simulation.

Since Urata et al. reported on the Smith Purcell superradiance, numerous studies have been carried out to develop novel type of terahertz free electron lasers. The particle-in-cell finite-difference time-domain (PIC-FDTD) method has been widely employed to numerically study the process. We show our studies on the parallel computing based on the general purpose computation on the graphic processing unit (GPGPU) to accelerate our homemade PIC-FDTD simulation. We have succeeded in reducing the computational time to the quarter of that required for the same simulation using only CPU.

Traditional numerical analyses of laser beam transmission through “active” nonlinear materials have involved many assumptions that narrow their general applicability. As more complex optical phenomena are widely employed in research and industry, it is necessary to expand the use of numerical simulation methods. Historically, laser-matter interactions have involved calculations of “classical” wave propagation by Maxwell’s equations and photon absorption through rate equations using numerous approximations. We describe a novel numerical modeling framework that adapts itself for simulation of different types of active materials provided by a simple graphical input. Our framework combines classical electric field propagation with “active” photon absorption kinetics using computational active photonic building blocks (APBB). It allows investigating a plane electromagnetic wave propagating through generic organic or inorganic photoactive materials; while, “active” photo-transitions are implemented using the APBB algorithm on the user interface. To date we have used the method in multiphoton absorbers, upconversion, semiconductor quantum dots, rare earth ions, organic chromophores, singlet oxygen formation, energy transfer, and optically-induced chemical reactions. We will demonstrate the method with applications of amplification in rare-earth ions and multiple two-photon absorbers materials in tandem.

Optical injection locking of semiconductor lasers has attracted significant attention due to its applications in laser analysis, modulation characteristic enhancement, and nonlinear dynamics. In many cases, the analysis of the optically injected laser is done by simulation, requiring an accurate laser model and, therefore, an adequate modeling of the gain compression at high photon densities. We use the Kobayashi-Lang rate equations to numerically compare the stable locking range considering four different gain models. Results reveal that at low bias currents, gain compression is significant only under weak injection regime. In contrast, for higher bias current, gain compression must be considered both in weak and strong injection regimes.

We analyze a plasmonic gap-mode Fabry-Perot nanocavity containing a metallic nanowire. The proper choice of the cladding layer brings about a decent confinement inside the active region for the fundamental and first-order plasmonic gap modes. We numerically extract the reflectivity of the fundamental and first-order mode and obtain the optical field inside the cavity. We also study the dependence of the reflectivity on the thickness of Ag reflectors and show that a decent reflectivity above 90 % is achievable. For such cavities with a cavity length approaching 1.5 μm, a quality factor near 150 and threshold gain lower than 1500 cm⁻¹ are achievable.

We demonstrate and characterize the microwave frequency combs utilizing both the dynamical single-beam and dual-beam injection schemes numerically. The dynamical single-beam injection scheme is realized by optical pulse injection to the slave laser (SL) from a pulsed laser. When the SL subjected to only the optical pulse injection from the pulsed laser, microwave frequency combs are generated by the nonlinear dynamics of the frequency-locked states with different locking ratios. The amplitude variation of ±18 dB in a 30 GHz range is obtained by precisely varying the operational parameters, injection strength, repetition frequency, and detuning frequency. In this paper, we propose the dynamical dual-beam injection scheme to improve the amplitude variation of the microwave frequency comb generated. The dynamical dual-beam injection is realized by both optical pulse injection and optical cw injection to the semiconducor laser. By utilizing the hybrid scheme consists of double optical injections, the advantages of each individual dynamical system are added and enhanced. As the result, the amplitude variation of the microwave frequency comb of ±3.0 dB in a 30 GHz range is achieved when operating the cw and pulse injection to the slave laser in stable locking and frequency locked states, respectively. In addition, the bandwidth enhancement of over 25 GHz is also observed.

In this paper we present a frequency domain method to model the physical behavior of widely tunable (1-100GHz) and spectrally pure (1Hz linewidth) RF source, generated by down-mixing of two coherent DFB lasers with a desired RF frequency offset. Rate equations that govern master and injection locking laser behavior are used, and linearization process is followed to derive phase and intensity noise responses by carefully examining the components in the system. Various noise sources are incorporated into the model to explore their significance to final system performance. The phase noise, and RF linewidth are simulated to evaluate the system performance of the generated RF sources.

Optical fibers are commonly used as evanescent wave sensors. Many factors affect the performance of fiber optic-based evanescent sensors, including, but not limited to, cladding thickness and the refractive index of the external medium. A lot has been done on analytical and numerical models to predict the effects of these factors in order to aid sensor design. However, many of these models are often complicated and difficult to solve. In this paper, the free open source finitedifference time-domain (FDTD) simulation software called Meep (MIT Electromagnetic Equation Propagation) is used to predict the performance of a fiber optic evanescent wave sensor. The software is based on Maxwell’s equations and it is used for this analysis due to its simplicity of setting up the simulation as well as its reasonable running time. Electromagnetic flux is calculated at various points along the structure to determine the power loss based on the physical dimensions and refractive indices of the structure. The dimensions used in the simulation are relative and therefore the results offered in this work are mainly qualitative. However, they are useful in guiding the overall design of evanescent fiber optic sensors. To validate the accuracy of the simulation results experimentally, optical fibers of 105μm diameter core are etched with sensing regions of length 13mm and cladding thicknesses of 0.1-0.4μm. The change in transmitted power is then measured when an external medium of refractive index up to 1.466 is put in contact to the sensing region. The results are used to explore the advantages and limitations of using this free and open source software in the design, modeling and characterization of this type of photonic sensors.

In this work, we report on In_xGa_1-xAs_1-ySb_y/GaSb structures, where the indium mole fraction (x) varies from x=0 to x<0.50. Although there has been considerable effort to exploit high-indium content In_xGa_1-xAs_1-ySb_y for longer wavelength applications, high misfit dislocation densities are inevitable and the miscibility gap remains a formidable barrier. In addition to atomically smooth structures, we observed three-dimensional networks of quantum dashes and other results reveal a self-organized composition modulation. Some physical features of the quantum dashes include near one-micron lengths, 90° flip in orientation, and uniformity across a 20 x 20 μm area. We also observe network formation up to a film thickness of 10-nm.

Metal nanocavity-based lasers show promise for dense integration in nanophotonic devices, thanks to their compact size and lack of crosstalk. Thermal considerations in these devices have been largely overlooked in design, despite the importance of self-heating and heat dissipation to device performance. We discuss the sources of self-heating in electrically-pumped wavelength-scale nanolasers, and the incorporation of these heat sources into a heat dissipation model to calculate laser operating temperature. We apply this thermal model to an example electrically-pumped nanolaser operating at room temperature.