We investigate novel quantum photonic devices and applications in quantum communications and enhanced measurements.

We analyze the impact of both an incoherent and a coherent continuous excitation on our proposal to generate a two-photon state from a quantum dot in a microcavity [New J. Phys. 13, 113014 (2011)]. A comparison between exact numerical results and analytical formulas provides the conditions to efficiently generate indistinguishable and simultaneous pairs of photons under both types of excitation.

It is well known that current modulation in diode lasers generates amplitude (AM) and optical frequency (FM) modulations. The frequency chirp under direct current modulation originates from variations in the carrier density and from the finite difference in carrier density between the laser on and off states. Modulation of the carrier density modulates the gain and the optical index causing the resonant mode to shift. This frequency chirp broadens the spectrum, which is a serious limitation for high-speed applications and optical fiber communications. At low frequencies, thermal effects also alter the frequency chirp. The aim of this paper is to show that the laser's frequency chirp can be modified using an external control technique. The chirp response is evaluated via the determination of the chirp-to-power ratio (CPR) through a Mach-Zehnder interferometer. Experiments demonstrate that when an external optical feedback is properly adjusted, the CPR can be severely decreased over a wide range of modulation frequencies as compared to the free-running case. These preliminary results obtained on quantum well distributed feedback lasers (QW DFB) with low normalized coupling coefficient (κL) demonstrate how to stabilize the CPR through the DFB facet phase effects or parameters such as the linewidth enhancement factor. In order to confirm this frequency chirp engineering, selfconsistent calculations based on the transfer matrix method are also presented.

A novel cascaded optical injection-locking scheme for modulation bandwidth enhancement and tailoring is proposed, involving a distributed-Bragg-reflector master laser monolithically integrated with two cascaded strongly injectionlocked whistle-geometry unidirectional microring lasers. Improved high-speed performance of the proposed cascaded injection-locking scheme is confirmed in numerical modeling by comparing it with the scheme based on a single strongly injection-locked whistle-geometry unidirectional microring laser.

We report an experimental study of the polarization-resolved nonlinear dynamics of a 1550nm single-mode linearly polarized VCSEL when subject to orthogonal optical injection. We measure high-resolution (10 MHz) optical spectra of the linear polarizations and the total power emitted by the VCSEL. Spectra are analyzed together with the simultaneous temporal series of linearly polarized powers. For periodic dynamics, both linear polarizations show spectra with equally spaced peaks with a separation that corresponds to the frequency detuning. As the injected power increases much more peaks are observed with larger (smaller) separation between them when the frequency detuning is positive (negative). For negative values of the frequency detuning, increasing the injected power leads to irregular dynamics that is characterized by optical spectra for both linear polarizations with broad pedestals and much less defined peaks specially for the parallel polarization.

We analyze the time dependent dynamics associated with the Polarization Switching (PS) induced in a 1550nm-Vertical Cavity Surface Emitting Laser (VCSEL) subject to polarized optical injection. We have investigated two different experimental configurations, namely single and double polarized optical injection into the 1550nm-VCSEL with polarizations parallel and orthogonal to that of the light emitted by the solitary device. We have simultaneously analyzed the temporal dynamics for the two orthogonal polarizations at the VCSEL output. Sub-ns response times were obtained for both experimental configurations. For single orthogonally-polarized optical injection we found that the operation speed is ultimately limited by the relaxation oscillation frequency of the VCSEL. On the other hand, with the device subject to double polarized optical injection a significantly enhanced operation speed was obtained. We believe that this improved time response is due to the faster carrier dynamics associated with the switching between the two injectionlocked states induced alternatively by the two polarized optically-injected signals. This enhanced operation speed for the PS attained in VCSELs at the important telecom wavelength of 1550nm offers exciting prospects for novel uses of these devices in optical signal processing and optical switching applications in present and future optical networks.

A comparative study of the gain spectra of quantum-dot lasers at high carrier densities is reported. The gain spectra of quantum dot lasers under a constant junction temperature (obtained by the use of Fabry-Perot modes as a temperature gauge) and under constant heat-sink temperatures are measured. Negative differential gain, observed for the ensemble of quantum dot ground-states is shown to be mainly due to free carrier effects, where increasing dephasing effects, combined with saturated gain, result in spectral broadening and a reduction in the peak gain.

In this work, a theoretical and model study of the temperature effects on threshold current, as tuning technique, and the comparison with experimental results of quantum dot (QD) diode lasers is presented. It is well known the dependence of output wavelength with temperature in semiconductor lasers. This property can be highly useful in order to obtain stable and easy tuning lasers getting two different specific wavelengths to achieve signals in the millimetre (mmW) and terahertz (THz) ranges by photomixing. Our model and study over QD lasers allow us to understand the behaviour of temperature inside the device and thus, we can estimate the best characteristics to obtain the desired results.

Nonlinear perturbation of effective group index is calculated numerically in semiconductor ridge waveguide laser structures under an influence of a strong driving wave (mode). Model of nonlinear interaction of waves is used to obtain conditions for appearance of anomalous dispersion of modal index and also for inversion of the group index of guided waves (modes of the ridge-waveguide laser structures). Ranges around critically anomalous dispersion (CAD) points, where the effective group index passes zero value, are calculated numerically. CAD points form closed loops in graphs of detuning vs. driving wave intensity. These loops define ranges where superluminal propagation, as well as slowed reflection of probe wave can be obtained. Numerical simulations are performed for an InGaAs/AlGaAs/GaAs double quantum well (DQW) laser structure and also for a GaAs/AlGaAs separate confinement heterostructure. The threshold intensities for the appearance of CAD points, as well as the influence of relaxation rate and optical confinement on the appearance of superluminal regime are compared for the DQW and SCH structures.

In this paper we report a hybrid quantum well (QW) and quantum dot (QD) structure to achieve a broad spontaneous emission and gain spectra. A single quantum well is introduced into a multi-layer stack of quantum dots, spectrally positioned to cancel the losses due to the second excited state of the dots. Attributed to the combined effect of QW and QDs, we show room temperature spontaneous emission with a 3dB bandwidth of ~250 nm and modal gain spanning over ~300 nm. We describe how this is achieved by careful design of the structure, balancing thermal emission from the QW and transport/capture processes in the QDs. We will also compare results from a QD-only epitaxial structure to describe how broadband gain/emission can be achieved in this new type of structure.

Gallium nitride based light emitting diodes have emerged as powerful devices which could replace incandescent and fluorescent lamps within the next years. The development of phosphor-free white LEDs is an ongoing field of research because of the lack of high efficiency green LEDs. A promising approach is the growth of InGaN/GaN nanowires with a continuously varied Indium content along the structure. The graded mole fraction profile is supposed to yield a multitude of emission colors due to many emission levels which can sum up to white light emission. The formation of strain and polarization charges is reduced because of the incremental varying lattice constants in combination with the facility of lateral relaxation of the wire. We report on the computational analysis of those nanowire structures in order to understand the electroluminescent behavior. The simulation software calculates the electrostatic potential and the carrier densities in the entire structure by solving the Poisson and the drift/diffusion equations in three dimensions. The luminescence is determined on the basis of a free carrier theory and enters the continuity equations as recombination term with strain and polarization effects included. This comprehensive physical model is employed to analyze carrier injection and luminescence for a white light-emitter design.

We present a computational study on the anisotropic luminescence and the efficiency of a core-shell type nanowire LED based on GaN with InGaN active quantum wells. The physical simulator used for analyzing this device integrates a multidimensional drift-diffusion transport solver and a k · p Schr¨odinger problem solver for quantization effects and luminescence. The solution of both problems is coupled to achieve self-consistency. Using this solver we investigate the effect of dimensions, design of quantum wells, and current injection on the efficiency and luminescence of the core-shell nanowire LED. The anisotropy of the luminescence and re-absorption is analyzed with respect to the external efficiency of the LED. From the results we derive strategies for design optimization.

The dependence of resonance energy transfer from Wannier-Mott excitons to an organic overlayer on exciton dimensionality is studied experimentally and by means of supporting simulations. The variation of temperature effectively tunes the balance between localized and free excitons, and allows to investigate the effect of the excitonic potential disorder on resonance energy transfer. Our theoretical calculations give insight into the experimentally observed temperature dependence of resonance energy transfer, and allow us to quantify the contribution from localized and free excitons. It is shown that free excitons can undergo resonance energy transfer at a rate that is an order of magnitude higher compared to localized excitons. In planar geometries nonradiative resonance energy transfer is dominating over radiative energy transfer and hence we propose hybrid inorganic-organic LEDs which are optimized for resonance energy transfer to an organic or QD-based color converter.

We present a finite element method (FEM) solver for computation of optical resonance modes in VCSELs. We perform a convergence study and demonstrate that high accuracies for 3D setups can be attained on standard computers. We also demonstrate simulations of thero-optical effects in VCSELs.

A meshless solution to vectorial mode fields has been applied to various micro-structured optical waveguides. The Finite Cloud Method (FCM), has been used to solve coupled field equations for both transverse components of the magnetic field as well as the effective index of refraction for the waveguides. Two methods using either a step-index or a graded-index have been implemented and compared. An approximation to the solution is found using a distribution of points and a cloud about each point, with no mesh and minimal geometric linking knowledge between the points. This gives the ability to use a highly irregular point distribution which can be easily modified or tailored to micro-structured fibers in order to accurately represent the vectorial modal solution. In addition, the use of Bayliss-Gunzburger-Turkel-like transparent boundary conditions (TBC) and an iterative process is compared with a perfectly matched layer (PML), both of which allow for the solution of leaky modes for the structures. Results for ridge waveguides and solid core fibers having low index contrast are in high agreement with the solutions from commercial solvers. Further results with high contrast air hole structures are compared with other solution methods giving promising results and highlight this methods versatility, accuracy and efficiency for a wide range of problems.

We show that the performance of iterative solvers of the frequency-domain Maxwell's equations is greatly affected by the kind of the perfectly matched layer (PML) used. In particular, we demonstrate that using the stretchedcoordinate PML (SC-PML) results in significantly faster convergence speed as compared with using the uniaxial PML (UPML). Such a difference in convergence behavior is explained by an analysis of the condition number of the coefficient matrices. Additionally, we develop a diagonal preconditioning scheme that significantly improves solver performance when UPML is used.

Plasmonic Near-Field Transducers (NFTs) find use in Energy-Assisted Magnetic Recording (EAMR) schemes, where a high-anisotropy recording medium is locally heated to the Curie temperature, allowing conventional magnetic recording heads to overcome the high coercivity of the medium. However, coupling efficiency is low, and the conditions for excitation and resonance are poorly understood. In this work, we explore the behavior of a canonical EAMR setup including rectangular dielectric waveguide, elliptic cylinder gold NFT, and conductive planar recording medium. We systematically examine the effects of polarization and angle; spacing between NFT, waveguide, and recording medium; and variations in NFT size and incident wavelength.

We present an analytical study of resonance properties of square subwavelength apertures at optical and near-IR frequencies. This approach allows accurate prediction of resonance responses, captures both propagating and evanescent modes, and can easily be implemented in other analytical techniques. In this approach we avoid analyzing the detailed behavior of the fields inside the metal walls, but still obtain the effects of the buildup of charges within those walls. We calculate the dispersion relation and find the cutoff frequency's dependence on cavity dimensions for a square aperture embedded in a silver film, and support our findings with finite-element simulations.

We present a theoretical study on an index-asymmetric double-electrode waveguide structure and identify a long-range surface plasmon polariton (LRSPP) super-mode for index-sensing. We propose to operate the LRSPP by monitoring its cut-off wavelength which promises ultra-sensitivity. The sensitivity is calculated to be 6.5×104 nm per refractive index unit (RIU), which is one order magnitude higher than most plasmonic sensors based on spectral interrogation. Additionally, based on computations from the transfer matrix theory, we present the properties of this LRSPP supermode.

In this paper we present the simulation results of two different methods of grating engineering (Genetic Algorithm and Discrete Layer Peeling) used for the synthesis of Bragg Gratings with a negative Group Time Delay. The physical structures of the resulting gratings, as well as their reflection spectra, are displayed for different initial parameters. These gratings could be employed (as it will be demonstrated) as cavity reflectors for the generation of a continuum laser emission by other means than those of nonlinear optics.

We have developed a 3D Finite Difference Time Domain (FDTD) algorithm to model obliquely incident waves through arbitrary birefringent and dichroic media with transverse periodic boundaries. Beginning with arbitrary conductivity and permittivity tensors, we employed the split-field method (SFM) to enable broadband sources with oblique incidence. We terminate our boundaries with a uniaxial perfectly matched layer (UPML) in one dimension and periodic boundaries in the other two dimensions. The algorithm is validated via several case studies: a polarizer pair, a twisted nematic liquid crystal, and an array of conducting particles. Using this approach, we simulate for the first time polarization gratings with light obliquely incident in directions orthogonal to the grating vector (i.e., at oblique angles outside the normal diffraction plane).

A scalar theory, verified by the Rigorous Coupled Wave Analysis (RCWA), is used to compare the performance of optical surfaces with a specified roughness. It is shown that for surfaces with identical micro roughness structures, backward scattered light level for a reflecting surface is much higher than the forward scattered light produced by the surface of a refractive optical element made from typical optical glass. This implies that application of refractive components (such as transmission gratings and lenses) in optical systems where scattered light background is a limiting factor of the instrument performance may be advantageous over reflective components such as reflection gratings and mirrors.

Recently, there has been much interest in a novel type of device, the 2D photonic crystal surface emitting laser (PCSEL). For commercialization of these devices a robust and high reliability manufacturing method is required. Previous GaAs wafer fusion and GaN regrowth techniques have utilised voids within the photonic crystal which suffer from reliability and reproducibility issues. We demonstrate a GaAs based PCSEL structure which uses epitaxial regrowth to completely infill the etched structure. We discuss the design, epitaxy, and operating characteristics of these devices over a range of temperatures.

Numerical simulations are an important tool for the design of opto-electronical components and devices. In order to obtain realistic results, a multitude of physical effects and theories have to be included, e.g., Maxwell's equations for lasing mode computations, heat transfer in active devices, and electronic transport. In our contribution we perform coupled electro-thermal simulations of high power diode lasers. We analyze the temperature dependence of the mode profile and far field characteristics. Our results will be compared to experimental measurements of broad area lasers and will quantitatively describe the effect of thermal blooming.

Conformal transformation and the beam propagation method are employed for the simulation of deeply-etched bent and serpentine waveguides on an InP substrate with an active region consisting of double InGaAs quantum wells. The modal properties are analyzed and the bending and transition losses are extracted from the propagation results. For the serpentine waveguides, the transition losses increase significantly for waveguides with bending radii less than 12 μm, yet careful choice of the transition point at which the curvature reverses is shown to minimize the losses induced by the transition. Effects of etch depth are also considered and conclusion that it is necessary to etch through the active region for deeply-etched bent waveguides is drawn.

In this work, we study and investigate the thermally effects on the compact continuous wave (CW) distributed feedback (DFB) laser as a tuning method using an external platinum μ-heater film in a vertical and lateral configurations. A low injection current into platinum heater produces the variation temperature inside the active and grating regions to shift the lasing wavelength. The frequency is continuously tuned up to 3 THz at operation wavelength of 937 nm, by controlling the temperature of the laser to achieve sub-millimetre (sub-mmW) and terahertz (THz) signals generation by photomixing.

We have compared and analyzed the theoretical possibility for the extreme reduction in the linewidth enhancement (α- factor) in strained layer quantum-well (QW) lasers for AlGaInAs and InGaAsP material. Valence band structure and optical gain in both types of QWs under compressive strain have been calculated using 4×4 Luttinger-Kohn Hamiltonian. The Luttinger parameters of these quaternary materials were determined from the linear interpolation between the values of their respective binaries. The α-factor has been calculated as the ratio of the carrier induced change in real component of the complex refractive index to that in imaginary component of the refractive index. We have used Kramers-Kronig relations to calculate the refractive index change due to carrier induced. The α-factor was up to 1.5 times smaller in AlGaInAs QW than in InGaAsP QW lasers. The material modal differential gain is found to be approximately 1.38 times larger and material carrier induced refractive index change is 1.16 times smaller in the former material than the latter, respectively.

Bulk InGaAs layers with a 1eV band-gap grown on GaAs substrates are attractive for high efficiency multi-junction solar cells. However, a large amount of lattice mismatch between bulk InGaAs layer and GaAs substrate necessitates development of novel metamorphic buffer layers (MBL). A number of research groups have reported various MBLs for applications including HBTs, HEMTs, lasers, and solar cells. In this study, we report carrier dynamics and defects in MOVPE-grown bulk InGaAs layers (E_g = ~ 1.0 - 1.1 eV at 300K) with two different types of MBLs including InGaAs and InGaPSb. We also report the effect of chemical-mechanical polishing (CMP) process on carrier lifetimes and the properties of the films subsequently grown on top of the MBL. We employed time-resolved photoluminescence (TR-PL) techniques to study carrier dynamics in InxGa1-xAs samples with and without the CMP process and a high resolution TEM to study defects in various structures.

This study concentrates on solar light absorption power in a silicon solar cell using a double diffraction triangular nano-grating. The first grating is located on top of the solar cell and the second grating is located on bottom of the solar cell above a reflective metallic substrate of Ar (Si₃ N₄ ) (Argon gas mixed with Silicon Nitride). We simulate the solar cell behavior over varying grating parameters as it absorbs sunlight and compare the average power output absorbed at the center of the solar cell. Each case simulates a period (A_t ) that varies from 100nm to 800nm in 100nm interval for the top lattice, while maintaining the bottom lattice at a constant period (A_b ). We repeat this procedure for the bottom lattice, changing the lattice period from 100nm to 800nm in 100nm interval in order to find the optimized case. We also consider solar spectrum irradiation under wavelengths ranging from 300nm to 1100nm in 50nm intervals. The total power absorption improvement is about 170% compared to the non-grating case, occurring in the weighted solar cell simulation with top grating period greater than 300nm and bottom grating period of 500nm.

This paper describes the modeling of a 2×2 multimode interference (MMI) switch, with a channel profile of Titanium indiffused Lithium Niobate. Design novelty lies in its satisfactory operation for two wide optical windows (100nm each with centre wavelengths, λ_centre of 1.3 μm and 1.55 μm) with low switching losses and crosstalk levels. Index tuned regions are optimized to achieve crosstalk levels of ≥ -18 dB and ≥ -14 dB for its operation in the wavelength range of 1.25 μm - 1.35 μm and 1.50 μm - 1.60 μm respectively. For either of these wavelength ranges, the switch losses (excess and insertion losses) are maintained lower than 1 dB.

The characteristics of exciton-polaritons in ZnO-based microcavities (MCs) are demonstrated with a large vacuum Rabi splitting due to large exciton binding energy and oscillator strength. The lower polariton branches (LPBs) can be clearly observed. For low temperature and large negative detuning conditions, a clear polariton relaxation bottleneck in bulk ZnO-based MCs has been observed in angle-resolved photoluminescence measurements from 100 to 353 K at different cavity-exciton detunings. The bottleneck is strongly suppressed with increasing the temperature and pumping power and reducing detuning. This observed results supposed to be due to more efficient phonon-assisted relaxation and a longer radiative lifetime of the polaritons. In addition, the linewidth broadening, blue-shift of the emission peak, and polarization of polariton lasing from below threshold to up threshold are also discussed.

An almost ideal thresholdless laser can be realized in the strong-coupling regime of the light-matter interaction, with Poissonian fluctuations of the field at all pumping powers. Here, we show that this ideal scenario is thwarted by quantum nonlinearities when crossing from the linear to the stimulated emission regime. A universal jump in the normalized intensity correlation function is predicted to occur, the measurement of which could be used to establish a standard fingerprint of the onset of lasing in the strong coupling regime.

This work presents a theoretical design and experimental optimization study on the improvements to pulsed diode laser Gain-Switched (GS) optical sources and an external compressor based on a Nonlinear Loop Mirror (NOLM). The designed and optimized NOLM will be adapted to the characteristics of GS optical sources by using a microstructured optical fiber and a semiconductor optical amplifier in a nonlinear Sagnac loop, avoiding the need to include in the compression and reshaping scheme pre-processing stages of the input optical pulses. This scheme reduces the system complexity and the assembly of an input stage being a commercial or Cost Of The Shelf (COTS) gain-switched diode laser and a compressor and reshaping stage giving rise to a compact, reliable low cost new picosecond optical pulse sources at high repetition rates, that can be used in many fields and applications.

In this paper, we investigate the dynamics of a nonlinear delay differential equation model for passive mode-locking in semiconductor lasers, when the delay model is seeded with parameters extracted from the gain and loss spectra of a quantum dot laser. The approach used relies on narrowing the parameter space of the model by constraining the values of most of the model parameters to values extracted from gain and loss measurements at threshold. The impact of the free parameters, namely, the linewidth enhancement factors that are not available from the gain and loss measurements, on the device output is then analyzed using the results of direct integration of the delay model. In addition to predicting experimentally observed trends such as pulse trimming with applied absorber bias, the simulation results offer insight into the range of values of the linewidth enhancement factors in the gain and absorber sections permissible for stable mode-locking near threshold. Further, the simulations show that this range of permissible values progressively decreases with increasing bias voltage on the absorber section. This is important for telecomm and datacom applications where such devices are sought as pulsed sources, as well as in military RF photonic applications, where mode-locked diode lasers are used as low noise clocks for sampling.

A laser diode (LD) has been used in many areas, such as optical communication systems. However, its oscillation frequency changes, with variations in ambient temperature and injection current, so its frequency stabilization is of vital importance. In these situations, Rb saturated absorption spectroscopy is the method of choice. We use the beat signal, both for the purpose of evaluating frequency stability between two independently stabilized LDs, and for generating THz waves. This work shows a basic experiment using our beat signal observation, by high-speed photodetector. In addition, we have also used a frequency-stabilized etalon, to improve frequency selectivity.

We have proposed the concept of a passive cavity laser for both surface emitting and edge emitting devices. Passive cavity surface emitting laser has an active medium placed in or even outside of a distributed Bragg reflector, whereas the optical cavity remains passive and can be formed of an arbitrary, e. g. a dielectric material. This approach allows a significant reduction of the thickness of the epitaxially grown semiconductor structure (e.g., by a factor of 3) and also allows fabricating a surface emitting laser combined with a true photonic crystals, the latter being formed directly in the optical cavity allowing advanced possibilities for engineering of the lasing optical modes and providing their extreme lateral confinement. Passive cavity edge emitting laser employs a thick passive waveguide, e.g. a transparent substrate, while gain medium is placed in the evanescent part of the field in the cladding. If the gain medium is placed in another, thin cavity coupled to the substrate (Tilted Wave Laser) an ultranarrow vertical beam (down to 0.65 degrees full width at half maximum) is generated. Additional processing of a thin active waveguide by its cutting by the trenches enables to prohibit undesired emission with a broad angular distribution. Two-dimensional modeling of tilted wave lasers provides the optimum laser geometry with zero scattering losses and a high efficiency.

We review our experimental and simulation-modeling studies on optoelectronic oscillators (OEOs). The OEO can have an intrinsic quality factor, Q that is orders of magnitude higher than that of the best electronic oscillators (i.e. Poseidon). However, our experimental results show that the OEO's current phase noise level is still worse than that of the Poseidon. This is caused by many noise sources in the OEO which reduce the "loaded-Q" in the loop system. In order to mitigate these noise sources, we have systematically studied such phenomena as the laser RIN, Brillouin and Rayleigh scattering in the fiber, vibration, etc. These noise sources are convoluted in both optical and electrical domains by many different physical effects; hence, it is very difficult to experimentally separate them, and only the dominant phase noise is observed in each offset-frequency. Therefore, we developed a computational model to simulate our experimental injection-locked dual-OEO system. By validating the model with our experimental results from both individual components and OEO loops, we can start to trace the individual phase noise sources. The goal is to use the validated model to guide our experiments to identify the dominant phase noise in each spectral region, and mitigate these noise sources so that the OEO can reach its full potential.

In this paper we present an end-to-end system model for passive millimeter wave (mmW) imaging system based on an optical up-conversion process. Due to the complicated nature of the system, accurate and efficient model of such a system becomes extremely challenging. To this end, we establish a mathematical model to bridge all component and subsystem models together to complete the system performance evaluation. The subsystem models through theoretical simulation and experimental measurement provide accurate input for overall system performance evaluation. The developed tools have been used for the validation our First-Ever demonstrated passive mmW imager at 35 GHz and excellent agreement has been achieved between the simulation and experimental results.

We develop and investigate a dual-frequency Laser Doppler Velocimeter (DF-LDV) based on an optically injected semiconductor laser. By operating the laser in a period-one oscillation (P1) state, the laser can emit light with two coherent frequency components separated by about 11.25 GHz. Through optical heterodyning, the velocity of the target can be determined from the Doppler shift of the beat signal of the dual-frequency light. While the DF-LDV has the same advantages of good directionality and high intensity as in the conventional singlefrequency LDV (SF-LDV), having an effective wavelength in the range of microwave in the beat signal greatly reduces the speckle noise caused by the random phase modulation from the rough surface of the moving target. To demonstrate the speckle noise reduction, the Doppler shifted signals from a moving target covered by the plain paper are measured both from the SF-LDV and the DF-LDV. The target is rotated to provide a transverse velocity, where the speckle noise increases as the transverse velocity increases. The bandwidth of the Doppler signal obtained from the SF-LDV is increased from 4.7 kHz to 9.4 kHz as the transverse velocity increases from 0 m/s to 5 m/s. In contrast, the bandwidth obtained from the DF-LDV maintains at 0.09 Hz with or without the rotation limited by the linewidth of the P1 state used. By phase-locking the laser with a RF current modulation, the linewidth of the P1 state can be much reduced to further improve the velocity resolution and extend the detection range.

Erbium-doped fiber lasers have become a reliable source of sub-100 fs pulses at 1550 nm; however dispersion and nonlinearities in optical fiber make generation of multi-nJ pulses difficult. In this paper a two-stage fiber amplification system which consists of two sub-fiber-amplifiers was designed by introducing a filter between the two sub-amplifiers to manage or modify the spectrum of the pulse amplified by the first sub-fiber-amplifier before it goes into the second one. A systematic simulation, both in time domain and in frequency domain, for this fiber amplifier system was conducted. The role of the filter in the system is presented and discussed. The parameters of this two-stage fiber amplification system are determined by calculation results based on the high-concentration Er-doped fiber as gain media and high power laser diodes as pump light sources, All of the components in the system are commercially available. In addition, the optimal output of the amplification system was obtained based on simulations.

Conventional lens manufacturing is accomplished by injection molding followed by application of a thin film anti-reflection coating. This requires several production steps, each with the associated constraints. Here we report a technique for production of injection molded lenses with conical sub-wavelength grating anti-reflection structures. While similar structures have been made in the past, our technique allows the sub-wavelength structure to be created on curved surfaces during the injection molding process, reducing the number of steps in the manufacturing process. The advantage of this new technology is that anti-reflection function is created without any additional process(es) conventionally required but by a single injection molding process to make lens normally, through which substantial cost saving will be achieved.

A novel single-transistor configuration active pixel image sensor (APS) has been investigated in this paper. This device can realize the functions of the conventional 3T CMOS image sensor. In this paper, the basic performances including transient simulation, potential changes, and read endurance of the 1T image sensor will be discussed. Different from the conventional 3T CMOS image sensor, holes are used as signal charges in the proposed device. Comparison with the conventional 3T APS will be discussed as well.

Based on the equivalence theorem of a unitary optical system. We proposed an analytical approach to characterize the cell parameters of a twisted nematic liquid crystal device (TNLCD) with full field resolution. The spatial distribution of three characteristic parameters of a TNLCD were measured by using a polarizer-sample-analyzer imaging ellipsometer, thus the untwisted phase retardation, cell thickness and twisted angle of a TNLCD can be directly calculated through the explicit expressions as a function of its characteristic parameters. The measured results are very close to the design values provided by TNLCD manufacture. This method shows that both the system setup and parameters calculating process are quite simple. It would be more helpful to characterize a TNLCD in the manufacturing process.

III-nitride visible light emitters employ deep QWs and feature strong disparity of electron and hole transport in diode structures. As a result, multi-QW active regions of such devices suffer from inhomogeneous carrier injection, large residual charges of active QWs, and overall active region electrical non-uniformity which unfavorably affects the emitter efficiency. In this work, we show that electron and hole populations of deep optically active III-nitride QWs are highly imbalanced and substantially deviate from thermodynamic equilibrium with corresponding mobile carrier subsystems. Non-equilibrium QW populations are self-consistently determined by carrier injection and light generation processes in active QWs. In turn, QW residual charges impose strong feedback on the active region electrical uniformity. Our selfconsistent modeling of QW radiative characteristics and multi-QW carrier transport in diode structures relates the effects of non-equilibrium QW populations, inhomogeneous QW injection and residual QW charges to the structure internal efficiency. Comparative modeling of polar and nonpolar diodes shows that in both types of structures the nonequilibrium effects tend to decrease the QW operational electron populations; this trend benefits the active region electrical uniformity. For device simulation, we use COMSOL-based Optoelectronic Device Modeling Software (ODMS) developed at Ostendo Technologies Inc.

An optical 90° hybrids based on silicon-on-insulator (SOI) 4×4 MMI couplers have been fabricated in 340nm top silicon using E-Beam technology. Below 2.2° phase deviation of the hybrids for the across C-band of TE mode have been simulated, which is well satisfied with the typical systems requirements. The measured optical transmission powers from port to port show that the devices function well as a 6dB power divider with excess loss around 1dB at wavelength λ=1550nm for TE mode. The measured transmission spectra of the 4×4 MMI coupler are seriously affected by the FP resonance noise, which bring in error in phase deviation testing.

Numerical simulation based on first-principles calculations is applied to study the energy band structural characteristics and the band-gap properties of wurtzite InGaN. The results show that the direct band gap, the band gap bowing parameter, the width of valence band, and the width of top valence band increase with compressive strain and decrease with tensile strain. The biaxial strain effect on the indirect band gap is little. In general, there is a larger band gap bowing parameter and larger strain-induced band gap bowing variation in Ga-rich alloys. In addition, the direct band gap, the indirect band gap, the width of valence band, and the width of top valence band decrease with increase of indium composition. Wurtzite InGaN remains the characteristic of a direct band gap material under biaxial stress.

Random numbers can be classified as either pseudo- or physical-random, in character. Pseudo-random numbers are generated by definite periodicity, so, their usefulness in cryptographic applications is somewhat limited. On the other hand, naturally-generated physical-random numbers have no calculable periodicity, thereby making them ideal for the task. Diode lasers' considerable wideband noise gives them tremendous capacity for generating physical-random numbers, at a high rate of speed. We measured a diode laser's output with a fast photo detector, and evaluated the binary-numbers from the diode laser's frequency noise characteristics. We then identified and evaluated the binary-number-line's statistical properties. We also investigate the possibility that much faster physical-random number parallel-generation is possible, using separate outputs of different optical-path length and character, which we refer to as "coherence collapse".

Even as long ago as the 1960's, scientists understood that diode lasers' oscillation wavelengths demonstrated significant shifts to the shorter wavelength side, when subjected to strong magnetic fields, at extremely low temperatures. When we exposed Fabry-Perot type diode lasers oscillating at 780 nm to weak magnetic fields, at room temperature, the oscillation wavelength was observed to have shifted to the longer wavelength side. In discussions of shift mechanisms aimed at explaining how/why our results differ from those obtained in studies conducted in the 1960's, we noted a rise in temperature and an increase in the carrier density, and how it affected the characteristic shifts observed, when a magnetic field was applied to the Fabry-Perot type laser diodes parallel to the injection current. In the present work, we tested the oscillation wavelength shift of a vertical-cavity surface-emitting laser (VCSEL) in a magnetic field, because we expected that, by doing so, the VCSEL would show a shorter wavelength side shift.

This study explores the optical field distribution of 1.55μm InGaAsP distributed feedback Laser with an air gap in the middle section. The optical field distribution was analyzed by different depth and width of an air gap. From the calculation, we could observe how the gap affect the coupling of the optical field into the other cavity. The percentage of the coupling is a crucial factor to the injection-locking operation. Both effective index model and commercial software were used to predict this coupling.

Anomalous transmission through sub-wavelength aperture metamaterials, frequency selective surfaces and sub-wavelength sized aperture arrays has been a topic immense interest in the present decade. The ability to manipulate electromagnetic energy as it propagates through a metamaterial has ushered in a an age of sub-wavelength optical devices. Optical devised are prone to diffraction and back scattering. Diffraction effects inhibit the transmission performance of metamaterial sub-wavelength films. Depending on the application, back scattered light could be beneficial or undesirable. A method to reduce back scattered light is explored in this paper. This method involved placing sub-wavelength square apertures within a film to suppress the diffraction. Coupling of the fields between the apertures was observed in one of the studied structures. There is a spatial relationship between the distance separating the apertures and the coupling of the light. To characterize the coupling behavior and thereby reduce the far-field back scattering of light, more apertures were placed in various positions within the unit cell. This enabled reduction of the back scattering thereby, enhancing the forward transmission of light. It was found that populating the unit cell with more apertures resulted in a higher transmission. Increasing the spacing between the apertures resulted in couple cavity effects between the apertures. This effect is due to the fact that the apertures have a wider bandwidth hence broader transmission channels which aid light transmission rather than light scattering or reflection.

Associative memory, also known as fault tolerant or content-addressable memory, has gained considerable attention in last few decades. This memory possesses important advantages over the more common random access memories since it provides the capability to correct faults and/or partially missing information in a given input pattern. There is general consensus that optical implementation of connectionist models and parallel processors including associative memory has a better record of success compared to their electronic counterparts. In this article, we describe a novel optical implementation of associative memory which not only has the advantage of all optical learning and recalling capabilities, it can also be realized easily. We present a new approach, inspired by tomographic imaging techniques, for holographic implementation of associative memories. In this approach, a volume holographic material is sandwiched within a matrix of inputs (optical point sources) and outputs (photodetectors). The memory capacity is realized by the spatial modulation of refractive index of the holographic material. Constructing the spatial distribution of the refractive index from an array of known inputs and outputs is formulated as an inverse problem consisting a set of linear integral equations.

Generation and applications of the optical pulses with a parabolic intensity profile has developed into the area of dynamic research activity over recent years. Parabolic pulses can propagate remaining their parabolic profile. Particularly these pulses resist to the deleterious effect of the optical wave breaking. They are of great interest for a number of applications including the high power pulse generation, and all optical signal processing. Alternative methods of generating parabolic pulses are of especial interest in the context of non-amplification usage, such as optical telecommunications. It is found that Gaussian waveforms provide best quasi-parabolic pulses among others and within shortest distance. There is a range of soliton numbers where the shape of quasi-parabolic pulse is closest to parabolic one.

Thermal and optical properties of Buried structures laser are simulated in the case where we include a waveguide layer beneath the Multi Quantum Well's. The role of this waveguide is twofold. On one hand It attracts the optical field on lower side of the active waveguide where the losses are low due to n doped side of the laser. On the other hand, we can improve the coupling coefficient to the fiber by increasing the divergence of the beam together with its waist increase. Finite element software is used to calculate thermal resistance of the structures. Beam Propagation method is use for optical modeling. We optimize active waveguide composition and thickness for various multi-quantum wells number. Optical modeling is used to check the single mode operation of the structure together with beam shape optimization according to the objectives. Waveguide parameters are optimized to reduce the thermal resistance of investigated structures. Trade of between thermal and optical properties is discussed.

In this paper, we have theoretically analyzed and designed a 1D PhC microcavity sensor with SPR based on the total internal reflection mirror using analytic calculation and FDTD methods. The proposed structure has many advantages. One of that is a high sensitivity using SPR characteristics. Another is a high Q-factor of the characteristics in the PhC microcavity structure. The incident light has double resonance characteristics, because the filtered light by PhC structure is met the thin metal film for SPR effect. We have also observed the change of resonance characteristics according to the variation of effective index on the metal film.

External cavity diode laser (ECDL) systems are presently experiencing a surge in popularity as laser light-sources, in advanced optical communications- and measurement-applications. Because such systems require that their external reflectors be precisely controlled, to eliminate low frequency fluctuations in optical output, we conducted experiments with a two-cavity version of the ECDL system for a vertical cavity surface emitting laser (VCSEL). This technique brings the added advantages of a narrower linewidth than would be achievable via a single optical feedback. VCSELs are characterized by wider oscillation linewidths than edge emitting types, so the larger effect of double optical feedback system is expected.

The simulation of electromagnetic problems using the Finite-Difference Time-Domain method starts with the geometric design of the devices and their surroundings with appropriate materials and boundary conditions. This design stage is one of the most time consuming part in the Finite-Difference Time-Domain (FDTD) simulation of photonics devices. Many FDTD solvers have their own way of providing the design environment which can be burdensome for a new user to learn. In this work, geometric and material modeling features are developed on the freely available Google SketchUp, allowing users who are fond of its environment to easily model photonics simulations. The design and implementation of the modeling environment are discussed.