We theoretically investigate the optical transmission through a subwavelength slit covered with a nanostrip and surrounded by corrugations in a metal film. Simulations results show that with a nanostrip on top of the slit, the optical transmission efficiency through the slit surrounded by grooves is greatly enhanced for various angles of incidence compared with the structure without the nanostrip. The nanostrip should be thick enough to result in an air nanocavity with high Q value and enhanced transmission efficiency.
To characterize and predict the dynamics of the nonlinear polarization rotation (NPR) in semiconductor optical amplifiers (SOA) an experimental method based on the frequency response technique and a model based on the density matrix and effective index formalisms are presented. Particularly, the frequency response of the NPR is obtained by determining, for each studied frequency, the angular displacement, at the Poincare Sphere, that separates the initial and final points of the polarization evolution of the output beam.
The effect of growth temperature on InAs QDs grown by metal-organic chemical vapor deposition (MOCVD) was investigated in detail. Growth temperature affects InAs QDs in three ways, including the reconstruction mode of new InAs crystal faces, the migration length of adatoms, band gaps of InAs QDs, and the interaction among three aspects was studied. The variation of density, size and wavelength was experimentally demonstrated. The high density of 5.2 x 10(10)cm(-2) was obtained. The room temperature wavelength of InAs/GaAs QDs using GaAs as capping layer reached 1240nm.
We investigate theoretically the effect of two-dimensional photonic crystal (PC) defect waveguide parameters embedded into vertical-cavity surface-emitting laser (VCSEL) on static operation of PC-VCSEL like spatial hole burning (SHB) and temperature of active region. In structures with larger pitch of PC holes SHB occurs dramatically and temperature increases in active region. In large hole diameter to pitch ratio, SHB has a little effect and temperature is decreased in active region.
A dual-depletion-region lumped electroabsorption modulator (DDR-LEAM) based on InP at 1550nm is designed and fabricated. The measurement results reveal that the dual depletion region structure can reduce the device capacitance significantly without any degradation of extinction ratio. The simulation results show that the highly doped charge layer can concentrate almost all of the external applied voltage in MQW region and thus contribute to the identical extinction ratio curves. The expected 3-dB bandwidth of the DDR-LEAMs using an equivalent circuit model is more than twice lager than that of the conventional LEAM.
We demonstrated and fabricated a 20μm-long ultra-compact variable optical attenuator based on thermo-optical effect with slow light photonic crystal waveguide (PCWG). In simulation, we optimize the line-defect width and radius/period ratio (r/a) of the PCWG for deep photonic band gap and large slope photonic band edge. An r/a=140nm/410nm W1 PCWG is selected for its -60dB depth and 36dB variable attenuation range when the tunable refractive index change is 0.01. We also study different shapes of micro-heaters for low power consumption and high heat transfer efficiency. A 24.6mW and 75.9% heat transfer efficiency are achieved in a 2μm-wide right-angle-shaped micro-heater. In experiment, A 4.6nm red shift at the cutoff wavelength of the fundamental mode and a 10dB tunable attenuation range are achieved through tuning the temperature of the W1 PCWG by an 4.7μm-wide aluminum micro-heater with a maximum power consumption as low as 30.7mW.
In this paper, we present a multi quantum dot (MQD) white light emitting Diode structure. In order to construct, white light spectrum, we use different quantum dot layers to generate blue, green and red colors. These layers contain quantum dots with active layers of In(x)Ga(1.x)N with GaN barrier. We investigate that these three colors is theoretically are extracted from each set of quantum dots, then these colors are combined with a desired intensities together and finally a light near white light will be created. Through adjusting material composition and quantum dot sizes, the white color quality can be improved. Piezoelectric and spontaneous polarization internal field are entered in our calculations.
An ultraviolet photosensor based on ZnO nanoplates has been successfully fabricated. ZnO nanoplates was synthesized by sonochemical method and coated on Cu interdigitated electrodes. The method is simple, rapid and applicable to research prototypes for further studies of ZnO nanoplates for nano-device applications. The current-voltage (I-V) characteristics show linear behavior and the photosensor exhibits a response of similar to 803mA/W for UV light under 15 V bias. Compared to other nano detectors, the fabricated detector shows fast photo response with a rise time of 150 ms and fall time of 50 ms compared to the other nanomaterial based photosensors.
We present an analysis of polarization sensitive electro-optic measurement using Jones matrix formulation. Based on our formulation, we present an optimisation of the angle of incidence within the electro-optic probe and its ability to measure electric-fields in a three dimensional Cartesian coordinate system.
This research is based on the Fresnel’s equations and the ellipsometric technique that investigate the sample of SiO2 thin-film on Si substrate. The investigation is made by a probing beam which is in the form of a rotating linearly polarized light generated by the polarizing Mach-Zehnder interferometer (pMZi). The detection of the changed polarization states of the incident light due to reflection on the sample surfaces led to a set of unique characteristics describing a thin-film substrate system in terms of ellipsometric parameters ψ and Δ. SiO2 thin-films were chosen to study because of their well known characteristics. The accuracy of measurements was confirmed by comparisons to calculated values derived from Fresnel’s equations and a standard instrument. The results clearly reveal a feasibility of using the rotating linearly polarized light produced by pMZi for a non-destructive characterization of the thin-film system.
Photosensors based on quantum dot and star like PbS has been successfully fabricated. Lead sulfides were synthesized by sonochemical and hydrothermal methods and coated on Cu interdigitated electrodes. The current-voltage (I-V) characteristics show linear and exponential behavior for quantum dots and star like PbS respectively. The photosensitivity is high for fabricated detectors by star like PbS. However, fast response time was observed for the detector fabricated by quantum dots.
In this work, a direct DQPSK receiver was fabricated, which comprises a polymer waveguide based delay-line interferometer (DLI); a polymer based optical hybrid, and two monolithic pairs of > 25 GHz bandwidth photodiodes that are vertically coupled to the polymer planar lightwave circuit (PLC) via integrated 45° mirrors. The common mode rejection ratio (CMRR) is used to characterize the performance of coherent receivers, by indicating the electrical power balance between the balanced detectors. However, the standard CMRR can only be measured when the PDs can be illuminated separately. Also, the standard CMRR does not take into account the errors in the relative phases of the receiver outputs. We introduce an adapted CMRR to characterize the direct receiver, which takes into account the unequal responsivities of the PDs, the uneven split of the input power by the DLI and hybrid, the phase error and the extinction ratio of the DLI and hybrid.
Modulation Instability is known as intrinsic property of a nonlinear medium like Kerr medium or photorefractive medium; through the such media, the system behavior is possible to transit form stationary regime to chaotic regime; this paper deals with Modulation Instability (MI) in a nonlinear medium and investigates the analogy of MI of optical nonlinear medium and the consequent chaotic regime based on extracting Lyapunov exponent through the power spectrum and equivalently intensity-time diagram of MI; the experimental observation truly confirms the results of MI as the route to the chaotic regime.
A hybrid-integrated coherent receiver module has been achieved using flip-chip bonding technology, consisting of a silica-based 90 degrees-hybrid planar lightwave circuit (PLC) platform, a spot-size converter integrated waveguide photodiode (SSC-WG-PD), and a dual-channel transimpedance amplifier (TIA). The receiver module shows error-free operation up to 40Gb/s and OSNR sensitivity of 11.5 dB for BER = 10(-3) at 25 Gb/s.
We have proposed a new dual band quantum cascade photodetector with ability of detecting UV and IR through two independent paths. Because of large band gap of GaN and AlGaN, we have used AlxGa1-xN/AlN quantum wells. For detecting of IR and UV intersubband and interband transitions have been used respectively. For IR and UV path we have achieved peak of Responsivity about 60 mA/W at 2.7 um and 25 mA/W at 245 nm at 300K respectively.
The paper considers results of designing and modeling analogue-digital converters (ADC) based on current mirrors for the optical systems and neural networks with parallel inputs-outputs. Such ADC, named us multichannel analog-to-digital converters based on current mirrors (M ADC CM). Compared with usual converters, for example, reading, a bit-by-bit equilibration, and so forth, have a number of advantages: high speed and reliability, simplicity, small power consumption, the big degree of integration in linear and matrix structures. The considered aspects of designing of M_ADC CM in binary codes. Base digit cells (ABC) of such M_ADC CM, series-pipelined are connected in structures, consist from 20–30 CMOS the transistors, one photodiode, have low (1,5–3,5) supply voltage, work in current modes with the maximum values of currents (10–40)µA. Therefore such new principles of realization high-speed low-discharge M_ADC CM have allowed, as have shown modeling experiments, to reach time of transformation less than 20–30 nS at 5–6 bits of a binary code and the general power 1–5 mW. The quantity easily cascadable ABC depends on wordlength ADC, and makes n, and provides quantity of levels of quantization equal N=2n. Such simple enough on structure M ADC CM, having low power consumption ≤ 3 + 5mW, supply voltage (3–7)V, is provided at the same time with good dynamic characteristics (frequency of digitization even for 1,5µm or 0,35 µm- CMOS-technologies has made 40 MHz, and can be increased 10 times) and accuracy (Δquantization = 156,25nA for Imax = 10µA) characteristics is show. The range can be transformed optical signals, taking into account sensitivity of modern photodetectors makes 20–200 µ in such ADC. M_ADC CM open new prospects for realization linear and matrix (with picture operands) micro photoelectronic structures which are necessary for neural networks, digital optoelectronic processors, neurofuzzy controllers, and so forth.
Broad gain lasers attract much interest due to the practical gas sensing applications. A step well structure with double optical transitions is implemented in the active region of injectorless quantum-cascade lasers (QCLs) to achieve extended gain bandwidth. The step well is constructed by a “short period superlattice” which provides an equivalent GaInAlAs alloy quantum step well in each active module. The fabricated devices show an ultrabroadband gain spectrum of 480 cm-1 (4 μm) at room temperature in pulsed mode. The laser threshold current density is as low as 1.1 kA/cm2 which is the lowest among the broad gain QCLs emitting at similar wavelengths and the slope efficiency is 1.6 W/A at room temperature.
Vertical-cavity surface-emitting lasers (VCSELs) using hybrid III-V / Si microcavities and based on double photonic crystal reflectors for the heterogeneous integration on complementary metal-oxide-silicon (CMOS) are presented. The latest achievements in optical mode engineering and technological processing are shown and discussed.
In this paper we describe two silicon based optical modulators that have been fabricated as part of two projects in which the Surrey group is involved, the "UK Silicon Photonics project" funded by the UK Engineering and Physical Sciences Research Council (EPSRC), and the European "HELIOS" project funded by the European Union. The modulators exploit the carrier depletion effect in MZI structures, but have different advantages and disadvantages. One has a performance that is close to polarisation independence, whilst the other demonstrates a very high extinction ratio for a 40Gb/s silicon modulator. Both are shown to operate at 40Gb/s.
In this work we extract a novel formula for optical absorption coefficient of Quantum Dots (QDs) in frame of 8band k.p modeling. Also this is useful for any other several band k.p frame. Using this formula, we analyze and simulate absorption spectra for a typical InAs/In0.4Ga0.6As QD, both for TE and TM components of absorption spectra. Size and alloy fraction of QD is chosen such that the absorption spectra has some components around 1.55μm that will be applicable for single photon fiber optic communication.
