Ab initio quantum trajectory simulations of a cavity QED system comprising an atomic beam traversing a coherently driven standing-wave cavity are carried out. The intensity correlation function in transmission is computed and compared with the experimental measurements of Rempe et al. [Phys. Rev. Lett. 67, 1727 (1991)] and Foster et al. [Phys. Rev. A 61, 053821 (2000)]. It is shown that atomic beam density fluctuations induced by the motion of the atoms can account for the reported disagreement of the experimental results with theory (by an overall scale factor of 2 to 4). Moderate misalignments of the atomic beam produce large intracavity photon number fluctuations which significantly degrade the quantum correlations. One parameter fits to the experimental data are made in the weak-field limit with the adjustable parameter being the atomic beam tilt. Departures of the experimental conditions from the weak-field limit are discussed.

We experimentally demonstrate a complete, end-to-end, quantum key distribution system using a continuous wave laser and standard optical components. Our implementation encodes random bits as weak Gaussian modulations onto the phase and amplitude quadratures of the laser beam. We process data from the quantum channel using a post-selection procedure and subsequently apply information reconciliation and privacy amplification procedures to generate an absolutely secure secret key. The maximum information that an eavesdropper may have obtained about this secret key, from the quantum channel and classical communications, is bounded to below one bit. Under the assumption of individual Gaussian eavesdropping attacks, we achieve a secret key generation rate of 25 Mbits/s for a lossless channel and 1 kbit/s for 90% channel loss, per 17 MHz of detected bandwidth.

We investigate the use of nanocrystal quantum dots as a versatile quantum bus element for preparing various quantum resources for use in photonic quantum technologies. The ability to Stark tune nanocrystal quantum dots allows an important degree of control over the cavity QED interaction. Using this property along with the bi-exciton transition, we demonstrate a photonic CNOT interaction between two logical photonic qubits comprising two cavity field modes each. We find the CNOT interaction to be a robust generator of photonic Bell states, even with relatively large bi-exciton losses. These results are discussed in light of the current state-of-the-art of both microcavity fabrication and recent advances in nanocrystal quantum dot technology. Overall, we find that such a scheme should be feasible in the near future with appropriate refinements to both nanocrystal fabrication technology and micro-cavity design. Such a gate could serve as an active element in photonic-based quantum technologies.

Light emission with a wavelength of 1272 nm at room temperature (RT) from self-assembled InAs quantum dots embedded in the GaAs matrix has been obtrained. Growth interruption during the formation of InAs quantum dots (QDs) on a GaAs (100) substrate has been investigated in detail. 1.9 mono layers (MLs) of an InAs QD nucleation layer was grown continuously to form a "seed" with high density. Further, the supply of up to 3 MLs of InAs with a growth interruption of 15 s for every 0.11 ML showed that photoluminescence intensity was improved by 23 times and redshifted the photoluminescence emission nearly 42 nm. The continuous growth up to 1.9 MLs helped to double the dot density. 3.3 MLs of InAs embedded in a GaAs matrix, grown using interruption showed a strong RT photoluminescence peak at around 1272 nm with a very narrow FWHM of 27.1 meV.

In the recent years, there has been an increased interest in the exploitation of the far-infrared spectral region for applications based on chemical recognition. The fact that on the one hand many packaging materials are transparent for THz radiation and on the other hand the THz-spectra of many pharmaceuticals, illicit drugs, and explosives show very specific fingerprints show the potential that THz spectroscopy holds for identification of concealed substances by comparing the spectral signatures with the entries in a database. Yet, due to the lack of appropriate techniques the far-infrared region had for a long time be relatively unexplored, and therefore a detailed study of the far-infrared spectra and the character of the molecular vibrations that give rise to the characteristic spectral signatures can help to evaluate the applicability of THz spectroscopy and imaging for quality control, chemical recognition and biomedical applications.

We use passive and active techniques to study microrheology of a biopolymer solution. The passive technique is video tracking of tracer particles in the biopolymer, a technique which is well established. The active technique is based on rotating optical tweezers, which is used to study viscosity. A method to actively measure viscoelascity using time varying rotation of a particle trapped in optical tweezers is also presented.

Recently we have shown that protein crystals could be grown while they were three-dimensionally trapped by optical tweezers. This permitted studies of modifications of single crystals while gradually changing the conditions in the growing solution. Furthermore it allowed the crystals to grow far away from container walls favoring high quality crystal growth. Many protein crystals themselves consist of fairly large molecules, with sizes up to tens of nanometers. Here we present experiments studying the effect of optical trapping potentials on large molecules, with the aim to explore ways to further enhance crystal growth. For this purpose we extended our tweezers setup with a specially developed detection system allowing us to monitor changes in the molecule concentration of a solution. Using polyethylene oxide (PEO) molecule solutions we were able to demonstrate that the trapping potential of an optical trap is sufficient to collect large single molecules. Our results show that the optical trap induces an increase in the molecule concentration in the focal region. As expected only molecules above a certain molecular weight could be manipulated, and the concentration in the focal region depended on the power of the trapping laser. The ability to locally increase the concentration of molecules may be useful in assisting nucleation of crystals.

This paper reports on two techniques for creating Fabry-Perot cavities in conventional single- and multi-mode optical fibres. The authors have reported previously on the design and fabrication of extrinsic fibre Fabry-Perot interferometric multi-functional sensors. Here, the authors report on two novel techniques for creating intrinsic fibre optic sensors based on the Fabry-Perot etalon. The first technique involved the use of hydrofluoric acid to preferentially etch the core of the optical fibre. This technique is simple to carry out and provides a cost-effective means for manufacturing intrinsic fibre Fabry-Perot sensors. In the second technique, a 157 nm excimer laser along with a custom-designed beam delivery system was used to ablate (micro-machine) near-paralleled walled cavities through the diameter of the optical fibre (outer diameter of 125 μm). The paper details the experimental methodology and the associated instrumentation for the two techniques. The acid etched and laser ablated cavities were characterised using a 3-D surface profiler, optical and scanning electron microscopy. The feasibility of using these cavities as intrinsic fibre Fabry-Perot strain sensors is demonstrated. This was achieved by surface-mounting the acid etched cavities on to composite tensile test specimens. The output from the optical fibre devices was compared with surface-mounted electrical resistance strain gauges.

Gallium-doped germanium (Ge:Ga) extrinsic photoconductor is one of a excellent quantum detector in the terahertz range. Design of a novel wave-guide Ge:Ga photoconductor integrated with silicon solid immersion lens and fabrication technology for linear arrays is presented. The possibilities to extend this technology for realizing large format Ge:Ga waveguide 2D-array detector are discussed.

We have designed and fabricated GaAs/AlGaAs QWIP photodetector for THz range of spectrum (3THz, 100 μm). To evaluate suitability of this type of detector for real-time THz imaging, a prototype of a small array have been built by integrating detector elements with cryogenic readout electronics. Up to 32 individual channels can be measured with this system at temperatures down to 4K. In this paper we present the design and expected performance of GaAs/AlGaAs THz QWIP integrated with cryogenic readout electronics (CRE), and discuss key development issues related to the design.

We investigated Si nanocrystal samples produced by high dose 600 keV Si+ implantation of fused silica and annealing using cathodoluminescence (CL). CL spectra collected under 5-25 keV electron irradiation show similar features to reported photoluminescence spectra, including the strong near IR peak. The CL intensity distribution is formulated as a linear inverse problem and two methods namely the regularisation method and maximum entropy method can be applied to determine the depth profile without making any assumptions concerning the profile function, i.e. a free form solution. We show using simulated CL data that the maximum entropy method is the most appropriate as it preserves the positivity and additivity of the depth profile. This method is applied to experimental CL data and we have localised the spatial origin of the near IR emission to the near-surface region of the implant, 400 nm from the surface, containing the smallest Si nanocrystals.

Recent progress in the field of terahertz (THz) imaging is overviewed. First, various THz-wave sources developed and recently improved in our group are described. Second, imaging of samples can be achieved in different modes, of which we discuss here the transmission mode and the reflection-scattering mode. An emphasis in placed on the latter, which can be used to detect and determine for example the distribution of powders inside THz-transparent containers and packages. One-frequency or wide-spectrum imaging can be extended to chemical imaging, a technique by which images acquired at different THz frequencies can be combined to allow the identification of the chemical composition of the target at each spatial position. Other THz imaging applications are also discussed.

Quantum-electrodynamic calculations predict that truly incoherent light can be used to efficiently generate quantum-degenerate exciton population states. Resonant incoherent excitation directly converts photons into excitons with vanishing center of mass momentum. The populated exciton state possesses long-range order, is very stable against perturbations, and should be observable via its unusual directional and density dependence in luminescence measurements.

The reflection characteristic of terahertz radiation (T-rays) in stratified media is being explored through the use of computer models. When T-rays are reflected off a sample, the measured T-ray signal contains coherent spectroscopic information about the sample. In the time domain, this spectroscopic information becomes the time response of the sample-a useful method for determining layer thickness and the number of interfaces in the sample. In order to confidently determine thickness and interfaces, the propagation characteristic of T-rays in a stratified medium needs to be understood. Internal reflections, interference, and water absorption within the layers can significantly alter the T-ray signal. This paper reports on a study of T-ray propagation in tissue layers inside the head, in reflection mode. Simulated results are presented and discussed.

All optical switching devices based on kerr-effect, where light switches light, are enjoying renewed interest. The dream of ultra compact devices operating at very low power and integrable on a chip is entering the realm of reality thanks to the advent of photonic crystal, enabling high Q/V ratio. We show that marrying photonic crystal and a new class of highly non linear material, Chalcogenide glasses, is a very promising way to achieve an all-optical chip. We describe the fabrication techniques we have developed for manufacturing two-dimensional Chalcogenide photonic crystal. Different types of photonic crystal resonances are investigated. Coupling technique to chalcogenide based photonic crystal waveguides and cavities via tapered nanowires is thoroughly described. We demonstrate resonant guiding in a chalcogenide glass photonic crystal membrane using a fano probe technique. We observe strong resonances in the optical transmission spectra at normal incidence, associated with Fano coupling between free space and guided modes. We obtain good agreement with modeling results based on three-dimensional finite-difference time-domain simulations, and identify the guided modes near the centre of the first Brillouin zone responsible for the main spectral features.

Optical surface modes are specific states of electromagnetic waves localized at the interface separating two dissimilar media where the wave vector becomes complex causing the wave to exponentially decay away from the surface. These general conditions permit surface modes to form in a wide range of systems including layered optical media, optical waveguides, metallic thin films, carbon nano-tubes, and photonic crystals. Equally remarkable are the effects based on surface modes, such as extraordinary optical transmission through subwavelength apertures and beaming of light. In this paper, we analyse the surface modes, also known as Tamm states for electronic systems, along two surface orientations of a semi-infinite binary photonic crystal formed by a square lattice of high dielectric rods in vacuum. We reveal the conditions required to form localised surface modes in this system without perturbation of the surface layer, such as a reduction in the surface rod radius or refractive index. In this way, we demonstrate the existence of intrinsic surface modes at a photonic crystal surface. In addition to the study of linear surface states, we introduce a third-order optical nonlinearity to the surface layer and analyse the properties of the nonlinear surface Tamm states. We investigate the energy threshold, dispersion, and modal symmetries of the surface states, and illustrate their nonlinearity-induced tunability.

Computational study of nanosecond pulse laser radiation in periodically poled LiNbO₃ and LiTaO₃ crystals reveals the complex spacio-temporal evolution of the 1.064 μm fundamental harmonic (FH) and second harmonic (SH) energy fields with associated temperature fields, leading to the thermal dephasing and inhibition of second harmonic generation (SHG). The investigated range of the laser input power is W₀=0.5-50 W (with the pulse energy Q₀=0.01-1 mJ/pulse and repetition rate of 50 kHz). For input laser powers W₀>10 W the FH and SH energy fields are found to strongly couple with non-uniform temperature field leading to significant thermal dephasing and SHG efficiency loss. Heat generation and temperature distributions also exhibit very significant non-uniformities along and across the laser beam, maximizing at the rear or inside the crystal, depending on the input power. Performed study shows the feasibility of the effective thermal control with temperature gradient along the crystal allowing one to maintain (i) the irradiated zone within the temperature tolerance range and (ii) high SHG efficiency under high input laser powers.

In this paper, a novel reconfigurable 5-tap photonic RF filter based on Opto-VLSI processor is proposed where an Opto-VLSI processor is used in conjunction with a 5-fibre Bragg grating (FBG) array to slice the spectrum of a broad band light source, thus achieving commensurate true-time delays and variable tap weights. The proposed photonic RF filterstructure is experimentally demonstrated by means of several examples which show the capability of the Opto-VLSI processor to synthesise transversal RF filter responses with adaptive weights.

Reconfigurable multi-channel optical filters are presented in this paper. The operation principle of the reconfigurable filter is based on the dynamic beam steering capacity of Opto-VLSI processor in conjunction with a high dispersion free space grating. The dispersion grating separates the input signal spectrum while the Opto-VLSI processor is driven by optimised phase holograms to dynamically select the wavelengths to be coupled into the output port. Experimental results show that up to 8 bands can be synthesised, with a wavelength tuning span of 10 nm and a 3dB bandwidth less than 0.5nm.

We describe two optical layer schemes which simultaneously facilitate local area network emulation and automatic protection switching against distribution fiber breaks in passive optical networks. One scheme employs a narrowband fiber Bragg grating placed close to the star coupler in the feeder fiber of the passive optical network, while the other uses an additional short length distribution fiber from the star coupler to each customer for the redirection of the customer traffic. Both schemes use RF subcarrier multiplexed transmission for intercommunication between customers in conjunction with upstream access to the central office at baseband. Failure detection and automatic protection switching are performed independently by each optical network unit that is located at the customer premises in a distributed manner. The restoration of traffic transported between the central office and an optical network unit in the event of the distribution fiber break is performed by interconnecting adjacent optical network units and carrying out signal transmissions via an independent but interconnected optical network unit. Such a protection mechanism enables multiple adjacent optical network units to be simultaneously protected by a single optical network unit utilizing its maximum available bandwidth. We experimentally verify the feasibility of both schemes with 1.25 Gb/s upstream baseband transmission to the central office and 155 Mb/s local area network data transmission on a RF subcarrier frequency. The experimental results obtained from both schemes are compared, and the power budgets are calculated to analyze the scalability of each scheme.

Several problems in nanophotonics are uniquely suitable for frequency domain modeling methods. We first present a new method for sensitivity analysis of nanophotonic devices. The algorithm is based on the finite-difference frequency-domain method and uses the adjoint variable method and perturbation theory techniques. We show that our method is highly efficient and accurate and can be applied to the calculation of the sensitivity of transmission parameters of resonant nanophotonic devices. Frequency-domain methods are also essential in modeling of plasmonic devices due to the complicated dispersion properties of metals at optical frequencies. Here we demonstrate the existence of a bound optical mode supported by a slot in a thin metallic film deposited on a substrate, with slot dimensions much smaller than the wavelength. The modal size is almost completely dominated by the near field of the slot. Consequently, the size is very small compared with the wavelength, even when the dispersion relation of the mode approaches the light line of the surrounding media. In addition, the group velocity of this mode is close to the speed of light in the substrate, and its propagation length is tens of microns at the optical communication wavelength.

Recently there has been a drive to create artificial optical materials, or meta-materials, with a specified electrical permittivity and magnetic permeability at optical frequencies. Control over these properties can give rise to new physical phenomena, such as a negative refractive index and "super lensing", with potential applications in nanophotonic systems and nanolithography. Because most materials do not exhibit magnetic behaviour at optical frequencies, control over the effective magnetic permeability is achieved using patterned metal structures much smaller than the wavelength of light. The electric currents induced in the structures produce magnetic fields that may be in phase or may oppose the magnetic field of the incident light. When combined with dielectric materials, these structuresform coupled inductor-capacitor (LC) circuits that can resonate at frequencies in the optical spectrum. Since the resonant properties of the LC circuits control the properties of the meta-material, it is important to understand how changes in shape, size and the position of the subwavelength components affect the resonances. Using the Finite Difference Time Domain (FDTD) method, we study a number of different inductor-capacitor configurations. By applying the concepts of lumped impedance to the electromagnetic fields, the resonant frequencies and Q factors of the tuned optical circuits are determined from the FDTD data. Our in-house electron beam lithography system has been used to fabricate some of the structures. Results of the simulations, the nano-fabrication process and experiments on the meta-materials will be presented.

Artificial structures with periodically modulated index of refraction such as photonic crystals offer novel ways of controlling light propagation due to the existence of a range of forbidden frequencies corresponding to a photonic bandgap. We discuss physical phenomena which do not allow for the existence of complete electromagnetic band gaps in dielectric structures with variation of the refractive index in one spatial dimension. We also demonstrate that the limitations imposed on one-dimensional dielectric structures can be removed by using the so-called left-handed materials, and that such a structure can posses a full photonic band gap.

Exposure of optically curing resin with highly focussed femtosecond laser pulses provides excellent means to produce high resolution micron sized structures. We use the process to fabricate micromechanical components for lab-on-a-chip applications. We present here our experimental realization of the microscope system used for photopolymerization and detail the advantage of our fabrication process. We characterize our structures using scanning electron microscopy, and compare the results with available data. We demonstrate the technique by manufacturing a movable joint and a free floating cross which is three dimensionally trapped. Future applications of this technique will focus on developing optically driven motors and an all optical measurement of applied torques.

The microscopic and macroscopic models of photoinduced anisotropy in general and photoinduced optomechanical effect in particular are critically reviewed. Based on current experimental data available a revised macroscopic model of photo-induced anisotropy is given. As opposed to expansion and contraction phenomena considered previously, the photoinduced polarization dependent viscosity change is proposed to explain the experimental data of the optical actuation in chalcogenide glasses.

We introduce a novel method of attaining all-optical beam control in an optofluidic device by displacing an optically trapped silica micro-sphere though a light beam. The micro-sphere causes the beam to be refracted by various degrees as a function of the sphere position, providing tunable attenuation and beam-steering in the device. The device itself consists of the manipulated light beam extending between two buried waveguides which are on either side of a microfluidic channel. This channel contains the micro-spheres which are suspended in water. We simulate this geometry using the Finite Difference Time Domain method and find good agreement between simulation and experiment.

The ability to exert optical torques to rotationally manipulate microparticles has developed from an interesting curiosity to seeing deployment in practical applications. Is the next step to genuine optically-driven micromachines feasible or possible? We review the progress made towards this goal, and future prospects.

We present an over of our work on the micro/nano-scale design, fabrication and integration of optical waveguides and photonic devices for optical printed circuit board (O-PCBs) application. The O-PCBs consist of planar circuits and arrays of waveguides and devices of various sizes and characteristics to perform the functions of transporting, switching, routing and distributing optical signals on flat modular boards. We have assembled O-PCBs using optical waveguide arrays and circuits fabricated via embossing of polymer materials. The waveguides optically interconnect various photonic devices like directional couplers, multimode interference devices, light sources, detectors, and filters. We use specially designed microlenses, 45-degree mirrors and curved mirrors to maximize the light coupling efficiency between devices. The information handling performances of the O-PCBs are measured up to 10 Gbps. For nano-scale photonic integration and applications, we designed power splitters, wavelength splitters, and waveguide filters using photonic crystals and plasmonic waveguide structures. We discuss scientific issues and technological issues concerning the miniaturization, interconnection, and integration of micro/nano-photonic devices and circuits and discuss potential utilities of O-PCBs and micro/nano-photonic modules for applications in computers, telecommunication systems, transportation systems, and bio-sensing microsystems.

Photoluminescent water-soluble silicon nanocrystals were synthesized using solution-phase wet chemistry techniques. Adjustment of the mean size and size distribution was achieved by adjusting the rate of addition of the hydride reducing agent. When the reducing agent was added slowly the mean size of the silicon nanocrystals was 1.4nm with a monodisperse size distribution. However, when the reducing agent was added rapidly the size distribution enlarged and concomitantly the mean sized also increased. The photoluminescence and photoluminescence excitation spectra from the monodisperse sample show narrower features when compared to the solution with the large size distribution. This provides direct evidence for size dependant effects on the photoluminescence of silicon nanocrystals.

In this paper we report on new techniques for making self-ordered porous layers of alumina of varying aspect ratios on glass, without the use of lithographic or masking techniques. Use of RF etching in one of the hole forming steps and also when filling the holes with sputtered metal is shown to be advantageous over additional anodisation. These hole arrays have intrinsically interesting optical responses which will be reported, but their main use is for nano-patterning of subsequent deposited layers either as templates or as masks. High resolution images demonstrate the uniformity in nanohole diameter and in the spacing between holes, which can be achieved when care is used in production. While many nanostructured materials can be deposited using these Porous Anodic Alumina (PAA) templates we focus here on filling the vertical cylindrical holes with silver. Etching during hole filling leads to better-controlled structures and more efficient processes. Novel optical data on the resultant conducting columnar rings will be presented. Spectrally much sharper plasmon resonant features are found than those reported for classical and more random silver column and island arrays. The optical properties are analysed from an effective medium perspective using data from spectrophotometry and ellipsometry. Fitting this data gives modelled layer thickness and the vertical profile in close agreement with direct SEM imaging. The effective refractive indices of the silver columnar layer have interesting and potentially useful dispersion characteristics.

A technique for fabricating ultra-high precision optics is presented. The technique employs a thin multiple aperture mask positioned in front of the substrate during sputter deposition to selectively occlude the beam. The apertures are small in regions where low material deposition is required and correspondingly larger in regions requiring more. During deposition, the substrate is slowly moved back and forth behind the mask over a distance equal to the pitch of the apertures (typically around 2 - 4 mm). This smoothes out any residual patterning of the substrate due to the aperture design of the mask. Using this technique, a transmission optic having an rms physical thickness uniformity less than 0.5 nm, or λ/1000 (measured at 632.8nm) has been produced from a lithium niobate substrate. We believe that this technique will enable the production of the next generation optics for semiconductor fabrication.

Organic photovoltaics promise a number of key advantages over conventional silicon, namely: Ease of processing, low cost, physical flexibility and large area coverage. However, the solar power conversion efficiencies of pure polymer devices are poor. When nanocrystals are blended with a conducting polymer to create a bulk heterojunction structure the optical and electronic properties of both materials combine synergistically to enhance overall performance. We have investigated the dependence of efficiency on the polymer molecular weight, together with the role of nanocrystals in the photogeneration of charge carriers in bulk heterojunction solar cells. We found that a high molecular weight polymer resulted in the formation of small nanocrystals, and that nanocrystals act to enhance the natural spectral response of the polymer.

The gradient index (GRIN) inhomogeneous materials optical glass micro-lens and polymer microlens and arrays were investigated in our Lab, in recent years. The different series of GRIN lenses have been fabricated using ion-exchanged in the special glass material. The GRIN lenses are done in applications for using to construct micro-optic devices. We analyzed and demonstrated results on propagation and imaging properties of GRIN lenses. On the other hand, we have also developed a drop-on-demand ink-jet printing method to produce micro-lens array using nano-scale polymer droplets involved with a uniform ultraviolet (UV) light and heat solidifying process. The experimental setup for manufacturing polymer microlens array and the measurement results of performance parameter are also given.

A key device in all optical networks is the optical filter. There are different types of optical filters, for examples, Bragg grating, thin film filter, and arrayed waveguide grating. The use of fiber-optic filters based optical Add/Drop multiplexing (OADM) can process the optical wideband signals in the optical network. In this paper, the designed and simulated filtering characteristics of a serially coupled triple ring optical resonator (STRR) are modeled and investigated. The mathematical relations of the coupling coefficients with the transmission characteristics of the STRR filter are expressed by Z-transform analysis. The transmission spectra of the through port and the drop port of each input of the four-port STRR configuration are simulated. Results are presented on the characteristics of the output as a function of wavelength for various values of the coupling coefficients. With the derived approximate formulas, it is shown that the coupling of the ring fiber system can be changed and thus that the transmission properties of the filter can be controlled and used.

A simple and high precision method to measure the phase modulation characteristics of Liquid Crystal Spatial Light Modulator, namely, the relationship between phase and voltage(gray), is proposed. Using the Digital Wave Front Phase-shifting Interferometer, the phase difference from different voltage (gray) can be obtained directly from the interferometer, so it is easy to get the phase modulating characters of Liquid Crystal Spatial Light Modulator. The wavefront correction has been realized by using the Liquid Crystal Spatial Light Modulator in adaptive Optics. The distorted wavefront can be tested in the Interferometer and be expressed by Zernike Polynomial, using the phase modulation character of Liquid Crystal Spatial Light Modulator, the corresponding gray picture can be set up. The conjugate wavefront can be obtained, and thus the correcting of the static distorted wavefront is completed and the effect is displayed as proved by the improvement of correlative parameters such as PV value, rms value and strehl ratio.

A new method for small displacement measurement based on surface plasmon resonance and heterodyne interferometry is presented. A heterodyne light is focused on a mirror and reflected from it, and then it is incident on a prism which was coated with a thin gold film. When the mirror or the objective lens has a small displacement, the light will be converging or diverging into the prism, and the phase variation between two parts of the test beam under the condition of surface plasmon resonance (SPR) can be measured by using a two-segment photodiode and a lock-in amplifier. This phase difference between two parts of the test beam is proportional to the departure of the mirror from the focal plane, so the displacement can be obtained in real-time. It has some merits, such as, simple, stable, very high sensitivity and resolution. And its resolution is better than 1nm.

We investigate the classification of the T-ray response of normal human bone cells and human osteosarcoma cells, grown in culture. Given the magnitude and phase responses within a reliable spectral range as features for input vectors, a trained support vector machine can correctly classify the two cell types to some extent. Performance of the support vector machine is deteriorated by the curse of dimensionality, resulting from the comparatively large number of features in the input vectors. Feature subset selection methods are used to select only an optimal number of relevant features for inputs. As a result, an improvement in generalization performance is attainable, and the selected frequencies can be used for further describing different mechanisms of the cells, responding to T-rays. We demonstrate a consistent classification accuracy of 89.6%, while the only one fifth of the original features are retained in the data set.

Terahertz spectroscopy, which investigates the electromagnetic spectrum of samples between 0.1 and 10 THz, allows not only for exploration of molecular structures but also of molecular dynamics. One difficulty in performing THz spectroscopy is that the data can be noisy and difficult to interpret. Ab initio molecular modelling has recently become more and more useful in the prediction of, for example, molecular structures, dynamic states and isomeric forms. Since the structure of biomolecules is closely related to their functionality there are broad ranging applications in biomedicine, for example in DNA sensing. An a priori knowledge of the expected THz spectra allows for improved experimentation. There is a growing and recognised need for THz spectroscopic databases to be created and made available along with classifiers that are able to effectively detect a specific substance. We show, for a specific example, the 9-cis and all-trans retinal isomers, how ab initio molecular orbital calculations and quantum chemical modelling programs, such as Gamess, can aid in this endeavour.

The electronic state of Y doped ZnO (YZO) was calculated using the density functional theory. In this study, the program used for the calculation on theoretical structures of ZnO and YZO was Vienna Ab-initio Simulation Package (VASP), which is a sort of pseudo potential method. The detail of electronic structure was obtained by the discrete variational Xα (DV-Xα) method, which is a sort of molecular orbital full potential method. The density of state and energy levels of dopant elements was shown and discussed in association with optical properties, especially related to down-conversion effect. The down-conversion effect of YZO was experimentally investigated by preparing thin films deposited on F doped SnO2 (FTO) glass substrates by sol-gel method using the spin-coating system. A homogeneous and stable solution was prepared by dissolving acetates in the solution added diethanolamine as sol-gel stabilizer. In order to confirm a ultraviolet ray interruption and down-conversion effects, the transmission spectrum and the fluorescent spectrum of YZO films were estimated. The results obtained by experiment were compared with the calculated structure.

In this paper, we propose a time-token multi-Gb/s Wavelength Division Multiplexing Fibre Distributed Data Interface (WDM/FDDI) architecture and examine its throughput efficiency and delay under heavy load for different network configuration using discrete event simulator.

This work reports on simulation and experimental investigation into the charge transport and electroluminescence in a quantum well (QW) organic light emitting diode (OLED) consisting of a N,N'-di(naphthalene-1-yl)-N,N'-diphenylbenzidine (NPB) as a hole transport layer, tris (8-hydroxyquinoline) aluminum (Alq₃) as a potential barrier and electron transporting layer, and rubrene as potential well layer. Indium tin oxide was used as an anode, while LiF/Al was employed as a cathode. The carrier transport was simulated using one-dimensional time-independent drift-diffusion model. The influence of the well width, barrier width, and the number of QWs on the carrier distribution, recombination rate, and device performance was investigated. Finally, the device structures which yielded most promising simulation results were fabricated and characterized. The comparison between the experimental and theoretical results is discussed.

Electromagnetic actuation shows promising suitability for constructing actuators and sensors with an optical fiber in terms of speeds, device dimensions, and power consumption. In this work we invented a fiber scanner which is composed of an optical fiber coated with nickel powder based ferromagnetic gel. The optical scanner, in which the optical fiber is mechanically steered with external electromagnetic fields, satisfies the applications that require small sizes, precise optics, low power consumption and prefers non-electrical control in the device. The device architecture makes the scanner dimensions in the same scales of an optical fiber diameter and the optics is well preserved in the fiber. In addition, the external actuation eliminates the needs of voltage or current in the scanner. Magnetization hysteresis curve of the nickel based ferromagnetic gel, which gives relevant magnetic material properties, is characterized in order to carry out the calculation of static and dynamic responses. A rotary gel coating technique is used to construct fiber optical scanners. The material preparation and fabrication method is described in this paper. We characterized the scanner in two modes. The static scanning results showed a 0.5 mm displacement under the influence of static magnetic field of 14.5 KA/m. At the first peak of resonant frequency in dynamic scanning, a linear displacement of 0.75 mm with a magnetic field amplitude of 6.69 KA/m was demonstrated. In this paper, we discussed the fabrication procedures and performance characterization of the fiber scanner as well as some of the potential applications.

The conventional self-mixing sensing systems employ a detection scheme utilizing the photocurrent from an integrated photodiode. This work reports on an alternative way of implementing a Vertical-Cavity Surface-Emitting Laser (VCSEL) based self-mixing sensor using the laser junction voltage as the source of the self-mixing signal. We show that the same information can be obtained with only minor changes to the extraction circuitry leading to potential cost saving with reductions in component costs and complexity. The theoretical linkage between voltage and photocurrent within the self-mixing model is presented. Experiments using both photo current and voltage detection were carried out and the results obtained show good agreement with the theory. Similar error trends for both detection regimes were observed.

We investigate the effect of transmitter and receiver array configurations on the stray-light and diffraction-caused crosstalk in free-space optical interconnects. The optical system simulation software (Code V) is used to simulate both the stray-light and diffraction-caused crosstalk. Experimentally measured, spectrally-resolved, near-field images of VCSEL higher order modes were used as extended sources in our simulation model. Our results show that by changing the square lattice geometry to a hexagonal configuration, we obtain the reduction in the stray-light crosstalk of up to 9 dB and an overall signal-to-noise ratio improvement of 3 dB.

Electro-optical channel waveguide is fabricated using an optical nonlinear polymer developed by doping dye organic molecules in a host polymer system and followed by an electric field poling step. A single-mode polymeric electrooptical channel waveguide is modeled using the BeamProp. Photolithography followed by wet chemical etching is used to fabricate the polymeric channel waveguide. A fabrication process is described. Results from a systematic evaluation of the film and waveguide physical and optical properties using AFM, profilometer, ellipsometer and the Maker Fringe technique is presented.

We consider Carbon Nanotube (CNTs) counter electrode as alternative material to Platinum counter electrode for dye sensitized solar cells (DSSCs). Also, CNT counter electrodes having different visible light transmittance were prepared on fluorine-doped tin oxide (FTO) glass substrates by spray coating method. Microstructural images show that there are CNT-tangled layers coated on FTO glass substrates. Using such CNT counter electrodes and screen printed TiO₂ electrodes, DSSCs were assembled and its I-V characteristics have been studied and compared. Light energy conversion efficiency of DSSCs increased with decreasing in light transmittance of CNT counter electrode. Our result shows that CNT counter electrode is compatible to Pt counter electrode.

Upscaling the dye sensitized solar cell (DSSC) is a key issue that confronting the entry of this type cells in commercial market. Performance of large size DSSCs is always poor than small size cells because of high resistive losses associated with sheet resistance of conducting glass substrates. Here we show a simple method to reduce resistive loss, also, efficient collection of photo generated carriers through silver current collectors which are prepared on both working electrode and counter electrode substrates by screen printing method in analogy to conventional silicon solar cells. For long-term stability, to protect corrosion and to avoid charge recombination, silver current collectors were laminated by surlyn sheet. Using these substrates, DSSCs were prepared and their I-V characteristics have been studied as a function of light intensity and compared with normal cells which don't have silver carrier collectors.

In this paper, we report a compact 1x2 MEMS optical switch actuated by less than one voltage. Over past few years, micro-electro-mechanical systems (MEMS) have emerged as a leading candidate for achieving true all-optical multi-wavelength network. Due to the inheritance of mechanical vibration in the under damping condition, most MEMS switches might need external control circuit or mechanical stoppers to suppress the undesired jittering of optical signal. To overcome this difficulty, we redesigned a MEMS optical switch monolithically integrated with a vertical micromirror with large surface area. The micromirror is made by the low-cost anisotropic wet etching technique. The size of the micromirror is 500 μm x 1200 μm, which is large enough to accommodate the optical beam diameter of 62 μm from a ball lens fiber. Because the moving direction of the MEMS optical switch is perpendicular to the surface normal of the micromirror, the effect of the mechanical vibration is compensated by the large surface area of the micromirror. In addition, a capacitor of 100 μF is connected in parallel with the MEMS switch to serve as a low pass filter. The switching time can be improved in the 5 ms range. Finally, a calculated driving waveform derived from the square wave is used as the triggering signal, after analyzing the switching performance by Fourier transform function. Our experimental results show the rising time and fall time of the MEMS switch is 3 ms and 3.1 ms, respectively. The optical insertion loss caused by the micromirror is 0.45 dB. The actuation voltage is around 0.3 volt and the switch is actuated by electromagnetic force. The footprint of the packaged device is 18 mm x 12 mm. A low cost, small size and high performance optical switch is experimentally demonstrated.

Optical communication and sensor industry face critical challenges in manufacturing for system integration. Due to the assembly complexity and integration platform variety, micro optical components require costly alignment and assembly procedures, in which many required manual efforts. Consequently, self-assembly device architectures have become a great interest and could provide major advantages over the conventional optical devices. In this paper, we discussed a self-assembly integration platform for micro optical components. To demonstrate the adaptability and flexibility of the proposed optical device architectures, we chose a commercially available MEMS fabrication foundry service - MUMPs (Multi-User MEMS Process). In this work, polysilicon layers of MUMPS are used as the 3-D structural material for construction of micro component framework and actuators. However, because the polysilicon has high absorption in the visible and near infrared wavelength ranges, it is not suitable for optical interaction. To demonstrate the required optical performance, hybrid integration of materials was proposed and implemented. Organic compound materials were applied on the silicon-based framework to form the required optical interfaces. Organic compounds provide good optical transparency, flexibility to form filters or lens and inexpensive manufacturing procedures. In this paper, we have demonstrated a micro optical filter integrated with self-assembly structures. We will discuss the self-assembly mechanism, optical filter designs, fabrication issues and results.

The refractive index and thermo-optic coefficient of composite polymers of polystyrene and polymethylmethacrylate were measured at 1.55μm using an optical fiber refractometer and were found to be 1.483 and 1.570, respectively, at room temperature. The refractive index and thermo-optic coefficient of the copolymers were consistent with the rule of mixtures.

In this paper, we propose and demonstrate a new MicroPhotonic structure for optical packet header recognition based on the integration of an optical cavity, optical components and a photoreceiver array. The structure is inherently immune to optical interference thereby routing an optical header within optical cavities to different photoreceiver elements to generate the autocorrelation function, and hence the recognition, of the header using simple microelectronic circuits. The proof-of-concept is simulated and experimentally demonstrated.

In this work we discuss the implementation of sensing devices based on ring-coupled hysteretic systems. In particular, the emergent oscillations in a ring coupled system formed by overdamped nonlinear devices having an hysteretic magnetic and electric behaviour are considered with applications to B-field and E-field measurements, respectively. Details on the implementation strategy, on the materials adopted and on the technologies will be given. The concept introduced is then extended to the area of E-field sensors taking into account nonlinear ferroelectric devices where oscillations can be obtained through a suitable connection topology in a similar way as for the magnetic field systems. The evaluation of the output signal dependence on the target electric field to be measured will be discussed and some device implementation issues will be reported. The proposed system combines benefits coming from reconsidering dated physical electro-static phenomena, with miniaturization levels provided by micro-technologies, to realize important electric field amplification. Devices based on different technologies, ranging from PCB to hybrid integrated microsystems, will be presented and discussed. Preliminary experimental results on E field sensor will be presented; the studies on B-field sensor are more mature and more comprehensive experimental results will be discussed to validate the working principle and to qualify the sensors in terms of sensitivity and noise floor.

We report on detailed simulations of the emission from microcavity OLEDs consisting of widely used organic materials, N,N'-di(naphthalene-1-yl)-N,N'-diphenylbenzidine (NPB) as a hole transport layer and tris (8-hydroxyquinoline) (Alq₃) as emitting and electron transporting layer. The thick silver film was considered as a top mirror, while silver or copper films on quartz substrate were considered as bottom mirrors. The electroluminescence emission spectra, electric field distribution inside the device, carrier density and recombination rate were calculated as a function of the position of the emission layer, i.e. interface between NPB and Alq₃. In order to achieve optimum emission from a microcavity OLED, it is necessary to align the position of the recombination region with the antinode of the standing wave inside the cavity. Once the optimum structure has been determined, the microcavity OLED devices were fabricated and characterized. The experimental results have been compared to the simulations and the influence of the emission region width and position on the performance of microcavity OLEDs was discussed.

For improving the sensitivity of a D-type SPR fiber sensor, we simulated the optimum parameters, such as, the thickness of coatings, the length of sensor, and the angle of incidence for different ranges of refractive index. These simulations are based on SPR theory and the intensity and phase methods. It is clearly that, the sensitivity is improved by increasing the length of sensor and/or the thickness of the gold film. And the sensitivity of the phase method is higher than the intensity method by two orders. It is used to detect the refractive index or concentration of gas or liquid in real-time, and it has some merits, such as, small, simple, cheaper, and in vivo test.

A dewetting process of an evaporating solution is used to form micrometer-sized amorphous droplets, or "domes", of organic compounds, both polymeric and low-molar-mass, on various substrates such as silicon, mica, glass, and indiumtin-oxide. The produced patterns are characterized by a regular 2-dimensional array of similar-sized domes. Here we report on the reversible shape change of polymeric domes (between lens and sphere) and the irreversible shape change of domes made of low-molar-mass compounds, e.g. due to crystallization. Control of crystallization leads to the formation of single crystallites of a non-linear-optically active p-nitro phenol salt.

Lateral confinement for cylindrical micro-resonator light emitters improves the ratio of the number of the axial resonant modes to the number of the spontaneous emitting lateral modes. We have observed resonator-behaviour of cylindrical micro-structures, whose lateral surfaces were coated with coaxial MgO/ZrO₂ and a-Si/SiO_χ Braggre flectors. Glass rods with circularly shaped basal planes and ZnO wires with hexagonally shaped basal planes were used as cavity material. Bragg-reflectors were deposited using pulsed laser deposition and plasma enhanced chemical vapour deposition at the lateral surface of the ZnO wires and the glass rods. The optical properties of the Bragg-reflectors were investigated using a confocal micro-reflectometer, spatially resolved spectroscopic ellipsometry technique, and spatially resolved cathodoluminescence measurements.

This study investigates the application of one dimensional discrete wavelet transforms in the classification of T-ray pulsed signals. The Fast Fourier Transform (FFT) is used as a feature extraction tool and a Mahalanobis distance classifier is employed for classification. In this work, soft threshold wavelet shrinkage de-noising plays an important part in de-noising and reconstructing T-ray pulsed signals. In addition, Mallat's pyramid algorithm and a local modulus maxima method to reconstruct T-ray signals are investigated. Particularly the local modulus maxima method is analyzed and comparisons are made before and after reconstruction of signals. The results demonstrate that these two methods are especially effective in analyzing and reconstructing T-ray pulsed responses. Moreover, to test wavelet de-noising effectiveness, the accuracy of the classiffication is calculated and results are displayed in the form of scatter-plots. Results show that soft threshold wavelet shrinkage de-noising improves the classification accuracy and successfully generates visually pleasing scatter plots at selected three frequency components.