We review the operation of both twisted and parallel-aligned nematic liquid-crystal displays (LCD's) for applications in optical computing, image processing, pattern recognition and diffractive optical elements. For these applications, three spatial modulation characteristics are of interest: phase-only, amplitude-only, and combined full amplitude and phase. We review how to achieve these three operating conditions. We begin with a discussion of the Jones matrix model for the twisted-nematic LCD displays. We examine optical configurations for achieving amplitude-only modulation and polarization eigenvectors for achieving phase-only modulation. Then we review an extremely successful technique for obtaining combined full amplitude and phase modulation with a single LCD by spatially modulating the maximum phase depth. Finally we discuss new advances in achieving 2D polarization modulation.

This paper represents recent results and efforts in developing the concept and the implementation of an all fiber optical on-off switch based on Faraday Effect exhibited by magneto-optic (MO) materials such as rare earth doped iron garnets. The on-off function of the switch is useful for isolation and connection of node/nodes from the network without having to electronically turn off the laser. In this paper Faraday rotation of the polarization of light with a variable bias magnetic field is demonstrated. An extinction ratio of about 19dB is measured. It can be improved further by additional Faraday rotation created by another MO material in the light path. The interferometric configuration of the switch design reduces its dependence on the polarization. The biasing circuit for the magnetic field should be able to change the voltage rapidly in order to obtain fast operating time of the optical switch. The inductance of the coil used for generating the required magnetic field is the bottleneck for rapid switching of the magnetic field in the magneto-optic material. Circuits used to change the voltage across the bias circuit rapidly are discussed. The switching speed of magneto-optic materials depends on the speed of the domain walls. The switching time for the magneto-optic material will be discussed. Thick film ferrimagnetic bismuth-substituted rare-earth iron garnets are used as the Faraday rotators.

Photonic THz laser digitizing with thin-film GaAs on glass is demonstrated. In fact, the GaAs/glass interface can be used for an effective all-optical digitizer (35%) of transmitted and reflected laser beams. The films have been formed with pulsed-laser deposition. The switching principle is extremely straightforward: two (or more) laser rays were crossed at the same spot on the interface. Most of the experiments have been carried out with red (read) and green (write) laser rays. The information of the write beam is transferred to the read beam by means of alteration of the electronic state of the interface. Pump-probe experiments revealed that the absorption change, i.e., the alteration of the electronic state, takes place within a few picoseconds. Therefore, logic operations in the THz range become feasible. In addition, NOR and NAND gate realizations with laser crossing are possible. Besides the formation of smart all-optical cross-links, all-optical computing is further application of laser crossing. Based on the unmatched simplicity of the switch realization, switching speed, and the fairly low material quality demands, laser crossing in thin-film GaAs has the potential to be used in future optical networks. This work further stresses the hybrid mode with laser crossing in thin-film GaAs/glass interfaces.

Abstract-Transformers are a vital part of transmission and distribution systems. Monitoring the transformers for problems before they occur can prevent faults that are costly to fix and result in a loss of service. Current systems can provide information about the state of a transformer, but are very expensive to implement. This paper outlines a new approach that is based using light absorbance to monitor the transformer oil. Oil is continually sampled from the transformer, and light is passed through the oil and tested for absorbance. Preliminary experiments demonstrated that a system based on one wavelength could determine the difference between an acceptable or unacceptable sample of oil. Samples of transformer oil were failed in controlled failure modes, which showed a general increase in absorbance during the experiment. Additional wavelengths can be measured, which provides more information about the state of the transformer and makes the system more versatile in determining fault types. All the equipment necessary for the prototype system is outlined, as well as a method for analyzing the data that the prototype can provide.

This research proposes use of Fiber Bragg Grating (FBG) sensors to measure and monitor patient body temperature non-intrusively on a Smart Bed Sheet. The use of FBG sensors allows smart bed sheet to have the look and feel of an ordinary conventional bed sheet since FBG sensors have a very thin and light linear geometry. Additionally, they are dielectric in nature, and have a total immunity to electromagnetic and RF interferences. Recent developments in FBG research have made these sensors considerably inexpensive but very reliable. Simple signal processing techniques can extract very precise temperature from FBG sensors.

It is very important to generate high-speed optical synchronization signal for high speed computer. The rational harmonic (RH) modelocking scheme is a useful technology to generate pulses at a repetition rate higher than the modulation frequency. Such a technique can vary the clock rate of the synchronous optical signal in future high speed computer backplane for optical clock distribution. In this paper, we demonstrate an variable RH active modelocking light signal technique using a figure eight fiber cavity (F8C) incorporating a nonlinear amplifier loop mirror (NALM) using phase modulator to generate high repetition rate optical pulses above 10 GHz.

The Compressive Optical MONTAGE Photography Initiative (COMP-I) is an initiative under DARPA's MONTAGE program. The goals of COMP-I are to produce 1 mm thick visible imaging systems and 5 mm thick IR systems without compromising pixel-limited resolution. Innovations of COMP-I include focal-plane coding, block-wise focal plane codes, birefringent, holographic and 3D optical elements for focal plane remapping and embedded algorithms for image formation. In addition to meeting MONTAGE specifications for sensor thickness, focal plane coding enables a reduction in the transverse aperture size, physical layer compression of multispectral and hyperspectral data cubes, joint optical and electronic optimization for 3D sensing, tracking, feature-specific imaging and conformal array deployment.

Based on compound-eye imaging, a compact image capturing system called TOMBO (Thin Observation Module by Bound Optics) is developed. The TOMBO system consists of a microlens array, a signal separator, and an image sensor. The captured compound image is a set of low-resolution unit images, which is processed to retrieve information of the target object. Owing to flexibility in configuration of the compound imaging system, the TOMBO system can be used for versatile applications. Possible configurations of the TOMBO system are summarized. As examples of the applications, multispectral imaging, 3-D data acquisition, short range imaging, gonio-imaging, and 3-D image interface are presented.

One of the major purposes of National Ignition Facility at Lawrence Livermore National Laboratory is to accurately focus 192 high energy laser beams on a nanoscale (mm) fusion target at the precise location and time. The automatic alignment system developed for NIF is used to align the beams in order to achieve the required focusing effect. However, if a distorted image is inadvertently created by a faulty camera shutter or some other opto-mechanical malfunction, the resulting image termed "off-normal" must be detected and rejected before further alignment processing occurs. Thus the off-normal processor acts as a preprocessor to automatic alignment image processing. In this work, we discuss the development of an "off-normal" pre-processor capable of rapidly detecting the off-normal images and performing the rejection. Wide variety of off-normal images for each loop is used to develop the criterion for rejections accurately.

The growth of research into microfluidics, especially towards micro-Total Analysis Systems (μTAS), is leading to a demand for highly efficient and accurate methods for analyte delivery, sorting, mixing and analysis. Optical techniques, due to their non-invasive, non-contact properties are ideally suited to integration in to microfluidic systems. One of the key abilities in a μTAS device is the ability to sort microscopic matter. When done optically this typically involves fluorescence detection, management of the information detected and subsequent action such as the actuation of an electric field or electro-mechanical valve. We present here a method whereby the detection of a micro-particle's properties is done passively, with simultaneous separation of those particles. To do this particle streams are injected into a three-dimensional crystal-like lattice of optical intensity maxima. A particle's response to the three-dimensional optical potential landscape formed by the lattice depends on its polarisability. This leads to a sensitivity to size, refractive index and shape. More strongly interacting particles are deflected away from the main flow whilst those that interact weakly are washed straight through the lattice without little or no net deflection. We present analysis of both injection and subsequent re-routing/sorting of particle streams, using body-centred tetragonal and three-dimensional "log-pile" optical lattices to separate both inert colloid and blood cells by refractive index or size. Sorting with an efficiency as high as 96% has been achieved with particle deflections in excess of 45 degrees.

In recent years, many research and development projects have focused on the study of fiber Bragg gratings. Fiber Bragg gratings have been used in the field of sensors, lasers and communications systems. The coupled-mode theory is a suitable tool for analysis and for obtaining quantitative information about the spectrum of a fiber Bragg grating. The transfer matrix can be used to solve non-uniform fiber Bragg gratings. Uniform, chirped, sampled Bragg gratings have already been simulated by using the direct numerical integration method and the transfer matrix method. Many of the applications for optical fibers in an in vivo setting, i.e., applied to the living human body. Using optical fibers for in vivo sensing is at a far less mature stage of evolution but nevertheless shows great promise for the provision of quantitative, minimally-invasive diagnostic information. There are few light-based systems sufficiently sensitive to detect the weak reflections typically present in biological and biomedical imaging and distance measurement applications. There are a number of interesting and potentially very beneficial applications of a biomedical instrument allowing quantitative surface profiling of larger internal hollow tube organs in living humans. Long period gratings, also known as transmission gratings, are periodic structures, in which coupling occurs between modes traveling in the same direction. Long period Bragg gratings are of interest to optical researchers for their higher sensitivity to sensing and some other applications. The reflected and transmitted spectra and time delay of fiber Bragg gratings can be obtained by using this simulation program. At the same time, the maximum reflectivity, and centre wavelength can also be obtained. Object-oriented programming (OOP) techniques are widely used for their advantages in the simulation software field.

We present both the estimation of main parameters and the previously obtained experimental data related to some algorithms and components for all-optical digital processors- multipliers. An all-optical multiplication in a mixed binary format may be designed with an array of non-collinear second-harmonic generation based optical AND-gates arranged in a square-law optically nonlinear medium. The modern approach, based on the concept of arranging light beams in space and time using the regime of spatiotemporall solitons or light bullets, is generally discussed.

In laser beam alignment in addition to detecting position, one must also determine the rotation of the beam. This is essential when a commissioning new laser beam for National Ignition Facility located at the Lawrence Livermore National Laboratory. When the beam is square, the positions of the corners with respect to one another provides an estimate of the rotation of the beam. This work demonstrates corner detection in the presence or absence of a second order non-uniform illumination caused by a spatial mask. The Hough transform coupled with illumination dependent pre-processing is used to determine the corner points. We show examples from simulated and real NIF images.

We discuss how all-optical signal processing might play a role in future all-optical packet switched networks. We introduce a concept of optical packet switches that employ entirely all-optical signal processing technology. The optical packet switch is made out of three functional blocks: the optical header processing block, the optical memory block and the wavelength conversion block. The operation principle of the optical packet switch is explained. We show that these three functional blocks can be realized by using the nonlinearities of semiconductor optical amplifiers. Some technologies in these three functional blocks are described. The header processor is realized using a Terahertz Optical Asymmetric Demultiplexer. We also describe a header pre-processor to improve the extinction ratio of the header processor output. In the optical memory block, we show that an all-optical memory can be obtained by using two coupled lasers that form a master-slave configuration. The state of the optical memory is distinguished by the wavelength of the master laser. We extend the concept to an optical memory can have multiple states. In the wavelength conversion block, we demonstrate a 160 Gbit/s wavelength conversion using a single semiconductor optical amplifier in combination with a well-designed optical bandpass filter. The semiconductor optical amplifier has a gain recovery time greater than 90 ps, which corresponds to a less than 20 GHz bandwidth for conventional wavelength conversion. We show that by properly using the optical bandpass filter, ultrafast dynamics in the semiconductor optical amplifier can be employed for wavelength conversion at ultrahigh bit-rates.

A fiber-based surveillance network overcomes the distance barrier. We are proposing a high performance, very flexible fiber-based real time visual surveillance network system that can be easily customized to the needs of the application. The system employs an FPGA-based DSP processor at the central processing unit to process and analyze video data from a network of cameras transmitted through an optical fiber network. The system is capable of handling various types of cameras including the reuse of existing cameras. This paper will show a proof of concept of certain functionalities of the system including the tracking of objects in a three-dimensional space using a stereo pair of cameras.

This paper describes the theory and experimental results of a dynamic holographic wavelength filtering for use in optical telecommunication Coarse and Dense Wavelength Division Multiplexing (CWDM/DWDM) applications. The enabling component is a ferroelectric liquid crystal (FLC) spatial light modulator (SLM) where dynamic holograms are implemented in real time; as a consequence, tuning of the filter is possible according to the light modulation. The great advantage of this FLC device is a polarization insensitivity operation, allowing low crosstalk and potential low loss in optical communications. Other applications, such as demultiplexers and wavelength routers, have been studied and practical values have been obtained according to central wavelengths recommended in ITU G. 694.1 and G. 694.2. Lab experiments have demonstrated the capability of a phase FLC-SLM to diffract the incident light, according its wavelengths and the hologram patterns, for the use in the former applications.

Erbium-doped fiber lasers (EDFL) are attracting a great deal of attention in the optical communications industry. This is due mainly to the fact that the gain spectrums of these lasers are well matched to the output spectrum of erbium doper fiber amplifiers (EDFA) in the 1550 nm operating window. Many different configurations for the fiber lasers have been developed in recent years. The two most popular are ring and linear cavity lasers. Ring lasers can be designed to have a large tuning range when consideration is given to active fiber length and output coupling ratios. Here an erbium-doped fiber ring laser is modeled for comparison of input pump powers and active fiber lengths. Theoretical analysis is given based on values of optical component losses for couplers, isolators, and tuning elements. We will present the laser output powers that are dependent on the output couplers reflectivity for a range of optical pump powers and various active fiber lengths.

The Multiscale Retinex With Color Restoration (MSRCR) is a non-linear image enhancement algorithm that provides simultaneous dynamic range compression, color constancy and rendition. The overall impact is to brighten up areas of poor contrast/lightness but not at the expense of saturating areas of good contrast/brightness. The downside is that with the poor signal-to-noise ratio that most image acquisition devices have in dark regions, noise can also be greatly enhanced thus affecting overall image quality. In this paper, we will discuss the impact of the MSRCR on the overall quality of an enhanced image as a function of the strength of shadows in an image, and as a function of the root-mean-square (RMS) signal-to-noise (SNR) ratio of the image.

This work deals with the problem of recognition of Urdu characters using Fourier descriptors for optical networks. In particular, the scope of this work has been to develop a robust Urdu characters pattern classification, representation, and recognition system, which can classify patterns even if they are deformed by transformations like rotation, scaling, and translation or any combination of these, in the presence of noise. Fourier descriptors are used to uniquely describe, classify, and recognize Urdu characters within one sub-class, that provide a remarkably simple way to draw definite conclusions from vague, ambiguous, noisy or imprecise information. Although current information transmission media i.e. cable, Ethernet etc. may still be used for communications but we proposed new technology i.e. WDM (Wavelength Division Multiplexing) due to its high speed and low loss transmission. Finally experimental results are presented to show the power and robustness of the proposed technique for Urdu character recognition.

We study the non-linear behavior of the KIII model for natural image classification. The KIII model is designed to be a dynamic computational model that simulates the sensory cortex. The KIII model has been explored for rudimentary pattern recognition and classification in noisy environment. We extend the study of KIII models in understanding whether self-organized neural populations can be exploited into perceptual and memory producing systems such as in natural image classification. Our goal is to obtain a quantitative index on how well the KIII model behaves when it is assigned the task to identify and distinguish one class of natural image from the other based on color and texture features. For twenty training data, twenty validation data and eighty test data set for four image classes, we obtain 80% correct classification using the KIII. We compare a standard non linear neural network tools such as back propagation for the classification of the same set of natural images and obtain 65% correct classification. We conclude that dynamic neural computational models such as KIII may be suitable candidates for natural image classification.

Selecting the correct feature set is an essential basis for video sequence analysis that leads to applications such as tracking and recognition of vehicles. This paper selects diverse multiple features and tests their accuracy for tracking a static vehicle. The static vehicle images are captured with airborne infrared and color video cameras. The camera collects 30 frames per second of compressed video in Motion JPEG format. The diverse features are selected from representative histogram-based, invariant-based, spatial-temporal-based and the center-symmetric autocorrelation-based family of features. A small dataset of airborne video sequences that include static vehicles with variations in quality, orientation, resolution, foreground lighting and background lighting are used to test feature selection and static tracking. The track of the vehicles is hand selected frame-to-frame to create a truth track. The result of each feature to maintain track is tested and scored based on distance from the truth track. Once a significant break from track occurs, the truth data is used to reacquire track. One goodness score is based on how often a feature breaks track. This analysis shows promise for identifying appropriate features for improved tracking results. The suggested algorithm is demonstrated on only a few video sequences with limited variations in operating conditions but demonstrates improvement possibilities for near real-time application.

An all-optical triode based on a tandem wavelength converter was realized in reflective InGaAsP-InP semiconductor optical amplifiers using the same 1551 nm wavelength for input, control and output. The output power ranged from 0 to 2 mW when the average control power was varied from 0 to 0.3 mW. Therefore, the output-input characteristics can be changed dynamically by low control powers. The output modulation degree was retained over a wide control power range of 0.01-1 mW. Because of its characteristics, this device can become a key component in future all-optical signal processing. In addition, a negative feedback optical amplification effect was confirmed using negative feedback based on cross-gain modulation in the all-optical triode. The optical amplification is capable of providing an output signal whose gain, waveform and baseline are stabilized without generating excessive noise. The amplification degree is retained at around 0 dB at an input power range of 0.01-1 mW and reaches -2 dB at 5 mW. The desired amplification can be adjusted by changing the amount of the negative feedback using the variable optical attenuator. The distortion of the waveform was extremely small in the wide frequency band of 0.1-10 GHz. The optical amplifier is physically considered as the optical equivalent of a non-inverting negative feedback amplifier and is capable of constituting an optical limiter.

In this paper, we derive the Mott-Gurney Law for space-charge-limited current and model the current density characteristics for a bilayer polymer light emitting diode (ITO/PPV/CN-PPV/Al). The organic material is assumed to be trap free and the influence of electric field on the carrier mobilities is neglected. Since the hole energy barrier between the ITO and PPV is less than 0.60 eV, the bottleneck for current flow is bulk-limited, resulting in space-charge-limited current. We discuss future plans for interposing a thin-layer of metal (Au, Pt, Pd, or AuPd) between the ITO and PPV. Experimental data will be compared to the J-V curve produced in this model, providing insight on how the metal buffer influences the range of potentials for which the current is space-charge-limited. Finally, the emissive spectrum is modeled with consideration of phonon-exciton coupling.

Both theoretical and experimental studies of an advanced rather integrated acousto-optical processor exploiting the algorithm of digital multiplication via analogue convolution and based on collinear interaction between a pair of the co- or counter-propagating non-optical waves in crystals are presented. The regime of wave digital multiplication of multi-bit binary data streams using the intermediate mixed binary format is analyzed and tested experimentally. The specific method of digitization for the mixed-binary format signals applying the optical components of spatial solitary waves in the form of multi-pulse non-collinear three-wave weakly coupled acousto-optical states is described and algorithmically estimated.

In this paper, we present a design and a design scheme for the phase locked-in loops satisfying given specifications. The proposed design suggests imposing an additional control signal on the normal input to the variable controlled oscillator (VCO) of the phase locked-in loop (PLL). Based on this design, a scheme of using the second method of Lyapunov is developed to choose the additional control signal and the loop filter parameters of the PLL. The proposed design and design scheme have improved the conventional PLL design results by obtaining a phase locked-in loop with pre-specified performance. The design scheme is based on nonlinear model of the PLL and it is applicable to the design of high order PLLs. Simulations results are reported to demonstrate the effectiveness of the proposed scheme.

Dynamic optical add-drop multiplexer (OADM) is a key component in computer networks in the future. Also the optical add-drop multiplexer played an important role in enabling greater connectivity and flexibility in dense wavelength-division multiplexing (DWDM) computer backplane networks. Based our previous simulation works, we have fabricated the electric tuning optical add-drop multiplexer devices. Owing to the large index step difference between SiO₂ and Si, it permits good confinement of light and the size reducibility of using the SOI structure. Different from traditional tunable optical add-drop multiplexer, we design a tunable optical add-drop multiplexer which uses MMI structure based on SOI wafer. In this paper, we measure the optical properties of characteristics and ability of electric tuning OADM devices as well as discuss the difference between experimental and theoretical results.

A novel power splitter based on self-imaging phenomena in multimode heterostructure is designed and analyzed. Such a photonic crystal waveguide is a hybrid structure combining square and hexagonal photonic crystal lattices. The size of our designed new power splitter is much smaller in comparison with the conventional MMI power splitter. The devices can be applied to optical communication systems and be integrated easily with other optical devices. The plane-wave expansion (PWE) method is used to calculate the bandgap structure of photonic crystals. The finite-difference time-domain (FDTD) method is adopted for the numerical simulation of related structure. This approach can be extended to novel design of MMI device based on photonic crystals.

In this paper, we provide an arrangement for use as optical power mapping from nanowire laser array to a single multimode fiber (MMF) within the visible spectral range. Nanowire laser, which might arrange in array, can be launched into a single MMF by microlens. Based on ray tracing, multi-beam elements of nanowire laser have a good light outputs, which are meridional rays and skew rays input, at the exit face of a single MMF with a length of several ten times millimeter. The research results are useful for realization of high-density information storage and information transfer in the field of digital multimedia and networking, local-loop communication, and medical diagnostics and therapeutics. Our proposed systems allow multimode operation, and have good transmittance. It is a guildline for future micro-photonic device with sub-micron width structure.

The method of optical signal generation with repetition rate frequency of about 30-50 THz based on interaction of two femtosecond laser pulses propagating collinearly in transparent nonlinear media with different group velocities is presented. It was shown that for high input pulses intensities their interaction may result in formation of quasi-discrete spectrum with temporal structure consisting of many ultrashort pulses of near rectangular shape. It was demonstrated that generated sequence could be used in information technologies.

Electrokinetic phenomena become an increasingly efficient fluid transport mechanism in micro- and nano-fluidic fields. These phenomena have also been applied successfully in microfluidic devices to achieve particle separation, pre-concentration and mixing. Electrokinetic is the flow produced by the action of an electric field on a fluid with a net charge, where the charged ions of fluid are able to drag the whole solution through the channels in the microfluidic device from one analyzing point to the other. We will present the simulation results of electrokinetic transports of fluid in various typical micro-channel geometries such as T-channel, Y-channel, cross channel and straight channel. In practice, high-speed micro-PIV technique is used to measure transient fluidic phenomena in a microfluidic channel. Particle Image Velocimetry (PIV) systems provide two- or three-dimensional velocity maps in flows using whole field techniques based on imaging the light scattered by small particles in the flow illuminated by a laser light sheet. The system generally consists of an epifluorescent microscope, CW laser and a high-speed CMOS of CCD camera. The flow of a liquid, (water for example), containing fluorescent particle is then analyzed in a counter microchannel by the highly accurate PIV method. One can then compare the simulated and experimental microfluidic flow due to electroosmotic effect.