Using liquid crystals to control the propagation of microwaves is a potentially interesting technology. By incorporating small amounts of liquid crystal in thin slat metal structures through which the microwaves may resonantly pass a whole new range of voltage tuned microwave devices are becoming available. Metallic sub-wavelength slit structures at microwave frequencies have been constructed which show Fabry-Perot type resonances in very thin slits. If the dielectric in such thin slits is an aligned liquid crystal it is found possible to voltage-control the resonant frequencies. Novel selective filters and structures for microwave beam steering have been fabricated leading to a new generation of liquid crystal controlled devices.

It is well established that much more radiation may be transmitted through a set of apertures in a metallic screen than a simple calculation from the transmission through the aperture area alone would predict. There has been substantial debate regarding the exact cause of this enhanced transmission, and confusion over the difference between the behaviors of subwavelength apertures as opposed to subwavelength slits. In this study we have analyzed the transmission response of individual slits, using microwave radiation to ensure that transmission is in no part due to direct passage through the metal screen itself. A set of resonant transmission peaks is caused by the excitation of standing-wave-coupled surface plamsons in the finite length slit. It is also found that the high but finite value of the metals’ conductivity influences the transmission response of such slit channels when they are less than 100 microns in width. Indeed there is a strong decrease in transmitted resonant frequency, remarkably tending to zero as the slit width decreases. In addition we have explored the effect of misalignment of the two metal plates that comprise the slit. This modifies resonant frequencies and transmitted intensities through the changing boundary conditions at the slit ends.

Laser damage thresholds of 8μm- and 22μm-core diameter solid-core photonic crystal fibres (PCF) and hollow-core photonic band gap (PBG) fibres have been measured. The studies were carried out using a 1.06μm Nd:Yag laser (30nsec pulses at 10Hz), which is optimally coupled into these fibres by careful mode matching, providing a coupling efficiency greater than 90%. It has been shown that the damage threshold of the 8µm core PBG fiber occurs at pulse energies close to 1 mJ, equivalent to a fluence well in excess of 1kJ/cm² propagating down the fibre. This is a factor of 4 larger than the damage threshold of a solid-core PCF of similar core diameter. In comparison, the damage threshold of the large-core PBG is smaller than that of the equivalent PCF. Theoretical modelling based only on the optical modal properties of the single mode PBG fibre shows that an enhancement of a factor of 25 should be obtainable. Thus there are different damage mechanisms potentially responsible for the fragility of larger core PBG fibres. In an experimental study of bend losses it has been found that it is possible to bend the 8μm PBG fibre up to the breaking point bend radius (<1mm). The critical bend radius for the 22μm core PBG is close to 2 mm, which is 50 times smaller than the critical bend radius of a 20μm core PCF.

FDTD algorithms are being used as a numeric tool for the analysis of photonic crystals. The definition of the modes associated with them is of interest for the study of the capabilities of photonic crystal devices. The Principal Component Analysis (PCA) has been applied here to a sequence of images corresponding to the electromagnetic fields obtained from the FDTD simulations. PCA has revealed and quantified the importance of the modes appearing in the photonic crystals. The capability of PCA to produce spatial structures, or maps, associated with temporal evolutions has made possible the calculation of the modulus and phase of the modes existing in the photonic crystal. Some other modes, contributing with an almost negligible amount to the total variance of the original data, are also revealed by the method. Besides, PCA has been used to quantify the contribution of the numerical noise of the algorithm and to identify the effect of artifacts related with the matching of the computational grid and the inner geometry of the photonic crystal.

The infrared (IR) spectrum is of significant importance in many defence applications including free-space communication, thermal imaging and chemical sensing. The materials used in these applications must exhibit a number of suitable properties including mid-IR transparency, rare-earth solubility and low optical loss. When moving towards miniaturised optical devices one tends to adopt the concepts introduced by integrated optics; multiple devices operating harmoniously on a single photonic chip. Our work focuses on the use of a laser to directly write into a novel chalcogenide glass to engineer optical waveguide devices. Our material of choice is gallium lanthanum sulphide (Ga:La:S) glass, an exceptional vitreous chalcogenide material possessing these aforementioned properties as well as a broad range of other properties. These Ga:La:S glasses have a wide transmission window between 0.5 to 10 μm. Furthermore, these low-phonon energy glasses have a high transition temperature (T_g = 560°C), high refractive index, the highest reported non-linearity in a glass, excellent rare-earth solubility with well documented near-mid IR spectroscopic properties. We report on low loss single-mode active channel waveguides in Ga:La:S glass engineered through direct laser writing (λ= 244 nm). We discuss laser operation at 1.075 µm (neodymium) and IR emission at 1.55, 2.02 and 2.74 µm (erbium) from these waveguides.

Using deep-dry etching techniques it is possible to realise filters for use in optical telecommunication based on silicon/air cavities with a high degree of finesse, and which are oriented substantially perpendicular to the surface of the silicon substrate. This geometry is well suited to their incorporation in hollow-waveguides or within ridge waveguide structures. The optical characteristics of such devices are determined by a number of factors, including the designs of the optical cavities and the degree of surface perfection achievable by the deep-dry etching process.

A Superluminescent Light Emitting Diode (SLED) is an ideal optical broadband source for applications like Fiber Optic Gyroscopes and other fiber optic based sensors used in navigation systems. High optical output power and large optical bandwidth are key features for these devices. The short coherence length related to this large bandwidth allows the realization of sensors with improved sensitivity. Semiconductor devices based on quantum dots (QD) are ideally suited as the active material for SLEDs since the size dispersion typical of self-assembled growth naturally produces a large inhomogeneous broadening. The large spacing between different energy levels can lead to improved thermal stability as well. In this paper we report, ridge-waveguide devices based on five stacks of self-assembled InAs/GaAs QDs. SLED devices with output powers up to 1.5 mW emitting around 1300 nm have been realized. Spectral analysis at 20°C shows a 121 nm FWHM. Temperature characteristics in the range 10-80°C are also reported.

This paper presents recent developments in the packaging of 40GHz receivers for radio over fiber applications. First, we present a hybrid 40GHz photoreceiver module. It integrates 40GHz waveguide photodiode technology and narrow band MMIC amplifier. We give key elements for the design and the realisation of such photoreceiver. With an input optical power of 0dBm, an RF ouptut power of -3dBm is obtained in the 38-44GHz frequency range with a flatness of ±0.5dBm. The maximal input optical power is +6dBm. Secondly, a small footprint 40GHz photoreceiver scheme is presented. It includes high optical coupling tolerances 40GHz tapered waveguide photodiodes and the same type of MMIC amplifier than used in the hybrid package. The interconnect of the several elements (MMIC, capacitors, photodiode biasing network) uses Microwave High Density Integration (MHDI) technology on a Si substrate. The photodiode is flip-chip mounted on the same substrate. This technology is very promising for packaging of optoelectronic devices, since it combines compactness and reproducibility thanks to wire bonding suppression.

Chaos-based secure communication is intended to operate as an additional encryption mean at the physical layer, with the unique capability for operating at several 10s of Gb/s. Different chaos generators have been recently explored for optical telecommunications, among which three setups were particularly interesting in terms of encryption speed capability: the all-optical external cavity semiconductor laser, the direct optoelectronic feedback semiconductor laser, and the nonlinear electrooptic feedback. The latter solution was mainly investigated by our group during the last 5 years. We report its numerous advantages in terms of chaos complexity (attractor dimension as high as several hundreds have been obtained), architecture reliability (different chaos generator have been performed experimentally), encryption bandwidth capability (more than 30GHz chaotic spectrum has been observed), stability, and decoding quality. The potential for high speed operation was recently demonstrated with an electrooptic chaos generator at 3Gb/s, with BER as low as 10^-9}.

A new high power laser diode has been developed and tested. The possibilities for driving high power laser diode bars and stacks at high frequencies have been shown. The driver is with 0.05% noise and ripples at DC, and can be modulated with 15 ns rise/fall times at 100A, with maximum frequency for square wave modulation up to 5 MHz. The spikes for the optical output at switching on/off are not exceeding 5%. The limitation of the used scheme with the existing commercial components allows frequencies up to 25 MHz and currents to 400A to be reached. The driver opens new applications for high rate data transmission at long range, fast scanning designators, materials processing, etc. with laser diodes with more than 100W output power, which will be discussed.

This paper documents the fundamental and practical limits on the performance of the demultiplexing class of photonic analog-to-digital converters (ADCs). First, we review the classes of photonic ADCs that have been investigated to date. Then the reported performance of several demultiplexing photonic ADCs is compared to performance recently obtained with high rate, high resolution electronic ADCs. Next, the paper derives the fundamental limits on ADC performance that are determined by amplitude noise, timing jitter and the finite width of the optical sampling pulse. Finally, we review practical limits for the demultiplexing ADC. These practical limits are generally determined by the performance of the electronic-to-optical and optical-to-electronic interfaces, the optical modulator and the photodetector, and by the requirements on component/path matching.

An optically controlled RF/microwave/mm-wave phased array antenna has been developed operating at 10 GHz with 30 kHz reconfiguration rate via the use of a micromachined silicon Spatial Light Modulator. A communications function has been demonstrated with a variety of Phase Shift Keying modulation schemes (BPSK, QPSK, MSK) at data rates up to 200 Mbit/s and low BER (<1×10^-9). A single channel has been demonstrated at 35 GHz. The properties of photonic components are taken advantage of in several ways: (i) since the carrier frequency is derived from heterodyning of lasers, it is tuneable from almost DC-100 GHz, (ii) the use of optical fiber allows for EMI immune antenna remoting, and (iii) the wide information bandwidth of optical modulators, which in this configuration is carrier frequency independent. The above is achieved in a lightweight and compact format, with considerable scope for further reductions in size and weight.

A low phase noise optoelectronic source has been developed operating at 10 GHz. Custom surface acoustic wave (SAW) devices operating at high frequency and high acoustic power have been developed and are used as the critical element in an optical phase locked loop. Improved performance could be attained via lasers with larger control loop bandwidths. The source is antenna remoteable via the use of optical fibre and is compact and lightweight, suggesting applications in phased array radar.

We present a new coherent optical Beamformer for the receive mode based on a Dual Frequency Laser and Spatial Light Modulation matrixes. This coherent architecture, described and detailed by different building blocks, allows a full reconfiguration of the beam thanks to the SLM matrixes and a first down conversion due to the conjoint use of a heterodyne source and an external modulator.

A fibered optoelectronic arbitrary waveform generator for radar applications is demonstrated. The proposed optoelectronic arbitrary radar waveform generator permits to generate predefined electrical waveforms according to radar specifications. Through the use of an optical frequency shifter, a beat signal at the central frequency of the radar is generated in a homodyne optical setup. An original Doppler module based on acousto-optic techniques permits to generate multiple arbitrary frequencies around the central frequency of the radar to simulate the Doppler signature of a target. In this paper, we demonstrate the ability to generate microwave arbitrary waveforms with a radar central frequency fro 12 GHz up to 14 GHz with up to 700 Doppler frequency components and more than 17 dB spurious extinction ratio.

“Closed field” magnetron (CFM) sputtering offers high throughput, flexible deposition process for optical coatings and thin films required in display technologies. CFM sputtering uses two or more different metal targets to deposit multilayers comprising a wide range of dielectrics, metals and conductive oxides. CFM provides a room temperature deposition process with high ion current density, low bias voltage and reactive oxidation in the entire volume around the rotating substrate drum carrier, depositing films over a large surface area at a high rate with excellent and reproducible properties. Machines based on CFM are scaleable to meet a range of batch and in-line size requirements. Thin film thickness control to <±1% is accomplished using time, although quartz crystal or optical monitoring are used for more demanding applications. Fine layer thickness control and deposition of graded index layers is also assisted with a special rotating shutter mechanism. This paper presents data on optical properties for CFM deposited coatings relevant to displays, including anti-reflection, IR blocker and color and thermal control filters, graded coatings, barrier coatings as well as conductive transparent oxides such as indium tin oxide. Benefits of the CFM process for a range of display technologies; OLED, EL and projection are described.

Techniques of polarized latent image formations on liquid crystal (LC) cells have been proposed for optical security devices. The glass plate coated with a photo-reactive polymer film is prepared as a substrate of the LC cell. The polymer surface is rubbed and subsequently modified by exposing with a non-polarized UV light through the photo-mask. The LC cell using the patterned substrate surface is homogeneously transparent under the normal condition (without polarizers). However, the image with continuous grey levels appears when the cell is set between two polarizers. The latent image can also be optically and thermally written on the cell filled with the LC. The guest-host LC cell which has dual latent images is also demonstrated using another photo-reactive polymer. The LC alignment on both substrate surfaces are respectively patterned by the photo modification and rubbing. The latent image can individually be visible and selected by replacing the polarizer in front or behind the LC cell. Our LC patterning process is very simple compared to other patterning methods and the patterning technique which is utilized the mechanical rubbing and photo modification gives great advantages of not only the large area but also the high density patterning.

The use of liquid crystal spatial light modulators in applications, require good characterization of phase, polarization and amplitude shifting properties. This report presents a new approach for simultaneously characterizing the depolarization and controlling the polarization properties of a reflective twisted nematic liquid crystal spatial light modulator (LC SLM). The SLM was set up as a part of a Michelson interferometer. The phase response was determined by using a piezo-electric actuator for phase stepping in the reference arm. During the polarization measurement the reference beam was removed and the polarization state of the input and output was determined by a polarization state generator (PSG) and a polarization state analyzer (PSA), each consisting of a polarizer and a quarter-wave plate. Hereby, both phase response and polarization control properties could be determined independently in the same measurement configuration simply by changing static polarization components. The systematic rotation of the quarter wave plates of the PSG and the PSA using stepper motors gives out-put data whose Fourier transform in terms of angular frequency components can be used to determine all the elements of the Mueller matrix. The Mueller matrix of a commercial SLM (Holoeye LC-2500) was determined for 17 evenly spaced voltage levels addressed to the SLM.

The polarization properties of a one-dimensional, 1x4096 pixels, zero-twist nematic liquid crystal (NLC) spatial light modulator (SLM) were investigated. The fringing electric field between pixels can introduce twist deformations in addition to the wanted splay and bend. The twist will affect the polarization and couple energy between polarization modes. The electric fields and director distribution in the LC were numerically determined by solving a set of coupled partial differential equations. The optical propagation in the resulting inhomogeneous anisotropic crystal was performed by the finite-difference time-domain (FDTD) method. The simulated results were validated by comparison with experimental diffraction patterns. As the numerical scheme is slow a simple semi-empirical model was also developed. Using parameters from the simulated results the model was adjusted to allow rapid calculations of the polarization distribution of the light modulated by the SLM.

In this paper, a new stereoscopic 3D imaging communication system for real-time teleconferencing application is implemented by using IEEE 1394 digital cameras, Intel Xeon server computer system and Microsoft’s DirectShow programming library and its performance is analyzed in terms of image-grabbing frame rate. In the proposed system, two-view images are captured by using two digital cameras and processed in the Intel Xeon server computer system. And then, disparity data is extracted from them and transmitted to the client system with the left image through an information network and in the recipient two-view images are reconstructed and displayed on the stereoscopic 3D display system. The program for controlling the overall system is developed using the Microsoft DirectShow SDK. From some experimental results, it is found that the proposed system can display stereoscopic images in real-time with a full-color of 16 bits and a frame rate of 15fps.

In this paper, as an approach for a wide 3D real image display system without special glasses, a 100" Fresnel lens-based 3D real-projection display system is implemented and its physical size is designed by 2800x2800x1600 mm³ in length, width and depth, respectively. In this display system, the conventional 2D video image is projected into the air through some projection optics and a pair of Fresnel lens and as a result, it can form a floating video image having a real depth. From some experiments with the test video images, the floated 3D video images with some depth have been realistically viewed, in which forward depth of the floated 3D image from the display screen is found to be 35~47 inches and the viewing angle to be 60 degrees, respectively. This feasibility test for the prototype of 100" Fresnel lens-based 3D real image rear-projection display systems suggests a possibility of its practical applications to the 3D advertisements, 3D animations, 3D games and so on.

We report on the development of different surface-normal multiple quantum well (MQW) modulator devices. Owing to their unique speed advantage, arrays of surface-normal MQW modulators are very well suited for fast and parallel signal processing, and can be developed for both digital or analogue signals. We present the design and fabrication process for single surface-normal MQW modulators, as well as for high fill factor (80-90%) 1-D arrays of such modulators. Design issues and trade-offs in terms of modulator size, speed and contrast ratios are described. Contrast ratios in excess of 100:1 have been demonstrated. 3-dB frequency modulation bandwidths in excess of 1GHz have been obtained for single modulator devices of 125μm in diameter. Performances of 1-D arrays of 64 and 128 modulators (pixel size: 2mmx80μm and 2mmx40μm, respectively) are also presented, with response time for programmable filtering in the order of 10 ns.