Electronic Materials and Devices Laboratory
Nanoscale Science Laboratory
Polysilicon Thin-Film Transister Group
Silicon Micromachining for MEMS
Michromechanical Clips to hold Optic Fibres in V-Grooves in Silicon
Irradation of the Superconductor YBaCuO to Produce Josephson Junction Devices
The Aerodynamic Design of Multi-Sensor Pressure Probes for MEMS
Microliquid Transfer Methods for Laboratory-on-a-chip Technology
Scanning Electron Miroscopy and Transmission Electron Microscopy
Highly Integrated Electronic Systems
CUED 125th Anniversary Celebration
Power Electronic Devices and Circuits
Photovoltaic Devices and Solar Power
Vaccum Electronic Devices
Liquid Crystal Photonics for Telecommunications and Display Systems
Flat Panel and 3D Displays
Professor W.I. Milne
Dr J. Robertson
Dr F. Udrea
Research in the group continues to be centred on the deposition, characterisation and application of thin film amorphous semiconductors.
Work on Diamond Like Carbon has expanded to include research on carbon nanotubes (CNTs). The growth, synthesis and functionalisation of the CNTs is ongoing in collaboration with Professor Windle's group in the Department of Materials Science. Also aligned CNTs are being used as the nanoscale electron sources for a novel parallel e-beam lithographic system being designed in collaboration with Thomson CSF and others as part of a Framework V EC proposal NANOLITH(J159). Large area CNTs and other carbon based thin film materials are being investigated for use in Field Emission Displays in collaboration with Samsung Displays. Further work on aligned CNTs and other Carbon nanostructures is also being pursued for use in super capacitors and electrochemical applications in collaboration with Innogy, Montena, Microcoat and the Universities of Milan and Friborg through another EU Collaborative project CARBEN.
The use of tetrahedrally bonded amorphous carbon (ta-C) for cold cathode emitters for application in back lights for Active Matrix Liquid Crystal Displays and for the production of field emission (FE) displays themselves was completed this year(J46,J47,J66,J89,J121,J122,J124,J127,J129,J132,J133,J134,J135,J189,J190,J191,J192,J210). This was carried out as part of an EU ESPRIT project in collaboration with CRL, Hayes and Sextant Avionique, Bordeaux. Recent results have indicated that electron emission from these films is from sp2 clusters embedded within a sp3 matrix. The work on FE is strongly supported by effort on the structural optical and electrical characteristic of the ta-C and hydrogenated ta-C (ta-C:H) the understanding of the modelling of the growth process themselves and the plasma process during growth(J33,J57,J88,J94,J95,J153,J154,J180,J200,J207). The latter work continues to be funded through collaboration with Kawasaki Heavy Industries(J143). The use of ta-C, ta-C:H, and a-CN as hard coatings for magnetic disks and reading heads is also ongoing in collaboration with Seagate and a consortium including IBM(J58,J59,J123,J126,J128,J179,J181,J182,J199). Scanning Probe Microscopy of ta-C and related films has also been continued in close collaboration with the CUED Nanoscale Science group. The potential use of ta-C for TFT manufacture also continues to be investigated(J103). The interaction between the group and the School of EEE in NTU, Singapore on the electrical characterisation of DLC and related materials is also continuing and a British Council funded interaction between us and the University of Barcelona, Spain on DLC films continues(J21,J160,J183).
Finally in this area we have recently begun to look at the potential application of DLC to MEMS production and work on this will be carried out as part of the Cambridge/MIT Institute (CMI) collaboration.
Philips Research Laboratories, Redhill, continue to support work on the growth and application of amorphous silicon (a-Si:H) and related thin films for displays. The main thrust of this work at present is to investigate the deposition of both the active layer (a-Si:H and microcrystalline Si) and the gate insulator layer (SiOx or SiNx) for the manufacture of Thin Film Transistors (TFTs) at temperatures compatible with the use of plastic substrates(J65,J70). Currently, we are investigating the use of both ECR and ECWR deposition systems for this purpose. Theoretical work on the growth through STM measurements, and stability of a Si:H based devices is also progressing(J67) and recently a project on metal-induced crystallisation has begun.
High Dielectric constant oxides such as barium strontium titanate and tantalum pentoxide are to be used as the dielectric layer in DRAMs and ferroelectrics such as lead zirconate titanate (PZT) and Strontium Bismuth Tantalate are to be used in ferroelectric non-volatile memories (FeRAMS). We have calculated the Schottky Barrier heights for these oxides and used this to model leakage in such devices(J127,J132).
Finally work on sensors has continued and EPSRC has funded a project on SOI-based Smart MOSFET Sensors in collaboration with Professor Gardner at the University of Warwick and collaboration with Professor Oda, funded by Mombusho, has now ended(J152).
Professor M.E. Welland
The Nanoscale Science Laboratory is primarily concerned with developing and applying methods related to the fabrication and characterisation of structures with dimensions down to that of single atoms. A wide range of characterisation tools that can uniquely determine the physical properties of, ultimately, single atoms, compliments extensive fabrication facilities that can produce continuous structures on the nanometre scale(J224). In the last year, significant breakthroughs have been made in understanding the limits that define how small a future computer, or data storage system, can be.
As an electronic device shrinks in size its properties become dominated by the size and shape of the structure rather than the intrinsic physical properties. For example, metallic wires with cross sectional area of a few thousand atoms, where a particular interest is the stability of the wires as current is passed through them. We have shown that surface effects dominate failure of such wires so that during electrical stressing of a wire, considerable restructuring takes place that eventually results in failure of the wire at one site(J16,J52,J53). This combination of experiment and modelling has determined the importance of size effects in current carrying wires; a crucial consideration as the wire inside a computer chip shrinks further in size.
In the future development of information storage technology the role of patterned magnetic media will become increasingly important. We have been studying the fundamental properties of individual magnetic structures with dimensions less than 100 nm. In addition to allowing for the optimisation of shape of magnetic nanostructures for data storage, we have also been able to design simple logic circuits based purely on magnetics(J1,J3,J4,J35,J36,J37,J38,J39,J41,J96). This has culminated in the first demonstration of magnetic based logic where both the logic functionality and signal propagation are effected purely by magnetic coupling of information. This opens up the potential of a new class of computer chip requiring no electrical power.
In collaboration with the Polysilicon Thin-Film Transistors Group, we have been exploring the fundamental properties of Piezo electric thin films that form the basis for future computer displays and elements of a memory storage device. By combining imaging and electric characterisation at sub nanometre resolution, we demonstrated the intrinsic limit within which electronic polarisation of the material can be stably written(J50,J52,J55,J56). These measurements put a limit on the feasible size of a piezoelectric circuit element beyond which stored memory information would disappear.
Sensor technology based on microelectronics is a rapidly expanding field. In addition to modelling the behaviour of such sensors, applications in electrochemistry and biochemistry are being pursued. In particular we have shown that a sensor measuring less than 100 micron in size can accurately determine the relative levels of high and low density liproprotein in human blood. In a similar experiment we have shown that such sensors were able to measure the binding reaction of a single protein layer on a surface(J144,J145). These two applications are now being funded to produce products in the health care and pharmaceutical sector.
Professor P. Migliorato
One key aim of this research is the development of the so-called "System-on-Panel", a concept expected to revolutionise the field of portable computing and instrumentation through monolithic integration of complex circuitry on glass or plastic substrates. The most promising approach is based on low temperature Polycrystalline Silicon (Poly-Si) Thin Film Transistors (TFTs). In order to achieve a system on panel it is necessary to develop this technology to the point where TFTs can replace single crystal silicon MOSFETs not only in circuits such as display drivers but also in memories and processors. This target, which is obviously beyond the capability of a university group alone, is pursued by us in close collaboration with Seiko Epson. Epson has been funding the activity of the Polysilicon Group since 1995, for a total of over £1,000,000. In addition it has established the Epson Cambridge Laboratory (ECL), in September 1998, to expand its research activities in Cambridge. Presently five ECL members of staff are working with our Group in this Department. These activities are organised in three main research lines: Material and Device Characterisation, Device Modelling, Circuit Testing and Modelling. The Material and Device Characterisation activity aims at developing experimental and data analysis techniques to correlate the fabrication conditions with the device performance and provide input parameters for device and circuit simulation. In the current academic year the TFT transient response has been extensively studied and correlated with carrier generation times and floating body effects. For these measurements an in-house system has been developed, which allows us to specify a variety of driving waveforms. The study of materials for non-volatile ferroelectric memories. The ferroelectric characteristics of sol-gel deposited PZT films have been correlated with material deposition parameters, texture and contacts and a model has been proposed to account for the presence of non ferroelectric boundary layers. The conduction mechanisms responsible for the leakage currents of ferroelectric capacitors are also under investigation. In collaboration with the Nanoscale Science Group (Professor Welland) a new technique for a quantitative microscopic measurement of hysteresis curves has been established. This is likely to prove a powerful tool to investigate the effect of impurities and other crystallographic defects such as grain boundaries. The highlight of our device modelling work has been the incorporation in a commercial simulator (SILVACO Atlas) of our model for the off-current of Poly-Si TFTs, developed in previous years. State-of-the art equipment for circuit design and testing has been installed. Both analogue and digital TFT circuits are being developed. In particular special pixel drive architectures to accurately control light emission in organic LEDs have been designed. The proprietary circuit simulation tools, described in previous reports, have been essential for this work as they yield a much higher degree of accuracy than available from existing commercial packages(J18,J55,J56,J93,J204).
A new application of polysilicon TFT, which we have started to explore is the use of these devices in biological sensor micro-arrays, in collaboration with the Cambridge Institute of Biotechnology. This approach is expected to yield cheap, disposable, intelligent biosensors providing high throughput parallel processing with important implications for point-of-care medical and genetic testing, drug discovery, security and forensic applications.
Dr D.F. Moore
Microelectromechanical systems (MEMS) combine micrometer and millimetre sized electrical and mechanical components on a chip. They are typically fabricated by batch processing techniques similar to those used for silicon integrated circuits(J140). Much of current MEMS research concentrates on different materials, new processes and novel applications(J152). In one project to make physical sensors using relatively simple processing(J48), bonded silicon-on-insulator starting material is used to fabricate microaccelerometer structures. The readout gaps are milled obliquely into silicon beams used focused ion beam etching. In a joint EPSRC-sponsored project with Imperial College London and Strathclyde University, MEMS Technology for Silicon Opto-Hybrids is being developed in close collaboration with four companies in the industry. The programme aim is to combine the most successful aspects of MOEMS (Microoptoelectromechanical systems) to lower the packaging costs of manufacturing optoelectronic hybrids. This involves the design, simulation, fabrication and assessment of a range of simple and also relatively complex mechanisms(J139).
Dr D.F. Moore
The use of single-mode optical fibre in telecommunications brings many advantages including higher bandwidth, but optical device packaging involves the complex assembly of miniature components with extremely good alignment accuracy. In this project flexible silicon nitride clips have been developed to hold optical fibres kinematically in grooves etched anisotropically into silicon substrates(J138,J139). Good light coupling between two fibres buried in the same V-groove has been demonstrated, and clipped fibres have passed the standard environmental and reliability tests for telecommunications applications. Potential uses of thin film mechanical packaging technologies include fibre connect, Fabry-Perot devices, waveguide sensor and electronic packaging applications(J140).
Dr D.F. Moore
There is intensive research worldwide into the fabrication of reliable junctions in the high temperature superconductors for sensor applications in SQUID (superconducting quantum interference devices) and other electronics. A high-voltage electron beam has been used to create high quality Josephson junctions in a single layer of YBaCuO, but the throughput of junctions is limited because of the high dose required and the serial nature of the process. An fabrication alternative method with higher throughput is a combination of high resolution masking with irradiation in an ion implanter(J17). In this joint EPSRC-sponsored project with the Materials Science Department and with the University of Surrey, the electrical properties of ion irradiated YBaCuO are being studied in detail. There are good prospects for developing a junction technology based on focused ion beam stencil microfabrication and ion implantation.
Dr D.F. Moore
Professor M.E. Welland
Dr H. Babinsky
Dr H.P. Hodson
A family of novel planar geometries suitable for the construction of a silicon-based MEMS (Microelectromechanical System) five-hole sensor has been invented. The necessary directional sensitivity is to be achieved by placing fences on the planar frontal surface of a cylindrical probe. The effectiveness of such flow manipulation devices has been demonstrated experimentally on a large-scale probe at twenty-five times size. In an EPSRC-sponsored project the technology for a MEMS version with faster response is currently under development.
Dr D.F. Moore
Professor W.I. Milne
Microarraying, which is revolutionising the study of genes and genomes, is a technique that involves laying down an ordered array of genetic elements onto a solid substrate. This enables genetic analysis to take place on a massively parallel scale, with thousands of genes and markers being tested in a single experiment. The best way of preparing microarrays is to use a robotic platform to transfer samples from the wells of a microtitre plate to the surface of a glass slide in the form of a spot of order 200 m m in diameter. This automation ensures that high-density microarrays can be prepared quickly, accurately and reproducibly. A new microarray spotting pin has been developed during a BBSRC-funded TCS Programme with S. Elmes and M. Davies of BioRobotics Ltd. This technology incorporating a microreservoir was commercialized in 2000, and has already given the company a significant advantage in the biotechnology marketplace. The MicroSpot2500 pin allows genetics scientists to produce microarrays, or biochips, faster and with less wastage of valuable DNA material (see www.biorobotics.co.uk). In the joint project a novel laser process has been developed for fabricating stainless steel or tungsten pins, with a quill design and a tip diameter of 100 microns. Each pin holds 80 nanolitres of fluid containing DNA and can deposit one-nanolitre volumes of it onto a genetic chip. Each pin leaves a spot less than 200 mm in diameter. This approach to microfabrication is likely to lead to further advances in the technology to miniaturise arrays (i) using contact-based technologies, and (ii) using MEMS-based noncontact liquid transfer technology.
Dr D.M. Holburn
Recent work on the development of effective sharpness measures for scanning electron microscope images has led to the design and implementation of novel instrumental control algorithms. These perform automatic focus, astigmatism correction, and beam alignment in the scanning electron microscope. Research continues into the development of knowledge-based applications for scanning electron microscopy, decision support and other tasks. The diagnostic expert system (FIRST A.I.D.) has been re-implemented as an Internet-based application (WebFIRSTAID) and has been undergoing commercial trials. Progress has been made in extending the XpertEze knowledge-based system to cover variable-pressure as well as conventional microscopes. An initial prototype of an embedded version of XpertEze for use in production instruments has been implemented and is being evaluated. The Web-based version of XpertEze (WebXpertEze) has also been enhanced(J19). Future work will involve further development of the embedded XpertEze system, combining it with recent results in automating the setting of individual microscope parameters. An extensive research collaboration with the Engineering Design Centre, Napier University, and the University of Middlesex has continued. This has developed the prototype web-based decision support and knowledge management system (WebCADET) for engineering design(J20,J175,J176,J177,J178).
Further progress has been made in the development of VSEM (Virtual Scanning Electron Microscope), a software package which emulates the interactions and behaviour of the instrument using a library of image sequences(J84). VSEM has been extended to incorporate a "virtual reality" model of the instrument column(J83). International scientific and industrial interest in VSEM continues to grow. Future work will include the investigation of algorithmic approaches to simulate changes in instrumental settings, the production of suitable support material, and the evaluation of VSEM as a teaching and training tool.
Dr D.M. Holburn
Dr R.J. Mears
Earlier work on the development of compact digital monitors for heart-rate and movement monitoring has led to a field study which has confirmed that the method has potential for estimation of human energy expenditure(J162).
Further progress has been made in the development of high speed optical transceivers for in-building free space data networks. Delivery of data and communications services to mobile users has come to be regarded as a key area for development as users increasingly demand more complex services and mobility. Test structures based on a commodity CMOS process have been fabricated and have shown the feasibility of achieving adequate bandwidth, sensitivity, stability, noise characteristics and power economy in both the transmitter and receiver. Work is now under way on the development of a demonstrator unit which it is expected will confirm that a low-cost CMOS solution can provide the required performance. Systems work on holographic beam-steering has been applied to an adaptive optical system, with the potential for higher bandwidth delivery. The project is being carried out under the EPSRC Optical Systems Integration programme, and is also the subject of a new patent application.
The Engineering Department celebrated its 125th anniversary in the year 2000. To mark this occasion, a series of multimedia web-based presentations were developed and published on the Department's web site. These demonstrate some of the important milestones in the Department's contributions to engineering and technology. A commemorative booklet and CD-ROM were also produced and distributed to all members of staff and to alumni of the Department.
As a result of this project the Multimedia Group has been formed to further develop and promote the use of multimedia technology within the Department. Ongoing projects include enhancing the commemorative web site to provide further information about current research projects within the Department, and producing a new version of the undergraduate prospectus, which will be interactive and available on the Department's web site and on CD-ROM.
Techniques for producing courses suitable for Distance Learning are also being investigated with a view to enhancing the Department's role in this area, particularly for projects being proposed through the Department's new links with MIT. Video conferencing facilities have been introduced and made use of in this context.
Professor G.A.J. Amaratunga
Dr P.R. Palmer
Dr R.A. McMahon
Dr F. Udrea
The research programme on MOS controlled electronic devices for power switching continues to flourish(J12,J85,J86,J194,J198). Trench gate IGBT devices(J24,J208) resulting from this research programme have been commercially released by Dynex Semiconductors (formerly GEC-Plessey). Research into extending electronic device structures to higher voltage ratings in Si and SiC to make them suitable for power system and traction applications is currently a focus of research(J119,J120,J151,J155,J195,J196,J197).
The EPSRC funded Power and High Voltage Microelectronics (PHIMEC) and other programmes are concentrated on integrated circuits suitable for power transfer and control of equipment rated up to 1KW. The research at Cambridge covers two aspects. One is new and optimum device structures(J12,J212) for Si technologies which allow integration of multiple power devices. The other is circuit configurations for this novel class of integrated circuits. The circuit objectives are carried out within the context of demonstrating an integrated motor control and drive chip which acts as the interface between a motor and a power supply(J155,J217,J218). A key technology being developed within the group for power Ics is silicon on Insulator(J70,J3,J74,J75,J193,J215,J216).
Capsule IGBTs connected in the series have been tested for the first time. The capsule package is mechanically robust and their internal design offers performance benefits to the active gate control method(J155). The sponsor is Hill Graham Controls. Partners are sought for power systems applications.
The modelling of various MMDs in PSPICE to assess their impact in circuits has been completed, with models based on the Ambipolar Diffusion Equation reproducing the terminal characteristics of the devices with great accuracy. Research on accurate analytical models for power devices and study of their high frequency performance is being actively pursued(J197).
Measurements regarding the performance of high current multi-chip IGBT modules continues. The theory shows that the current sharing depends on a range of issues and these are being addressed, with the intention of eliminating the problem.
Dr R.A. McMahon
The work on drives on drives for domestic appliances has led to the successful demonstration of an induction motor drive for a washing machine to Hotpoint, the industrial partner. The work on high phase number induction motor drives continues, and a study of this type of drive to replace a single phase motor shows that an increase in efficiency and reduction in motor size are possible(J218). The application of this approach to battery powered vehicles, giving benefits of extended motor life and increased efficiency, has also been reported(J146). Work has started on simple torque, as opposed to speed, control schemes for battery driven applications. Emerging power integrated circuits reduce the complexity of inverters for variable speed drives and their possibilities were reviewed in an invited paper(J109). Studies of practical drives using power integrated circuits have been presented(J217). A brushless doubly fed induction motor has been constructed and tested. Variable speed operation has been demonstrated and the performance of a larger machine constructed by Laurence, Scott and Electromotors is now being studied.
Dr A.C. Metaxas
Numerical modelling in computational electromagnetics continues to be the focus of the research activity at the Electricity Utilisation Group. for solving microwave heating problems. The basic EUG code was extended to use second and higher order edge elements in its formulation and to simulate thin films in packages for processing foodstuffs. A fully explicit finite element and a hybrid FDTD/FETD code are also under development. The group's numerical simulation activities were presented in review article(J114).
The simulation of radio frequency heating systems for industrial processing has been completed. The code is able to also to simulate a combined "tank" and applicator resonant circuits(J148,J149).
A parallel finite element package using MPI message passage standard has been implemented. The software not only shows a scalable reduction in solution time but has also proven easily portable between different computer platforms and can handle problems with over a million edge discretisations using an SG1 origin 2000 supercomputer(J105).
The work on the simulation of streamers and coronas continues using the in-house FE-FCT code for solving the particle continuity and Poisson equations. Further simulations at radio frequencies were reported(J77) including the effects of attachment, secondary emission and diffusion(J78). A 2D version of the code has now been written(J79,J80). The addition of the coupled energy equations to the 2D code is under development and will enable the simulation of the corona to arc transition at radio frequencies.
A new power supply using the Boucherot effect for industrial microwave heating applications was reported(J76) and which subsequently won the best paper award by the International Microwave Power Institute.
The Group continues to be the strategic and administrative centre for the AMPERE organisation and publishes its quarterly Newsletter(J115,J116,J117,J118).
Professor G.A.J. Amaratunga
Professor W.I. Milne
Dr R.A. McMahon
Dr F. Udrea
A new research programme on low cost photovoltaic solar cells for terrestrial power generation has been initiated. Reduction of the energy pay back time, that is the recovery of energy used in fabricating the cell through power generation from the cell, is the major focus. Novel polymer/carbon nanotube composite material are being explored for this purpose. Cost and energy savings through use of Carbon based materials in combination with amorphous Si(J219), and in all Carbon devices is being explored. Another aspect of the research programme is research on efficient power conditioning and transfer circuits for integrating solar panels to the ac mains. Integrated power circuits for solar panel interfacing is a domestic microgeneration installation are being studied in collaboration with Semelab.
Professor G.A.J. Amaratunga
Field emission based vacuum electronic devices for high frequency signal amplification and power switching are being explored. For the former, a new integrated vacuum microtriode structure has been developed in the Department and experimentally demonstrated(J9). The Si microtriode research is being extended to investigate the possibility of the THz range signal generation.
Research on field emission based vacuum electronic devices for switch mode power transfer has been initiated. The research is concerned with novel cathode materials and structures which can provide large current densities at low electric fields. Novel Carbon based materials and large area Carbon nanotube deposition has been developed for this application. Research is also carried out on the fundamental structure and electronic properties of novel carbon materials as part of this programme(J5,J6,J7,J8,J9,J10,J11,J15,J26,J27,J29,J185,J186,J187,J188). Overall vacuum device design for power switching applications is also being investigated. The research is supported by Toshiba Corporation and VATech Reyrolle.
Dr T.J. Flack
Ongoing research is being carried out into: the application of new finite-element techniques, such as domain decomposition, to 2-D time-domain modelling of induction motors with a view to vastly reducing the CPU time required to apply such models; application of this new method to the determination of stray losses(J64), and the effects of voltage supply imbalance in induction motors(J30); modelling, design, optimisation and control of brushless double-fed induction motors; the analysis of damper bars in stand-alone diesel-generator systems with the aim of damping speed oscillations caused by the inherent torque pulsations of diesel engines(J104); modelling and optimisation of electromechanical shakers, under an EPSRC grant and in conjunction with Ling Dynamics Ltd(J158); modelling and optimisation of small multiphase induction motors; development of parallel algorithms and finite-element methods for micromagnetic simulations.
Professor W.A. Crossland
Dr T.D. Wilkinson
The Photonics and Sensors Group continues its interest in opto-electronic systems combining the use of free space optics with liquid crystal over silicon (LCOS) spatial light modulators (SLMs). We have a special interest in 'smart pixel systems' that combine liquid crystals with silicon VLSI to make intelligent opto-electronic chips for use in telecommunications and display systems.
Two emerging themes are the inclusion of massive electronic processing power into these chips and the introduction of very large arrays of pixels that modulate the phase rather than the intensity of incident light. These developments open the door to a wide range of miniature, low-cost adaptive optic systems.
Recent developments based on our technology and devices are highlighted below:
- The first telecommunications optical switches using phase holograms to steer beams between optical fibres(J42,J43,J225). This technology offers a uniquely versatile solution to the central problem of providing an optically transparent cross-connect for the backbone network servicing the Internet. The wider implication of this technology for WDM systems is now the subject of active research. Initial work in this area has been supported by Thomas Swan Ltd. (who are setting up facilities to design and make these devices for major telecomm companies), and Nortel Networks. There is now widespread interest in this area in the telecommunications industry.
- Dynamic 3D displays using Giga-pixel computer generated holograms and based on adaptive tiling(J91). Moving holographic images of automobiles have been written to volumes of space to demonstrate the potential for next generation CAD systems (at DERA).
- Chips that combine the function of microdisplays and camera chips for embedded video systems with electronics for wavelet compression and motion estimation integrated into the deep sub-micron CMOS backplane circuitry (at Intelligent Pixels Inc.).
Facilities for the fabrication of LCOS devices in a class 10/1000 clean area are maintained. Notable developments have taken place in phase modulators(J206,J225), high speed modulators(J227,J228) and DERA has supported our activity of LCOS electrically addressed spatial light modulators. We are also a lead figure in a major initiative by DERA in optically addressed spatial light modulators for Giga pixel holographic displays.
The role of optics in the design of high capacity electronic IP packet switches and networks is now a substantial area of research(J32). Switch modelling using real IP packet data is clarifying architectures in which header translation and buffering are moved out of an 'optical core' whose purpose is to provide a level of connectivity that is difficult to accomplish in electronics. Our recent 'VIVALDI' project employs systems in which optical channels based on vertical cavity lasers (VCSELs) traverse free space. We have demonstrated (by modelling) the benefits of slow reconfiguration of the optical core, and we are developing the hardware for reconfigurable free space optics links based on VCSELs and liquid crystal switching(J227,J228). Aspects of this work have been supported by EPSRC, Nortel, Marconi, British Aerospace and DERA.
Important initiatives are now being taken concerning the role of 'soft materials' (plastics and liquid crystals) in telecommunications systems. Via the Brite Euram Thematic Network 'PhotoNet' European collaborations have been proposed concerning ultra-high speed modulators based on optically non-linear polymers and reconfigurable grating devices based on polymer waveguides. Nortel Networks are supporting this work and Cambridge is the UK lead house.
LCOS devices and phase modulation are also the basis of a new type of optical image comparator (or optical correlator) for pattern recognition(J225). The system is based on a single LCOS SLM. Using this technology a complex Fourier based image processor can be miniaturized to the size of a paperback novel, whilst avoiding the main problem of other optical solutions to this problem - mechanical instability. The new architecture successfully combines electronic and optical processing. Many image processing techniques such as edge enhancement and adaptive thresholding are being used within the system. Applications for this type of pattern recognition include industrial inspection, security systems, headtracking, motion estimation for video compression and a number of applications in automobiles and other vehicles. This work has been the subject of a DTI SMART Award and is now approaching commercialization.
A new class of liquid crystal display has been developed within the group, known as photoluminescent liquid crystal displays (PLLCD) PLLCD combines all the power consumption and compactness advantages of conventional flat panel liquid crystal displays with the viewing characteristics of a cathode ray tube. They promise to allow large screens to be made by seamlessly tiling together smaller panels thereby enabling liquid crystal display panels to meet the increasingly stringent requirements of new markets that are emerging for emissive flat panel displays. In collaboration with Screen Technology Ltd. Prototype monochrome and colour single panel video displays have been demonstrated.
The Photonics and Sensors Group benefits considerably from the presence of a number of Senior Research Associates or Fellows who are nationally and internationally recognized research figures in their own right. These include Dr Tony Davey in liquid crystals and Dr Neil Collings in the optics of spatial light modulator based systems.
Dr R.J. Mears
Optical amplifiers continue to play a major role. The fundamental patent on the EDFA has now been granted in Japan(J112). Work is also underway with Nortel to develop Raman amplifiers(J68) which offer more WDM bandwidth, although with increased noise figure, compared to the EDFA.
The rapid expansion of WDM over the past couple of years has placed emphasis on techniques for WDM channel management. Recent work in this area has extended the spatial light modulator-based approach to "holographic wavelength switching"(J31) and demonstrated the potential for a new class of active arrayed-waveguide grating devices(J156). Exploitation of the holographic wavelength filter is being undertaken by BTG.
Two new projects under the EPSRC Optical Systems Integration program are now underway. The first concerns the integration of an indoor optical wireless system, and is run in conjunction with the CMOS group under Dr Holburn. Work on holographic beam-steering(J113) has been applied to an adaptive optical system, which is also the subject of a new patent application. New research on arrayed-waveguide gratings and their application to access networks is the subject of the second EPSRC proposal. This research is further supported by Nortel and Fujitsu.
Dr A.R.L. Travis
A new concept for flat panel display has been demonstrated. The screen is an unpatterned sheet of glass or acrylic which is thinner at the top than the bottom, and the image is projected into the bottom edge from a small video projector. The demonstrator has an image the size of a postcard with colour pixels smaller than 0.5 mm. Video projectors are following a trend similar to Moore's law, so we are now making screens which we believe will be bigger than plasma panels, thinner, lighter and cheaper to manufacture.
Although this screen is being developed for conventional display, it can also display a three dimensional image similar to that of a hologram (and was originally intended for that purpose). The three dimensional displays made in the department over the last several years have been bulky and difficult to manufacture, but with the new screen we expect to eliminate these problems. We have also demonstrated a way of getting fields of view of at least 45° , and work on these 3D displays and virtual reality spectacles continues.
Dr R.G.S. Plumb
A combination of modelling and measurements on laser based devices, working closely with industry, continues to be productive and stimulating.
Work on general lasers with external, frequency dependent feedback now gives excellent agreement between computed and measured behaviour. This area has been extensively studied in the past by analytical methods, with useful results, but these were neither complete nor accurate in many cases, and our work allows numerical prediction of behaviour with accuracy comparable to that obtainable by measurement.
Time domain modelling of 4-contact tunable interrupted grating DBR lasers is still slow, but new faster computers help, and valuable results are being generated. Agreement with measured results is now excellent in broad outline, and we are beginning to understand more detailed aspects of behaviour, and hence model them more precisely. One very important step is that we can now confidently model the dynamics of switching from one wavelength to another, which is crucial for expected applications.
Systematic modelling of multi-contact Fabry-Perot lasers with weak reflections between sections has confirmed that these simple devices should have good, well-behaved wavelength switching characteristics, along with narrow linewidths and high output powers. Efforts have started to construct real devices in order to confirm and strengthen our theoretical predictions.
Dr P.A. Robertson
Sensor systems research in the group has continued on micro-fluxgate magnetic sensors, fabricated by thin film processing techniques. The sensors comprise multiple patterned layers of metals and insulators, deposited on top of one another to produce a miniature 3-dimensional structure. These devices are connected with RF interface and signal processing electronics to give sensor bandwidth and noise figures an order of magnitude better than those of Hall effect devices(J173). These devices are being developed for use in electrical instrumentation and magnetic microscopy.
Research has also continued on a new biochemical sensing system for monitoring proteins on surfaces. The novel technique utilises acoustic pulses to create tiny electrical signals at the liquid/solid interface. Specialised electronics and signal processing techniques have been developed to reliably extract these signals, allowing the study of protein layers on surfaces without the need for molecular labelling.
Electrical Engineering References
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Last modified: September 2001