In the EarthCARE mission the BBR (Broad Band Radiometer) has the role of measuring the net earth radiance (i.e. total reflected-solar and thermally-emitted radiances), from the same earth scene as viewed by the other instruments (aerosol lidar, cloud radar and spectral imager). It does this measurement at 10km scene size and in 3 view angles. It is an imaging radiometer in that it uses micro-bolometer linear-array detector (pushbroom orientation), to over-sample these required scenes, with the samples being binned on-ground to produce the 10km radiance data. For the measurements of total earth radiance, the BBR is based on the heritage of Earth Radiation Budget (ERB) instruments. The ground calibration methods of this type of sensor is technically very similar to other EO instruments that measure in the thermalIR, but with added challenges: (1) The thermal-IR measurement has to have a much wider spectral range than normal thermal-IR channels to cover the whole earth-emission spectrum i.e. ~4 to >50microns; (2) The 2nd channel (reflected solar radiance) must also have a broad response to cover almost the whole solar spectrum, i.e. ~0.3 to 4microns. And this solar channel must be measured on the same radiometric calibration as the thermal channel, which in practice is best done by using the same radiometer for both channels. The radiometer is designed to be very broad-band i.e. 0.3 to 50microns (i.e. more than two decades), to cover both ranges, and a switchable spectral filter (short-pass cutoff at 4μm) is used to separate the channels. The on-ground measurements which are required to link the calibration of these channels will be described. A calibration of absolute responsivity in each of the two bands is needed; in the thermal-IR channel this is by the normal method of using a calibrated blackbody test source, and in the solar channel it is by means of a narrow-band (laser) and a reference radiometer (from NPL). A calibration of relative spectral response is also needed, across this wide range, for the purpose of linking the two channels, and for converting the narrow-band solar channel measurement to broad-band.
SPICE is an imaging spectrometer operating at vacuum ultraviolet (VUV) wavelengths, 70.4 – 79.0 nm and 97.3 - 104.9 nm. It is a facility instrument on the Solar Orbiter mission, which carries 10 science instruments in all, to make observations of the Sun’s atmosphere and heliosphere, at close proximity to the Sun, i.e to 0.28 A.U. at perihelion. SPICE’s role is to make VUV measurements of plasma in the solar atmosphere. SPICE is designed to achieve spectral imaging at spectral resolution >1500, spatial resolution of several arcsec, and two-dimensional FOV of 11 x16arcmins. The many strong constraints on the instrument design imposed by the mission requirements prevent the imaging performance from exceeding those of previous instruments, but by being closer to the sun there is a gain in spatial resolution. The price which is paid is the harsher environment, particularly thermal. This leads to some novel features in the design, which needed to be proven by ground test programs. These include a dichroic solar-transmitting primary mirror to dump the solar heat, a high in-flight temperature (60deg.C) and gradients in the optics box, and a bespoke variable-line-spacing grating to minimise the number of reflective components used. The tests culminate in the systemlevel test of VUV imaging performance and pointing stability. We will describe how our dedicated facility with heritage from previous solar instruments, is used to make these tests, and show the results, firstly on the Engineering Model of the optics unit, and more recently on the Flight Model. For the keywords, select up to 8 key terms for a search on your manuscript's subject.
The Far Infrared Spectroscopic Explorer (FIRSPEX) is a novel European-led astronomy mission concept developed to enable large area ultra high spectroscopic resolution surveys in the THz regime. FIRSPEX opens up a relatively unexplored spectral and spatial parameter space that will produce an enormously significant scientific legacy by focusing on the properties of the multi-phase ISM, the assembly of molecular clouds in our Galaxy and the onset of star formation; topics which are fundamental to our understanding of galaxy evolution. The mission uses a heterodyne instrument and a ~1.2 m primary antenna to scan large areas of the sky in a number of discreet spectroscopic channels from L2. The FIRSPEX bands centered at [CI] 809 GHz, [NII]1460 GHz, [CII]1900 GHz and [OI]4700 GHz have been carefully selected to target key atomic and ionic fine structure transitions difficult or impossible to access from the ground but fundamental to the study of the multi-phase ISM in the Universe. The need for state-of-the-art sensitivity dictates the use of superconducting mixers configured either as tunnel junctions or hot electron bolometers. This technology requires cooling to low temperatures, approaching 4K, in order to operate. The receivers will operate in double sideband configuration providing a total of 7 pixels on the sky. FIRSPEX will operate from L2 in both survey and pointed mode enabling velocity resolved spectroscopy of large areas of sky as well as targeted observations.
SPICE is a high resolution imaging spectrometer operating at extreme ultraviolet wavelengths, 70.4 - 79.0 nm and 97.3 - 104.9 nm. It is a facility instrument on the ESA Solar Orbiter mission. SPICE will address the key science goals of Solar Orbiter by providing the quantitative knowledge of the physical state and composition of the plasmas in the solar atmosphere, in particular investigating the source regions of outflows and ejection processes which link the solar surface and corona to the heliosphere. By observing the intensities of selected spectral lines and line profiles, SPICE will derive temperature, density, flow and composition information for the plasmas in the temperature range from 10,000 K to 10MK. The optical components of the instrument consist of an off axis parabolic mirror mounted on a mechanism with a scan range of 8 arc minutes. This allows the rastering of an image of the spectrometer slit, which is interchangeable defining the instrument resolution, on the sky. A concave toroidal variable line space grating disperses, magnifies, and re-images incident radiation onto a pair of photocathode coated microchannel plate image intensifiers, coupled to active pixel sensors. For the instrument to meet the scientific and engineering objectives these components must be tightly aligned with each other and the mechanical interface to the spacecraft. This alignment must be maintained throughout the environmental exposure of the instrument to vibration and thermal cycling seen during launch, and as the spacecraft orbits around the sun. The built alignment is achieved through a mixture of dimensional metrology, autocollimation, interferometry and imaging tests. This paper shall discuss the requirements and the methods of optical alignment.
SPICE is a high resolution imaging spectrometer operating at extreme ultraviolet wavelengths, 70.4 – 79.0 nm and 97.3 -
104.9 nm. It is a facility instrument on the Solar Orbiter mission. SPICE will address the key science goals of Solar
Orbiter by providing the quantitative knowledge of the physical state and composition of the plasmas in the solar
atmosphere, in particular investigating the source regions of outflows and ejection processes which link the solar surface
and corona to the heliosphere. By observing the intensities of selected spectral lines and line profiles, SPICE will derive
temperature, density, flow and composition information for the plasmas in the temperature range from 10,000 K to
10MK. The instrument optics consists of a single-mirror telescope (off-axis paraboloid operating at near-normal
incidence), feeding an imaging spectrometer. The spectrometer is also using just one optical element, a Toroidal Variable
Line Space grating, which images the entrance slit from the telescope focal plane onto a pair of detector arrays, with a
magnification of approximately x5. Each detector consists of a photocathode coated microchannel plate image
intensifier, coupled to active-pixel-sensor (APS). Particular features of the instrument needed due to proximity to the Sun
include: use of dichroic coating on the mirror to transmit and reject the majority of the solar spectrum, particle-deflector
to protect the optics from the solar wind, and use of data compression due to telemetry limitations.
OPTIMOS-EVE (OPTical Infrared Multi Object Spectrograph - Extreme Visual Explorer) is the fibre fed multi object
spectrograph proposed for the European Extremely Large Telescope (E-ELT), planned to be operational in 2018 at Cerro
Armazones (Chile). It is designed to provide a spectral resolution of 6000, 18000 or 30000, at wavelengths from 370 nm
to 1.7 μm, combined with a high multiplex (>200) and a large spectral coverage. Additionally medium and large IFUs
are available. The system consists of three main modules: a fibre positioning system, fibres and a spectrograph.
The recently finished OPTIMOS-EVE Phase-A study, carried out within the framework of the ESO E-ELT
instrumentation studies, has been performed by an international consortium consisting of institutes from France,
Netherlands, United Kingdom and Italy. All three main science themes of the E-ELT are covered by this instrument:
Planets and Stars; Stars and Galaxies; Galaxies and Cosmology.
This paper gives an overview of the OPTIMOS-EVE project, describing the science cases, top level requirements, the
overall technical concept and the project management approach. It includes a description of the consortium, highlights of
the science drivers and resulting science requirements, an overview of the instrument design and telescope interfaces, the
operational concept, expected performance, work breakdown and management structure for the construction of the
instrument, cost and schedule.
EarthCARE, the third of ESA's Earth Explorer Core Missions, is aimed at improving the understanding of interactions
between clouds, aerosols and radiation - three factors believed to be important in the understanding of global warming.
The Broadband Radiometer instrument will serve to confirm the radiated energy estimates which will be derived from
the profiles of clouds and aerosols measured by the other instruments on the satellite.
The BBR instrument will use 3 arrays of uncooled microbolometers to measure the Top Of the Atmosphere flux in 2
channels (0.2μm - 4μm, 0.2μm - 50μm), simultaneously in 3 directions (nadir, forward and backward). The long wave
channel will be inferred from subtraction of the short wave from the total wave measurements.
This paper will describe the status of the BBR instrument design, trade-offs and performance. A novel design is required
to perform at much higher spatial resolutions than previous Earth Radiation Budget instruments and the method of
achieving this will be described.
The Broadband Radiometer (BBR) is an instrument being developed for the ESA EarthCARE satellite. The BBR
instrument objective is to provide top-of-atmosphere (TOA) radiance measurements in two spectral channels, and over
three along-track directions. The instrument has three fixed telescopes (one for each view) each containing a broadband
detector. Each detector consists of an uncooled 30-pixel linear focal plane array (FPA) coated with gold black in order to
ensure uniform spectral responsivity from 0.2 μm to 50 μm. The FPA is hybridized with a readout integrated circuit
(ROIC) and a proximity electronics circuit-card assembly (CCA) packaged in an aluminum base plate with cover. This
paper provides a technical description of the detector design and operation. Performance data at the FPA pixel level as
well as unit-level test results on early prototypes of the detectors are also presented.
In preparation for the Laser Interferometer Space Antenna (LISA) space mission, the prototype engineering model of the LISA-Pathfinder optical bench instrument has been built and tested. The instrument is the central part of an interferometer whose purpose is to measure the separation of two free-floating test masses in the spacecraft, with required accuracy to a noise level of 10 pm/Hz?1/2 between 3 mHz and 30 mHz. This will allow the spacecraft to achieve drag-free flight control to a similar level, as a demonstration of technology capability for detection of gravitational waves in the later LISA mission. The optical bench design, fabrication, and experimental results are described in detail, with attention to the strategies for building and alignment. These are particularly problematic in this instrument due to restrictions on the allowable materials and devices, the limited size, the tight alignment requirements for interferometry and interfaces, and the challenging environment specification for space flight. The finished optical bench was integrated to the complete optical metrology package for system-level tests, which were successful, both in meeting the metrology accuracy and in environmental testing. This verifies the feasibility of the design and build methods demonstrated here for use in the space-flight version.
We describe the integration and test phase of the construction of the VISTA Infrared Camera, a 64 Megapixel, 1.65 degree field of view 0.9-2.4 micron camera which will soon be operating at the cassegrain focus of the 4m VISTA telescope. The camera incorporates sixteen IR detectors and six CCD detectors which are used to provide autoguiding and wavefront sensing information to the VISTA telescope control system.
Between 25-35% of the Earth's outgoing longwave radiation (OLR) lies in the far-infrared (FIR) spectral region from 0- 500cm-1 where the emission is primarily due to water vapour located in the upper and mid troposphere. The local maximum in the absorption spectrum of ice means that high, cold cirrus clouds have a large effect on intensity of the OLR here. To date, no FIR measurements of the OLR have been made from space, resulting in a major gap in our understanding of the Earth's radiative energy budget. Such measurements will provide vital information about the spatial and temporal variability of the OLR with relation to upper tropospheric humidity and clouds which will better constrain radiation parameterisations in general circulation models. REFIR (the Radiation Explorer in the Far-Infrared) is a polarising interferometer designed to bridge this knowledge gap by measuring the OLR from 100-1100cm-1 at a spectral resolution of 0.5cm-1. This instrument's performance is critically dependent on the properties (transmittance and reflectance) of the wire grid polarisers it uses as beamsplitters. These properties have been measured at Imperial College and incorporated into a mathematical (Jones' matrix) model of the interferometer's performance to produce simulated interferograms and spectra. When coupled to a model of detectors suitable for the FIR spectral region, potential spectral noise characteristics of the calibrated radiance spectra produced by REFIR have been modelled. So far, cryogenically cooled detector systems are far preferable to ambient temperature detectors, although measurements with un-cooled devices with suitable accuracies are possible with longer integration times. The effects of the changing scene beneath the interferometer during the interferogram acquisition time have been analysed.
The VISTA IR Camera has now completed its detailed design phase and is on schedule for delivery to ESO’s Cerro Paranal Observatory in 2006. The camera consists of 16 Raytheon VIRGO 2048x2048 HgCdTe arrays in a sparse focal plane sampling a 1.65 degree field of view. A 1.4m diameter filter wheel provides slots for 7 distinct science filters, each comprising 16 individual filter panes. The camera also provides autoguiding and curvature sensing information for the VISTA telescope, and relies on tight tolerancing to meet the demanding requirements of the f/1 telescope design. The VISTA IR camera is unusual in that it contains no cold pupil-stop, but rather relies on a series of nested cold baffles to constrain the light reaching the focal plane to the science beam. In this paper we present a complete overview of the status of the final IR Camera design, its interaction with the VISTA telescope, and a summary of the predicted performance of the system.
The LISA Technology Package (LTP) aboard of LISA pathfinder mission is dedicated to demonstrate and verify key technologies for LISA, in particular drag free control, ultra-precise laser interferometry and gravitational sensor. Two inertial sensor, the optical interferometry in between combined with the dimensional stable Glass ceramic Zerodur structure are setting up the LTP. The validation of drag free operation of the spacecraft is planned by measuring laser interferometrically the relative displacement and tilt between two test masses (and the optical bench) with a noise levels of 10pm/√Hz and 10 nrad/√Hz between 3mHz and 30mHz. This performance and additionally overall environmental tests was currently verified on EM level. The OB structure is able to support two inertial sensors (≈17kg each) and to withstand 25 g design loads as well as 0...40°C temperature range. Optical functionality was verified successfully after environmental tests. The engineering model development and manufacturing of the optical bench and interferometry hardware and their verification tests will be presented.
VISTA is a 4-metre survey telescope currently being constructed on the NTT peak of ESO’s Cerro Paranal Observatory. The telescope will be equipped with a dedicated infrared camera providing images of a 1.65 degree field of view. The telescope and camera are of an innovative f/3.26 design with no intermediate focus and no cold stop. The mosaic of 16 IR detectors is located directly at Cassegrain focus and a novel baffle arrangement is used to suppress stray light within the cryostat. The pointing and alignment of the telescope and camera is monitored by wavefront sensing elements within the camera cryostat itself. This paper describes the optical, mechanical, electronic and thermal design of the combined curvature sensor and auto-guider units positioned at the periphery of the camera field of view. Centroid and image aberration data is provided to the telescope control system allowing real time correction of pointing and alignment of the actively positioned M2 unit. Also described are the custom optics, mounted in the camera filter wheel, which are used to perform near on-axis high order curvature sensing. Analysis of the corresponding defocused images allows calibration tables of M1 actuator positions to be constructed for varying telescope declination and temperature.
As detailed instrument design progresses, judgements have to be made as to what changes to allow and when models such as thermal, stray-light and mechanical structure analysis have to be re-run. Starting from a well-founded preliminary design, and using good engineering design when incorporating changes, the design detailing and re-run of the models should bring no surprises. Nevertheless there are issues for maintaining the design and model configuration to a reasonably concurrent level. Using modern modeling software packages and foresight in setting up the models the process is made efficient, but at the same time the level of detail and number of cases now needed for instrument reviews is also large in order to minimise risks.
We describe examples from the detailed instrument design of the VISTA IR Camera to illustrate these aspects and outline the design and analysis methods used.
The design of the Fourier Transform Spectrometer for the Herschel sub-millimetre Spectral and Photometric Imaging Receiver (SPIRE) is described. This is an innovative design for a sub-millimetre spectrometer as it uses intensity beam splitters in a Mach-Zehnder configuration rather than the traditional polarising beam splitters. The instrument is required to have a resolution of 0.04 cm-1; have a relatively large field of view (2.6 arcmin circular) and cover a large wavelength range - 200 to 670 microns. These performance requirements lay stringent requirements on all aspects of the design. The details of the optical; mechanical and electrical implementation of the instrument are discussed in the light of the science and engineering requirements and laboratory testing on development models of the mechanism and control system are reported.
We describe the requirements and the main design features of the ground test and calibration facility for the Herschel SPIRE instrument. SPIRE has a large cold focal plane unit (approx 700 x 400 x 400 mm) with several internal temperature stages, and is designed to operate in orbit viewing a low emissivity 80-K telescope. The calibration facility is designed to allow all aspects of instrument behaviour, performance, calibration, and optimisation of observing modes to be investigated under flight representative conditions. The facility includes the following features:
- A large test cryostat replicating the in-orbit thermal environment
- An external telescope simulator and sub-millimetre sources allowing the instrument to be fed with a beam that accurately simulates the beam from the Herschel telescope.
- Internal cold black body for absolute radiometric and flat field calibration
- Cold neutral density filters and an internal shutter for control of the photon background conditions
- A far infrared laser used for spectral calibration of the SPIRE spectrometer channel and to present a source with well understood beam modes to the instrument.
- An external FTS to characterise the spectral response of the instrument in both the camera and spectrometer channel
The ground test facility will be used to evaluate the flight model before delivery and will also be used to house and carry out tests on the flight spare focal plane unit both before launch and during mission operations.
The SPIRE instrument for the FIRST mission will consist of a three band imaging submillimeter photometer and a two band imaging Fourier Transform Spectrometer (FTS) optimized for the 200 - 400 micrometers range, and with extended coverage out to 670 micrometers . The FTS will be used for follow-up spectroscopic studies of objects detected in photometric surveys by SPIRE and other facilities, and to perform medium resolving power (R approximately 500 at 250 micrometers ) imaging spectroscopy on galactic and nearby extra-galactic sources.
Solar diffuser based monitors are the preferred method for on- board calibration for short wavelength regions of Radiometric Earth Remote Sensing instruments where spectral matching and long term stability are paramount. This paper describes an aluminum integrating sphere, with internal photo-diode monitoring, being developed for the on-board short wavelength, (0.32 - 4 micrometer) calibration monitor of the GERB instrument. GERB will image the earth surface from geostationary orbit over a bandwidth of 0.32 - 30 micrometer and is mounted on the Meteosat Second Generation (MSG) spin stabilized satellite resulting in a very rapidly rotating field of view of GERB (100 RPM). The adopted arrangement for the integrating sphere is described and its performance illustrated with supporting test data and optical modeling. Comparisons with the ATSR-2, MS20 flat tile system are made and recommendations for future calibration systems, drawn.
HIRDLS is a space-borne instrument that will measure the concentration of certain trace gases in the Earth's atmosphere. This requires accurate spectro-radiometric infra red measurements of weak sources of small angular size in the presence of strong adjacent sources of unwanted radiation. The design of the principal optical system is described and the constraints are explained. In particular, the important stray- light problems will be described, including incoherent scatter, ghost reflections and diffraction effects.
At short wavelengths, optical systems can be designed such that a single aperture defines the beam that is used (system light gathering power), and another (the system field stop) defines the field-of-view (FOV). These components define the beam envelope and all other components are oversized so that they do not 'clip' or vignette this envelope. At longer wavelengths the diffraction caused by such clipping can seriously degrade the FOV response function and cause an increase in stray-light background. It is thus even more desirable to avoid clipping the beam as it passes through an instrument by oversizing all the optical elements. In space borne instruments, however, accommodation constraints can turn such oversizing into an unaffordable luxury. Instrument design must therefore consider the impact of multiple beam clipping and in particular any degradation in the FOV function. In this paper we describe such an analysis, based on advanced ray- tracing software, and give results for its application to two instruments: (1) The infra-red space observatory Long Wavelength Spectrometer (ISO-LWS, wavelength range 46 - 198 micrometer), where the FOV response is modeled for use with on-board calibration and data retrieval. (2) The imaging photometer in the Far Infra-Red Space Telescope SPIRE instrument (Spectral & Photometric Imaging Receiver, wavelength range 200 - 650 micrometer), where the analysis is needed for (a) Trade-off studies between instrument sensitivity (aperture size) and FOV degradation by clipping (b) Predicting the FOV performance of the final proposed design.
The Earth Radiation Budget (ERB), the balance between the incoming solar radiation from the sun and the outgoing reflected and scattered solar radiation and the thermal infrared emission from the Earth, provides information on the fundamental energy source of the climate system. To fulfil global coverage and sampling requirements, the ERB measurements have to be made from space. Broad-band measurements are necessary because all spectral regions in both the solar and infrared contribute to the radiative fluxes. Satellite data are used in a wide range of basic studies of the radiative forcing of the climate, such as understanding the effects of variations in trace gases, clouds and the surface. They also provide essential validation for climate models. All such measurements to date have been made from satellites in low earth orbit (LEO). There are strong diurnal variations in the radiation budget, particularly over land, in response to the diurnal variation of solar heating. Four LEO satellites could provide coverage of the diurnal cycle with a temporal resolution of 3 hours. At least hourly measurements are needed to resolve the diurnal cycle of tropical convection properly, and no practicable system of polar orbiting or other LEO satellites can deliver this. From the above, it appears that the only viable solution to the problem of diurnal sampling of the Earth's radiation budget is the inclusion of suitable sensors on the geostationary satellites which would allow for an essentially perfect temporal sampling. Disadvantages include the fact that geostationary satellites are much further from the Earth than polar orbiters, which affects the instrumental design, and each one can only provide a limited coverage of the globe. The Geostationary Earth Radiation Budget instrument (GERB) is a highly accurate visible-infrared radiometer designed to make unique measurements of the outgoing shortwave and longwave components of the Earth's Radiation Budget (ERB) from geostationary orbit. Such measurements have not been achieved previously, and are extremely important, because they will permit a rigorous test of our understanding of the diurnal variations in the ERB: this will enable improved operational weather monitoring and permit further important developments in climate change research. GERB will be launched on the (MSG) geostationary satellite in the year 2000. Both short-wave (0.32 - 4 micrometer) and total (0.32 - 30 micrometer) radiance measurements would be made, with longwave (4 - 30 micrometer) data obtained by subtraction. The accuracy requirements (1% short-wave and 0.5% longwave) are consistent with previous radiation budget measurements. The availability of GERB on MSG will also allow a more accurate calibration of the principal Meteosat Second Generation (MSG) operational sounding instrument, SEVIRI (Spinning, Enhanced Visible and InfraRed Imager).
This talk concerns applications of a ray-trace model to the computation of the effect of diffraction on beam propagation. It reports the use of the technique in the design of apertures for space-borne instruments having critical diffraction properties. The modeling technique used is that of gaussian beam decomposition, a numerical beam propagation technique incorporated in a commercially available ray-trace program. The result is the powerful capability to model the optical field at any point, in systems of any geometry, with any amount of aberration. The technique is particularly useful for design problems where `non-imaging' effects are important, and examples of its use will be given. Although the computation requirements for such detailed analysis may seem daunting, the continuing increase in readily available computing power is now overcoming this drawback. The application here is to certain `diffraction-critical' situations, where the design of correctly sized apertures is needed for the control of unwanted diffraction effects. Three recent design studies are illustrated: (1) Millimeter wave imaging with off-axis reflectors. Analysis of the effects of aberration on coherent detection efficiency. (2) Long-distance beam propagation in space-borne laser interferometry. This involves the analysis of coherent detection efficiency in the presence of aberrated gaussian beams. (3) Design of a Lyot stop system for an infra-red radiometer which is to view the Earth's limb from space. Here the critical (and unwanted) diffraction is that from the bright Earth disc, lying just outside of the instrument field of view. The analysis technique is explained, and examples given of diffracted energy patterns analyzed at progressive stages in the system. It is shown how these aid the design and analysis of the systems. The aim is to show the range problems in which this method is useful, and to hopefully learn from others at the conference about other cases where such techniques have been used or else might be useful.
This paper describes recent progress in the development of a new class of spatial light modulator (SLM). These new SLMs modulate light by the interaction of some active material with a high intensity evanescent field generated by surface plasmon resonance. Such devices have the potential for substantial advantages over conventional SLMs, including higher speed and better response uniformity, as well as high sensitivity in devices with thin active layers. A new optically addressed plasmon device, based on a thin amorphous silicon/liquid crystal sandwich structure, has been developed and tested. The performance characteristics compare favorably with those of conventional liquid crystal SLMs in terms of resolution and speed. The design of more advanced devices based on higher performance ferro-electric and electroclinic liquid crystals is now in progress; in particular, the special pseudo-plasmon modes found in highly birefringent materials, and the application of these to modulation, have been analyzed. Surface plasmon SLMs using electro-optic effects in semiconductor active layers are also discussed.
The status and potential of a new type of device, the surface plasmon spatial light modulator
(SPSLM) is reported. The attractive features of surface plasmon resonance (SPR) for use in SLM's
are explained and results from prototype devices reported. These are of the liquid crystal (LC) light
valve configuration, using nematic LC with a silicon photodiode backplane. Demonstrated advantages
include process simplification and increased response speed. These are obtained due to the thin,
single surface nature of the plasmon active region, whilst high sensitivity is retained due to the
resonant enhancement of the optical field in this region.
The theoretical principle of the liquid crystal SPSLM is described, in terms of the propagation of
plasmons on anisotropic materials. Various alignment configurations are considered to show how both
nematic and smectic materials could provide high sensitivity and speed in future devices.
The need for a grating coupled SPR technology is explained, and the design and fabrication of
holographic gratings for SPSLM's is discussed.
Finally, the present and ultimate performance limitations of these new SLM devices are assessed,
and related to their potential use in optical information processors such as image correlator and
neural network systems.