Coded aperture imaging has been used for astronomical applications for several years. Typical implementations use a fixed mask pattern and are designed to operate in the X-Ray or gamma ray bands. More recent applications have emerged in the visible and infra red bands for low cost lens-less imaging systems. System studies have shown that considerable advantages in image resolution may accrue from the use of multiple different images of the same scenerequiring a reconfigurable mask.We report on work to develop a novel, reconfigurable mask based on micro-opto-electro-mechanical systems (MOEMS) technology employing interference effects to modulate incident light in the mid-IR band (3-5µm). This is achieved by tuning a large array of asymmetric Fabry-Perot cavities by applying an electrostatic force to adjust the gap between a moveable upper polysilicon mirror plate supported on suspensions and underlying fixed (electrode) layers on a silicon substrate.A key advantage of the modulator technology developed is that it is transmissive and high speed (e.g. 100kHz) -allowing simpler imaging system configurations. It is also realised using a modified standard polysilicon surface micromachining process (i.e. MUMPS-like) that is widely available and hence should have a low production cost in volume. We have developed designs capable of operating across the entire mid-IR band with peak transmissions approaching 100% and high contrast. By using a pixelated array of small mirrors, a large area device comprising individually addressable elements may be realised that allows reconfiguring of the whole mask at speeds in excess of video frame rates.

Studies of weak millimeter-wave cosmic radio sources in the next generation of millimeter interferometers will, for optimal sensitivity to continuum radio sources, require continuum cross correlators with an input passband of approximately 10 GHz, in comparison to the 500 MHz devices presently installed. We have designed and tested an optoelectronic continuum correlator which can achieve such high bandwidths using integrated optic Mach-Zehnder interferometric modulators (to convert the IF signals from the radio telescope receivers to optical signals) and photoreceivers (to convert the optical signals back to electrical signals). A prototype real-channel continuum correlator of this type is described. It performs with an overall efficiency of 81 +__ 3%, which compares favorably with typical electronic digital and analogue correlators currently used in radio astronomy. For the latter, which are seen in the early universe at high redshifts, the broadband thermal radiation emitted then might be detectable now at millimeter and submillimeter bands, since it would be redshifted by a factor of 10 or so.Most types of cosmic radiation at millimeter wavelengths are very faint. Nonthermal synchrotron emission, which is strongly emitted at centimeter wavelengths by cosmic rays in supernovae radio galaxies and quasars, becomes very weak at millimeter wavelengths. Other types of continuum radiation at millimeter wavelengths are thermal bremsstrahlung and thermal emission from cosmic

No abstract

The development of a micro-opto-electro-mechanical system (MOEMS) technology employing interference effects to modulate incident light in the near-IR band (1550nm) over a wide angular range (120 degrees) is reported. Modulation is achieved by tuning a large array of Fabry-Perot cavities via the application of an electrostatic force to adjust the gap between a moveable mirror and the underlying silicon substrate.The optical design determines the layer thicknesses; however, the speed and power are determined by the geometry of the individual moveable elements. Electro-mechanical trade-offs will be presented as well as a key innovation of utilising overshoot in the device response in reduced pressure environment to reduce the drive voltage.Devices have been manufactured in a modified polysilicon surface micromachining process with anti-reflection coatings on the back of the silicon substrate. Measurements of individual mirror elements and arrays of mirrors at 1550nm show excellent uniformity across the array. This enables good response to an incident signal over a wide field of view when integrated with a silicon retroreflector in a passive optical tag. In conjunction with appropriate anti-stiction coatings, lifetimes of over 100 million cycles have been demonstrated.Key advantages of the modulator are that it is low cost being based on standard polysilicon micromachining; high speed (>100kHz) and robust due to utilising a massively parallel array of identical compact devices; low power for portable applications; and operates in transmission -allowing simple integration with a retroreflector in a passive tag for halfduplex free-space optical communications to a remote interrogator.

No abstract