David M. Budgett

A novel high-accuracy microstereolithography method employing an adaptive electro-optic mask

Abstract A new stereo-photolithography technique to create three-dimensional micro-components using a planar, layer-by-layer, process of exposure has been developed. With this procedure, it is possible to build components with dimensions in the range 50xa0μm–50xa0mm, and feature sizes as small as 5xa0μm with a resolution of less than 1xa0μm. This newly developed system consists of eight elements: a Computer Aided Design environment supporting solid or surface modelling; a resin bath with an integrated high resolution translation stage and component built platform; an ultraviolet laser light source operating at 351.1xa0nm; an optical shutter; a diffractive optical element designed to re-distribute the irradiance of the laser beam from a Gaussian to a top-hat profile; a polysilicon thin film twisted nematic SVGA resolution (800×600) spatial light modulator; a multi-element lithographic reduction lens system; and a comprehensive control system. In this paper, the experimental set-up is described and examples of the microcomponents fabricated by the system are shown.

Fully complex optical modulation with an analogue ferroelectric liquid crystal spatial light modulator

Full complex modulation in the Fourier plane is demonstrated using a 128 x 128 analogue ferroelectric liquid crystal spatial light modulator. The device can modulate along both the positive and negative real axes. Two pixels were used together as a macro pixel, one representing the real component and the other the imaginary component, phase shifted by pi/2 using a phase detour technique. Using this method, a fully complex Fourier spectrum was displayed on the SLM and an asymmetric reconstruction into the first diffraction order was produced. (

Microfabrication by use of a Spatial Light Modulator in the Ultraviolet: Experimental results

We report the development of a new microstereophotolithography technique for creation of three-dimensional microcomponents by use of a planar, layer-by-layer process of exposure, in which a spatial light modulator is used as a dynamic lithographic mask. The system operates in the UV to take advantage of the wide supply of commercially available photopolymers designed for conventional stereolithography. With this novel procedure it is possible to build components with feature sizes as small as a few micrometers. The experimental setup is briefly described, and the first microcomponent fabricated by this system is shown.

Two-pixel computer-generated hologram with a zero-twist nematic liquid-crystal spatial light modulator

We present a method of producing a computer-generated hologram by use of a zero-twist linear nematic liquid-crystal spatial light modulator. A 2x1 macro pixel method is used; one pixel represents the real data, and one, the imaginary. A method is shown that produces both positive and negative analog amplitude modulation.

Dynamic complex wave-front modulation with an analog spatial light modulator

A method of producing an arbitrary complex field modulation by use of two pixels of an analog ferroelectric spatial light modulator (SLM) is demonstrated. The method uses the gray-scale modulation capabilities of a SLM to spatially encode the complex data on two pixels. A spatial filter is used to remove the carrier signal. This technique gives fast gray-level amplitude and phase modulation.

Optical and electronic design of a hybrid digital-optical correlator system

The design of a digital-optical hybrid correlator is detailed. The design of the optical-Fourier-transform lens and the mechanical lens housing are detailed, as well as the video-rate fast-Fourier-transform digital signal-processing hardware and overall electronic control. Example results using several different filters and modulation techniques are described.

Experimental implementation of a Wiener filter in a hybrid digital–optical correlator

We present the implementation of a clutter-tolerant filter in a hybrid correlator system. Wiener filters were mapped with a complex encoding technique onto a smectic A(*) liquid-crystal spatial light modulator (SLM). The technique overcomes the problem of representing high-dynamic-range data on SLMs that have limited modulation capabilities. It also provides a compact image recognition system that is robust enough for many real-world applications. Experimental results are presented.

A comparison of the iterative Fourier transform method and evolutionary algorithms for the design of diffractive optical elements

Three methods of designing diffractive optical elements (DOE) are compared. The iterative Fourier transform algorithm (IFTA) is compared to an evolutionary strategy (ES) approach and a combination of both methods. It is shown that the combination of both methods produces a better solution than the iterative method and is faster than using the evolutionary strategy only.

Computer-generated complex filter for an all-optical and a digital-optical hybrid correlator

We present results of a correlation filter utilizing a computer-generated hologram using an analog ferroelectric liquid-crystal spatial light modulator (SLM). The SLM amplitude-modulates light and can induce a 0-p phase shift, which is equivalent to modulating along the real axis. Two pixels are combined into a macropixel using a phase-detour technique enabling full complex modulation. The method is used as the filter for a conventional optical correlator and in a digital-optical hybrid correlator.

A Pattern Recognition Wiener Filter for Realistic Clutter Backgrounds

The Wiener filter can be used in place of the matched filter in correlation based pattern recognition. It has been shown to be capable of detecting a target in severe clutter backgrounds provided the clutter power spectrum is included in the filter transfer function. It is shown here that the performance degrades very markedly if a different background from that used to create the filter is present at the input. However, multiple input scene power spectrum averaging is shown to considerably improve the performance, even when previously unknown backgrounds are encountered that have not been included in the averaged spectrum. This leads to the generation of a clutter power spectrum model and it is shown that use of this in the filter transfer function allows much improved clutter resistance when unknown background scenes are encountered, improving the prospects for the practical application of the filter to demanding pattern recognition problems.