Alan Purvis

Liquid-crystal prisms for tip-tilt adaptive optics

Results from an electrically addressed liquid-crystal cell producing continuous phase profiles are presented. The adaptive deflection of a beam of light for use in a tip-tilt adaptive optics system is demonstrated. We compare the optical performance of liquid-crystal prisms with experimental data on atmospheric seeing at the William Herschel Telescope.

Electrically Controllable Liquid Crystal Fresnel Lens

Two orthogonally aligned liquid crystal lenses with spherical Fresnel zone plate electrode configurations have been demonstrated to focus an unpolarised broadband object with resulting good quality images. Switch on times of 15ms are reported along with modulation depths of 91.5%.

A real-time closed-loop liquid crystal adaptive optics system: first results

Abstract We present the first results from a real-time closed-loop adaptive optics system incorporating a liquid crystal based corrector device and a Shack-Hartmann wavefront sensor. The system is designed to operate at a bandwidth which would be useful in astronomical applications. Here we show results of the system correcting laboratory simulated Kolmogorov-like turbulence.

REAL-TIME OPTICAL ABERRATION CORRECTION WITH A FERROELECTRIC LIQUID-CRYSTAL SPATIAL LIGHT MODULATOR

Real-time correction of an optically aberrated wave front by use of a 10 x 10 ferroelectric liquid-crystal spatial light modulator as the correction device and a point-diffraction interferometer as the wave-front sensor is demonstrated. This type of interferometer requires no reference arm and so can be used, in theory, in an astronomical adaptive-optics system. We discuss some of the unusual features of the point-diffraction interferometer for wave-front sensing.

Nonplanar photolithography with computer-generated holograms.

We outline a method for accomplishing photolithography on grossly nonplanar substrates. First we compute an approximation of the diffraction pattern that will produce the desired light-intensity distribution on the substrate to be patterned. This pattern is then digitized and converted into a format suitable for manufacture by a direct-write method. The resultant computer-generated hologram mask is then used in a custom alignment tool to expose the photoresist-coated substrate. The technique has many potential applications in the packaging of microelectronics and microelectromechanical systems.

Designing convergent cellular automata.

Cellular automata (CA) have been used by biologists to study dynamic non-linear systems where the interaction between cell behaviour and end-pattern is investigated. It is difficult to achieve convergence of a CA towards a specific static pattern and a common solution is to use genetic algorithms and evolve a ruleset that describes cell behaviour. This paper presents an alternative means of designing CA to converge to specific static patterns. A matrix model is introduced and analysed then a design algorithm is demonstrated. The algorithm is significantly less computationally intensive than equivalent evolutionary algorithms, and not limited in scale, complexity or number of dimensions.

Fabrication of a 3D electrically small antenna using holographic photolithography

We describe the novel fabrication of a 3D electrical small antenna and its subsequent characterization. The patterning of meander lines conformed onto a hemispherical substrate is achieved by 3D holographic photolithography, which uses time-division multiplexing of a series of iteratively optimized computer-generated holograms. The meander lines have a line width of 100 µm and line separation of 400 µm, with a line pitch of 500 µm and a total meander length of 145 mm. The working frequency is found to be 2.06 GHz, with an efficiency of 46%. This work demonstrates a new method for the fabrication of 3D conformal antennas.

Concepts of Self-Repairing Systems

Systems fail. Period. No matter how much planning and fault analysis is performed, it is impossible to create a perfectly reliable machine. The existing approach to improving reliability invariably involves advances in fault prediction and detection to include specific mechanisms to overcome a particular failure or mitigate its effect. While this has gone a long way in increasing the operational life of a machine, the overall complexity of systems has improved sharply, and it is becoming more and more difficult to predict and account for all possible failure modes. What is discussed here is a possible shift in approach from specific repair strategies to autonomous self-repair. Rather than focusing on mitigating or reducing the probability of failure, the focus is instead on what can be done to correct a failure that will invariably occur at some point during operation. By taking this approach, it is not just expected failure that can be designed for, unexpected failure modes are also inherently compensated for, extending the potential life of a system and reducing the need for through-life servicing.

STELLAR IMAGE STABILIZATION USING PIEZO-DRIVEN ACTIVE MIRRORS

As applied to the 4.2-m William Herschel Telescope, the multiaperture real-time image-normalization system presented implies a wavefront whose size requires a mask of six optimally-scaled subapertures. These subaperture images are separated and examined on a single image photon detector which yields x, y, and t coordinates for each recorded photon. The motions of these images feed back to six independent piezoactuated active mirrors which act to null the image motions at a CCD focus. Data are presented from two image normalization runs, with and without active mirrors, which illustrate the size and variation behavior of the coherent seeing length, characteristic seeing times, and power spectra.

Controlled-width track in through silicon via using 3D holographic photolithography with modified electrodepositable photoresist

We present a novel lithographic process for patterning controlled-width tracks onto anisotropically micromachined silicon. The technique is based on the use of computer-generated holographic masks with a custom alignment and exposure tool. Experimental and simulation results are presented. 3D holographic photolithography significantly reduces the problem normally present with photolithography on non-planar surfaces—namely diffractive line broadening. A negative-acting electrodepositable photoresist (InterVia 3D-N) is used in the study. Its deposition onto the 3D substrate is optimized by modification of coating temperature and thickness and of pre-exposure bake conditions. We show the successful patterning of a constant-width 8 µm line down the sloping sidewall of a 500 µm thick silicon wafer. This is beyond the conventional resolution limit and indicates the potential of the technique for realizing high-density vertical routing in electronic packages and MEMS.