The Design, Fabrication & Characterisation of Optical ASICs

Principal Investigator: Dr P D Sewell

Recognised Researcher: Mr C Styan

Starts: 1 January 2005
Ends: 31 December 2007

Value: £283649

The use of light to transmit signals has permitted major advances in the field of communication technology. Circular optical fibres and planar optical circuits are well known media for the transmission and processing of optical signals. In both technologies materials of different optical densities are arranged in such a way that the optical signal is trapped in the optically denser region. Fibres and planar circuits differ significantly in their shape and material compositions and problems arise when they need to be connected together, generally experienced as a deterioration of the signal quality. Similarly, different optical components, such as lasers, waveguides, routers and couplers are usually designed and fabricated separately, often using different materials, which again causes problems when they need to be integrated together into a system. Finding a common platform onto which devices with different functionalities can be integrated has proven to be a difficult challenge and indeed some very desirable functionalities are difficult to design in any technology. These problems are holding back further advances in communication technology and need to be resolved to release the full potential of optical networks for providing ever higher speeds and capacities. One exciting technology that has emerged in recent years are Photonic Bandgap Structures (PBGs). This technology consists of a number of small holes, usually less than micrometre in size, drilled into a sheet of transparent material and arranged in a regular, periodic pattern from which light scatters and re-combines in useful ways. For example, different colours of light are refracted by significantly different amounts so that a super prism can be made. These PBGs have been shown to offer significant advantages for the integration of future optical circuits, promising compact devices with theoretically loss-less transmission of light. The core idea of this project is, if the regular hole patterns of PBG can provide so much, how much more could be obtained by not restricting the holes to be laid out in a regular pattern? Unfortunately, it is hard enough to analyse the behaviour of regular patterns of holes so to determine which non-regular layout gives the closest behaviour to a required functionality is extremely time consuming. However, as the fabrication technology is available and the potential is so great, it is of paramount importance to start to address this design issue as soon as possible. In order to truly exploit the fabrication facilities of PBG devices, the project proposes to provide computer programs that perform automatic synthesis of optical circuits which provide multiple functionalities on a common platform, thus also overcoming the problem of coupling separately devices together. This concept would enable the realisation of Optical Application Specific Integrated Circuits (OASICs) that can offer an efficient solution for the current problems which are blocking large scale optical integration. Automatic synthesis describes when a designer specifies the desired functionality of the circuit to the computer program and it identifies the best possible circuit design for achieving it in a particular technology. This is in contrast to analysis programs which simply determine how a particular circuit behaves. This project will develop the necessary analysis and synthesis programs to allow the design of the OASICs as well as to use them to establish specific design solutions for key components. These will then be made and measured to provide convincing support for this new approach to integrated optics.