ADVANCED OPTICAL TECHNIQUES

SUMMARY

This sub-theme will address the use of novel methods and components necessary to enhance the sensing capability of EO systems and reduce their cost. This will lead to enhanced performance, pointing and stabilisation, and novel design concepts for EO systems, applicable to imaging, target illumination and long range sensing.

MILITARY BENEFITS

Exploitation of adaptive optics techniques will aim to increase performance and reliability of military laser systems, while at the same time reducing costs, size and complexity. The feasibility of using aperture synthesis in real military applications is highly relevant to NCTI, with significant advantages in terms of size and weight. Development of photonic fibres for active systems has the potential for multiple military uses, specifically for integrating laser systems into sensors (on board aircraft) and additionally for use in laser DEW, LIRCM and vibrometry. A smart, flexible method for temperature referencing in IR cameras would confer significant benefits in terms of cost, size and reliability of sensors. The development of complex structured surfaces in diffractive optics technology affords possibilities to improve performance and reduce manufacturing costs of IR sensors.

RESEARCH OBJECTIVE

Use of adaptive optical techniques to reduce the complexity and cost of military EO systems
Feasibility of synthetic aperture techniques in the visible/infrared spectrum
Use of novel fibre optic methods for high energy laser beam distribution
Improvements to methods of non uniformity correction in IR cameras
Complex diffractive optics for enhanced sensor performance

RESEARCH OUTLINE

The research aims to exploit physical concepts and emerging technologies to create novel EO solutions to address capability gaps and improve sensors. The research will address issues of improving target acquisition by increasing operational range and target discrimination, and providing sensors with greater reliability and lower cost, size, weight and power consumption. The programme will comprise a portfolio of projects balanced in terms of technical risk and potential benefits. A feature of this sub-theme will be the assessment of technologies and methods from other areas for application in military EO sensing. The development of higher technical risk concepts will be tempered by a structured management approach to mitigate programme risk and financial exposure and to provide focus on evaluation of the research in a military context.

Adaptive optics (AO) is an example of a technology which is mature within the astronomical community and which has potential benefits for the military user. In astronomy, AO is used primarily to increase resolution by providing compensation for wavefront distortion by atmospheric non-uniformities.

However, it is recognised that the technology has the potential to enable laser and sensor designs with greater affordability and superior integration characteristics as well as performance enhancements in image quality and laser beam delivery. The initial programme looks at the fundamental issues of using AO concepts in military systems as a possible precursor to an independent sub-theme.

Synthetic aperture (SA) techniques are established in the RF spectrum and hold the potential for a stepwise increase in the resolution capability of EO systems. The resolution of EO systems is limited by the size of the optical aperture. SA utilises the phase properties of the wavefront from the target to construct the optical equivalent of a very large aperture from much smaller apertures at a known separation. It is recognised that there are physical limitations to the applicability of this technique, as well as formidable practical difficulties in implementation.

However, the potential benefits from synthetic aperture technology are so substantial that the programme will undertake an investigation of the feasibility of using SA in military applications.

The emerging technology of photonic crystal fibres presents a number of possibilities for applications in EMRS. Laser systems suffer from beam quality issues and divergence, which reduces the amount of energy that can be delivered to the target. This in turn increases the power requirements of the laser or adds bulky optical systems for beam control. Photonic fibres offer the possibility of producing high quality, high power laser beams. The initial programme will investigate the use of this technology to improve efficiency in laser delivery systems.

Temperature referencing is a fundamental requirement for achieving sensitivity and stability of operation in IR sensors. It is also a well-established problem for IR sensor designs, and current technologies add bulk, cost and complexity. The programme will look at novel approaches aimed at providing simpler integrated solutions.

Hybrid optics using diffractive technology has enabled more compact, high performance designs with integral thermal compensation. Implementation of this technology has focused on simple linear phase gratings. Analogous techniques in RF applications have demonstrated significant gains in efficiency and noise suppression using graduated structures. The programme will investigate the benefits and issues associated with applying these methods in design and manufacture of EO systems.

CO-ORDINATION WITH EXISTING / PREVIOUS RESEARCH

Existing CRP work in adaptive optics would be used, in particular, simulations of typical aberrations expected due to atmospherics and corresponding real-time correction techniques. This CRP also examined potential hardware solutions for solving beam transport issues in aperture synthesis. Much of the early development work in high power photonic fibres was funded under the CRP.

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