This paper describes recent progress in developing a wireless optical link between the fuselage of a cockpit and an aviation helmet. Such a link is desired to replace the physical umbilical cable existing in current cockpit systems, for reasons of potential bandwidth, immunity to EM interference, and freedom from physical constraints within the cockpit. The link concept consists of multiple transmitters embedded in the cockpit fuselage, each sending video (or symbology) data out in a cone of light over free space, which is detected by an array of receivers positioned on the helmet - the data is then sent to the eyepieces or visor of the pilot (after any intermediate processing). The design is such that one of these links is always maintained throughout possible movement of the head. In a recent proof-of-principle demonstration we showed uncompressed, 100 Mbps video data streamed live from the fuselage of a cockpit simulator to an angled cluster of silicon-based receivers mounted on the helmet, via a pair of ~1 Watt free-space lasers operating at 810 nm. Fast Ethernet media converters were used here for convenience and cost. The bespoke optical and electrical link components were developed in close collaboration with suppliers. The system performance arises from: the high dynamic range of the receivers (up to 25 dB), which are equipped with optical antennae to magnify the optical gain; the high power of the lasers; and the switching electronics used to control the signal path on the helmet. Future potential improvements to the technology are discussed, with an indication of wireless link requirements for relevant BAE Systems applications.

Coarse wavelength-division multiplexing (CWDM) systems offer significant advantages over the more conventional dense wavelength-division multiplexing (DWDM) networks for aerospace applications. In DWDM, the spacing between adjacent channels is typically <1nm, whereas the CWDM standard is 20nm channel spacing. By exploiting this WDM standard, the requirement for an optical source to transmit at a specific, well-defined wavelength is somewhat relaxed, enabling a degree of centre wavelength drift with temperature to be tolerated -the CWDM standard defines a 13nm filter bandwidth. This promises significant reductions in device cost, weight, volume and power consumption, since it may be possible to use un-cooled laser sources. However, this assumes that the CWDM filter technology is stable over the aerospace operating conditions. This paper looks at both source and filter CWDM devices and in particular their performance over the airframe (-55 to +125degC) and avionic (-40 to +85degC) temperature ranges. CWDM filters from two different COTS providers were studied, as well as several different commercial CWDM transceivers. In all cases the devices were at times subject to temperatures beyond those specified by the manufacturers.

Fibre optic cable is an essential component for delivering both communications and sensor information over an avionic fibre optic network. This paper discusses the performance of some potential simplex cable designs for future applications with an operating temperature of -55 to 125degC

The holographic recording properties, in particular response time, of the photorefractive materials GaAs and BSO are experimentally analysed and compared. The results from two Fourier based optical image processing systems are presented.

A brief review of a band transport model for the photorefractive effect is given. Distinction is made between the influence of intrinsic material dependent parameters and externally controlled parameters on the form of the optical nonlinearity. These considerations are made in the context of dynamic holographic optical processing applications. Examples of adaptive optical and Fourier-plane image processing using four-wave mixing in photorefractive bismuth silicon oxide crystals are discussed. Critical assessment is then made of the use of photorefractive materials in image cross-correlation schemes.