AN OPTICAL memory chip that senses, stores and then displays the light it has received has sent a buzz of excitement round the imaging world. "We've never seen anything like this before," says Trevor Whittley, an expert in optical devices at the University of Edinburgh in the UK.

Such a device could delay light signals in optical-fibre networks, or allow the police to compare mug shots 1000 times faster than with today's computers.

The chip works in a similar way to the charge-coupled device (CCD) image sensors in digital cameras. A CCD turns light falling on its surface into an array of electrical charges, which in a camera are shunted off into a memory card for storage. The difference with the new photon storage device (PSD) is that it holds onto the charges, and then converts them back into light.

The idea for a chip that senses, stores and displays ...