Optical allusions

Appearing for the first time in the late 1960s, photonics only began to be regarded as a discrete technology in the 1980s, with the development of semiconductor lasers for use in the communications sector. David Smith is chief technology officer for CIP Technologies, a leading developer of photonics products which emerged out of BT's Martlesham Heath research laboratory. How does he define photonics and how does he differentiate the technique from optoelectronics? "It's a fuzzy boundary," he conceded, "but photonics is really about the manipulation of photons. Optoelectronics has a broader definition, which brings in semiconductor devices." In fact, he believes optoelectronics has become a bit of a 'catch all' term. "Optoelectronics is now seen to cover photonics, lighting, displays and even solar technologies; everything that includes light in some way or another." CIP's telecommunications heritage has led it to view photonics as the manipulation of light for transmitting, switching and processing information. "And our emphasis is working out how you can carry out more complex functions in components." Smith believes photonics has parallels with the electronics industry. "If you look at how the electronics world has evolved, that's gone from discrete components to integrated devices. In many ways, photonics is following a parallel path, driven by the need for integration." And the need for integration is being driven by exactly the same concerns as those specifying and purchasing semiconductors. "The whole thing with communications systems," Smith observed, "is that people want ever more capacity. That means those developing the components for those systems have to do more and more in less space and at lower cost. In doing that, people have recognised that they have to come up with more complex ways of generating signals and detecting them. Rather than on/off keying, people are now deploying more sophisticated systems using the phase of light. That means the transmitters and receivers are more complicated and functions are having to be integrated." While the term photonics was originally used almost exclusively in the telecommunications domain, application for the technology are now found in a wide range of sectors. "Look in consumer goods and you'll find photonics technology," Smith pointed out. "A good example are those devices with cds and dvds. The semiconductor lasers which enable these products were originally developed for the communications world. But it turns out that, today, the largest consumer of semiconductor lasers is the consumer sector; something that was not the original intention." Nevertheless, telecommunications remains at the leading edge of photonics technology. "Today, we're looking at how to integrate more and more functions," Smith said, "and you get to the point where you have to ask what are the technologies you need in order to go down that track. We are developing technologies for the integration of photonics components and many of these technologies will migrate to other applications." Smith pointed to the current boom in lighting applications. "White light leds are finding volume application in the lighting sector," he noted, "but the technology was pushed to achieve particular performance points in the telecomms world. The process then evolved to broader use." CIP remains focused on developing solutions to particular problems, generally in the telecomms sector. "They are tough challenges," Smith admitted. With photonics still a relatively young technology, the sector is typified by research partnerships. One such collaborative effort has recently received £1.85million from the Technology Strategy Board (TSB) to develop integrated InP based photonic devices and new active materials. The three year project, part of the TSB's Collaborative Research and Development programme, is called ETOE II (Extended Temperature OptoElectronics). ETOE II has two main thrusts. The first is the development of reliable active photonic components containing aluminium. This will help to support the high temperature operation of devices, such as integrated semiconductor optical amplifiers and electroabsorption modulators. The second, longer range, element is to explore alternative active layer materials for InP and GaAs devices, including nitrogen, antimony and bismuth. This work is being done in the knowledge that power consumption has become a significant challenge for the information and communications industry. "As processing speeds increase," said Smith, "so too does power consumption. At 40Gbit/s, photonics can bring power savings; it's not just the device footprint, it's also the power consumed." Smith noted that, for each watt of power consumed by a device, another 2W can be required to remove the heat it produces from the building. This is seen to be particularly important for optoelectronic components, such as lasers and amplifiers, because their operating temperatures need to be controlled with local thermoelectric cooling – wasting yet more power. ETOE II will tackle this power efficiency problem by raising the allowable operating temperature range of optoelectronic components and reducing or eliminating the fundamental need for cooling. Mike Biddle, the TSB's lead technologist for electrical systems, said: "This project brings together the UK's world class expertise to research and develop an innovative technology that could be exploited globally. We are delighted to offer our support and investment to CIP and its partners in this important project." CIP has also taken part in a European project which recently completed work to develop an optical firewall. The project was concerned with increasing data security problems as network speeds grew. Smith noted: "As data rates on the internet grow, it makes it harder to check packet headers and look for particular things." The traditional approach was to break everything down, but this brings an even higher processing load. "As part of the WISDOM project, we developed a hybrid optical ic which can work at 40Gbit/s. It can help a system to look at packet headers, identify particular patterns and pull out those of interest for further examination. This effort involved a combination of switching and pattern recognition technologies, amongst others." WISDOM was set up to develop new photonic firewall techniques, including novel hybrid photonic devices working in conjunction with new algorithms and protocols to extract and process wirespeed security information. The algorithms will combine the functionality of optical processing with secondary electronic security approaches in order to introduce new layers of security analysis on networks. When deployed, optical processing modules will be placed at the front end of the node's firewall to undertake wirespeed primary optical information filtering. This will include operations such as parity checking, flag status and header recognition. Suspect packets would then be subjected to secondary electronic processing, with a reduction in the amount of processing power needed. According to the project, in the longer term, it may be possible to perform a finer optical sift and to examine the packet payload for particular features at wirespeed. Much of this has been enabled by CIP's core technology expertise. "We can create complex circuits by mixing monolithic semiconductor optical devices with other types of optical component, usually passives. We combine the technologies because it provides a better economic solution and you also get the flexibility to do things which can't be done in one technology alone," he concluded.