The Physics of Polymer Photonic Devices: Experiment and Theory

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Remarkable progress has been made over the last decade in making optical sources such as LEDs and lasers out of flexible, plastic materials. This has a wide range of potential applications, such as roll up TV displays or having data communications systems woven into your clothing. The technology of polymer LEDs has now matured to the degree that plastic light-emitting displays are available as commercial products. Plastic lasers, optical amplifiers and other photonic devices are much less well developed. But these offer huge potential as sophisticated, yet inexpensive, visible light sources. We have reached a stage now where we have demonstrated this potential in the laboratory, and in order to take the next major step forward to practical devices we urgently need a deeper understanding of the behaviour of these materials at the microscopic level. The physics of how the polymer chains interact with intense light involves a rich combination of competing processes. The cumulative effect of these processes in devices is not yet well understood. This proposal seeks to develop this understanding by bringing together the expertise of two groups: one who are experts in measuring the optical performance of these polymers and in their application for photonics, and the other who are experts in the theory of optical materials. Through a combination of theory and experiment we will aim to understand the complex optical interactions of semiconducting polymers, and exploit them in new and more sophisticated ways. This would help us to optimise the performance (e.g. speed and efficiency) of current devices; but more significantly it would enable a new generation of photonic devices based on these materials. We will make optical measurements of how these polymers respond to light under device conditions. By doing this we can understand, for example, the loss mechanisms that increase the power required by a laser, or the processes that limit pulse durations and their propagation. Using quantum mechanics we can also simulate the microscopic physics which gives rise to these effects. We can then try to reduce the losses and improve operation, using our new knowledge. This approach of combining a microscopic quantum theory with experiment has previously been used to greatly improve inorganic semiconductor devices. Indeed it proved crucial to the development of optimised inorganic diode lasers such as those used in DVD players and laser printers. By bringing together complementary expertise, we hope to build a new level of understanding of organic semiconductors. To demonstrate the advantages of our approach, we will undertake two pilot studies. First we will develop optical switches with which we may use one light pulse to pass or block the propagation of another pulse. For such a device to work well, we will need a very fast process that can switch cleanly between on and off-states, while not distorting the propagating light pulses- a good understanding of the material physics will therefore be essential. In the second pilot study, we will aim to observe and explore an exotic phenomenon known as slow light , which has previously been found in inorganic semiconductors. This effect delays the propagation of light through a material, and may in the future form a basis for optical signal processors. The model will also be able to guide and inform the design of many other sophisticated photonic devices, including short-pulse plastic lasers, optical amplifiers and detectors; all key components of plastic photonic systems of the future.