In the first half of the project, our team formulated and applied models for the propagation of light and sound in a common structure, such as an optical fiber or a silicon chip. Using such models, we are able to predict and calculate precisely how light and sound waves affect each other. We already put these principles to work. In using light and sound waves together, we could map the properties of liquid media that surround optical fibers, over several kilometers. This measurements address a long-time challenge of the sensing community: optical fibers strongly confine the light that they guide, and make sure that nothing leaks outside. While this property is advantageous for data transfer, it makes the fibers "blind" to outside conditions. With the introduction of sound waves, we may now "listen" outside the optical fiber, where it is impossible to "look". We are now able to leverage the powerful advantages of optical fibers: long reach, small dimensions, compatibility with harsh environments and immunity to interfering radio waves, and use them for mapping of chemicals over a long range. The analysis, calculations, experimental demonstrations and applications of light and sound propagation over fibers appear in a series of publication by our group.
On the devices side, we were able to validate the main working hypothesis of the entire project. We were able to excite surface acoustic waves on a standard silicon chip, using incident light alone. Incoming light illuminates a target of metallic stripes that is patterned on the device surface for that purpose. Absorption of light leads to heating of the metals. As the intensity of incoming light is modulated to represent certain information, the metal pattern is heating and cooling, accordingly. Such changes in temperature, in turn, induce a pattern of mechanical strain to the underlying silicon. Stain then propagates away from the illuminated region towards the rest of the device, in the form of an acoustic wave. Further, we could detect and monitor the propagating surface waves using light that is also guided in the same chip. These demonstrations could form the basis of a new technology for the processing of data, in the form of surface-wave-photonics. In particular, the velocity of the acoustic waves is very slow: 100,000 slower than the speed of light. Due to their slow speed, signals are successfully delayed for a long time while they take up the form of acoustic waves, while remaining within a small area on the chip. Using such long delays, we have demonstrated the precise filtering of specific frequencies of incoming signals.
The results of the projects have been disseminated in 10 scientific papers in leading inter-disciplinary journals and high-impact journals of the optics community. More papers are currently under review and preparation. The results were also presented in over 20 presentations in international conferences.
