We have been awarded an NSF grant titled “Resonant acousto-optic devices in silicon for ultra-low power optical modulation and non-reciprocity”.
The objective of this program is to combine two major strands of research in chip-scale nanotechnology to address long-standing practical problems in silicon optical circuits. By merging the advances in circuit technologies developed for controlling the flow of light on a chip, with the invention of nanodevices capable of generating and detecting high frequency mechanical vibrations, this program aims to develop a remarkable class of new optical devices. The backbone of the Internet is entirely based on systems that use light and fiber optics to efficiently send large amounts of data quickly over vast distances. In the last decade, the rise of cloud computing, data centers, and ubiquitous high bandwidth wireless has led to an effort to increase our ability to perform more integrated and complex routing and modulation of optical data. This has led to several successful demonstrations of complex photonic circuits on Silicon and in other semiconductor materials. Despite the significant successes of these systems in increasing throughput and efficiency of computing networks, the growth of demand for data in the wider economy and the corresponding growth in information technology energy consumption has completely out-paced parallel technological advances. Therefore, successful new approaches to address these challenges are expected to have a significant economic as well as environmental impact. Currently, most high-speed optical switches and modulators, as well as all major industrial research efforts, are based on using electrons or electric fields to locally change the optical properties in material, leading to electrical control of optical fields. In contrast, this research program explores a novel approach using high frequency mechanical vibrations, or sound, in lieu of electrons to control the propagation of light. Remarkably, recent calculations and experimental results suggest the possibility of making optical high-speed modulators that operate nearly a thousand times more efficiently than state-of-the-art laboratory demonstrations, and more than one hundred thousand times more efficiently than commonly deployed technologies. This program will develop devices that experimentally demonstrate the potential of using sound to process light. Finally, in its later stage, this program will spearhead the development of a fundamental device that has been lacking from the optical circuit designer’s toolbox: the optical circulator. By dynamically modifying the properties of an optical structure with sound, it is possible to operate in a mode where light can propagate in only one direction and is inhibited from flowing backwards. This significantly simplifies the design of robust multi-element systems and can lead to new types of optical circuitry that are far less difficult to scale up.
The core concepts of this proposal are centered around the following recent technological developments: 1) simultaneous localization of light and motion leads to extremely efficient modulation of light in a micron-scale package, 2) microwave capacitive transduction of high frequency mechanical waves via nanopatterened transducers allows transduction frequencies into the GHz and above, 3) optical filters modulated at high frequencies can have highly non-trivial and tailorable responses based on the amplitude and phase of the drives and can be utilized for filter-shaping and non-reciprocal photon propagation engineering. This program will demonstrate ultra-low power (attojoule/bit) acousto-optic modulators and switches with application in data center and wireless back-end optical networks. The core technology to be developed is a way to efficiently electromechanically modulate photonic crystal cavities at frequencies up to 10 GHz. Finally, in its later phase, this program will develop novel devices utilizing mechanically modulated cavities to break time-reversal symmetry in photonic circuits enabling a new type of chip-scale photonic circulator as well as other interesting non-reciprocal elements.