Overcoming plasmonic loss to realize high performance telecommunication devices

Virginia Commonwealth University, Richmond VA

Investigators

Abstract

Non Technical Abstract: Today, optical technologies are the backbone of our information society, empowering impactful services such as virtual medical consultations, access to data stored in the cloud, and energy-efficient high-performance computing in largescale datacenters. Photonic solutions are particularly suited to enable these services due to the advantages of light such as multi-terabit bandwidths, low-loss propagation over kilometers, and low cross-talk. In fact, some internet provides have begun providing service entirely through light (fiber optics). As a result, the advancement of photonic telecommunications technologies will have a profound impact upon our nation by providing improved performance of internet-based services, reduced energy consumption, and a lower cost of construction/operation for networks. Current photonic modulators, small switches which convert electrical signals into optical pulses, are limited in their speed due to the weak interaction of light and matter. More recently, metals have been utilized to enhance this interaction, facilitating a reduction of device size and increase of speed. Yet, these devices struggle to achieve efficient transmission ~10%, which is simply insufficient for many applications. Here, we look utilize the benefits of both approaches by allowing the lossy metallic nature to be engaged and disengaged when desired. This approach limits the loss of the structure while still maintaining the benefits of metal plasmonic structures. By partnering with existing programs at the home university, the research will provide avenues for local high school students, teachers, and undergraduates to learn about impact of light-based technologies on our society while providing a platform to train a highly skilled workforce. Technical Abstract: Despite significant research in the areas of photonic and plasmonic-based approaches, there is yet to be a device which achieves efficient all-around performance (modulation strength, insertion loss, energy consumption, size, and speed). Photonic approaches suffer from poor light-matter interactions, requiring speed restricting resonators and long interaction lengths, while plasmonic approaches have yet to overcome the large insertion loss associated with their metallic components. This proposal seeks to solve this dilemma through a new design approach in which plasmonic elements are disengaged in the off- (transmissive) state to minimize insertion loss, yet are engaged in the on-state to achieve large modulation in a short distance. This is achieved through a specifically chosen set of oxide layers which appear dielectric to the optical mode under no electrical bias, yet can be modulated into an epsilon-near-zero condition (effectively engaging the plasmonic nature) to achieve efficient modulation through free-carrier accumulation and depletion. It is shown that this approach is able to produce the first modulator design capable of efficient all-around performance: area of 3 square microns, 1.5 dB, 9dB extinction ratio, 12 fJ/bit energy consumption, and 112 GHz bandwidth. Although it is impactful for integrated systems, the approach is general and may also find applications in related areas such as metamaterials and sensors. Additionally, the realization of the device will demonstrate that plasmonic systems are not synonymous with loss and the benefits of such systems (confinement, enhanced light-matter-interaction) can be employed without detrimental loss. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.