UC Berkeley

Abstract

"Physics of Optoelectronic and Plasmonic Devices: Cavities, Waveguides, Modulators and Lasers"

By

Volker Jendrik Sorger

Doctor of Philosophy in Engineering-Mechanical Engineering

And the Designated Emphasis In

Nanoscale Science and Engineering

University of California, Berkeley

Professor Xiang Zhang, Chair

This dissertation explores the fundamental interactions between light and matter towards devices applications in the field of Opto-electronics and metal-optics, or plasmonics. In its core, this dissertation attempts, and succeeds to demonstrate strong enhancements of such interactions. Here, surface plasmon polaritons, collective electronic oscillations at metal-dielectric interfaces, play a significant role, as they allow for nano-scale wavelengths with visible and near-infrared light. In particular the rate of spontaneous emission was shown to be significantly increased via increasing the local electromagnetic field density surrounding a photonic emitter. A nanoscale plasmonic cavity has been fabricated and shown to provide reasonable feedback while confining the optical mode beyond the diffraction limit of light. In addition microcavities cavities were coated with metal demonstrating the highest cavity quality-factor for a plasmonic system to date.

Furthermore, a low loss deep-subwavelength waveguide has been proposed and experimentally demonstrated. This novel waveguide uniquely combines ultra-small squeezed optical propagating fields with semiconductor technology, allowing for high waveguiding figure-of-merits; wave propagation versus mode confinement. Deploying near-field scanning optical microscopy, the tiny optical mode of such waveguides has been probed, revealing the first images of truly nanoscale optical waveguiding.

The challenge to demonstrate a sub-wavelength plasmon Nanolaser was successfully overcome by deploying the aforementioned hybrid plasmonic waveguide architecture. Such Nanolasers were found to operate close to the thresholdless, ideal regime for lasers. The high optical loss of such plasmon Nanolasers was mitigated by utilizing the unique physical mechanism inside the plasmon Nanolaser cavity. In particular, this dissertation shows, that ultra-small optical modes are enhancing laser-mode selection leading to higher laser efficiencies and potentially reduced laser thresholds. Furthermore, this study of plasmon Nanolasers suggests a direct laser modulation bandwidth far exceeding that of any traditional laser and lastly discusses the integration of coherent nanoscale light source into ultra-compact integrated photonic on-chip solutions.

Enhanced light-matter-interactions have further been explored towards combining photonic and logic, or computation. Here, plasmonic-optically enhanced architectures were used to create optical non-linear effects with unprecedented efficiency and ultra-small device foot-prints. In particular, the electro-optical effect was deployed in a novel device interfacing silicon-on-insulator technology with hybrid plasmonics. First results show that one to two volt of electrical bias can switch an optical signal requiring only a few micrometer-long light-matter-interaction lengths. Furthermore, higher order non-linear effects, e.g. 3rd order, have been predicted to boost such interactions even further paving the way towards efficient nanoscale all-optical transistors and routers.

Light-emitting tunnel junctions on the basis of metal-insulator-semiconductors were realized showing the highest quantum efficiency for such devices to date. Such 100% CMOS compatible on-chip silicon-based light sources were simulated yielding direct modulation speeds far exceeding the tea-hertz range.

In conclusion Opto-electronic device physics has been explored on a fundamental level towards enhancing light matter interactions. On this basis, novel nanophotonics building blocks have been realized and found to potentially out-perform traditional pure electronic or photonic devices. These findings are of importance towards fueling the global exponentially growing demand for data-bandwidth and novel functionalities such as sensing and bio-medical applications as well as ultrafast on-chip photonics. Especially with the raising energy consumption of information technology, nanoscale integrated hybrid circuits not only hold promise to deliver higher performance but also energy concise solutions due to enhanced physical effects.