2018 Fiscal Year Research-status Report

Monolithic on-chip waveguide-integrated plasmonic nanolaser

Research Project

Project/Area Number	18K13799
Research Institution	The University of Tokyo
Principal Investigator	何亜倫東京大学, 大学院工学系研究科(工学部), 助教 (20815386)
Project Period (FY)	2018-04-01 – 2020-03-31
Keywords	プラズモニクス / plasmonics / ナノレーザ / nanolaser / aluminum plasmonics
Outline of Annual Research Achievements	Plasmonic-waveguide lasers, which exhibit sub-diffraction limit lasing and light propagation, are promising for the next-generation of nanophotonic devices in computation, communication, and biosensing. However, plasmonic lasers supporting waveguide modes are often based on nanowires grown with bottom-up techniques that need to be transferred and aligned for use in optical circuits. We demonstrate a monolithically fabricated ZnO/Al plasmonic-waveguide nanolaser achieving lasing at room temperature and compatible with the fabrication requirements of on-chip circuits. This work demonstrates the realization of a plasmonic-waveguide nanolaser without the need for transfer and positioning steps, which is the key for on-chip integration of nanophotonic devices.
Current Status of Research Progress	Current Status of Research Progress 2: Research has progressed on the whole more than it was originally planned. Reason We experimentally demonstrate a ZnO/Al plasmonic-waveguide nanolaser without the need for any transfer or manipulation steps. The plasmonic-waveguide nanolaser design is composed of a gain material cavity coated on top by a plasmonically active metal layer, a design which differs significantly from reported nanowire and nanocavity lasers. The nanolaser design enables efficient energy transfer both between the photons of the incident pump light and excitons in the gain medium, and between excitons in the gain medium and plasmons of the plasmonic-waveguide mode. The ZnO/Al nanolaser shows single-mode lasing in the ultraviolet region from 147 to 330 K with a low threshold intensity (0.20 mJ/cm2 at room temperature) and a lasing mode cross-sectional size in the sub-wavelength regime.
Strategy for Future Research Activity	To decrease the threshold of the plasmonic nanolaser by designing the nanolaser with the hybrid photonic-plasmonic mode is the next step of the project. A dielectric (aluminum oxide) layer with the thickness of a few nanometers will be deposited under the metal top layer. The hybrid photonic-plasmonic lasing is sustained at the dielectric layer in between the metal and the gain material. The threshold of the nanolaser will be optimized with the dielectric layer thickness. Further, the nanolaser-coupled plasmonic waveguide will be fabricated by the focused ion beam and the light propagation from the nanolaser to the waveguide will be observed under the microscope. The coupling efficiency between the nanolaser and the few-tens-of-micrometer plasmonic waveguide will be evaluated.
Causes of Carryover	The results of the monolithically fabricated ZnO/Al plasmonic-waveguide nanolaser will be presented at the conferences next fiscal year.