Purcell enhancement of light emission in nanodiamond using a trenched nanobeam cavity

In this article, we propose a trenched nanobeam cavity as an efficient on-chip optical system that can be used to enhance light emission from color centers in nanodiamonds. The trench is created at the center of nanobeam cavity, and it is filled with a nanodiamond. The trench-nanodiamond system significantly perturbs the electric field profile of the original cavity mode. The antinodes of the electric fields relocate to the nano-sized air gap regions between the trench and the nanodiamonds, which lead to a large shrinking in the mode volume. By tuning the trench depth, a right balance is achieved between the deterioration of the quality factor and the reduction in the mode volume. At this depth, the ratio of quality factor to mode volume is maximized. Using silicon nitride nanobeam cavities of moderate experimental quality factors (∼1500), we are able to demonstrate a significant enhancement of the light emission compared to the conventional evanescent coupling approach.