Design of mechanically-tunable photonic crystal split-beam nanocavity

Abstract

Photonic crystal split-beam nanocavities allow for ultra-sensitive optomechanical transductions but are degraded due to their relatively low optical quality factors. We have proposed and experimentally demonstrated a new type of one-dimensional photonic crystal split-beam nanocavity optimized for an ultra-high optical-quality factor. The design is based on the combination of the deterministic method and hill-climbing algorithm. The latter is the simplest and most straightforward method of the local search algorithm that provides the local maximum of the chosen quality factors. This split-beam nanocavity is made up of two mechanical uncoupled cantilever beams with Bragg mirrors patterned onto it and separated by a 75-nm air gap. Experimental results emphasize that the quality factor of the second-order TE mode can be as high as 1.99×10(4). Additionally, one beam of the device is actuated in the lateral direction with the aid of a NEMS actuator, and the quality factor maintains quite well even if there is a lateral offset up to 64 nm. Potentially promising applications, such as sensitive optomechanical torque sensor, local tuning of Fano resonance, all-optical-reconfigurable filters, etc., are foreseen.

Nanomechanical control of optical field and quality factor in photonic crystal structures

“…It is well known 44,45 Remarkably, we note that a moderate bending can provide localized modes with extremely high optical Q factors (Q > 10 7 ), comparable with the ones obtainable in PhC cavities where the position and/or radius of each hole is carefully optimized to maximize the Q. [45][46][47][48][49] Moreover, the field localization of the S modes leads to a two-fold reduction of the mode volume V ( fig. 2i, left axis), which further increases the ratio Q/V, a typical figure of merit for cavity QED experiments and in particular for Purcell enhancement.…”

In-plane rotation of the doubly coupled photonic crystal nanobeam cavities

“…The device was tested on our fiber-based setup reported in [21]. The only difference is that the output light was collected by the low noise photo-receiver (The New Focus Model 1811) and monitored in real-time by the oscilloscope (DSO90404A).…”

Opto-Mechanical Photonic Crystal Cavities for Sensing Application

“…The longitudinally split PCN cavity consisted of an air gap in the middle of nanocavity and a pair of Bragg mirrors patterned on side cantilever beams. By altering the axial separation gap of two aligned cantilevers, the Q-factor of the cavity was largely tuned and yet, the resonant frequency was barely affected [65]. Longitudinally split PCN cavities could also be mechanically controlled by varying the offset laterally in-plane [66] and out-of-plane [67] When two PCN cavities are placed close to each other and their mode fields are coupled together, resonant frequencies of coupled supermodes can be adjusted by controlling the coupling strength between two cavities.…”