Efficient side-coupling to photonic crystal nanobeam cavities via state-space overlap

Abstract

We present design guidelines for realizing side-coupled photonic crystal nanobeam (PCN) cavities with efficient coupling to low order resonances through adjusting the overlap of the PCN cavity mode and a feeding bus waveguide in both physical and k-space. We show that optimal side-coupled configurations function at a non-zero k-vector offset between the bus waveguide and PCN cavity modes. The straightforward design of side-coupled PCNs with high contrast resonances opens the door to their practical implementation in multiplexed, on-chip photonic devices.

Optimal condition to probe strong coupling of two-dimensional excitons and zero-dimensional cavity modes

“…42 This low transmission efficiency may be avoided by decoupling the waveguidecoupled loss from the intrinsic cavity loss by using a side-coupled nanobeam or ring resonator. 38,41 This allows for an extra degree of freedom to increase the waveguide-coupled loss at a similar rate to that of the cavity broadening from the perturbing monolayer MoSe 2 .…”

High-Q slow light and its localization in a photonic crystal microring

“…Therefore, the fitting of these modes needs to be modified with an additional coupling channel. Such side-coupled standing wave cavities have been considered in numerous contexts, including PhC defect cavities 47,48 and WGM cavities in the limit of strong surface-roughnessinduced backscattering 49 . The transmission at the resonance center is given by:…”

Camera detection and modal fingerprinting of photonic crystal nanobeam resonances

“…To demonstrate modal fingerprinting using a camera, we choose to test an evanescently sidecoupled PCN cavity because it is relatively straightforward to minimize non-resonant scattering in such a structure [25]. For the PCN cavity tested in this work, we utilized a cavity taper length of 20 unit cells from the center of the cavity to the edge of the mirror regions and mirror regions of 10 extra unit cells.…”

“…We linearly tapered the hole radius from 127nm in the center of the cavity to 108nm at the edges of the cavity. To adequately side-couple into resonance modes, we utilize a coupling gap of 400nm and straight bus waveguide width of 410nm for appropriate overlap of bus waveguide and cavity modes in both physical and k-space [25].…”

“…To (2), reduce non-resonant scattering, we chose to utilize a side-coupled configuration with a straight bus waveguide to evanescently excite PCN resonance modes. We present guidelines on how to side-couple to PCN cavities with a straight bus waveguide in previous work [25]. Implementing a straight side-coupled bus waveguide instead of a curved side-coupled bus waveguide reduces scattering due to bending losses in a curved bus waveguide.…”