Fabrication of photonic crystal mirror into a silicon nitride membrane resonator

High Q silicon nitride membrane resonators have enabled a diversity of

quantum optomechanics experiments. A key limitation is their low

reflectivity, which limits their optomechanical coupling strength.

Here we report efforts to improve the reflectivity of a silicon

nitride membrane by patterning a photonic crystal (PtC) mirror into

it.  Our aim is to embed PtC mirrors into trampoline-like membranes

suspended from millimeter-long nanotethers. The main challenge is the

extreme aspect ratio and high tensile stress near the tether clamps,

which make them highly susceptible to breakage. We overcome this

challenge by using a combination of dry and wet etching techniques to

minimize the influence of turbulence, capillary, and thermal gradient

forces during the release process.  Trampolines with a reflectivity

greater than 80% at 860 nm were realized.  Ultimately these structures

will be integrated into optical cavities for quantum-limited

accelerometry and electro-optic conversion applications.