Bonding, antibonding and tunable optical forces in asymmetric membranes


Alejandro W. Rodriguez, Alexander P. McCauley, Pui-Chuen Hui, David Woolf, Eiji Iwase, Federico Capasso, Marko Loncar, and Steven G. Johnson. 2011. “Bonding, antibonding and tunable optical forces in asymmetric membranes.” Optics Express, 19, 3, Pp. 2225-2241.


We demonstrate that tunable attractive (bonding) and repulsive (anti-bonding) forces can arise in highly asymmetric structures coupled to external radiation, a consequence of the bonding/anti-bonding level repulsion of guided-wave resonances that was first predicted in symmetric systems. Our focus is a geometry consisting of a photonic-crystal (holey) membrane suspended above an unpatterned layered substrate, supporting planar waveguide modes that can couple via the periodic modulation of the holey membrane. Asymmetric geometries have a clear advantage in ease of fabrication and experimental characterization compared to symmetric double-membrane structures. We show that the asymmetry can also lead to unusual behavior in the force magnitudes of a bonding/antibonding pair as the membrane separation changes, including nonmonotonic dependences on the separation. We propose a computational method that obtains the entire force spectrum via a single time-domain simulation, by Fourier-transforming the response to a short pulse and thereby obtaining the frequency-dependent stress tensor. We point out that by operating with two, instead of a single frequency, these evanescent forces can be exploited to tune the spring constant of the membrane without changing its equilibrium separation. (C) 2011 Optical Society of America
Last updated on 05/23/2020