Bonding, antibonding and tunable optical forces in asymmetric membranes
Abstract
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.
- Publication:
-
Optics Express
- Pub Date:
- January 2011
- DOI:
- 10.1364/OE.19.002225
- arXiv:
- arXiv:1012.1009
- Bibcode:
- 2011OExpr..19.2225R
- Keywords:
-
- Physics - Optics
- E-Print:
- Optics Express, Vol. 19, No. 3, 2225-2241 (2011)