Optical and mechanical design of a zipper photonic crystal optomechanical cavity

Design of a doubly-clamped beam structure capable of localizing mechanical and optical energy at the nanoscale is presented. The optical design is based upon photonic crystal concepts in which patterning of a nanoscale-cross-section beam can result in strong optical localization to an effective optical mode volume of 0.2 cubic wavelengths ((lambda(c))(3)). By placing two identical nanobeams within the near field of each other, strong optomechanical coupling can be realized for differential motion between the beams. Current designs for thin film silicon nitride beams at a wavelength of lambda = 1.5 mu m indicate that such structures can simultaneously realize an optical Q-factor of 7 x 10(6), motional mass m(u) similar to 40 picograms, mechanical mode frequency Omega(M)/2 pi similar to 170 MHz, and an optomechanical coupling factor (g(OM) = d omega(c)/dx = omega(c)/L-OM) with effective length L-OM similar to lambda = 1.5 mu m. (C) 2009 Optical Society of America