From membrane-in-the-middle to mirror-in-the-middle with a high-reflectivity sub-wavelength grating

摘要

We demonstrate a "membrane in the middle" optomechanical system using asilicon nitride membrane patterned as a subwavelength grating. The grating hasa reflectivity of over 99.8%, effectively creating two sub-cavities, with freespectral ranges of 6 GHz, optically coupled via photon tunneling. Measurementsof the transmission and reflection spectra show an avoided crossing where thetwo sub-cavities simultaneously come into resonance, with a frequency splittingof 54 MHz. We derive expressions for the lineshapes of the symmetric andantisymmetric modes at the avoided crossing, and infer the grating reflection,transmission, absorption, and scattering through comparison with theexperimental data.