Optimized optomechanical crystal cavity with acoustic radiation shield

Abstract

We present the design of an optomechanical crystal nanobeam cavity that combines finite-element simulation with numerical optimization, and considers the optomechanical coupling arising from both moving dielectric boundaries and the photo-elastic effect. Applying this methodology results in a nanobeam with an experimentally realized intrinsic optical Q-factor of 1.2 × 10 6 , a mechanical frequency of 5.1 GHz, a mechanical Q-factor of 6.8 × 10 5 (at T = 10 K), and a zero-point-motion optomechanical coupling rate of g = 1.1 MHz.The use of radiation pressure forces to control and measure the mechanical motion of engineered micro-and nanomechanical objects has recently drawn significant attention in fields as diverse as photonics [1], precision measurement [2], and quantum information science [3]. A milestone of sorts in cavity circuit-and optomechanics is the recent [4,5] cooling of a mechanical resonator to a phonon occupancy n < ∼ 1 using cavity-assisted radiation pressure backaction [6,7]. Backaction cooling involves the use of an electromagnetic cavity with resonance frequency ω o sensitive to the mechanical displacement, x, of the mechanical resonator. The canonical system is a Fabry-Perot cavity of length L with one end mirror fixed and with the other end mirror of mass m eff mounted on a spring with resonance frequency ω m . The coupling between the electromagnetic field and mechanics is quantified by the frequency shift imparted by the zero-point motion of the mechanical resonator, given byOne of many technologies recently developed to make use of radiation pressure effects are optomechanical crystals (OMCs) [8,9]. Optomechanical crystals, in their most general form, are quasi-periodic nanostructures in which the propagation and coupling of optical and acoustic waves can be engineered. In this work we present the comprehensive design, fabrication, and characterization of a quasi-1D OMC cavity formed from the silicon device layer of a silicon-on-insulator (SOI) microchip. Our design incorporates both moving-boundary and photoelastic (electrostriction) radiation pressure contributions, and simultaneously optimizes for optical and acoustic parameters.The nominal unit cell of a nanobeam OMC, geometrically a silicon block with an oval hole in it, is shown schematically in Fig. 1a. The corresponding optical and mechanical bandstructure diagrams are shown in Figs. 1c and d, respectively. As indicated by the gray shaded region in the photonic bandstructure, the continuum of unguided optical modes above the light line precludes the existence of a complete photonic band gap (only a quasibandgap exists for the guided modes of the beam). The physical dimension of the unit cell block (see caption of Fig. 1a) are chosen to yield a photonic quasi-bandgap surrounding a wavelength λ ∼ 1550 nm. The corresponding mechanical bandstructure has a series of acoustic bands in the GHz frequency range (the ratio of the optical frequencies to that of the mechanical frequencies is roughly the ratio of the speed of light to sound in si...

Non-classical correlations between single photons and phonons from a mechanical oscillator

“…We design the nanobeams such that the fundamental mechanical breathing mode is at 5.3 GHz (cf. Figure 2a, main text) and the optical resonance is around 1550 nm (the measured wavelength for the device used here is 1556 nm) [33]. The optical and the mechanical modes are co-localized in the center of the beam, where we create a defect region of the photonic-and phononic-bandgap, allowing for an optomechanical coupling rate g 0 /2π = 825 kHz.…”

Quantum nonlinear optics — photon by photon

“…The state-of-the-art systems are currently within two orders of magnitude of this regime. 104 (Fig. 6e).…”

Open quantum dynamics of single-photon optomechanical devices

“…(102) and its left-hand side. The current record of this nonlinearity is achieved in optomechanical crystal setups, with the ration being ≈0.007 [17]. According to Ludwig et al, it is possible to enhance the optomechanical nonlinearity to be larger than 1, at least in twomode optomechanical systems [18].…”