Brillouin cavity optomechanics with microfluidic devices

Abstract

Cavity optomechanics allows the parametric coupling of phonon- and photon-modes in microresonators and is presently investigated in a broad variety of solid-state systems. Optomechanics with superfluids has been proposed as a path towards ultra-low optical- and mechanical-dissipation. However, there have been no optomechanics experiments reported with non-solid phases of matter. Direct liquid immersion of optomechanics experiments is challenging since the acoustic energy simply leaks out to the higher-impedance liquid surrounding the device. Conversely, here we confine liquids inside hollow resonators thereby enabling optical excitation of mechanical whispering-gallery modes at frequencies ranging from 2 MHz to 11,000 MHz (for example, with mechanical Q = 4700 at 99 MHz). Vibrations are sustained even when we increase the fluid viscosity to be higher than that of blood. Our device enables optomechanical investigation with liquids, while light is conventionally coupled from the outer dry side of the capillary, and liquids are provided by means of a standard microfluidic inlet.Comment: 15 pages, 6 figure

Fabrication and Testing of Microfluidic Optomechanical Oscillators

“…Confinement of the liquid inside 19,20 the capillary resonator, as opposed to outside it, enables high mechanical-and optical-quality factors simultaneously, which allows the optical excitation of mechanical modes by means of both RP and SBS. As has been shown, these mechanical excitations are able to penetrate into the fluid within the device 12,13 , forming a shared solid-liquid resonant mode, thus enabling an opto-mechanical interface to the fluidic environment within.…”

“…Recently, a new type of hollow optomechanical oscillator with a microcapillary geometry was introduced [12][13][14][15] , and which by design is equipped for microfluidic experiments. The diameter of this capillary is modulated along its length to form multiple 'bottle resonators' that simultaneously confine optical whispering-gallery resonances 16 as well as mechanical resonant modes 17 .…”

Stimulated Brillouin scattering and Brillouin-coupled four-wave-mixing in a silica microbottle resonator

“…In silica optical fibers, if the pump (at 1550 nm band) and Stokes fields are counter-propagating the acoustic frequency is 11 GHz, and if the pump and Stokes are copropagating, it is in the range of MHz to a few GHz. SBS has been of increasing interest due to its underlying physics and potential applications such as ultra-narrow linewidth Brillouin laser [4][5][6][7], Brillouin optomechanics [8,9], microwave photonics [10,11], slow and fast light generation [12,13], and nonreciprocal light propagation [14,15]. Four-wave-mixing (FWM) is yet another nonlinear process that has found widespread use in many areas ranging from optical frequency conversion [16][17][18] and quantum light generation [19-23] to quantum nondemolition measurements [24] and frequency combs [25][26][27].…”

Cavity ring-up spectroscopy for dissipative and dispersive sensing in a whispering gallery mode resonator

“…Alternatively, a perturbation may increase the optical linewidth of the WGM by introducing more dissipation [21,22], or may change the back-scattering strength [23] and subsequent mode splitting if modal coupling is present [17,20]. The optomechanical properties of WGRs can also be used for force [24] or viscosity sensing [25].Currently, in order to retrieve the dispersive, dissipative and mode splitting information, the transmission spectrum of a WGR through an externally coupled waveguide, such as a tapered optical fibre, is usually measured. Light from a tunable laser source is coupled into the tapered fibre and the transmission is monitored.…”

“…Alternatively, a perturbation may increase the optical linewidth of the WGM by introducing more dissipation [21,22], or may change the back-scattering strength [23] and subsequent mode splitting if modal coupling is present [17,20]. The optomechanical properties of WGRs can also be used for force [24] or viscosity sensing [25].…”