Karen E. Grutter

Low loss hollow-core waveguide on a silicon substrate

Abstract Optical-fiber-based, hollow-core waveguides (HCWs) have opened up many new applications in laser surgery, gas sensors, and non-linear optics. Chip-scale HCWs are desirable because they are compact, light-weight and can be integrated with other devices into systems-on-a-chip. However, their progress has been hindered by the lack of a low loss waveguide architecture. Here, a completely new waveguiding concept is demonstrated using two planar, parallel, silicon-on-insulator wafers with high-contrast subwavelength gratings to reflect light in-between. We report a record low optical loss of 0.37 dB/cm for a 9-μm waveguide, mode-matched to a single mode fiber. Two-dimensional light confinement is experimentally realized without sidewalls in the HCWs, which is promising for ultrafast sensing response with nearly instantaneous flow of gases or fluids. This unique waveguide geometry establishes an entirely new scheme for low-cost chip-scale sensor arrays and lab-on-a-chip applications.

Quantum correlations from a room-temperature optomechanical cavity

Quantum effects in ambient conditions Quantum back action—the “reaction” of a quantum mechanical object to being measured—is normally observed at cryogenic temperatures, where it is easier to distinguish from thermal motion. Purdy et al. managed to tease out the effects of quantum back action at room temperature by using a mechanical oscillator and probing it with light (see the Perspective by Harris). The fluctuations of the force produced by the light probe caused correlated changes to the motion of the oscillator and the properties of the transmitted light. These correlations revealed the effects of the back action, which allows the system to be used as a quantum thermometer. Science, this issue p. 1265; see also p. 1232 An optomechanical system containing a Si3N4 nanobeam is used to tease out the effects of quantum backaction. The act of position measurement alters the motion of an object being measured. This quantum measurement backaction is typically much smaller than the thermal motion of a room-temperature object and thus difficult to observe. By shining laser light through a nanomechanical beam, we measure the beam’s thermally driven vibrations and perturb its motion with optical force fluctuations at a level dictated by the Heisenberg measurement-disturbance uncertainty relation. We demonstrate a cross-correlation technique to distinguish optically driven motion from thermally driven motion, observing this quantum backaction signature up to room temperature. We use the scale of the quantum correlations, which is determined by fundamental constants, to gauge the size of thermal motion, demonstrating a path toward absolute thermometry with quantum mechanically calibrated ticks.

Enhancement of mechanical Q for low phase noise optomechanical oscillators

A self-sustained Radiation-Pressure driven MEMS ring OptoMechanical Oscillator (RP-OMO) attaining an anchor-loss-limited mechanical Q-factor of 10,400 in vacuum has posted a best-to-date phase noise of -102 dBc/Hz at a 1 kHz offset from a 74 MHz carrier, more than 15 dB better than the best previously published mark [1]. While enhanced optical and mechanical Q both serve to lower the optical threshold power required to obtain oscillation, it is the mechanical Q that ends up having the strongest impact on phase noise [2], much as in a traditional MEMS-based oscillator [3]. This motivates a focus on increased mechanical Q-a challenge in previous such devices measured in air-and requires measurement in the absence of gas-damping using a custom optical vacuum measurement system. The improved phase noise performance of these RP-OMOs is now on par with many conventional MEMS-based oscillators and is sufficient for the targeted chip-scale atomic clock application.

Si

The development of

_{\bf 3}

{\text{Si}}_{\text{3}}{\text{N}}_{\text{4}}

N

nanobeam optomechanical crystals is reviewed. These structures consist of a 350-nm thick, 700-nm wide doubly-clamped

_{\bf 4}

{\text{Si}}_{\text{3}}{\text{N}}_{\text{4}}

Nanobeam Optomechanical Crystals

nanobeam that is periodically patterned with an array of air holes to which a defect region is introduced. The periodic patterning simultaneously creates a photonic bandgap for 980 nm band photons and a phononic bandgap for 4 GHz phonons, with the defect region serving to colocalize optical and mechanical modes within their respective bandgaps. These optical and mechanical modes interact dispersively with a coupling rate

A multi-material Q-boosted low phase noise optomechanical oscillator

g_{0}/2\pi \approx

Slot-mode optomechanical crystals: a versatile platform for multimode optomechanics

100 kHz, which describes the shift in cavity mode optical frequency due to the zero-point motion of the mechanical mode. Optical sidebands generated by interaction with the mechanical mode lie outside of the optical cavity linewidth, enabling possible use of this system in applications requiring sideband-resolved operation. Along with a review of the basic device design, fabrication, and measurement procedures, we present new results on improved optical quality factors (up to