789 research outputs found
Optimized optomechanical crystal cavity with acoustic radiation shield
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 1.2x10^6, a mechanical
frequency of 5.1GHz, a mechanical Q-factor of 6.8x10^5 (at T=10K), and a
zero-point-motion optomechanical coupling rate of g=1.1MHz.Comment: 4 pages, 4 figure
Two-dimensional phononic-photonic bandgap optomechanical crystal cavity
We present the fabrication and characterization of an artificial crystal
structure formed from a thin-film of silicon which has a full phononic bandgap
for microwave X-band phonons and a two-dimensional pseudo-bandgap for
near-infrared photons. An engineered defect in the crystal structure is used to
localize optical and mechanical resonances in the bandgap of the planar
crystal. Two-tone optical spectroscopy is used to characterize the cavity
system, showing a large vacuum coupling rate of 220kHz between the fundamental
optical cavity resonance at 195THz and a co-localized mechanical resonance at
9.3GHz.Comment: 4 pages, 4 figure
Observation of Quantum Motion of a Nanomechanical Resonator
In this Letter we use resolved sideband laser cooling to cool a mesoscopic mechanical resonator to near its quantum ground state (phonon occupancy 2.6±0.2), and observe the motional sidebands generated on a second probe laser. Asymmetry in the sideband amplitudes provides a direct measure of the displacement noise power associated with quantum zero-point fluctuations of the nanomechanical resonator, and allows for an intrinsic calibration of the phonon occupation number
Constitutive modeling for isotropic materials (HOST)
The results of the third year of work on a program which is part of the NASA Hot Section Technology program (HOST) are presented. The goals of this program are: (1) the development of unified constitutive models for rate dependent isotropic materials; and (2) the demonstration of the use of unified models in structural analyses of hot section components of gas turbine engines. The unified models selected for development and evaluation are those of Bodner-Partom and of Walker. A test procedure was developed for assisting the generation of a data base for the Bodner-Partom model using a relatively small number of specimens. This test procedure involved performing a tensile test at a temperature of interest that involves a succession of strain-rate changes. The results for B1900+Hf indicate that material constants related to hardening and thermal recovery can be obtained on the basis of such a procedure. Strain aging, thermal recovery, and unexpected material variations, however, preluded an accurate determination of the strain-rate sensitivity parameter is this exercise. The effects of casting grain size on the constitutive behavior of B1900+Hf were studied and no particular grain size effect was observed. A systematic procedure was also developed for determining the material constants in the Bodner-Partom model. Both the new test procedure and the method for determining material constants were applied to the alternate material, Mar-M247 . Test data including tensile, creep, cyclic and nonproportional biaxial (tension/torsion) loading were collected. Good correlations were obtained between the Bodner-Partom model and experiments. A literature survey was conducted to assess the effects of thermal history on the constitutive behavior of metals. Thermal history effects are expected to be present at temperature regimes where strain aging and change of microstructure are important. Possible modifications to the Bodner-Partom model to account for these effects are outlined. The use of a unified constitutive model for hot section component analyses was demonstrated by applying the Walker model and the MARC finite-element code to a B1900+Hf airfoil problem
Nonlinear radiation pressure dynamics in an optomechanical crystal
Utilizing a silicon nanobeam optomechanical crystal, we investigate the
attractor diagram arising from the radiation pressure interaction between a
localized optical cavity at nm and a mechanical resonance at
GHz. At a temperature of K, highly nonlinear
driving of mechanical motion is observed via continuous wave optical pumping.
Introduction of a time-dependent (modulated) optical pump is used to steer the
system towards an otherwise inaccessible dynamically stable attractor in which
mechanical self-oscillation occurs for an optical pump red-detuned from the
cavity resonance. An analytical model incorporating thermo-optic effects due to
optical absorption heating is developed, and found to accurately predict the
measured device behavior.Comment: 5 pages, 3 figure
Linear and nonlinear capacitive coupling of electro-opto-mechanical photonic crystal cavities
We fabricate and characterize a microscale silicon electro-opto-mechanical
system whose mechanical motion is coupled capacitively to an electrical circuit
and optically via radiation pressure to a photonic crystal cavity. To achieve
large electromechanical interaction strength, we implement an inverse shadow
mask fabrication scheme which obtains capacitor gaps as small as 30 nm while
maintaining a silicon surface quality necessary for minimizing optical loss.
Using the sensitive optical read-out of the photonic crystal cavity, we
characterize the linear and nonlinear capacitive coupling to the fundamental 63
MHz in-plane flexural motion of the structure, showing that the large
electromechanical coupling in such devices may be suitable for realizing
efficient microwave-to-optical signal conversion.Comment: 8 papers, 4 figure
Highly efficient coupling from an optical fiber to a nanoscale silicon optomechanical cavity
We demonstrate highly efficient coupling of light from an optical fiber to a silicon photonic crystal optomechanical cavity. The fiber-to-cavity coupling utilizes a compact (L ≈ 25 µm) intermediate adiabatic coupler. The optical coupling is lithographically controlled, broadband, relatively insensitive to fiber misalignment, and allows for light to be transferred from an optical fiber to, in principle, any photonic chip with refractive index greater than that of the optical fiber. Here we demonstrate single-sided cavity coupling with a total fiber-to-cavity optical power coupling efficiency of 85%
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