1,959 research outputs found
Chemically etched ultrahigh-Q wedge-resonator on a silicon chip
Ultrahigh-Q optical resonators are being studied across a wide range of fields, including quantum information, nonlinear optics, cavity optomechanics and telecommunications. Here, we demonstrate a new resonator with a record Q-factor of 875 million for on-chip devices. The fabrication of our device avoids the requirement for a specialized processing step, which in microtoroid resonators8 has made it difficult to control their size and achieve millimetre- and centimetre-scale diameters. Attaining these sizes is important in applications such as microcombs and potentially also in rotation sensing. As an application of size control, stimulated Brillouin lasers incorporating our device are demonstrated. The resonators not only set a new benchmark for the Q-factor on a chip, but also provide, for the first time, full compatibility of this important device class with conventional semiconductor processing. This feature will greatly expand the range of possible ‘system on a chip’ functions enabled by ultrahigh-Q devices
Design of Optomechanical Cavities and Waveguides on a Simultaneous Bandgap Phononic-Photonic Crystal Slab
In this paper we study and design quasi-2D optomechanical crystals,
waveguides, and resonant cavities formed from patterned slabs. Two-dimensional
periodicity allows for in-plane pseudo-bandgaps in frequency where resonant
optical and mechanical excitations localized to the slab are forbidden. By
tailoring the unit cell geometry, we show that it is possible to have a slab
crystal with simultaneous optical and mechanical pseudo-bandgaps, and for which
optical waveguiding is not compromised. We then use these crystals to design
optomechanical cavities in which strongly interacting, co-localized
photonic-phononic resonances occur. A resonant cavity structure formed by
perturbing a "linear defect" waveguide of optical and acoustic waves in a
silicon optomechanical crystal slab is shown to support an optical resonance at
wavelength 1.5 micron and a mechanical resonance of frequency 9.5 GHz. These
resonances, due to the simultaneous pseudo-bandgap of the waveguide structure,
are simulated to have optical and mechanical radiation-limited Q-factors
greater than 10^7. The optomechanical coupling of the optical and acoustic
resonances in this cavity due to radiation pressure is also studied, with a
quantum conversion rate, corresponding to the scattering rate of a single
cavity photon via a single cavity phonon, calculated to be 292 kHz.Comment: 18 pages, 10 figures. minor revisions; version accepted for
publicatio
Chip-based Brillouin lasers as spectral purifiers for photonic systems
High coherence lasers are essential in a wide range of applications, however,
such performance is normally associated with large laser cavities, because
increasing energy storage reduces quantum phase noise and also renders the
laser frequency less sensitive to cavity vibration. This basic scaling rule is
at odds with an emerging set of optical systems that place focus on compact
(optimally integrable) sources of high coherence light. These include
phase-coherent optical communication using quadrature-amplitude-modulation, and
also record-low phase noise microwave sources based upon optical comb
techniques. In this work, the first, chip-based Brillouin laser is
demonstrated. It features high-efficiency and single-line operation with the
smallest recorded Schawlow-Townes frequency noise for any chip-based laser.
Because the frequency offset between the laser's emission and the input pump is
relatively small, the device provides a new function: spectral purification of
compact, low coherence sources such as semiconductor lasers
Steady-State Ab Initio Laser Theory for N-level Lasers
We show that Steady-state Ab initio Laser Theory (SALT) can be applied to
find the stationary multimode lasing properties of an N-level laser. This is
achieved by mapping the N-level rate equations to an effective two-level model
of the type solved by the SALT algorithm. This mapping yields excellent
agreement with more computationally demanding N-level time domain solutions for
the steady state
Identifying Vessel Branching from Fluid Stresses on Microscopic Robots
Objects moving in fluids experience patterns of stress on their surfaces
determined by the geometry of nearby boundaries. Flows at low Reynolds number,
as occur in microscopic vessels such as capillaries in biological tissues, have
relatively simple relations between stresses and nearby vessel geometry. Using
these relations, this paper shows how a microscopic robot moving with such
flows can use changes in stress on its surface to identify when it encounters
vessel branches.Comment: Version 2 has minor clarification
Power Loss Characteristics of a Sensing Element Based on a Polymer Optical Fiber under Cyclic Tensile Elongation
In this study, power losses in polymer optical fiber (POF) subjected to cyclic tensile loadings are studied experimentally. The parameters discussed are the cyclic load level and the number of cycles. The results indicate that the power loss in POF specimens increases with increasing load level or number of cycles. The power loss can reach as high as 18.3% after 100 cyclic loadings. Based on the experimental results, a linear equation is proposed to estimate the relationship between the power loss and the number of cycles. The difference between the estimated results and the experimental results is found to be less than 3%
Spontaneous emission rates of dipoles in photonic crystal membranes
We show theoretically that finite two-dimensional (2D) photonic crystals in
thin semiconductor membranes strongly modify the spontaneous emission rate of
embedded dipole emitters. Three-dimensional Finite-Difference Time-Domain
calculations show over 7 times inhibition and 15 times enhancement of the
emission rate compared to the vacuum emission rate for judiciously oriented and
positioned dipoles. The vertical index confinement in membranes strongly
enhances modifications of the emission rate as compared to vertically
unconfined 2D photonic crystals. The emission rate modifications inside the
membrane mimic the local electric field mode density in a simple 2D model. The
inhibition of emission saturates exponentially as the crystal size around the
source is increased, with a length that is inversely proportional to the
bandwidth of the emission gap. We obtain inhibition of emission only close to
the slab center. However, enhancement of emission persists even outside the
membrane, with a distance dependence which dependence can be understood by
analyzing the contributions to the spontaneous emission rate of the different
vertically guided modes of the membrane. Finally we show that the emission
changes can even be observed in experiments with ensembles of randomly oriented
dipoles, despite the contribution of dipoles for which no gap exists
A microchip optomechanical accelerometer
The monitoring of accelerations is essential for a variety of applications
ranging from inertial navigation to consumer electronics. The basic operation
principle of an accelerometer is to measure the displacement of a flexibly
mounted test mass; sensitive displacement measurement can be realized using
capacitive, piezo-electric, tunnel-current, or optical methods. While optical
readout provides superior displacement resolution and resilience to
electromagnetic interference, current optical accelerometers either do not
allow for chip-scale integration or require bulky test masses. Here we
demonstrate an optomechanical accelerometer that employs ultra-sensitive
all-optical displacement read-out using a planar photonic crystal cavity
monolithically integrated with a nano-tethered test mass of high mechanical
Q-factor. This device architecture allows for full on-chip integration and
achieves a broadband acceleration resolution of 10 \mu g/rt-Hz, a bandwidth
greater than 20 kHz, and a dynamic range of 50 dB with sub-milliwatt optical
power requirements. Moreover, the nano-gram test masses used here allow for
optomechanical back-action in the form of cooling or the optical spring effect,
setting the stage for a new class of motional sensors.Comment: 16 pages, 9 figure
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