472 research outputs found
Scanning probe microscopy of thermally excited mechanical modes of an optical microcavity
The resonant buildup of light within optical microcavities elevates the
radiation pressure which mediates coupling of optical modes to the mechanical
modes of a microcavity. Above a certain threshold pump power, regenerative
mechanical oscillation occurs causing oscillation of certain mechanical
eigenmodes. Here, we present a methodology to spatially image the
micro-mechanical resonances of a toroid microcavity using a scanning probe
technique. The method relies on recording the induced frequency shift of the
mechanical eigenmode when in contact with a scanning probe tip. The method is
passive in nature and achieves a sensitivity sufficient to spatially resolve
the vibrational mode pattern associated with the thermally agitated
displacement at room temperature. The recorded mechanical mode patterns are in
good qualitative agreement with the theoretical strain fields as obtained by
finite element simulations
Theoretical and experimental study of radiation pressure-induced mechanical oscillations (parametric instability) in optical microcavities
Radiation pressure can couple the mechanical modes of an optical cavity structure to its optical modes, leading to parametric oscillation instability. This regime is characterized by regenerative oscillation of the mechanical cavity eigenmodes. Here, we present the first observation of this effect with a detailed theoretical and experimental analysis of these oscillations in ultra-high-Q microtoroids. Embodied within a microscale, chip-based device, this mechanism can benefit both research into macroscale quantum mechanical phenomena and improve the understanding of the mechanism within the context of laser interferometer gravitational-wave observatory (LIGO). It also suggests that new technologies are possible that will leverage the phenomenon within photonics
Characterization and scanning probe spectroscopy of radiation-pressure induced mechanical oscillation of a microcavity
Microcavities can enter a regime where radiation pressure causes oscillation of mechanical cavity eigenmodes. We present a detailed experimental and theoretical understanding of this effect, and report direct scanning probe spectroscopy of the micro-mechanical modes
Coupling ideality of integrated planar high-Q microresonators
Chipscale microresonators with integrated planar optical waveguides are
useful building blocks for linear, nonlinear and quantum optical devices. Loss
reduction through improving fabrication processes has resulted in several
integrated micro resonator platforms attaining quality (Q) factors of several
millions. However only few studies have investigated design-dependent losses,
especially with regard to the resonator coupling section. Here we investigate
design-dependent parasitic losses, described by the coupling ideality, of the
commonly employed microresonator design consisting of a microring resonator
waveguide side-coupled to a straight bus waveguide. By systematic
characterization of multi-mode high-Q silicon nitride microresonator devices,
we show that this design can suffer from low coupling ideality. By performing
full 3D simulations to numerically investigate the resonator to bus waveguide
coupling, we identify the coupling to higher-order bus waveguide modes as the
dominant origin of parasitic losses which lead to the low coupling ideality.
Using suitably designed bus waveguides, parasitic losses are mitigated, and a
nearly unity ideality and strong overcoupling (i.e. a ratio of external
coupling to internal resonator loss rate > 9) are demonstrated. Moreover we
find that different resonator modes can exchange power through the coupler,
which therefore constitutes a mechanism that induces modal coupling, a
phenomenon known to distort resonator dispersion properties. Our results
demonstrate the potential for significant performance improvements of
integrated planar microresonators, achievable by optimized coupler designs.Comment: 8 pages, 3 figures, 1 tabl
Photonic clocks, Raman lasers, and Biosensors on Silicon
Micro-resonators on silicon having Q factors as high as 500 million are described, and used to demonstrate radio-frequency mechanical oscillators, micro-Raman and parametric sources with sub-100 microwatt thresholds, visible sources, as well as high-sensitivity, biological detectors
Analysis of radiation-pressure induced mechanical oscillation of an optical microcavity
The theoretical work of V.B. Braginsky predicted that radiation pressure can
couple the mechanical, mirror-eigenmodes of a Fabry-Perot resonator to it's
optical modes, leading to a parametric oscillation instability. This regime is
characterized by regenerative mechanical oscillation of the mechanical mirror
eigenmodes. We have recently observed the excitation of mechanical modes in an
ultra-high-Q optical microcavity. Here, we present a detailed experimental
analysis of this effect and demonstrate that radiation pressure is the
excitation mechanism of the observed mechanical oscillations
Large second harmonic generation enhancement in SiN waveguides by all-optically induced quasi phase matching
Integrated waveguides exhibiting efficient second-order nonlinearities are
crucial to obtain compact and low power optical signal processing devices.
Silicon nitride (SiN) has shown second harmonic generation (SHG) capabilities
in resonant structures and single-pass devices leveraging intermodal phase
matching, which is defined by waveguide design. Lithium niobate allows
compensating for the phase mismatch using periodically poled waveguides,
however the latter are not reconfigurable and remain difficult to integrate
with SiN or silicon (Si) circuits. Here we show the all-optical enhancement of
SHG in SiN waveguides by more than 30 dB. We demonstrate that a Watt-level
laser causes a periodic modification of the waveguide second-order
susceptibility. The resulting second order nonlinear grating has a periodicity
allowing for quasi phase matching (QPM) between the pump and SH mode. Moreover,
changing the pump wavelength or polarization updates the period, relaxing phase
matching constraints imposed by the waveguide geometry. We show that the
grating is long term inscribed in the waveguides, and we estimate a second
order nonlinearity of the order of 0.3 pm/V, while a maximum conversion
efficiency (CE) of 1.8x10-6 W-1 cm-2 is reached
Probing the loss origins of ultra-smooth integrated photonic waveguides
On-chip optical waveguides with low propagation losses and precisely
engineered group velocity dispersion (GVD) are important to nonlinear photonic
devices such as soliton microcombs. Yet, despite intensive research efforts,
nonlinear integrated photonic platforms still feature propagation losses orders
of magnitude higher than in standard optical fiber. The tight confinement and
high index contrast of integrated waveguides make them highly susceptible to
fabrication induced surface roughness. Therefore, microresonators with
ultra-high Q factors are, to date, only attainable in polished bulk
crystalline, or chemically etched silica based devices, that pose however
challenges for full photonic integration. Here, we demonstrate the fabrication
of silicon nitride () waveguides with unprecedentedly smooth
sidewalls and tight confinement with record low propagation losses. This is
achieved by combining the photonic Damascene process with a novel reflow
process, which reduces etching roughness, while sufficiently preserving
dimensional accuracy. This leads to previously unattainable \emph{mean}
microresonator Q factors larger than for tightly confining
waveguides with anomalous dispersion. Via systematic process step variation and
two independent characterization techniques we differentiate the scattering and
absorption loss contributions, and reveal metal impurity related absorption to
be an important loss origin. Although such impurities are known to limit
optical fibers, this is the first time they are identified, and play a tangible
role, in absorption of integrated microresonators. Taken together, our work
provides new insights in the origins of propagation losses in
waveguides and provides the technological basis for
integrated nonlinear photonics in the ultra-high Q regime
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