31 research outputs found
Moving boundary and photoelastic coupling in GaAs optomechanical resonators
Chip-based cavity optomechanical systems are being considered for
applications in sensing, metrology, and quantum information science. Critical
to their development is an understanding of how the optical and mechanical
modes interact, quantified by the coupling rate . Here, we develop GaAs
optomechanical resonators and investigate the moving dielectric boundary and
photoelastic contributions to . First, we consider coupling between the
fundamental radial breathing mechanical mode and a 1550 nm band optical
whispering gallery mode in microdisks. For decreasing disk radius from
m to m, simulations and measurements show that changes
from being dominated by the moving boundary contribution to having an equal
photoelastic contribution. Next, we design and demonstrate nanobeam
optomechanical crystals in which a GHz mechanical breathing mode couples
to a 1550 nm optical mode predominantly through the photoelastic effect. We
show a significant (30 ) dependence of on the device's in-plane
orientation, resulting from the difference in GaAs photoelastic coefficients
along different crystalline axes, with fabricated devices exhibiting
as high as 1.1 MHz for orientation along the [110] axis.
GaAs nanobeam optomechanical crystals are a promising system which can combine
the demonstrated large optomechanical coupling strength with additional
functionality, such as piezoelectric actuation and incorporation of optical
gain media
Quantifying and mitigating optical surface loss in suspended GaAs photonic integrated circuits
Understanding and mitigating optical loss is critical to the development of
high-performance photonic integrated circuits (PICs). Especially in high
refractive index contrast compound semiconductor (III-V) PICs, surface
absorption and scattering can be a significant loss mechanism, and needs to be
suppressed. Here, we quantify the optical propagation loss due to surface state
absorption in a suspended GaAs photonic integrated circuits (PIC) platform,
probe its origins using X-ray photoemission spectroscopy (XPS) and
spectroscopic ellipsometry (SE), and show that it can be mitigated by surface
passivation using alumina (). We also explore potential routes
towards achieving passive device performance comparable to state-of-the-art
silicon PICsComment: 8 pages, 8 figures, Comments welcome !!! v2: fixed typo in equation
1, minor edits in tex
Tuning and Stabilization of Optomechanical Crystal Cavities Through NEMS Integration
Nanobeam optomechanical crystals, in which localized GHz frequency mechanical
modes are coupled to wavelength-scale optical modes, are being employed in a
variety of experiments across different material platforms. Here, we
demonstrate the electrostatic tuning and stabilization of such devices, by
integrating a SiN slot-mode optomechanical crystal cavity with a
nanoelectromechanical systems (NEMS) element, which controls the displacement
of an additional "tuning" beam within the optical near-field of the
optomechanical cavity. Under DC operation, tuning of the optical cavity
wavelength across several optical linewidths with little degradation of the
optical quality factor () is observed. The AC response of the
tuning mechanism is measured, revealing actuator resonance frequencies in the
10 MHz to 20 MHz range, consistent with the predictions from simulations.
Feedback control of the optical mode resonance frequency is demonstrated, and
alternative actuator geometries are presented
Acousto-optic and opto-acoustic modulation in piezo-optomechanical circuits
Acoustic wave devices provide a promising chip-scale platform for efficiently
coupling radio frequency (RF) and optical fields. Here, we use an integrated
piezo-optomechanical circuit platform that exploits both the piezoelectric and
photoelastic coupling mechanisms to link 2.4 GHz RF waves to 194 THz (1550 nm)
optical waves, through coupling to propagating and localized 2.4 GHz acoustic
waves. We demonstrate acousto-optic modulation, resonant in both the optical
and mechanical domains, in which waveforms encoded on the RF carrier are mapped
to the optical field. We also show opto-acoustic modulation, in which the
application of optical pulses gates the transmission of propagating acoustic
waves. The time-domain characteristics of this system under both pulsed RF and
pulsed optical excitation are considered in the context of the different
physical pathways involved in driving the acoustic waves, and modeled through
the coupled mode equations of cavity optomechanics.Comment: 8 pages, 6 figure
Waveguide integrated GaN distributed Bragg reflector cavity using low-cost nanolithography
This work presents the design, fabrication and measurement of gallium nitride (GaN) distributed Bragg reflector cavities integrated with input and output grating couplers. The devices are fabricated using a new, low-cost nanolithography technique: displacement Talbot lithography combined with direct laser writing lithography. The finite-difference time-domain method has been used to design all the components and measured and modelled results show good agreement. Such devices have applications in GaN integrated photonics and biosensing.</p
Coherent coupling between radio frequency, optical, and acoustic waves in piezo-optomechanical circuits
The interaction of optical and mechanical modes in nanoscale optomechanical
systems has been widely studied for applications ranging from sensing to
quantum information science. Here, we develop a platform for cavity
optomechanical circuits in which localized and interacting 1550 nm photons and
2.4 GHz phonons are combined with photonic and phononic waveguides. Working in
GaAs facilitates manipulation of the localized mechanical mode either with a
radio frequency field through the piezo-electric effect, or optically through
the strong photoelastic effect. We use this to demonstrate a novel acoustic
wave interference effect, analogous to coherent population trapping in atomic
systems, in which the coherent mechanical motion induced by the electrical
drive can be completely cancelled out by the optically-driven motion. The
ability to manipulate cavity optomechanical systems with equal facility through
either photonic or phononic channels enables new device and system
architectures for signal transduction between the optical, electrical, and
mechanical domains
High frequency guided mode resonances in mass-loaded, thin film gallium nitride surface acoustic wave devices
We demonstrate high-frequency (> 3 GHz), high quality factor radio frequency
(RF) resonators in unreleased thin film gallium nitride (GaN) on sapphire and
silicon carbide substrates by exploiting acoustic guided mode (Lamb wave)
resonances. The associated energy trapping, due to mass loading from the gold
electrodes, allows us to efficiently excite these resonances from a 50
input. The higher phase velocity, combined with lower electrode damping,
enables high quality factors with moderate electrode pitch, and provides a
viable route towards high-frequency piezoelectric devices. The GaN platform,
with its ability to guide and localize high-frequency sound on the surface of a
chip with access to high-performance active devices, will serve as a key
building block for monolithically integrated RF front-ends.Comment: 5 pages, Submitted for revie