10 research outputs found
Elastic Wave Eigenmode Solver for Acoustic Waveguides
A numerical solver for the elastic wave eigenmodes in acoustic waveguides of
inhomogeneous cross-section is presented. Operating under the assumptions of
linear, isotropic materials, it utilizes a finite-difference method on a
staggered grid to solve for the acoustic eigenmodes of the vector-field elastic
wave equation. Free, fixed, symmetry, and anti-symmetry boundary conditions are
implemented, enabling efficient simulation of acoustic structures with
geometrical symmetries and terminations. Perfectly matched layers are also
implemented, allowing for the simulation of radiative (leaky) modes. The method
is analogous to eigenmode solvers ubiquitously employed in electromagnetics to
find waveguide modes, and enables design of acoustic waveguides as well as
seamless integration with electromagnetic solvers for optomechanical device
design. The accuracy of the solver is demonstrated by calculating
eigenfrequencies and mode shapes for common acoustic modes in several simple
geometries and comparing the results to analytical solutions where available or
to numerical solvers based on more computationally expensive methods
Integrated optical isolators using electrically driven acoustic waves
We propose and investigate the performance of integrated photonic isolators
based on non-reciprocal mode conversion facilitated by unidirectional,
traveling acoustic waves. A triply-guided waveguide system on-chip, comprising
two optical modes and an electrically-driven acoustic mode, facilitates the
non-reciprocal mode conversion and is combined with modal filters to create the
isolator. The co-guided and co-traveling arrangement enables isolation with no
additional optical loss, without magnetic-optic materials, and low power
consumption. The approach is theoretically evaluated and simulations predict
over 20 dB of isolation and 2.6 dB of insertion loss with 370 GHz optical
bandwidth and a 1 cm device length. The isolator utilizes only 1 mW of
electrical drive power, an improvement of 1-3 orders of magnitude over the
state-of-the-art. The electronic driving and lack of magneto-optic materials
suggest the potential for straightforward integration with the drive circuitry,
possibly in monolithic CMOS technology, enabling a fully contained `black box'
optical isolator with two optical ports and DC electrical power.Comment: 14 pages, 5 figures, 1 table. Relies on an acoustic-optical
multiplexer introduced in arXiv:2007.11520, which has been separated out in
this updated version of the paper for clarity. Additionally, this updated
version included additional discussion of design considerations of the
isolato
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Vernier optical phased array lidar transceivers
Optical phased arrays (OPAs) which beam-steer in two dimensions (2D) are currently limited to grating row spacings well above a half wavelength. This gives rise to grating lobes along one axis which limit the field of view (FOV), introduce return signal ambiguity, and reduce the optical efficiency in lidar applications. We demonstrate a Vernier transceiver scheme which uses paired transmit and receive phased arrays with different row periodicities, leading to mismatched grating lobe angular spacings and only a single aligned pair of transmit and receive lobes. This permits a return signal from a target in the desired lobe to be efficiently coupled back into the receive OPA while back-scatter from the other grating lobes is rejected, removing the ambiguity. Our proposal goes beyond previously considered Vernier schemes in other domains like RF and sound, to enable a dynamic Vernier where all beam directions are simultaneously Vernier aligned, and allow ultra-fast scanning, or multi-beam, operation with Vernier lobe suppression. We analyze two variants of grating lobe suppressing beam-steering configurations, one of which eliminates the FOV limitation, and find the conditions for optimal lobe suppression. We present the first, to the best of our knowledge, experimental demonstration of an OPA Vernier transceiver, including grating lobe suppression of 6.4 dB and beam steering across 5.5°. The demonstration is based on a pair of 2D-wavelength-steered serpentine OPAs. These results address the pervasive issue of grating lobes in integrated photonic lidar schemes, opening the way to larger FOVs and reduced complexity 2D beam-steering designs.
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Low-cost solar simulator design for multi-junction solar cells in space applications
Multi-junction solar cells are commonly used in space applications where they are exposed to the air mass 0 (AM0) spectrum. Solar simulators are used to emulate the AM0 spectrum for ground testing of the solar cells before the space application is launched. A low-cost solar simulator was designed using LEDs for the visible spectrum and halogen lamps for the infrared spectrum. A design procedure is provided to determine the intensity and geometry of the lights needed to meet spectral match and spatial uniformity requirements. The presented solar simulator design is adequate for testing GaInP2/GaAs/Ge triple-junction solar cells intended for use in a cube satellite application and has a significantly lower cost than commercially-available solar simulators