ABSTRACT
This article discusses combination of tetragonal crystals with LiTaO3 (LT) thin plate for complete transverse resonance suppression of surface acoustic wave (SAW) devices without k2 deterioration by manipulating the slowness shape. Besides, better lateral energy confinement is achieved as well by the use of a double bus-bar structure. First, the mechanism of slowness shape manipulation by combining tetragonal crystals is studied. By comparison, YZ-lithium tetraborate (LBO) shows better performance than 69°Y90°X quartz. Then, numerical simulations are carried out using a periodic 3-D finite method assisted by a hierarchical cascading technique (HCT), and the effectiveness of transverse mode suppression by flattening the slowness shape is revealed. Also, the possibility to realize temperature compensation (TC) is discussed owing to the unique material property of LBO. Moreover, the capability of other tetragonal crystals for slowness manipulation is compared, and LBO is the best choice among these tetragonal crystals.
ABSTRACT
This article describes a new transverse edge structure with double busbar for surface acoustic wave (SAW) devices employing a 42°YX-lithium tantalate thin plate such as incredible high-performance (I.H.P.) SAW. This design offers good energy confinement and scattering loss suppression for a wide frequency range. First, preexisting transverse edge designs are reviewed, and their difficulties are pointed out using the dispersion relation for lateral SAW propagation. Then, numerical simulations are performed using the periodic 3-D finite-element method (FEM) powered by the hierarchical cascading technique, and effectiveness of the proposed structure is revealed. In addition, we also provide a possible solution to expand the frequency range giving well energy confinement and demonstrate effectiveness of manipulating the SAW slowness curve shape for transverse mode suppression.
ABSTRACT
Low-loss photonic crystal (PC) mirrors exhibit positive and negative Goos-Hänchen shift (GHS) due to the strong angular and wavelength dependencies of their reflected phase. This Letter demonstrates the existence of large positive and negative GHS in PC mirrors through theoretical, numerical, and experimental approaches. A simple algebraic relation shows that positive effective thickness yields positive (negative) GHS for resonances that blue (red) shift with angle, while the opposite is true for interfaces with negative effective thickness. Spatiotemporal coupled-mode theory demonstrates the above relation for simple systems with one or two resonance modes, and it also shows the existence of both positive and negative GHS. These effects are numerically and experimentally verified in complex PCs with several resonance modes.
ABSTRACT
Single-crystal silicon is an excellent optical and mechanical material, but its properties are compromised by the incorporation of other materials required for functionality or structural support. Here we describe a monolithic silicon acoustic sensor based on a sensing diaphragm with an integrated Photonic Crystal (PC) mirror. Diaphragm deflection is measured in a Fabry-Perot resonator formed between the PC mirror and a gold coated single-mode fiber. The sensors are fabricated on standard silicon wafers by standard CMOS processing technologies, yielding monolithic, low-stress sensing diaphragms. The packaged sensor exhibits a minimum detectable pressure of 10 µ Pa / Hz in the 8 kHz to 17 kHz frequency range.
ABSTRACT
Resonant mirrors introduce large spectral gradients in reflected phase while maintaining high reflectivity, allowing synthesis of optimized reflected phase for many practical applications. In this paper we show theoretically that asymmetry is required for negative group delay in lossless mirrors and explore the limits of reflected phase in resonant mirrors through the use of coupled mode theory and rigorous couple wave analysis. Our coupled mode theory shows that the phase response of resonant mirrors is determined by interacting resonances and gives insight into tradeoffs in design of mirrors with desired phase response.
Subject(s)
Computer-Aided Design , Lenses , Light , Refractometry/instrumentation , Scattering, Radiation , Equipment DesignABSTRACT
Fabry-Perot cavities made with photonic crystal (PC) mirrors and other resonant structures exhibit nontraditional characteristics due to the strong wavelength dependence of their reflected phase. This Letter describes how engineering the phase of PC mirrors enables sensors that are tolerant to variations in laser center frequency and line width. Reflection spectra measurements of Fabry-Perot cavities made with PC mirrors were collected as a function of wavelength and cavity length, providing experimental verification of theory and simulations.
