Focusing of surface-acoustic-wave fields on (100) GaAs surfaces

Lima, M. M. de; Alsina, F.; Seidel, W.; Santos, P. V.

doi:10.1063/1.1625419

Cited by 70 publications

(50 citation statements)

References 29 publications

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“…The focusing IDTs were designed for an operation wavelength SAW = 5.6 m ͑corresponding to a resonance frequency of approximately 520 MHz͒ following the procedure discussed in detail in Ref. 8. These IDTs generate a SAW beam with full width at half maximum ᐉ Ϸ 15 m that are collimated over hundreds of microns.…”

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confidence: 99%

Compact Mach-Zehnder acousto-optic modulator

Lima

Beck

Hey

et al. 2006

Applied Physics Letters

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The authors demonstrate a compact optical waveguide modulator based on a Mach-Zehnder interferometer driven by surface acoustic waves. The modulator was monolithically fabricated on GaAs with an active region length of approximately 15 m. It yields peak-to-peak modulation exceeding 90% of the average transmission and operation in the gigahertz frequency range. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2354411͔ Acousto-optic effects have been used for optical modulation for a long time, with the Bragg cells being probably the best known example. 1 The demand for fast and compact devices together with required phase matching, however, imposes several limitations on conventional acousto-optic devices in future generations of integrated photonics. Therefore, great attention has recently been devoted to alternative concepts for light modulation. A promising approach to increase the operation speed employs all-optical light control, which allows operation down to the subpicosecond time scales. 2 These devices are typically a few hundreds of microns long since they rely on optical nonlinearities that are usually small. An effective approach to reduce device dimensions employs photonic crystals ͑PhCs͒. Examples are thermo-optical switches based on a PhC Mach-Zehnder interferometer ͑MZI͒ with 12-m-long arms on AlGaAs/ GaAs system 3 as well as electro-optical switches based on carrier injection of 80-m-long silicon PhC-MZI. 4 In both cases the switching time is on the order of microseconds. Faster PhC-based all-optical switching devices have been realized in the ͑Al,Ga͒As system by taking advantage of the nonlinear properties of quantum dots embedded in the MZI arms. 5 PhC fabrication, however, requires a sophisticated technology with very strict tolerances.In this letter, we demonstrate a compact and monolithic modulator based on conventional ridge waveguides ͑WGs͒ on GaAs. The modulator consists of a MZI driven by a surface acoustic wave ͑SAW͒ in the gigahertz range, where the length of the interaction region between the acoustic and optical waves ͑the active region͒ is reduced to approximately 15 m. The design used, which is a modified version of the acousto-optic MZI proposed by Gorecki et al.,6 is based on the refractive index modulation of the interferometer arms by the wave fronts of a SAW propagating perpendicularly to the arms. The changes in refractive index are induced by the elasto-optic and electro-optic effects associated with the strain and piezoelectric fields, respectively. For photon energies away from electronic transitions-which is the case discussed here-the elasto-optical effect dominates. 7 The width of the WGs forming the arms is chosen to be much smaller than the acoustic wavelength ͑ SAW ͒ in order to ensure a constant modulation amplitude across the WG width. In our design, we introduce two fundamental modifications to increase the modulation efficiency and reduce the length of the active region. First, we enhance the modulation efficiency by modulating simultaneously both interferom...

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confidence: 99%

Compact Mach-Zehnder acousto-optic modulator

Lima

Beck

Hey

et al. 2006

Applied Physics Letters

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“…16 In the focusing devices, the fingers are curved in order to produce a converging SAW beam. Further details about the focusing IDTs can be found in Ref.…”

Section: Methodsmentioning

confidence: 99%

“…As mentioned previously, these IDTs have curved fingers with a shape following curves of constant SAW group velocity. 16 Due to the acoustic anisotropy inherent of crystalline materials, the design of focusing IDTs relies on the precise knowledge of the dependence of the SAW properties on the propagation direction. 16 In SF IDTs, the latter also depends sensitively on the dimensions of the metal grating (Fig.…”

Section: Focusing Performancementioning

confidence: 99%

Embedded interdigital transducers for high-frequency surface acoustic waves on GaAs

Lima

Seidel

Kostial

et al. 2004

Journal of Applied Physics

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We investigate high-performance, high-frequency interdigital transducers (IDTs) for the generation of surface acoustic waves (SAWs) on GaAs substrates, where the metal fingers are embedded in the substrate. We demonstrate that the acoustic reflections and the scattering of the surface modes into the substrate become considerably reduced in these transducers, leading to an increased output power. The finger embedding process is particularly relevant for the generation of powerful beams of high-frequency SAWs on weak piezoelectric substrates (such as most of the semiconducting materials) using long IDTs. We also show that the reflection reduction is important for the design of focusing single-finger IDTs, since it minimizes the effects of the finger grating on the angular dependence of the phase velocity.

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“…There is a simple and direct relation between the slowness curve and the wave surface, v g ͑ ͒ = ͓s͑ ͒cos͑ ͔͒ −1 , with as the beam-steering angle and = + . 2,3 Accurate knowledge of the slowness curve is needed in the design of SAW devices, as illustrated by tailored interdigital transducers ͑IDTs͒ that can focus a SAW beam 4 or even create a subwavelength acoustic source. 5 Wickramasinghe and Ash 6 showed that SAW slowness curves can be measured using a phase sensitive laser probe.…”

Section: Materials Anisotropy Unveiled By Random Scattering Of Surfacementioning

confidence: 99%