Phonon propagation dynamics in band-engineered one-dimensional phononic crystal waveguides

Abstract

The phonon propagation dynamics in a phononic crystal waveguide, realized via a suspended onedimensional membrane array with periodic air holes, is investigated as function of its geometry. The bandstructure of the phononic crystal waveguide can be engineered by modifying the characteristics of the phonon waves by varying the waveguide width and the pitch of the air holes. This enables the phonon transmission bands, the bandgaps, the velocity and the nonlinear dispersion in the phononic crystal to be controlled. Indeed the engineered bandstructure can even be tuned to sustain multiple phonon modes in a given branch which while being spectrally degenerate can be temporally resolved via their differing group velocities. Furthermore, the ability to tune the bandstructure and thus the nonlinear dispersion can be harnessed to efficiently activate nonlinear phenomena such as mechanical four wave mixing. This systematic study reveals the key geometric parameters that enable the phonon transport in phononic crystal waveguides to be fully controlled.

Broadband reconfigurable logic gates in phonon waveguides

“…The phonon WG, shown in Fig. 1(a) , consists of a one-dimensional array of coupled membrane mechanical resonators made from a GaAs/AlGaAs heterostructure 12 , 31 . Periodically arrayed air-holes are defined on the 1-mm long WG which are used to suspend the membranes as described in Methods.…”

“…1(b) where equidistant peaks from Fabry-Perot (FP) resonances can also be seen. Although the existence of the periodic air-holes can give rise to a phonon bandgap around 6.5 MHz in this device, the existence of another phonon branch at this frequency obscures it in the spectral domain thus permitting a continuous band of mechanical vibrations over two-octaves wide to be accessed (see Supplementary Note 1 ) 31 .…”

“…Here we demonstrate the above concepts using a phonon waveguide (WG) which is composed from an array of vibrating membranes that are strongly coupled and it results in their individual resonances merging to give rise to a broadband transmission band 12 , 31 . The broad transmission band can still host elastic nonlinearities such as third-order nonlinear effect corresponding to a cubic term of the mechanical vibration amplitude, which can be activated due to the strongly confined vibrations within the membrane array and by exciting the WG from the highly efficient piezoelectric transducers that are integrated directly into the membranes.…”

On-chip temporal focusing of elastic waves in a phononic crystal waveguide

“…In this study, by introducing the approach in the field of phononics, we demonstrate on-chip temporal pulse manipulation in a one-dimensional (1D) phononic crystal waveguide (PnC WG) 13 , 14 which is constructed by using nanoelectromechanical systems (NEMS) technology. Ultrasonic waves traveling through the WG experience pulse broadening due to the group velocity dispersion (GVD) effect.…”

Mechanical Kerr Nonlinearity of Wave Propagation in an On-Chip Nanoelectromechanical Waveguide

“…This hosts its excellent properties, such as engineerable dispersion, low propagation loss, design flexibility and semiconductor-based integration. Thus, this architecture has enabled the demonstration of electrical phonon manipulation, energy focusing by dispersion, and the active manipulation of phononic band structures on a chip [19][20][21][22] .…”