Phononic crystals (PnCs) are one of the most promising candidates for controlling phonon propagation [1]. The periodically modulated elastic structure of the PnC can sustain a phonon bandgap that enables the transmission of phonons such as sound, mechanical vibration, and even heat to be spatially controlled. This ability to control phonons has led to the concept of a novel phononic system in which information signals encoded in phonons can be processed. The key challenge to realizing this tantalizing prospect is the dynamic control of the phonons in the PnC, whereas to date, almost all PnC devices reported have been passive structures. To overcome this limitation, we have developed a unique class of PnCs via electromechanical resonators and have demonstrated dynamically controlled phonon vibrations [2].
The PnC waveguide (WG) consists of a one-dimensional array of GaAs/AlGaAs-based membrane resonators as shown in Fig. 1(a) which are suspended via the periodically arranged air-holes. At the center of the WG, a control mechanical resonator is created by increasing the air-hole separation to the adjacent membranes. Applying an alternating voltage with 5.74 MHz to the electrode on the right edge membrane can piezoelectrically excite phonon waves which travel down to the WG through the control mechanical resonator and are optically measured at the left edge membrane [dashed line in Fig. 1(b)]. Simultaneously, the control mechanical resonator is excited at 1.86 MHz which generates a localized phonon vibration. The strongly confined phonons in the control mechanical resonator induce a nonlinear elastic effect that causes the WG’s transmission spectrum to shift to higher frequencies, resulting in the suppression of the phonons at 5.74 MHz [solid line in Fig. 1(b)].
The electromechanical resonator based PnC WG permits the phonon transmission to be dynamically controlled which opens up the possibility of developing highly functional signal processing systems utilizing mobile phonons.
This work was supported by KAKENHI.
