Excitation of coupled phononic frequency combs via two-mode parametric three-wave mixing

Abstract

This paper builds on the recent demonstration of three-wave mixing based phononic frequency comb. Here, in this process, an intrinsic coupling between the drive and resonant frequency leads to a frequency comb of spacing corresponding to the separation between drive and resonant frequency. Now, in this paper, we experimentally demonstrate the possibility to further excite multiple frequency combs with the same external drive through its coupling with other identical devices. In addition, we also experimentally identify interesting features associated with such a frequency comb generation process.This paper builds upon the recent experimental demonstration of the phononic counterpart of optical frequency combs in a micromechanical vibratory device [1]. The generation of these phononic frequency combs is described by a nonlinear three-wave mixing process as theoretically outlined in [2]. Through this pathway, a single drive tone results in the equidistant and phasecoherent spectral lines corresponding to the frequency comb and the spacing of such a frequency comb corresponds to the separation between the drive and resonant frequency. In this paper, we experimentally demonstrate the excitation of frequency combs of two different characteristic spacing utilizing a single drive tone.For this demonstration, we consider an experimental system of two-coupled Si-based micromechanical free-free beam structures of dimensions 1100 X 350 X 11 . The mechanical coupler has dimensions 20 X 2 X 11 beam ( Figure 1A). The device also consists of the 0.5 thick AlN and 1 thick Al layers above the Si surface for its piezoelectric actuation. To preserve the uniformity, the AlN and Al patterns of the two free-free beam microstructures are identical. The signal derived from Agilent 335ARB1U is applied on the device through the Al electrodes and the resulting electrical response corresponding to the mechanical motion of the device is probed using Agilent infiniium 54830B DSO. For the independent validation, the resonant motion of the device is also monitored using Laser Doppler Vibrometer (LDV). Figure 1B shows the output spectrum when an electrical signal of ( = 3.86 ) = 23 is applied. In this figure, there exists two thick spectral features closer to and 2 . The zoomed-in views indicate the correspondence of these features to the frequency combs. To explore these frequency combs further, the experiments were carried out at wide-ranging drive power levels for

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