Tunable transmission and harmonic generation in nonlinear metamaterials

Abstract

We study the properties of tunable nonlinear metamaterial operating at microwave frequencies. We fabricate the nonlinear metamaterial composed of double split-ring resonators and wires where a varactor diode is introduced into each resonator so that the magnetic resonance can be tuned dynamically by varying the input power. We show that at higher powers the transmission of the metamaterial becomes power-dependent,and we demonstrate experimentally power-dependent transmission properties and selective generation of higher harmonics.PACS numbers: 41.20.Jb, 42.25.Bs, Engineered microstructured metamaterials demonstrate many intriguing properties for the propagation of electromagnetic waves such as negative refraction. Such materials have been studied extensively during recent years [1]. Typically, such metamaterials are fabricated as composite structures created by many identical resonant scattering elements with the size much smaller than the wavelength of the propagating electromagnetic waves; such microstructured materials can be described in terms of macroscopic quantities-electric permittivity ǫ and magnetic permeability µ. By designing the individual unit cell of metamaterials, one may construct composites with effective properties not occurring in nature.Split-ring resonators (SRRs) are the key building blocks for the composite metamaterials, in particularly the materials having the negative refractive index [2]. Recent theoretical studies have demonstrated how to dynamically tune or modulate the electromagnetic properties of metamaterials [3,4,5,6,7,8] and the fabrication of nonlinear SRRs has been demonstrated by placing a varactor diode [9] or a photosensitive semiconductor [10] within the gap of the resonator. The diode allows the SRR element to be tuned by an applied dc voltage or by a high-power signal as was shown already in experiment [9,11]. These recent advances open a way for both fabrication and systematic study of nonlinear tunable metamaterials which may change their properties such as the transmission characteristics by varying the amplitude of the input electromagnetic field.It was shown theoretically that nonlinear metamaterials can demonstrate many intriguing features such as unconventional bistability [3,12], backward phase-matching and harmonic generation [13,14,15], as well as parametric shielding of electromagnetic fields [16]. Some of these features have already been experimentally observed in nonlinear left-handed transmission lines which are model systems allowing for combining nonlinearity and anomalous dispersion [17,18,19]. Moreover, first results on harmonic generation in infrared were reported in Ref. [20]. Importantly, in such composite structures the microscopic electric fields can become much higher than the macroscopic electric field carried by the propagating electromagnetic waves. This provides a simple physical mechanism for enhancing nonlinear effects in the resonant structure with the left-handed properties. Moreover, a very attractive goal is to create tunable metamater...

Nonlinear metamaterials: a new degree of freedom

“…7 We also observed intensity-suppressed transparency for frequencies just below the resonant frequency. The material is transparent for low-level signals but when we increase the power the frequency is shifted to the region of positive susceptibility and the material becomes opaque.…”

Resonant meta-atoms with nonlinearities on demand

“…2). It is worth noting that the intrinsic high-order nonlinearities of the varactor are comparable 12 , in contrast to the usual behavior of optical materials. Figure 4 summarizes the results for the near-to-near field transmission spectrum.…”

“…The varactor diode, having a highly nonlinear I-V response, generates the entire comb of nonlinear harmonics 12 . While the intrinsic generation efficiency of those harmonics depends on the internal structure of the varactor, auxiliary material structures can either enhance or suppress both near-and farfield signatures of the nonlinear microscopic currents by performing linear filtering.…”

“…On the other hand, the RF technology offers mature fabrication and characterization techniques, suggesting a more amenable scenario for investigating nonlinear elements in this spectral range. In particular, higher-harmonic generation in various designs, such as varactor diodes embedded in RF circuits, has been demonstrated 12 . Further control of nonlinear responses in coupled-resonator geometries was achieved via tuning their relative positions 13 .…”

Enhanced Nonlinearities in Double-Fishnet Negative-Index Photonic Metamaterials

“…It was predicted that nonlinear MMs (NMMs) could provide a way not just to adopte the nonlinearities of their constituent materials but also to enhance them by orders of magnitude [24,25]. A lot of research in NMMs have been done including demonstrations of frequency generation [26,27], parametric amplification [28,29], selfphase modulation and bistability [30,31]. However, so far there are no works on nonlinear optical properties of realistic structures with negative index, such as the fishnet structures.…”