Zero phase delay in negative-refractive-index photonic crystal superlattices

Abstract

We show that optical beams propagating in path-averaged zero-index photonic crystal superlattices can have zero phase delay. The nanofabricated superlattices consist of alternating stacks of negative index photonic crystals and positive index homogeneous dielectric media, where the phase differences corresponding to consecutive primary unit cells are measured with integrated Mach-Zehnder interferometers. These measurements demonstrate that at path-averaged zero-index frequencies the phase accumulation remains constant and equal to zero despite the increase in the physical path length. We further demonstrate experimentally that these superlattice zero-n bandgaps remain invariant to geometrical changes of the photonic structure and have a center frequency which is deterministically tunable. The properties of the zero-n gap frequencies, optical phase, and effective refractive indices are well described by detailed experimental measurements, rigorous theoretical analysis, and comprehensive numerical simulations.A n intense degree of interest in negative-index metamaterials (NIMs) 1,2 has developed in recent years. Metal-based NIMs 3-11 have been actively studied because of their unusual physical properties and their potential for use in many technological applications [12][13][14][15][16][17][18][19][20][21][22] ; however, they usually have the disadvantage of demonstrating large optical losses in their metallic components. As an alternative to metal-based NIMs, dielectricbased photonic crystals (PhCs) have been investigated and shown to emulate the basic physical properties of NIMs [23][24][25][26][27] , while also having relatively small absorption losses at optical frequencies. Equally important, PhCs can be nanofabricated within current silicon foundries, suggesting significant potential for the development of future electronic-photonic integrated circuits.One particular type of PhC can be obtained by cascading alternating layers of NIMs and positive-index materials (PIMs) [28][29][30][31][32] . This photonic structure ( Fig. 1) has unique optical properties, including new surface states and gap solitons 33,34 , unusual transmission and emission properties [35][36][37][38][39] , complete photonic bandgaps 40 , and a phase-invariant field for cloaking applications 41 . Moreover, these binary photonic structures have an omnidirectional bandgap that is insensitive to wave polarization, incidence angle, structure periodicity and structural disorder [42][43][44] . Such a gap exists because the path-averaged refractive index is equal to zero within a certain frequency band [28][29][30][31][32]35 . At this frequency, the Bragg condition, kL ¼ (nv/c)L ¼ mp, is satisfied for m ¼ 0, irrespective of the period L of the superlattice (k and v are the wave vector and frequency, respectively, and n is the averaged refractive index). Because of this property this photonic bandgap is called zero-n, or zero-order bandgap 30,35 .Near-zero-index materials have a series of exciting potential applications, such as beam self-coll...

Double Dirac cones in phononic crystals

“…Around the double Dirac point frequency, we reveal that a slab of our acoustic system can be mapped onto an acoustic zero-index medium (ZIM) by using a standard retrieval method. ZIMs [23][24][25][26][27][28][29][30][31][32] have spectacular applications, such as beam self-collimation, energy squeezing, and tunneling. Here, we demonstrate with two examples the interesting wave transport behaviors in our systems.…”

Enhanced the Complete Photonic Band Gaps for Three-Dimensional Photonic Crystals Consisting of Epsilon-Negative Materials in Pyrochlore Arrangement

“…To overcome these drawbacks, researchers have to introduce metamaterials into the PCs to obtained tunable PBGs [14] and zero-n PBGs [15]. Obviously, the zero-refractive indices can be obtained by metamaterials [16,17]. Metamaterials are firstly proposed by Veselago in 1967 [18], and can exhibit a negative index of refraction in some frequency ranges.…”

Negative Index Photonic Crystals Superlattices and Zero Phase Delay Lines"

“…Specifically, at this frequency the Bragg condition, k = ( n ω/c) = mπ, is satisfied for m = 0, irrespective of the period  of the superlattice; here, k and  are the wave vector and frequency, respectively, and n is the averaged refractive index. Because of this property this photonic bandgap is called zero-n , or zero-order, bandgap [30,34]. Near-zero index materials have a series of exciting potential applications, such as diffraction-free beam propagation over thousands of wavelengths via beam self-collimation [34], extremely convergent lenses and control of spontaneous emission [35], strong field enhancement in thin-film layered structures [37], and cloaking devices [40].…”