Achieving Subdiffraction Imaging through Bound Surface States in Negative Refraction Photonic Crystals in the Near-Infrared Range

Abstract

We report the observation of imaging beyond the diffraction limit due to bound surface states in negative refraction photonic crystals. We achieve an effective negative index figure of merit [ ÿ Ren=Imn] of at least 380, 125 improvement over recent efforts in the near-infrared range, with a 0.4 THz bandwidth. Supported by numerical and theoretical analyses, the observed near-field resolution is 0:47, clearly smaller than the diffraction limit of 0:61. Importantly, we show this subdiffraction imaging is due to the resonant excitation of surface slab modes. DOI: 10.1103/PhysRevLett.100.187401 PACS numbers: 78.20.Ci, 41.20.Jb, 42.70.Qs, 78.67.ÿn Recently, it has been suggested theoretically that a lefthanded metamaterial (LHM) lens can recover evanescent waves and information in both propagating and evanescent fields can be reconstructed into a perfect image [1]. Metalbased left-handed metamaterials containing resonant metallic microstructures operating at optical frequencies have recently been demonstrated remarkably to possess negative refraction [2,3], negative magnetic permeability [4], and have even been introduced as superlenses [5]. Other approaches, such as materials with indefinite permittivity and permeability tensors [6], domain twin structures [7], and dielectric metamaterials in the midinfrared [8] and nearinfrared [9], also suggest interesting potential towards negative refraction. An alternative experimental approach is to use dielectric-based photonic crystals (PhCs) where optical losses are considerably smaller and whose dispersion properties can be engineered so that at specific frequencies, they possess negative refraction.While theoretical studies have predicted subwavelength imaging in PhC-based LHMs at optical and near-infrared frequencies [10,11], an experimental demonstration of this phenomenon at these frequencies is still critically lacking, primarily due to the significant challenges in device nanofabrication and measurements. Here, by using a twodimensional (2D) PhC slab, which emulates an effective negative refractive index over a specific frequency range, we achieve the first near-field observation of subdiffraction limit imaging at near-infrared frequencies in a photonic structure with a large negative index figure of merit (FOM) of at least 380. This FOM is about 125 improvement over recent experimental efforts [2] and more than 15 better than the best theoretical efforts [12]. Importantly, we also clearly observe, for the first time, that this subdiffraction limit imaging is due to resonant excitation of surface slab modes.The possibility of left-handed behavior of wave propagation in PhC is intimately related to the existence of photonic modes with negative phase index, i.e., modes for which Bloch wave vector k in the first Brillouin zone and the group velocity v g , defined as the gradient of the mode frequency !k, v g r k !k, are antiparallel, i.e., k v g < 0 [11,13]. In particular, negative refraction and subdiffraction limit imaging in such PhCs have been predicted theoreti...

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

“…Note that, for the second band, the effective index of refraction is negative because k decreases with v (ref. 23). …”

“…Metal-based NIMs [3][4][5][6][7][8][9][10][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.…”

Physics of the zero- photonic gap: fundamentals and latest developments

“…It is highly challenging even today to fabricate high-quality transparent LHMs at high frequencies, and the authors skillfully designed a PC with anomalous band structure to emulate an LHM [42] and then stack such PCs and positive-n dielectric materials to form a 1D superlattice. Actually, in 2006, Panoiu et al [43] already theoretically proposed the idea of combining normal PCs and negative-refraction PCs to realize a 1D superlattice exhibiting a zero-n -gap, but such an idea was only experimentally realized in 2009 [41] .…”

Guided resonance in negative index photonic crystals: a new approach

“…v0. [14][15][16][17][18]20,25,26 In this case, the photonic crystal behaves as a medium with an effective isotropic index n eff 521 for a wavelength of 1.55 mm. Experimental reflectivity spectra from the photonic crystal sample were obtained using a tunable CW diode laser (Ando AQ4321D) that emits monochromatic light with a maximum variable power of 5 mW and a wavelength varying between 1520 nm and 1620 nm.…”