Wide-angle reflection-mode spatial filtering and splitting with photonic crystal gratings and single-layer rod gratings

Abstract

New diffractive optical elements offering a frequency tolerant, very efficient, high-pass and bandpass spatial filtering over a broad range of incidence angles are demonstrated by numerical simulations. The device operates in reflection mode owing to the (nearly) perfect blazing. It relies on two-dimensional square-lattice photonic crystals composed of dielectric rods with simple corrugations at the interface. Similar performance can be obtained with gratings composed of a single rod layer placed in the near field of a metal mirror, indicating a route to geometries that can be easily fabricated with modern nanotechnologies. Also equal splitting between zero and first negative orders can be obtained for incidence-angle variations that are wider than 60°. The known mechanisms of spatial filtering include those using [2][3][4][5] or not using [1,8] specific dispersion features. The former can give more freedom in design, because the required features can remain within rather wide ranges of variation in frequency and/or angle of incidence. For instance, low-pass spatial filtering can be obtained by using isotropic-type dispersion, which corresponds to refractive index 0 < n < 1 [14]. In turn, highpass and bandpass filtering requires anisotropic-type dispersion. Generally, that can be achieved by using anticutoff media [2], which is often associated with hyperbolic metamaterials [15] or PhCs with the corresponding dispersion type that enables blocking transmission in the vicinity of zero tangential wavenumber [3][4][5]. The problem usually appears regarding the possibility of obtaining the same, desirably perfect, i.e., 100% efficiency within the entire wide pass and stop angular bands of transmission [9][10][11]. High-pass spatial filtering that matches this condition has been demonstrated in transmission mode in a slab of the two-dimensional, squarelattice PhC [3]. For operation in reflection mode, high-pass and bandpass spatial filters offering high efficiencies over broad angle intervals are required but have not been demonstrated yet. It is worth noting that designing spatial filters in reflection mode is much more difficult. In transmission, zero-order gratings may be used to redistribute the incident energy between two channels, the zero reflected and transmitted orders. In contrast, redistribution between zero and one of higher orders is required in a pure reflection mode. Hence, reflection mode spatial filtering is closely related to the blazing that is a classical problem of diffraction gratings.The blazing effect is probably the most important property of diffraction gratings. The structures enabling it have been studied in both frequency and incidence angle domains. Blazing at a single wavelength for a specific angle of incidence has been obtained in various structures. The difficulty arises when it should be performed over a broad spectral [16] or incidence angle [17] interval. The studies related to splitting [18] and the Littrow mount regime [19] should be mentioned in this concern. However, the earlie...

Temperature-mediated invocation of the vacuum state for switchable ultrawide-angle and broadband deflection

“…For the purpose of demonstration, we restrict our theoretical consideration to the effect of nearly perfect deflection (blaze) in the reflection mode, in very wide ranges of the frequency and the incidence angle 17 , 18 , these ranges being wider than those realizable from most of other known approaches to angular filtering 19 – 21 . The geometry of the chosen structure is similar to that suggested in ref.…”

Single–Band and Multiband Angular Filtering Using Two–Dimensional Photonic Crystals and One–Layer Gratings

“…In Ref. [34], it has been shown that efficient bandpass filtering with a sharp switching between the orders m D 0 and m D 1 can be obtained in reflection mode in rod-type PhC gratings created by introducing corrugations on a non-corrugated slab of PhC, like that in Fig. 23.3, inset, and relevant single-layer rod gratings backed with a metallic reflector.…”

“…In contrast with Ref. [34], the rods are assumed now to be square-shaped and located on a low-permittivity substrate. Figure 23.8c shows how out is changed depending on whether the order m D 0 is only one propagating order or the order m D 1 also may propagate and, moreover, all energy is transferred into this order.…”

Translationally invariant metamirrors for spatial filtering of light beams

“…These alternative methods, however, did not result in broad practical applications, for their low efficiency, and for inconveniences due to their relatively large size and precise alignment requirements. An alternative method for spatial filtering based on the photonic crystals (PhCs) was recently proposed and developed [5][6][7][8][9][10][11][12][13]. The method was first demonstrated in a single transmission scheme, later was applied for intracavity filtering arrangements in microchip [14] and semiconductor [15] microlasers, and increased the brightness of the radiation increased several times.…”