Using metallic photonic crystals as visible light sources

In this paper we study numerically and experimentally the possibility of using metallic photonic crystals (PC's) of different geometries (log-piles, direct and inverse opals) as visible light sources. It is found that by tuning geometrical parameters of a direct opal PC one can achieve substantial reduction of the emissivity in the infrared along with its increase in the visible. We take into account disorder of the PC elements in their sizes and positions, and we get quantitative agreement between the numerical and experimental results. We analyze the influence of known temperature-resistant refractory host materials necessary for fixing the PC elements, and we find that PC effects become completely destroyed at high temperatures due to the host absorption. Therefore, creating PC-based visible light sources requires that low-absorbing refractory materials for the embedding medium be found.

Figure 1

Normal-incidence reflection and absorption spectra of a log pile with number of layers $N=4$, rod spacing $a=4.2\mu \text{m}$, rod width $w=1.2\mu \text{m}$, and rod height $h=2.4\mu \text{m}$. A high-reflectance region at $\lambda >8\mu \text{m}$ corresponds to the IR band gap. A sharp peak appears at the IR band-gap edge. Inset: Scheme of the FDTD simulation geometry: 1, generating (total-field/scattered-field) border; 2 and $2^{\prime }$, detector arrays for reflected and transmitted signals.

Figure 2

Normal-incidence reflection (1) and absorption (2) spectra of a tungsten log pile at $T=2400$ K with $N=4$, $a=0.5\mu \text{m}$, $w=0.2\mu \text{m}$, and $h=0.2\mu \text{m}$. The reflection for the perfect metal PC (3) is shown for reference.

Figure 3

Normal-incidence absorption spectra of a tungsten log pile at $T=2400$ K with $N=4$, $a=0.5\mu \text{m}$, $h=0.2\mu \text{m}$, and varying $w$.

Figure 4

Normal-incidence transmission spectra of a perfect metal log pile with $N=4$, $a=0.5\mu \text{m}$, $h=0.2\mu \text{m}$, and varying $w$.

Figure 5

The absorption spectra of direct and inverse fcc opals at normal incidence and varying filling fraction $f$. The lattice period $a=0.45$ $\mu \text{m}$, number of layers $N=2$, and $T=2400$ K. The host medium is a vacuum.

Figure 6

The absorption spectra of PC at normal incidence for varying lattice constant $a$ and $R=0.156a$. $N=2$ and $T=2400$ K.

Figure 7

The absorption spectra of PC's at different angles of incidence $\theta$ of an $s$-polarized wave. $a=0.45$ $\mu \text{m}$, $R=0.07$ $\mu \text{m}$, $N=2$, and $T=2400$ K. The plane of incidence is determined by a normal to the layer and a 2D lattice primitive vector.

Figure 8

The absorption spectra of PC's at normal incidence and varying sphere radius $R$. $a=0.45$ $\mu \text{m}$, $N=2$, and $T=2400$ K.

Figure 9

The absorption spectra of PC at normal incidence and varying number of layers $N$. $a=0.45$ $\mu \text{m}$, $R=0.07$ $\mu \text{m}$, and $T=2400$ K.

Figure 10

The top view of the PC sample with the triangular lattice period $a=0.55$ $\mu \text{m}$.

Figure 11

The side view of the PC sample with the triangular lattice period $a=0.55$ $\mu \text{m}$.

Figure 12

The tungsten PC monolayer absorption spectrum at normal incidence at room temperature ($T=298$ K). The PC parameters are $a=0.55$ $\mu \text{m}$, sphere segment radius $0.1$ $\mu \text{m}$, and height $0.02$ $\mu \text{m}$. The plotted curves correspond to measurement, calculation for the perfect opal monolayer with $R=0.1$ $\mu \text{m}$, and calculation for the PC with the caps-on-posts geometry of elements. The perfectly periodic lattice is assumed in calculations.

Figure 13

The tungsten PC monolayer absorption spectrum at normal incidence at room temperature ($T=298$ K). The PC parameters are $a=0.55$ $\mu \text{m}$, sphere segment radius $0.1$ $\mu \text{m}$, and height $0.02$ $\mu \text{m}$. Comparison of the measured spectrum to the calculation is made with both the size dispersion and the lattice disorder taken into account: results for the varying lattice disorder parameter ${\rho }_{\max }$ are presented (see text).

Figure 14

The absorption spectra of the two-layer PC at normal incidence ($T=2400$) K: 1, PC embedded in hafnia at room temperature, $a=0.45$ $\mu \text{m}$, and $R=0.07$ $\mu \text{m}$; 2, the same as in 1, with $a=0.214$ $\mu \text{m}$ and $R=0.033$ $\mu \text{m}$; and 3, the finite thickness of the host taken into account, with $d$ given by (3). Inset: Two-layer PC embedded in a plane-parallel host with width $d$.

Figure 15

The absorption spectra of the PC at normal incidence ($T=2400$) K. The PC parameters are $a=0.214$ $\mu \text{m}$, $R=0.033$ $\mu \text{m}$, and $N=2$, with $d$ given by (3). Different values of the damping coefficient in the Lorentz formula for absorbing hafnia are considered (see text). The same FDTD parameters as in Fig. 6 are used.