Angular Selectivity

Optical Broadband Angular Selectivity

Background & Motivation:

The ability to control light has long been a major scientific and technological goal. In electromagnetic theory, a monochromatic electromagnetic plane wave is characterized (apart from its phase and amplitude) by three fundamental properties: its frequency, its polarization, and its propagation direction. The ability to select light according to each of these separate properties would be an essential step in achieving control over light. Tremendous progress has been made toward both frequency selectivity and polarization selectivity. Frequency selectivity can be obtained, for example, by taking advantage of photonic band gaps in photonic crystals. Polarization selectivity is accomplished, for example, by means of a “wire grid” polarizer or by exploiting birefringent materials. Methods based on interference and resonance effects have been explored for angular selectivity, but they have limited applications because they are sensitive to frequency.

Method:

In our work, we tailor the overlap of the bandgaps of multiple one-dimensional photonic crystals, each with a different periodicity, in such a way to preserve the characteristic Brewster modes across a broadband spectrum. We prove this idea theoretically and realize it experimentally with an all-visible-spectrum, p-polarized angularly selective material-system. Our method enables transparency throughout the visible spectrum at one angle, the generalized Brewster angle, and reflection at every other viewing angle.

Experimental setup and observation. (A) Schematic layout of the experimental setup. The system is immersed in a liquid that is index matched to ε1 = εSiO2 = 2:18. (B) Normal incident angle setup. The sample behaves as a mirror and reflects the image of the camera. (C) θi = 30 setup. The sample behaves as a mirror and reflects the image of MIT cups in the lab. (D) θi = θB = 55 setup. The sample becomes transparent for the entire visible regime for p-polarized light. (E) θi = 70 setup. The sample behaves as a mirror and reflects the figurine placed at the corner of the table. In B-E a polarizer is installed on the camera so it detects only p-polarized light.

References:

More detailed description can be found in our paper published on Science, March 28th, 2014:

Y. Shen, D. Ye, I. Celanovic, S. G. Johnson, J. D. Joannopoulos and M. Soljacic, "Optical Broadband Angular Selectivity", Science 343 (6178), 1499-1501 (2014) [pdf]

And an extended work published on Physical Review B, September 15th, 2014:

Y. Shen, D. Ye, L. Wang, I. Celanovic, L. Ran, J. D. Joannopoulos, and M. Soljacic, " "Metamaterial broadband angular selectivity", Physical Review B Vol.90, p.125422, (2014)

Here is a more detailed invited review paper published on Applied Physics Reviews, March 1st, 2016, which discussed many potential applications and outlook of this technology: