Transparent media are the foundation of almost all optical systems. However, due to general reflection caused by impedance mismatch, transparency has never been perfect in natural materials such as dielectrics. Here, we propose to utilize the spatial dispersive effective media to realize perfectly transparent media with omnidirectional impedance matching, which allows near 100% transmission of light at all incident angles. The equal frequency contours of the effective media are designed to be elliptical and shifted in k space, and thus contain strong spatial dispersions. The realization of such effective media is based on pure dielectric photonic crystals. By designing the nonlocal effective parameters of photonic crystals to special values, we demonstrate the ultratransparency effect [1] of photonic crystals, which can enhance the transparency of photonic crystals to an extreme level beyond any existing solid materials on earth. In an optimized example, near 100% transmission rate have been realized for almost any incident angle within (-90, 90) degrees. A proof-of-principle microwave experiment has been performed to demonstrate near 100% transmission within (-60, 60) degrees. Moreover, broadband, wide-angle, and polarization-insensitive impedance matching effect is obtained in one-dimensional dielectric photonic crystals [2], paving the way to broadband and polarization-independent ultratransparent media.

More interestingly, we demonstrate that such ultratransparent media provide an excellent platform for realizing transformation optics [3, 4] devices at optical frequencies. The impedance and refractive behavior of the dielectric photonic crystals can be flexibly tuned to satisfy the requirement of transformation optics. Interestingly, the shift of the dispersion in k space provides additional freedom beyond the original framework of transformation optics based on local media [1, 5].

ACKNOWLEDGEMENTS – Work in collaboration with Prof. Z. H. Hang and Prof. C.T. Chan.

REFERENCES:

[1] Luo, Y. Yang, Z. Yao, W. Lu, B. Hou, Z. H. Hang, C. T. Chan, and Y. Lai, “Ultratransparent media and transformation optics with shifted spatial dispersions,” Phys. Rev. Lett. 2016, 117, 223901.

[2] Yao, J. Luo, and Y. Lai, “Photonic crystals with broadband, wide-angle, and polarization-insensitive transparency,” Opt. Lett. 2016, 41, 5106-5109.

[3] B. Pendry, D. Schurig, and D. R. Smith, “Controlling electromagnetic fields,” Science 2006, 312, 1780-1782.

[4] Leonhardt, “Optical conformal mapping,” Science 2006, 312, 1777-1780.

[5] Yao, J. Luo, and Y. Lai, To be submitted.