Ultratransparent photonic crystals realize positive and negative refractions

The introduction of ultratransparent medium has not yet solved the problem of transmission loss caused by reflection in negative refraction (NR) devices. In this study, theoretical analysis and simulation verification are carried out and an ultratransparent medium with wide-angle NR-index is proposed; the imaging with its flat lens is discussed. A photonic crystal (PC) is designed as an instance of the medium, and the rationality was analyzed. The PC can realize NR within 50 & DEG; as well as positive refraction (PR) within 75 & DEG; with transmittances over 99%. It is an ideal material for multifunctional NR/PR devices with ultra-low loss.