Temperature-tuned and excellent omnidirectional bending of light to the normal for energy concentration in an index-continuous structure

We present an alternative concept for omnidirectional bending of light and concentration of energy in an index-continuous structure, comprising two gradient-index SiO_{x (0≤x≤2)} layers and a thermochromic VO₂ layer. The concept helps to overcome the constraints of conventional optics that are nonadjustable and only functional at designed wavelengths. The advantages of both gradient-index and thermochromic materials are combined in this work to realize temperature-tuned omnidirectional concentration of energy. Using a double-coated ICS component of AIR/SiO_x/SUB/SiO_x/VO₂ for light manipulation and application near the visible spectrum range, this concept was numerically and experimentally demonstrated. The incoming light under oblique incident angles (0°–80°) was bent effectively and concentrated regardless of polarization. Favorable results demonstrated that a notably high energy concentration efficiency P_e (1.93–2.52) was achieved by varying the ambient temperatures (25–75 °C). This concept is general and can be applied in a variety of elements in light energy-efficient devices.