Non-Hermitian systems have numerous alluring optical properties at exceptional points (EPs) and have attracted extensive attention because of their great prospects in applications such as optical sensing, integrated optics, and other fields.
metagrating and Si subwavelength grating is designed: the metagrating in the upper layer achieves the directional regulation of lightwave, and the lossy subwavelength grating in the lower layer achieves an adjustable absorption."
"When the proper absorption of Si subwavelength grating is selected, a wave vector-dependent perfect retroreflector and absorber is realized . The eigenvalues andFig 2. a, The spectra and schematics of the high-efficiency optical non-Hermitian meta-system at EP. The |r₋₁| is larger than 0.999 and |r₊₁| is less than 10⁻⁴. b, Trajectories of eigenvalues with the evolution of absorption parameter.
Fig 3. a, Top view and back view of the sample. The upper layer is TiO2 metagrating and the lower layer is Si grating. b, The far-field scattered light from all angles of the sample with incident angles of 30° and -30°. c, The experimental measured far-field scattered light from all angles with incident angles of 30° and -30° at 532 nm.
"We fabricated the sample and conducted two separate tests with incident angles of 30° and −30° as shown in the purple and red boxes of Fig. 3b. When the incident light impacted from the left, most of the light was reflected by the sample to the incident path. When the incident light came from the right, there was very little retroreflection light.
"Our work paves a new avenue toward the design of versatile optical metasurface platforms involving the EP or higher-order EP, which may inspire more functional photonic devices for wave manipulation," the scientists say.Light: Science & Applications