Subwavelength metal metagrating and mid-infrared tunable retroreflector

Abstract

The invention discloses a sub-wavelength metal superstructured grating and a mid-infrared adjustable retroreflector. The superstructured grating includes a metal base, and the metal base is provided with a number of first grooves and second grooves that are periodically and repeatedly distributed. A groove is filled with a first material to form a first structural unit, and a second groove is filled with a second material to form a second structural unit, the first structural unit and the second structural unit have a reflection phase difference of π, and the second structural unit The refractive index n of the two materials 2 greater than the refractive index n of the first material 1 . The structure of the reflective metal meta-grating of the present invention is simple and easy to realize. It only contains two structural units in a large period, and the retroreflection function of dual-channel mid-infrared light can be realized through a simple structural design; the metal meta-grating can maintain high At the same time, it reduces the loss caused by the structure and has extremely high retroreflection efficiency (>98%). Different retroreflection angles can be modulated only by changing the period length. It has high efficiency, adjustable, dual-channel retroreflection and other characteristics.

Description

technical field [0001] The invention relates to the technical field of optical devices, in particular to a sub-wavelength metal meta-grating and a mid-infrared adjustable retroreflector. Background technique [0002] How to effectively control the refraction, reflection, propagation and wavefront of light has always been one of the hot research topics in the field of optics. In the past few years, scientists have proposed the concept of graded metasurfaces, which introduce an effective wave vector κ along the direction of the interface by introducing a sudden phase covering a 2π variation within a period. According to the conservation of momentum in the tangential direction, when light is reflected and refracted on the interface, it satisfies the generalized law of reflection and refraction: k i sinθ in =k i sinθ r +κ and k i sinθ in =k t sinθ t +κ, so that the reflection, refraction and wavefront of light can be effectively controlled. The concept of local mutation...

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Problems solved by technology

[0004] In the prior art (Song G, Cheng Q, Cui T J, Jing Y 2018 Phys.Rev.Mater.2065201), it is proposed to use a two-layer meta-grating to realize a planar retroreflective device, but for a large incident angle, the retroreflective efficiency is relatively low. Low (at 60.0° incidence, the retroreflection efficiency is less than 50%), and the coupling between the two layers of metagrating also increases the complexity of the system

In the prior art (Shen C, Díaz-Rubio A, Li J, Cummer S A 2018 Appl.Phys.Lett.112183503), a three-channel planar retroreflective device can be realized by using a meta-grating, which solves the problem of large-angle incident retroreflective devices. However, the metagrating structure contains 6 different structural units in one cycle, and the geometric structure is relatively complex.

In general, more structural units may result in more electromagnetic losses, reducing the efficiency of retroreflection

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