Sub-wavelength metal superstructure grating and mid-infrared adjustable retroreflector

Abstract

The invention discloses a sub-wavelength metal superstructure grating and a mid-infrared adjustable retroreflector. The superstructure grating comprises a metal base body, and a plurality of first grooves and second grooves which are periodically and repeatedly distributed are arranged on the metal base body; the first grooves are filled with first materials to form first structural units; secondstructural units are formed by filling the second grooves with second materials; and the first structural units and the second structural units have a reflection phase difference of pi, and a refractive index n2 of the second materials is larger than a refractive index n1 of the first materials. The reflective metal superstructure grating of the invention has simple structure and is easy to realize. Only two structural units are included in one large period, and the retroreflective function of infrared light in two channels can be realized through a simple structural design. The metal superstructure grating has high retroreflective efficiency (> 98%), which can keep high performance and reduce the loss caused by structure. Different retroreflective angles can be modulated only by changingthe period length, and the retroreflector has the characteristics of high efficiency, adjustable, dual-channel retroreflectivity and so on.

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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