Abstract
Metalenses recently have attracted attention because of their more compact size in comparison with conventional lenses; they can also achieve better optical performance with higher resolution. Duplexer is an interesting function of a metalens that can distinguish different sources and divide them into two parts for specific purposes. In this article, we design tunable duplex metalenses with phase-change material Ge2Sb2Te5 for the first time. Two types of special unit cells are designed to modulate the incident lights, and four metalenses are designed based on the two types of unit cells. Specific phase profiles are calculated for different sections of metalens in which the corresponding unit cells are settled; accordingly, the metalenses can focus the incident lights at any positions according to our design. Moreover, the metalenses become selectable via tuning the state of phase-change material, which means that the output light field can be actively controlled. The proposal of our tunable duplex metalenses will offer new opportunities for active three-dimensional imaging or optical coding.
Highlights
These results demonstrate that our tunable duplex metalens can actively control the focusing in vertical direction, and it may have potential in three-dimension imaging
The results fit well with theoretical analysis because the phase modulation covers the whole 2π range linearly when the GST stays in amorphous state
When the GST in both sections stayed in a crystalline state, Figure 8d shows that the metalens M4 was turned off. These results prove that the tunable duplex metalens M4 can divide the two different lights in a vertical direction and actively control them if necessary
Summary
Researchers have begun to pay increasing attention to metasurfaces due to their extraordinary performance in electromagnetism fields [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21]. The combination of GST with metasurfaces has attracted increasing interest because active control is desirable in many nano-photonic devices. Several metadevices, such as display [36], filter [37], absorber [38], beam steering [39], modulation [40,41,42] and other novel devices [34,43,44,45,46], all of which are based on phase change materials, have been investigated. We design the tunable duplex metalens based on phase-change material GST in the communication wavelengths (1.55 μm and 1.31 μm) for the first time. We believe that the proposed tunable duplex metalens could be applied in active three-dimensional imaging or optical coding
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