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Van der Waals (vdW) materials have recently attracted a lot of attentions, because they possess a wide range of optoelectronic properties and can be applied over a wide spectral regions. For example, black phosphorus and graphene can exhibit direct and narrow band gaps, making them appeal to the mid-infrared or even far-infrared devices applications. The single layer transition metal dichalcogenides materials (TMDCs, i.e., MX2; M=Mo, W; X=S, Se, Te), have been known as direct gap semiconductors, useful in the infrared and visible spectral regimes. Additionally, due to the vdW nature, these materials can be assembled vertically to form the complex vdW heterostructures, and more importantly, can be easily transferred onto different device substrates without stringent constraints on lattice matching at the interfaces. Notably, such features can potentially lead to the novel hybrid device platforms that simultaneously take advantage of the state-of-the-art semiconductor manufacturing technologies and exotic characteristics of vdW materials
In this talk, we will demonstrate novel dielectric metalenses by exploiting the vdW molybdenum disulfide (MoS2) and hexagonal boron nitride as optical materials. By using the incomplete phase-based design approach (i.e. the maximum phase shift being less than 2π), we show the thicknesses of our created vdW metalenses can be far below the operating wavelength (∼0.1λ to 0.5λ). This circumvents the current fabrication challenges of making dielectric metalenses that require the high-aspect-ratio nanoscale scattering elements. More importantly, we demonstrate that the developed MoS2 (hexagonal boron nitride) metalenses not only can focus the near-infrared (visible) light into the diffraction limited spots, but also can be useful for creating the optical images. This could enable further downscaling of optoelectronics systems, and will significantly benefit the modern imaging, motion detection and spectroscopic applications. Furthermore, by exploiting the nature of vdW interactions, we show our proposed metalenses can be readily peeled off and then transferred onto the flexible and transparent polydimethylsiloxane (PDMS) substrate. When the mechanical strain was applied on the PDMS substrate, the axial focus length of transferred vdW metalens can be widely tuned in the range from 250 to 400 µm. This highlight the possibilities of realizing integrable and tunable dielectric metalenses based on our developed vdW nanophotonics. In addition to vdW nanophotonics, we will demonstrate that the vdW-based light emitters and photodetectors can be coupled with diverse photonic structures such as the waveguides and plasmonic resonators, and show the performed hybrid device platforms can hold great promise for the photonic circuits applications.
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