In this paper, we discuss flat programmable multi-level diffractive lenses (PMDL) enabled by phase change materials working in the near-infrared and visible ranges. The high real part refractive index contrast (Δn ∼ 0.6) of Sb 2 S 3 between amorphous and crystalline states, and extremely low losses in the near-infrared, enable the PMDL to effectively shift the lens focus when the phase of the material is altered between its crystalline and amorphous states. In the visible band, although losses can become significant as the wavelength is reduced, the lenses can still provide good performance as a result of their relatively small thickness (∼ 1.5λ to 3λ). The PMDL consists of Sb 2 S 3 concentric rings with equal width and varying heights embedded in a glass substrate. The height of each concentric ring was optimized by a modified direct binary search algorithm. The proposed designs show the possibility of realizing programmable lenses at design wavelengths from the near-infrared (850 nm) up to the blue (450 nm) through engineering PMDLs with Sb 2 S 3 . Operation at these short wavelengths, to the best of our knowledge, has not been studied so far in reconfigurable lenses with phase-change materials. Therefore, our results open a wider range of applications for phase-change materials, and show the prospect of Sb 2 S 3 for such applications. The proposed lenses are polarization insensitive and can have the potential to be applied in dual-functionality devices, optical imaging, and biomedical science.
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Visible and near-infrared dual band switchable metasurface edge imaging
Optical edge detection at the visible and near infrared (VNIR) wavelengths is deployed widely in many areas. Here we demonstrate numerically transmissive VNIR dual band edge imaging with a switchable metasurface. Tunability is enabled by using a low-loss and reversible phase-change material Sb2S3. The metasurface acts simultaneously as a high-pass spatial filter and a tunable spectral filter, giving the system the freedom to switch between two functions. In Function 1 with amorphous Sb2S3, this metasurface operates in the edge detection mode near 575 nm and blocks near infrared (NIR) transmission. In Function 2 with crystalline Sb2S3, the device images edges near 825 nm and blocks visible light images. The switchable Sb2S3metasurfaces allow low cross talk edge imaging of a target without complicated optomechanics.
more » « less- NSF-PAR ID:
- 10369584
- Publisher / Repository:
- Optical Society of America
- Date Published:
- Journal Name:
- Optics Letters
- Volume:
- 47
- Issue:
- 16
- ISSN:
- 0146-9592; OPLEDP
- Page Range / eLocation ID:
- Article No. 4040
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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