Enantioseparation is a fundamental problem in pharmaceutics and agrochemicals. Yet, the prevailing chemical techniques are not effective. In this paper, we proposed an achiral metasurface, which consists of a disk-double split ring (DDSR) resonator sustaining dipole-octupole (DO) Fano resonance (FR). We have proved that such a resonance can significantly enlarge the chiral gradient force of the enantiomers by numerical simulation. We find that the resonator has a large chirality density gradient near the DO-FR, which strengthens the chiral gradient force that can discriminate the sub-10 nm chiral nanoparticles. Therefore, the enantioselective optical potential can trap or push different enantiomers. We propose a method to enhance the chiral gradient force by using an achiral metasurface consisting of a disk and an asymmetric double split-ring resonator, which can promote the development of enantiomer purification and separation technology, and bring new prospects for the latest all-optical enantiomer synthesis technology.
Metasurface analogue of the phenomenon of electromagnetically induced transparency (EIT) that is originally observed in atomic gases offers diverse applications for new photonic components such as nonlinear optical units, slow-light devices, and biosensors. The development of functional integrated photonic devices requires an active control of EIT in metasurfaces. We demonstrate a reversible switching of the metasurface-induced transparency in the near-infrared region by incorporating a nonvolatile phase change material, Ge2Sb2Te5, into the metasurface design. This leads to an ultrafast reconfigurable transparency window under an excitation of a nanosecond pulsed laser. The measurement agrees well with both theoretical calculation and finite-difference time-domain numerical simulation. Our work paves the way for dynamic metasurface devices such as reconfigurable slow light and biosensing.
Chalcogenides are materials that substantially consist of sulphur, selenium, and tellurium. Their dielectric properties
can be tuned by thermally induced structural phase transitions, photostructural transitions, and dissolution
of metal dopants. We have designed active photonic structures using a range of `tuneable' chalcogenides. The
resonant frequency of plasmonic structures was tuned over a 100 nm band in the visible, metal-chalcogenidemetal
structures provide tuning of over a band of 0.5 μm in the mid-infrared, and hyperbolic metamaterials
incorporating chalcogenides provide a means to alter the radiative decay rate of
uorescent photons.
In this work, we present the optical characterization of a two-dimensional (2D) L3 photonic crystal (PhC) cavity biosensor in visible region by using 3D Finite Difference Time Domain (FDTD) method. The sensor is based on GaN material and integrated with a microfluidic channel. Sensing is performed by measuring the wavelength shift of the PhC cavity resonant peak, whose spectral position is sensitive to refractive index changes of dielectric material inside microfluidic channel. We simulate the PhC cavity with water (n=1.33) and two immersion oils (n=1.48 and n=1.518) overlaid. Spectral peak width was found to be 9.8nm around 650nm. A spectral shift of peak wavelength with index change of 35nm/RIU was observed. Measured peak shift (Δλ = 6.5nm) corresponds to a detectable index change Δn = 0.188.
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