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Register a new userRefractive index sensing with hybrid surfaces of photonic crystals and dielectric microsphere monolayers
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In this work, a refractive index (RI) sensor with an effective integration of colorimetric detection and optical sensing capabilities has been developed. Colorimetric detection relies on the sensitivity of the structural color of photonic crystal (PC) substrates to the changes in background RI, while the optical sensing is performed by measuring the magnification abilities of the dielectric microspheres, which depends on the position of the photonic nanojet. Based on this concept, we have successfully assembled 35 {mu}m-diameter barium titanate glass microspheres, 4.9 {mu}m-diameter polystyrene and silica microsphere monolayers on 1D or 2D PC substrates to perform RI sensing in various liquids. In addition, the developed RI sensor is highly compatible with commercial optical microscopes and applicable for RI sensing in areas as small as tens of square microns.
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We have theoretically demonstrated Rabi-like splitting and self-referenced refractive index sensing in hybrid plasmonic-1D photonic crystal structures. The coupling between Tamm plasmon and cavity photon modes are tuned by incorporating a low refractive index spacer layer close to the metallic layer to form their hybrid modes. Anticrossing observed in the dispersion validates the strong coupling between the modes and causes Rabi-like splitting, which is supported by coupled mode theory. The Rabi-like splitting energy decreases with increasing number of periods (N) and refractive index contrast ({eta}) of the two dielectric materials used to make the 1D photonic crystals, and the observed variation is explained by an analytical model. The angular and polarization dependency of the hybrid modes shows that the polarization splitting of the lower hybrid mode is much stronger than that of the upper hybrid mode. Further investigating the hybrid modes, it is seen that one of the hybrid modes remains unchanged while other mode undergoes significant change with varying the cavity medium, which makes it useful for designing self-referenced refractive index sensors for sensing different analytes. For {eta}=1.333 and N=10 in a hybrid structure, the sensitivity increases from 51 nm/RIU to 201 nm/RIU with increasing cavity thickness from 170 nm to 892 nm. For a fixed cavity thickness of 892 nm, the sensitivity increases from 201 nm/RIU to 259 nm/RIU by increasing {eta} from 1.333 to 1.605. The sensing parameters such as detection accuracy, quality factor, and figure of merit for two different hybrid structures ([{eta}=1.333, N=10] and [{eta}=1.605, N=6]) are evaluated and compared. The value of resonant reflectivity of one of the hybrid modes changes considerably with varying analyte medium which can also be used for refractive index sensing.
The article demonstrates uncommon manifestation of spatial dispersion in low refractive index contrast 3D periodic dielectric composites with periods of about one tenth of the wavelength. First principles simulations by the well established plane wave method reveal that spatial dispersion leads to appearance of additional optical axes and can compensate anisotropy in certain directions.
We report that the refractive index of transition metal dichacolgenide (TMDC) monolayers, such as MoS2, WS2, and WSe2, can be substantially tuned by > 60% in the imaginary part and > 20% in the real part around exciton resonances using CMOS-compatible electrical gating. This giant tunablility is rooted in the dominance of excitonic effects in the refractive index of the monolayers and the strong susceptibility of the excitons to the influence of injected charge carriers. The tunability mainly results from the effects of injected charge carriers to broaden the spectral width of excitonic interband transitions and to facilitate the interconversion of neutral and charged excitons. The other effects of the injected charge carriers, such as renormalizing bandgap and changing exciton binding energy, only play negligible roles. We also demonstrate that the atomically thin monolayers, when combined with photonic structures, can enable the efficiencies of optical absorption (reflection) tuned from 40% (60%) to 80% (20%) due to the giant tunability of refractive index. This work may pave the way towards the development of field-effect photonics in which the optical functionality can be controlled with CMOS circuits.
Optical fibre-based sensors measuring refractive index shift in bodily fluids and tissues are versatile and accurate probes of physiological processes. Here, we suggest a refractive index sensor based on a microstructured exposed-core fibre (ECF). By considering a high refractive index coating of the exposed core, our modelling demonstrates the splitting of the guided mode into a surface sensing mode and a mode that is isolated from the surface. With the isolated mode acting as a reference arm, this two-mode one-fibre solution provides for robust interferometric sensing with a sensitivity of up to 60,000 rad/RIU-cm, which is suitable for sensing subtle physiological processes within hard-to-reach places inside living organisms, such as the spinal cord, ovarian tract and blood vessels.
The use of relatively simple structures to achieve high performance refractive index sensors has always been urgently needed. In this work, we propose a lithography-free sensing platform based on metal-dielectric cavity, the sensitivity of our device can reach 1456700 nm/RIU for solution and 1596700 nm/RIU for solid material, and the FOM can be up to 1234500 /RIU for solution and 1900800 /RIU for solid material, which both are much higher than most sensing methods. This sensor has excellent sensing performance in both TE and TM light, and suitable for integrated microfluidic channels. Our scheme uses a multi-layers structure with a 10 nm gold film sandwiched between prism and analyte, and shows a great potential for low-cost sensing with high performance.
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