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Register a new userModal interferometric refractive index sensing in microstructured exposed core fibres
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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.
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Electrically-tunable optical properties in materials are desirable for many applications ranging from displays to lasing and optical communication. In most two-dimensional thin-films and other quantum confined materials, these constants have been measured accurately. However, the optical constants of single wall nanotubes (SWCNT) as a function of electrostatic tuning are yet to be measured due to lack of electronic purity and spatial homogeneity over large areas. Here, we measure the basic optical constants of ultrathin high-purity (>99%) semiconducting single wall carbon nanotube (s-SWCNT) films with spectroscopic ellipsometry. We extract the gate-tunable complex refractive index of s-SWCNT films and observe giant modulation of the real refractive index (~11.2% or an absolute value of >0.2) and extinction coefficient (~11.6%) in the near-infrared (IR) region (1.3-1.55 {mu}m) induced by the applied electric field significantly higher than all existing electro-optic semiconductors in this wavelength range. We further design a multilayer IR reflection phase modulator stack by combining s-SWCNT and monolayer MoS2 heterostructures that can attain >45{deg} reflection phase modulation at 1600 nm wavelength for < 200 nm total stack thickness. Our results highlight s-SWCNT as a promising material system for infrared photonics and electro-optics in telecommunication applications.
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.
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.
Which systems are ideal to obtain negative refraction with no absorption? Electromagnetically induced transparency (EIT) is a method to suppress absorption and make a material transparent to a field of a given frequency. Such a system has been discussed in [1]; however the main limitations for negative refraction introduced are the necessity of resonant electric and magnetic dipole transitions, and the necessity of very dense media. We suggest using frequency translators in a composite system that would provide negative refraction for a range of optical frequencies while attempting to overcome the limitations discussed above. In the process of using frequency translators, we also find composite systems that can be used for refractive index enhancement.
Multimode fibres (MMFs) are attracting interest for complex spatiotemporal dynamics, and for ultrafast fibre sources, imaging and telecommunications. This new interest is based on three key properties: their high spatiotemporal complexity (information capacity), the important role of disorder, and complex intermodal interactions. To date, phenomena in MMFs have been studied only in limiting cases where one or more of these properties can be neglected. Here we study MMFs in a regime in which all these elements are integral. We observe a spatial beam-cleaning process preceding spatiotemporal modulation instability. We show that the origin of these processes is a universal unstable attractor in graded-index MMFs. Both the self-organization of the attractor, as well as its instability, are caused by intermodal interactions characterized by cooperating disorder, nonlinearity and dissipation. The demonstration of a disorder-enhanced nonlinear process in MMF has important implications for telecommunications, and the multifaceted complexity of the dynamics showcases MM waveguides as ideal laboratories for many topics and applications in complexity science.
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