Optical chemical sensors have been the focus of much research attention in recent years because of their importance in industrial, environmental and biomedical applications [1]. This class of sensors combines chemical and biological recognition with advances in optoelectronic technologies. The application of solgel materials to these sensors, especially in the form of thin films, has attracted considerable interest due to the ease of fabrication and design flexibility of the process. The nature of the sol-gel process lends itself very well to the deposition of thin films using a variety of techniques such as dip-coating, spin-coating and spraying. In many sensor applications, the sol-gel film is used to provide a micro-porous support matrix in which analyte-sensitive molecules are entrapped and into which smaller analyte species may diffuse and interact [2,3]. Sol-gel films have many advantages as support matrices over polymer supports, including, for example, strong adhesion, good mechanical strength as well as excellent optical transparency. The versatility of the process facilitates tailoring of the physico-chemical film properties to optimize sensor performance. For example, films can be designed which have optimum porosity while minimizing leaching of the indicator molecules. In this chapter, the versatility of the sol-gel process with regard to the design of films for specific optical chemical sensor applications is highlighted.

Optical chemical sensors.

The guided, single-mode propagation of ultrashort optical pulses is commonly described by a well studied and understood generalized nonlinear Schrodinger equation. Here we present and discuss an extended version for multimode optical fibers and waveguides including polarization effects, high-order dispersion, Kerr and Raman nonlinearities, self-steepening effects, as well as wavelength-dependent mode coupling and nonlinear coefficients. We then investigate the symmetry properties of the nonlinear coupling coefficients for the cases of step-index and circularly symmetric conventional fibers and for microstructured fibers with hexagonal symmetry. Finally, we study the computational complexity of the proposed algorithm.

Description of ultrashort pulse propagation in multimode optical fibers

Remarkable developments can be seen in the field of optical fibre biosensors in the last decade. More sensors for specific analytes have been reported, novel sensing chemistries or transduction principles have been introduced, and applications in various analytical fields have been realised. This review consists of papers mainly reported in the last decade and presents about applications of optical fiber biosensors. Discussions on the trends in optical fiber biosensor applications in real samples are enumerated.

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Recent Development in Optical Fiber Biosensors

In the modern world, a number of therapeutic proteins such as vaccines, antigens, and hormones are being developed utilizing different sophisticated biotechnological techniques like recombinant DNA technology and protein purification. However, the major glitches in the optimal utilization of therapeutic proteins and peptides by the oral route are their extensive hepatic first-pass metabolism, degradation in the gastrointestinal tract (presence of enzymes and pH-dependent factors), large molecular size and poor permeation. These problems can be overcome by adopting techniques such as chemical transformation of protein structures, enzyme inhibitors, mucoadhesive polymers and permeation enhancers. Being invasive, parenteral route is inconvenient for the administration of protein and peptides, several research endeavors have been undertaken to formulate a better delivery system for proteins and peptides with major emphasis on non-invasive routes such as oral, transdermal, vaginal, rectal, pulmonary and intrauterine. This review article emphasizes on the recent advancements made in the delivery of protein and peptides by a non-invasive (peroral) route into the body.

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A review on the strategies for oral delivery of proteins and peptides and their clinical perspectives

https://researchrepository.ucd.ie/bitstream/10197/7800/1/Maher_et_al_2016_ADDR_researchgate.pdf

Intestinal permeation enhancers for oral peptide delivery.

We experimentally demonstrate a new compact surrounding refractive-index sensor using a MMF-CSF-MMF (MCM) structure. The evanescent waves in the coreless silica fibre (CSF) region can directly interact with the surrounding medium. Due to its distinctive resonant spectral feature, the MCM sensor showed a high sensitivity of 4.37 × 10−4 for a refractive index range of 1.30 to 1.44, suggesting that the proposed device may be suitable for a wide range of biomedical and chemical sensor applications.

https://iopscience.iop.org/article/10.1088/0957-0233/17/5/S32/pdf

Compact three segmented multimode fibre modal interferometer for high sensitivity refractive-index measurement

A new type of index-guided photonic crystal fiber is proposed to enhance chemical sensing capability by introducing a hollow high index ring defect that consists of the central air hole surrounded by a high index GeO2 doped SiO2 glass ring. Optical properties of the fundamental guided mode were numerically analyzed using the full-vector finite element method varying the design parameters of both the defects in the center and the hexagonal air-silica lattice in the cladding. Enhanced evanescent wave interaction in the holey region and lower confinement loss by an order of magnitude were achieved simultaneously, which shows a high potential in hyper sensitive fiber-optic chemical sensing applications.

Enhancement of chemical sensing capability in a photonic crystal fiber with a hollow high index ring defect at the center

We have investigated optical properties of an optical fiber having a six-fold symmetric quasiperiodic array of air holes in cladding, a six-fold symmetric photonic quasicrystal fiber. The photonic quasicrystal fiber exhibits larger cutoff ratio for endlessly single mode operation than that of a triangular photonic crystal fiber having six-fold symmetry and almost zero ultra-flattened chromatic dispersion, 0±0.05 ps/km/nm, in the range of wavelength from 1490 to 1680 nm. The dispersion value is much less than those of the proposed dispersion flattened PCFs.

Novel optical properties of six-fold symmetric photonic quasicrystal fibers.

We propose a photonic quasi-crystal fiber with a dual-core structure. The circular-like outer core caused by the quasi-periodic arrangement gives rise to an interesting dispersion property that is different from that of a photonic crystal fiber with a dual-core structure. The absolute value of negative dispersion for the dual-core photonic quasi-crystal fiber increases as the distance between the nearest holes increases, while the absolute value of negative dispersion for the dual-core photonic crystal fiber decreases. The dispersion property can be useful in reducing the coupling loss between the compensating dispersion fiber and a conventional single mode fiber.

Dispersion properties of dual-core photonic-quasicrystal fiber

We propose a modified rectangular lattice PCF and numerically investigate its birefringence and dispersion Based on the plane wave expansion method, it is shown that the proposed structure provides high birefringence and negative dispersion Numerical results show that the birefringence of the modified PCF reaches 10(-2) and the leakage loss is about 1000 times smaller than that of an original rectangular PCF because the modification gives rise to the strong confinement of guided modes Dispersion and its slope are also negative over the C band

Soan Kim

Papers

Compact three segmented multimode fibre modal interferometer for high sensitivity refractive-index measurement

Enhancement of chemical sensing capability in a photonic crystal fiber with a hollow high index ring defect at the center

Novel optical properties of six-fold symmetric photonic quasicrystal fibers.

Dispersion properties of dual-core photonic-quasicrystal fiber

Modified rectangular lattice photonic crystal fibers with high birefringence and negative dispersion