The present disclosure provides optical fiber preforms formed from core canes having large core-clad ratio, intermediate core-cladding assemblies, and methods for making the preforms and core cladding assemblies. The preforms are made from core canes having a contoured end surface. The contoured end surface(s) include a depression that acts to reduce the stress that develops at the junction of the end surface of the core cane with a soot cladding monolith arising from differences in the coefficient of thermal expansions of the core can and soot cladding monolith. The contoured end surface(s) leads to preforms having low defect concentration and low probability of failure during fiber draw.

An optical fiber having a core comprising silica and greater than 1.5 wt % chlorine and less than 0.5 wt % F, said core having a refractive index .sub.1MAX, and a inner cladding region having refractive index .sub.2MIN surrounding the core, where .sub.1MAX>.sub.2MIN.

A method is described of manufacturing an optical sensing element for detecting a presence and/or determining a concentration of an analyte in a fluid medium, in particular in an aqueous medium. The optical sensing element includes an optical waveguide (e.g. an optical fiber) comprising an optically transparent material for guiding light through the sensing element along a flightpath. The optical sensing element further includes an inorganic coating for adsorbing the analyte from the fluid medium and an adhesion promotion layer formed between the optical waveguide and the inorganic coating. The adhesion promotion layer includes an adhesion promotion material for promoting adhesion of the inorganic material.

A sensor system, the manufacturing of such system, and the use of such system for optical detection of a target analyte in a gaseous medium are described. The sensor system includes a hollow waveguide that is provided with a reflective mirror layer along its inner wall and a concentrating coating of an inorganic sorption material. The mirror layer defines a light path for guiding light between a light inlet and a light outlet that are provided on opposing terminal ends of the hollow waveguide. The concentrating coating increases an effective concentration of target analytes, if present, and allows optical, preferably spectroscopic, analysis of the medium by recording transmission of light, preferably infrared light, guided through the hollow waveguide.

A Photonic Crystal Fiber (PCF) a method of its production and a supercontinuum light source comprising such PCF. The PCF has a longitudinal axis and includes a core extending along the length of said longitudinal axis and a cladding region surrounding the core. At least the cladding region includes a plurality of microstructures in the form of inclusions extending along the longitudinal axis of the PCF in at least a microstructured length section. In at least a degradation resistant length section of the microstructured length section the PCF includes hydrogen and/or deuterium. In at least the degradation resistant length section the PCF further includes a main coating surrounding the cladding region, which main coating is hermetic for the hydrogen and/or deuterium at a temperature below T.sub.h, wherein T.sub.h is at least about 50 C., preferably 50 C.<T.sub.h<250 C.

A redrawable glass, in particular for light guide elements (1) such as glass fibres, is provided. In particular, highly transparent glasses, a method for producing same, and uses thereof. The glasses are preferably used as core glass in a light and/or image guide (1). A light and/or image guide (1) that includes the glass as core glass (2), and a cladding glass (3) is also provided. The use of such a glass in the fields of medical technology, in particular for endoscopic applications, imaging, projection, telecommunications, optical data transmission technology, mobile drive, laser technology and disinfection, and also optical elements or preforms of such optical elements.