Search

This article presents a fibre-optic sensor that measures temperature and pressure. Its operating principle is based on the amplitude modulation caused by the variation in the radius of a concave micro-mirror crafted into the end of an SMF optical fibre. In fact, a micro-cavity engraved into the end of the fibre by selective chemical etching is filled with a PDMS (Polydimethylsiloxane)-type polymer. Due to surface tension, the polymer micro-drop takes on a hemispheric shape characterised by a certain radius. After polymerisation in an oven at 100 °C for one hour, the hemispheric micro-drop is coated with a thin layer of gold using the vacuum evaporation technique. Typically, concave micro-mirrors can be obtained with bend radii of between 10μm and 30μm. Under the action of a temperature gradient or a variation in pressure, the thickness of the PDMS changes and causes a variation in the bend radius of the micro-mirror. As a result, the light intensity guided by the optical fibre and reflected by the micro-mirror is modulated by the variation in its bend radius. In this configuration, the sensor has a thermo-sensitivity of – 0.08dB/°C with a resolution of 0.13 °C in a range of between 20 °C and 100 °C. It also has a pressure sensitivity of 0.11dB/bar between 10 and 20 bars. The measurements are taken by a reflectometer (OTDR). In addition, the experimental results have been validated by theoretical modelling. This sensor is relatively simple to make and can be used in a wide range of applications, in particular biomedical and industrial ones.

In this paper, we present a technique for producing fibers optics micro-collimators composed of polydimethylsiloxane PDMS microlenses of different radii of curvature. The waist and working distance values obtained enable the optimization of optical coupling between optical fibers, fibers and optical sources, and fibers and detectors. The principal is based on the injection of polydimethylsiloxane (PDMS) into a conical micro-cavity chemically etched at the end of optical fibers. A spherical microlens is then formed that is self-centered with respect to the axis of the fiber. Typically, an optimal radius of curvature of 10.08 μm is obtained. This optimized micro-collimator is characterized by a working distance of 19.27 μm and a waist equal to 2.28 μm for an SMF 9/125 μm fiber. The simulation and experimental results reveal an optical coupling efficiency that can reach a value of 99.75%.