Michael Koerdt

UV-laser-assisted fabrication of integrated-optical Bragg sensor components in a planar polymer chip

By UV-laser irradiation the refractive index of some polymers can be locally increased in a controllable way. So by mask lithographic methods integrated-optical waveguiding and dispersive structures can be generated in the surface of a planar polymer chip. Thus a polymeric Bragg-sensor component in integrated-optical form was fabricated by the UV-light of an excimer laser. The surface morphology and optical-functional properties of the polymeric Bragg sensor component have been examined especially in dependence on the irradiation parameters and the temperature. The investigations yield the suitability of the Bragg-sensor for the measurements of temperature and deformation. For the realization of a passive fiber-chip coupling for the integrated-optical components a new technology has been developed and tested. The precise control and high-resolution ablation capability inherent in excimer laser machining make it ideally suited for creating grooves for passive alignment of optical fibers to planar channel waveguides.

Bend sensor based on fibreoptics and concept for a compact evaluation unit

A concept study for a bend sensor based on a fibre Bragg grating (FBG) and a compact evaluation unit for the investigated type of sensor is presented. For this, two independent measurands, one well known and one novel, are considered. The fibreoptic sensor principle is capable of resolving the radius and the direction of the bend. The measurement data evaluation principle is capable of resolving multiple distributed FBG sensors, which are present in a single fibre at different positions.

One-step holographic grating inscription in polymers

Volume holographic gratings have recently attracted interest as wavelength-selective devices, for applications such as wavelength stabilizers for laser diode sources. These thick gratings are usually produced using various photosensitive materials like photo-thermo-refractive glass and specially prepared polymers. These materials often require two or more process steps for production of volume holographic gratings. In this study several copolymers with MethylMethAcrylate as base material are compared. Unlike commercially available PMMA, the polymers have a glass transition temperature up to 155 °C, which enables the use on higher laser powers. The refractive index of the polymer is modified using 325-nm-radiation. The polymers were not sensitized by peroxidation prior to irradiation, and after the irradiation process, no development was needed. The gratings were recorded with both a Lloyd mirror setup and the well-known phase mask method. The gratings produced have a calculated refractive index variation in the range of 10-5. The reflection characteristics were measured with a modified Michelson interferometer and a tunable laser source. Volume holographic gratings with extremely narrow bandwidth and angular selectivity can be produced on some of the polymers. The production cost of the gratings is low and they can be used for multiple applications such as wavelength tuning and wavelength selection of diode lasers at high power levels.