Fabrication and characterization of planar Bragg gratings in TOPAS polymer substrates

We report on the fabrication of polymer planar waveguides with inscribed Bragg gratings in TOPAS employing an efficient UV based single writing step technique using excimer laser. Phase shifting Mach-Zehnder interferometry indicates an UV induced increase of the refractive index in TOPAS of 6 × 10−4 and a modification depth of about 30 μm, respectively. The planar Bragg grating structures in the cyclo-olefin copolymer are characterized by a high reflectivity of about 93% and are studied with respect to their potential in optical waveguide sensing, namely temperature and strain sensing. While the Bragg reflection shows almost no cross sensitivity against humidity, it exhibits a spectral blue shift with increasing temperature of −6.5 pm/°C after multiple thermal annealing cycles. Compressive and tensile strain measurements reveal a sensitivity of 0.70 pm/μɛ.