Influence of the UV dosage on planar Bragg gratings in cyclo-olefin copolymer substrates

Abstract

We report on the influence of the applied UV dosage on the fabrication of planar Bragg gratings in cyclo-olefin copolymers. Integrated waveguides with inscribed gratings are fabricated simultaneously using a single writing step technique and characterized by measuring the reflected and transmitted spectra. In addition, the effect of length and width of both waveguide and Bragg grating on the reflectivity and attenuation are studied using the cut-back method. The results show that in this material class, integrated waveguides with an attenuation as low as 1.2 dB/cm and Bragg gratings with a reflectivity of up to 99% can be realized. Most strikingly, we demonstrate that Bragg gratings with a length of only 2.1 mm still exhibit a distinct Bragg reflection facilitating miniaturized Bragg grating applications. Moreover, we demonstrate that the refractive index sensitivity of the planar Bragg gratings strongly depends on the UV dosage, in turn facilitating to tailor grating properties according device requirements in sensing applications.