Flexible thin film bending sensor based on Bragg gratings in hybrid polymers

We report on the fabrication of an optical, highly-flexible thin film bending sensor which is based on diffused channel waveguide Bragg gratings inscribed into sheets of OrmoStamp hybrid polymers. The inorganic-organic Ormocer thin films are prepared by non-structured UV-enhanced imprint lithography which allows the fabrication of sheet-like slab substrates with a desired thickness. By this approach, 120 mm thin and highly-flexible plane-parallel substrates are achieved. For the inscription of the diffused channel waveguide Bragg gratings, a fast and efficient single writing step concept is applied, which allows the simultaneous inscription of both waveguide and Bragg grating in only a few seconds. The accordingly fabricated waveguide Bragg gratings feature a defined Bragg reflection peak that lies within the telecom wavelength range and is well-suited for sensing applications that require a reliable detection and tracking of the reflected Bragg wavelength. The applicability of the thus achieved devices as highly-flexible thin film bending sensors is investigated by means of deflection measurements. Here, we found a quasi-instantaneous and highly-reproducible response of the diffused channel waveguide Bragg gratings reflected Bragg wavelength to even small deflections which features a linear dependency of 6.05E-4 nm/mm on the sensors displacement.