Highly Sensitive Waveguide Bragg Grating Temperature Sensor Using Hybrid Polymers

A waveguide Bragg grating temperature sensor implemented using a hybrid inorganic-organic material (Ormocer) with a 25-times higher temperature sensitivity than a typical silica fiber is presented. The sensor consists of second order gratings (1010-nm pitch) in 5 μm × 5 μm waveguides fabricated on a planar substrate using the replication-based methods. The gratings were imprinted in the under-cladding layer, and the waveguide cores were patterned on top by capillary filling of microchannels, which were defined in a transparent and flexible mold. The somewhat larger, slightly multimode waveguides facilitate pigtailing with an optical fiber but lead to three reflection peaks corresponding to the different excited waveguide modes. The peak at the longest wavelength (Bragg wavelength at 1539 nm, corresponding to the fundamental mode) was tracked during temperature testing, and a sensitivity of -249 pm °C
^-1
was found.