Abstract
Embedded channel waveguide Bragg gratings are fabricated in the Ormocer® hybrid polymers OrmoComp®, OrmoCore, and OrmoClad by employing a single writing step technique based on phase mask technology and KrF excimer laser irradiation. All waveguide Bragg gratings exhibit well-defined reflection peaks within the telecom wavelengths range with peak heights of up to 35 dB and −3 dB-bandwidths of down to 95 pm. Furthermore, the dependency of the fabricated embedded channel waveguide Bragg gratings on changes of the temperature and relative humidity are investigated. Here, we found that the Bragg grating in OrmoComp® is significantly influenced by humidity variations, while the Bragg gratings in OrmoCore and OrmoClad exhibit linear and considerably high temperature sensitivities of up to −250 pm/C and a linear dependency on the relative humidity in the range of −9 pm/%.
Highlights
Fiber Bragg gratings (FBGs) are a sinusoidal refractive index variation within a fiber core, and are well known to serve as efficient optical sensor elements [1,2,3]
It is striking that the reflected Bragg wavelengths of the embedded channel waveguide Bragg grating in OrmoComp® show a non-linear red-shift at an increasing relative humidity, while the reflected Bragg wavelengths of the Bragg gratings fabricated in OrmoCore and OrmoClad exhibit a linear blue-shift
Since water has a lesser refractive index than the applied Ormocer® s, an absorption of water results in a reduction of the effective refractive index of the guided mode and in a decrease of the reflected Bragg wavelength, as observable for the Bragg gratings fabricated in OrmoCore and OrmoClad
Summary
Fiber Bragg gratings (FBGs) are a sinusoidal refractive index variation within a fiber core, and are well known to serve as efficient optical sensor elements [1,2,3]. In order to enhance the temperature sensitivity of FBGs, the Bragg gratings can be coated with or directly written in a material — either fiber-based or as planar waveguide design — that features a higher TOC or CTE. By this measure, a sensitivity increase of typically three-to-ten-times the sensitivity of silica-based Bragg gratings can be achieved [9,10,11,12,13,14].
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