A spectral filter analyzer for Bragg grating based strain and temperature measurements

To measure several C-band Bragg grating based sensors simultaneously, a new combination of optical and electronical components has been developed for light intensity independent conversions of wavelength into electrical signal amplitudes adequate for electronical signal processing. A stabilized SLED has been connected by optical fibres to a coupler and a subsequent optical switch/circulator for addressing several sensors. The coupler directs the reflected light from a sensor to a detector. The detector consists of a beam splitter, two collimator lenses and two filters for complementary or independent wavelength-intensity conversion. The filtered light beams are converted independently by photodiodes on a single chip for subsequent electronical signal acquisition and processing. The contrast of the signals assures a light intensity independent spectral analysis. The system's spectral resolution was less than 25 pm within a spectral operating range of 5 nm. The linearity and stability of a system is comparable to other principles of measurement. The spectral analyzer prototype allows fast, stable, and precise measurements of strain and temperature with Bragg-grating based sensors.