FBG sensor multiplexing system based on the TDM and fixed filters approach

An analysis of the Bragg wavelength deviation generated by the TDM multiplexing of a large number of low reflective sensors at the same nominal wavelength using a single optical fiber has been proposed. In this paper, the demodulation technique based on Fixed Spectrum Filters is compared with peak position of full wavelength spectrum. Results indicate that the fixed filter approach is less sensitive to wavelength distortion due to shadow of other sensors operating at the same nominal wavelength. In addition, an experimental setup using combined TDM and WDM multiplexing technique was implemented. Experimental results indicate that a dynamic range of 1.7 nm was obtained with maximum uncertainties equivalent to approximately 20 pm. Experimental simulations indicate that it would be possible to use a number of approximately 70 sensors with 0.4% reflectivity at each nominal sensor wavelength. Considering the DWDM filter bandwidth (1539–1565 nm) used in this system, and a spectral separation of 7 nm by nominal sensor wavelength, a number of 210 sensors can be obtained, in three different nominal sensor wavelengths. Using the C-band and the L-band, a number of 1000 sensors can be obtained, in 14 different nominal sensor wavelengths. Using depolarization light the uncertainty can be improved.