Lossy mode resonance optical fiber sensor to detect organic vapors

A transmission sensor able to detect Volatile Organic Compounds (VOCs) has been developed using optical fiber with Plastic Cladding (PCS). Specifically, 1.5 cm of the cladding was removed in order to deposit an organometallic compound whose chemical structure is [Au2Ag2(C6F5)4(C6H5CCC6H5)2]n along this section. This complex reacts reversely in presence of organic vapors such as alcohols, therefore, it is used as sensing material. The compound was altered to show a negative charge, so it can be deposited combined with a positive charged polymer by means of the Layer-by-Layer (LbL) method. In this manner, as the nanolayers were deposited, Lossy Mode Resonances (LMRs) were induced and shifted. The polymer nanolayers doped with the organometallic material accelerated the LMRs appearance with respect to the nanolayers without additive and so, it enhanced the spectral shift. Once the construction process was completed, two LMRs were observed, choosing the second one to study the sensor behavior when it was placed at 663.57 nm. The sensor was exposed to different concentrations of ethanol, methanol and isopropanol vapors, showing sensitivities of 0.417, 0.520 and 263 nm ppm−1, respectively. In the case of methanol, the second LMR peak shows a remarkable blue shift of 100 nm. The interference with water vapors is minor to 1 nm below 60%, whereas the effect of temperature is insignificant between 20 °C and 60 °C.