Optical fiber-based sensor of harmful gas fabricated using the electronic self-assembly monolayer process

A dichloromethane (DCM) gas optical fiber sensor has been fabricated building up a grating with poly(diallyldimethyl ammonium chloride), poly(sodium-4-styrenesulfonate) and Poly S-119 using the Electrostatic Self-Assembly Monolayer (ESAM) Process. The mechanism of this sensor relies on the reflectance change of an optical grating deposited at the end of a standard communications multimode optical fiber. The total length of this grating is less than 1.5 μm and the structure is HLHLH, where H means material with higher refractive index and L means material with lower refractive index. Experiments with an Optical Spectrum Analyzer showed that with this technique it is also possible to choose the optical working wavelength and the reference wavelength of the sensor, in this case 1310 and 1645 nm respectively, around 1 dB of variation was observed at the working wavelength when the sensor was exposed to DCM gas. Neither hysteresis nor cross-sensitivity with temperature were detected. In addition, experimental results after 8 months from the fabrication of the sensors are also presented.