WIDE-RANGE PH FIBER SENSOR WITH CONGO-RED-DOPED AND METHYL-RED-DOPED POLY(METHYL-METHACRYLATE) CLADDING

We introduce an evanescent-wave-spectroscopic fiber optic pH sensor. T his sensor has part of the polymer cladding doped with either congo re d (CR): which responds to pH=3 to 5: or methyl red (MR), which respond s to pH=5 to 7: as the pH sensor film, In this study we succeeded in e xpanding the measurable pH range by using two pH sensor probes with th e different pH sensitivities. In addition making the pH fiber sensor i nto a probe structure enabled us to achieve high pH sensitivity and to monitor the pH value easily. Reducing the quantity of doped dye made it possible to use the sensor for objects highly sensitive to pH chemi cal equilibrium.