Nowdays, polymers like hydrogels that respond to well defined stimuli, have a particular interest in fields like
optoelectronics, biotechnology, materials, etc. One of this polymers is the NIPAAM, that posses thermo optics
properties. This work is oriented to the design and implementation of a temperature sensor using fiber optics and having
as sensitive part a sintetized hydrogel of polyNIPAAM and MeOXA of reversible thermosensible characteristics. For this
setup we use a glass ampoule which is coupled to two pieces of plastic, inside the ampoule it is placed the hydrogel. The
working principle relies in the turbidity changes in a well known temperature called critical. We present the experimental results of the designed and implemented device.
An alarm system as extrinsic sensor on optical fibers for detecting and controlling inflammable liquids based on thermosensitive
proprieties of the PNIPAAm hydrogel is presented. The changes on the optical proprieties of the PNIPAAm
with the temperature (being its LCST 32°C), induce abrupt changes on the light intensity and they act as an alarm signal,
which is transmitted by optical fibers and after they will be processed by an optoelectronic circuit, responsible to active
an alarm. An appropriate system consists of the hydrogel connected between its ends to two segments of plastic optical
fibers (source and receiver) and they turn on the alarm when a photo detector does not receive light when the hydrogel
becomes when it reaches threshold of temperature. The characterization of the hydrogel and the experimental results are
presented for a prototype.