A new optical reflective transducer for making temperature level measurements with the ability to be integrated in an all-fiber optical network is presented and discussed. The transducer is based on traditional Hg thermometers adapting this technology to the fiber optic technology. In order to demonstrate the viability of integrating the transducer in an optical fiber network a simple one has been designed and verified. The interrogation and measurement of the tranducers in the network have been made by suitable use of optical time domain reflectrometry. Experimental results are good.