TIME-DIVISION MULTIPLEXING OF COHERENCE TUNED OPTICAL FIBER SENSORS BASED UPON A MULTIMODE LASER DIODE

We describe a scheme in which a multimode laser diode, with effective coherence length less than 250-mu-m, is used to illuminate sensors multiplexed in time and with their status read by coherence sensing. Data is presented which shows that the spectral characteristics of the laser light remain essentially unchanged upon direct modulation of the laser injection current or whilst subject to laser feedback. This has allowed the multiplexing scheme network to be implemented without recourse to either a Bragg cell modular or an optical isolator. The technique was applied to measure displacement, strain and temperature.