Sensitivity enhanced fiber optic temperature sensor based on optical carrier microwave photonic interferometry with harmonic Vernier effect

A sensitivity enhanced fiber optic temperature sensor based on optical carrier microwave interferometry (OCMI) with harmonic Vernier effect is proposed and experimentally demonstrated. The sensor is composed of two cascaded Mach–Zehnder interferometers (MZIs) with different optical length differences. Harmonic Vernier effect in microwave frequency domain is generated due to the free spectral range (FSR) difference in the microwave frequency response. Temperature sensing is realized by detecting the intersection of the inner envelopes of the measured frequency response curve. Experimental results demonstrate that sensitivity up to 580.45kHz/°C has been obtained by employing the harmonic Vernier effect, whose sensitivity amplification factor is up to 18.61. Through the application of harmonic Vernier effect in microwave domain, the amplification factor can be easily adjusted with much higher manufacturing tolerance and alleviate the measurement range restriction induced by the periodic frequency response.