Study of the Sensitivity Limit of Vernier Effect and a Novel Tracking Method of Vernier Envelope

In recent years, optical fiber interferometric sensors based on the Vernier effect attract intensive attention due to their ultrahigh sensitivity. However, the limit of sensitivity enhancement via the Vernier effect has not been fully discussed in theory and verified in experiments. The main reason may lie that it is hard to control the free spectral range (FSR) difference between the sensing and reference interferometers precisely in the fabrication process, which causes it impossible to reach the maximum sensitivity. Moreover, tracking either the upper or the lower Vernier envelope usually draws an inconsistent measurement result. The information included in only one side envelope may lead to uncertainty in measurement sensitivity. In this letter, the limit of sensitivity via the Vernier effect is studied theoretically, and experimentally verified by utilizing a virtually tunable reference cavity and the novel determination method of the Vernier envelope tracking. A sensitivity of 42.05 nm/°C can be achieved in the temperature measurement, which verifies the limit of sensitivity enhancement of the Vernier effect, and the validity of the novel tracking method of the Vernier envelope that contains more comprehensive information from both upper and lower envelopes.