Fiber Optic Temperature Sensor Based on the Harmonic Vernier Effect Generated by Two Sagnac Interferometers

A fiber-optic temperature sensor based on the harmonic Vernier effect (HVE) was proposed, which consists of a sensing Sagnac interferometer (SSI) and a reference Sagnac interferometer (RSI) in parallel. Different order HVEs are generated by controlling the length of the panda fiber in the SSI to be about an integer multiple of that in the RSI. The sensitivity and detuning of different order HVEs compared with the normal Vernier effect (NVE) are investigated, and the results show that the HVEs have almost the same temperature sensitivity as the NVE when they have the same magnification factor, while their detunings are much larger than that of the NVE, and the higher the order of the HVE, the larger the detuning. As we all know that the larger the detuning, the easier the magnification factor is to be controlled, that is, the easier the sensor is to be prepared, so from the point of view, the sensors based on the HVEs are better than those based on the NVE. This conclusion is also suitable for other fiber-optic sensors based on Vernier effect.