Multimode Fabry-Perot Interferometer Probe based on Vernier Effect for Enhanced Temperature Sensing
in: Sensors (2019)
New miniaturized sensors for biological and medical applications must be adapted to the measuring environments and should provide large measurement resolution to sense small changes. The Vernier effect is an effective way of magnifying the sensitivity of a device, allowing for higher resolution sensing. We applied this concept in the development of a small size optical fiber Fabry-Perot interferometer probe that presents more than 60-fold higher sensitivity to temperature than the normal Fabry-Perot interferometer without the Vernier effect. This enables the sensor to reach higher temperature resolutions. The silica Fabry-Perot interferometer is created by focused ion beam milling the end of a tapered multimode fiber. Multiple Fabry-Perot interferometers with shifted frequencies are generated in the cavity due to the presence of multiple modes. The reflection spectrum shows two main components in the Fast Fourier transform that give raise to the Vernier effect. The superposition of these components presents a sensitivity enhancement to temperature. The same effect is also obtained by monitoring the reflection spectrum node without any filtering. A temperature sensitivity of 654 pm/°C was obtained between 30 °C and 120 °C, with an experimental resolution of 0.14 °C. Stability measurements are also reported.