Low Cutoff Wavelength Etched SMS Structures Towards Verification of the Quality of Automotive Antifreeze

Optical fiber single mode - multimode - single mode (SMS) structures can be used as wavelength detection-based sensors. In this work, we focus on the performance at short wavelengths, where optical sources and detectors are less expensive. Here, a self-image band with a high transmission power is monitored in this short-wavelength range. In addition, the diameter and the length of the SMS structure have been optimized in order to improve the sensitivity of the device. In this sense, a maximum refractive index sensitivity of 305 nm/RIU was achieved by an etched SMS with a diameter of 34~\mu \text{m} . Furthermore, the obtained devices were used for testing the quality of automotive coolant and antifreeze liquid.