Accurate microthermometer based on off center polymer caps onto optical fiber tips

We report on microscopic polymer spherical caps bonded onto the cleaved end of a single-mode fiber (SMF) for fast, accurate, and sensitive temperature sensing. The microcaps were fabricated by dispensing sub nano-liter amounts of UV-curable polymer onto the end face of a standard SMF that was cleaved at a small angle. A reflection from the SMF-polymer interface combined with a reflection from the polymer-external medium interface gives rise to a well-defined interference pattern. The high thermal expansion coefficient of the polymer used to build the micro-caps allowed us to achieve temperature sensitivity up to 270 pm/°C, resolution of 0.04 °C, and thermal response time of around 2.5 s. The simple fabrication process and the broad operating wavelength (from 800 to 1600 nm, approximately) of our devices along with the diversity of polymers currently available, make the concept and approach proposed here appealing for diverse sensing applications.