Temperature-independent refractometer based on fiber-optic Fabry–Perot interferometer

• A miniature sensing structure with a length of ~150 μm is proposed.
• The fabrication process only includes fusion and etching.
• RI and temperature response are characterized by monitoring the interference dip change.
• Simultaneous measurement for RI and temperature has been achieved.
• This sensor has been proved to be a good candidate for bio-sensing applications.

A miniature fiber-optic refractometer based on Fabry–Perot interferometer (FPI) has been proposed and experimentally demonstrated. The sensing head consists of a short section of photonics crystal fiber (PCF) spliced to a single mode fiber (SMF), in which the end-face of the PCF is etched to remove holey structure with hydrofluoric (HF) acid. A Fabry–Perot interference spectrum is achieved based on the reflections from the fusion splicing interface and the end-face of the core of PCF. The interference fringe is sensitive to the external refractive index (RI) with an intensity-referenced sensitivity of 358.27 dB/RIU ranging from 1.33 to 1.38. The sensor has also been implemented for the concentration measurement of λ-phage DNA solution. In addition, the dip intensity is insensitive to the ambient temperature variation, making it a good candidate for temperature-independent bio-sensing area.