A Fabry–Perot interferometer formed in the core of a composite optical fibre heavily doped with phosphorus oxide

We report a new method for manufacturing a Fabry–Perot interferometer in the form of a microcavity in the optical fibre core. The method is based on the use of the process of electric discharge fusion splicing of a conventional optical fibre and a special composite fibre having a core with a high content of phosphorus oxide. The possibility of using this interferometer as a sensitive element of a strain sensor with high temperature stability is shown.