Simultaneous Sensing of Refractive Index and Temperature With Supermode Interference

In general, a sensor is used to monitor a single parameter only, and in many cases, a reference sensor is necessary to compensate the effect of temperature. Here, we demonstrate that a single supermode interferometer is capable of monitoring two parameters simultaneously. Said interferometer was fabricated with a segment of strongly coupled multicore fiber fusion spliced at the end of a standard single mode fiber. The free end of the multicore fiber was flat, thus, it behaved as a low reflectivity mirror whose reflection depended on the external refractive index. The reflection spectrum of our supermode interferometer consisted of well-defined periodic maxima and minima whose values and position varied when the interferometer was exposed to refractive index and temperature changes. In the Fourier domain, the changes of the interference pattern can be decoded easily. We demonstrate that the supermode interferometer here proposed can be useful to measure the thermo-optic coefficient of a sample. An important advantage of the device reported here is that the length of the multicore fiber is not determinant on the performance of the sensor. In addition, the device can be reused multiple times.

Automated summary

This study demonstrates that a single supermode interferometer can monitor two parameters simultaneously by utilizing strongly coupled multicore fiber and standard single mode fiber. The reflection spectrum of the interferometer changes with refractive index and temperature, allowing for easy decoding of interference patterns in the Fourier domain. An important advantage of this device is that the length of the multicore fiber does not affect sensor performance, and the device can be reused multiple times.