Packaged magnetic sensor based on a saddle-shape Whispering Gallery Mode microresonator

Incorporating optical Whispering Gallery Mode (WGM) microresonators in real life sensing applications is of great interest due to their tiny volumes and very high quality factors. Taper-fiber coupled microresonators, in particular, suggest high simplicity, low cost, and wide range of achievable coupling regimes. Here we apply a unique packaging method based on a tapered fiber-coupled saddle-shape microresonator (SSM), providing high mechanical stability while preserving the quality (Q) factor of the microresonator. The ability to tune the SSM's WGMs mechanically is harnessed here to detect the elongation of a magnetostrictive Terfenol-D (Ter-D) rod, and therefore to measure variations in the ambient magnetic field. As we demonstrate here, this packaging technique enables the production of tightly packaged WGM-based devices. The simplicity in manufacturing SSMs, their high Q factors, the ability to tune their WGMs mechanically/magnetically, and the high mechanical stability they provide, make them great candidates as a platform for practical miniature WGM-devices.