VCSEL-Based Tilted Fiber Grating Vibration Sensing System

A fiber-optic vibration sensing system that uses a tilted fiber Bragg grating (TFBG) and a vertical-cavity surface-emitting laser (VCSEL) has been demonstrated. The backward-propagating low-order cladding modes excited by the TFBG can be effectively recoupled to the fiber core via a lateral-offset-splice upstream the TFBG and the amount of recoupling varies strongly with fiber curvature, providing the sensing mechanism. VCSEL with matched wavelength enables the recoupling to work at a high power level and an improved optical signal-to-noise ratio better than 40 dB is achieved. Meanwhile, VCSEL provides a high-speed continuous wavelength tuning over 1 $\sim$ 2 nm which perfectly covers the strongest recoupling band, making the demodulation filter unnecessary. Dynamic vibration measurement up to 200 Hz has been achieved via cost-effective normalized power detection.