Highly sensitive bending sensor based on Er³⁺-doped DBR fiber laser

A short cavity Er3+-doped distributed-Bragg-reflector (DBR) fiber laser with a low polarization beat frequency has been demonstrated for bending measurement. The polarization beat frequency of the DBR laser is extremely sensitive to bending and can measure curvature changes as small as 1.8 × 10-2 m-1. Excellent agreement between experimental and theoretical results was obtained for bending curvatures from 0 m-1 to 58.8 m-1 with corresponding changes in beat frequency from 18.6 MHz to 253 MHz. The sensor is insensitive to temperature fluctuations and has a temperature coefficient of the beat frequency of -25.4 kHz/°C, making the temperature compensation unnecessary in most practical applications. The very low beat frequency of the DBR fiber laser makes frequency downconversion unnecessary. This can greatly simplify the demodulation scheme and thus, allow the realization of low-cost but highly sensitive optical bending sensor systems.