In recent years, cavity ringdown and fiber loop ringdown (FLRD) spectroscopy have been introduced in fiber sensor technology,The FLRD spectroscopy transfers the cavity loss to the decay time measured in time-domain, and greatly enhances the detection sensitivity.

Researchers at Shanghai Key Laboratory of All Solid-state Laser and Applied Techniques——Shanghai Institute of Optics and Fines Mechanics (SIOM/China) have proposed a novel scheme for acquiring the spatial location based on FLRD configuration in the LCFBG sensor system. The strain position is readout by the round trip time of FLRD pulses; it is a new concept of time-domain reflectometry, different from the methods of low-coherence and OFDR. [Optics Letters 36 (6), 879, 2011]

The local Bragg wavelength of the LCFBG, which relates with the distributed sensing information, is acquired by synchronizing the wavelength of the injected optical pulse with the position obtained. Based on this scheme, a distributed strain sensor is performed experimentally for uniform and nonuniform strain distribution, which exhibits 2mm spatial resolution within the LCFBG. The sensor network is also explored and researched experimentally.