All-fibre optical sensing system: Bragg grating sensor interrogated by a long-period grating

We report here a simple, low-cost all-fibre grating strain sensing interrog ation technique offering high static-strain resolution (0.5 mu epsilon) and large dynamic range (>8100 mu epsilon). A key interrogating component of t his technique is a long-period grating which acts as an edge filter convert ing strain-induced wavelength variation into optical power measurement. The transmission profile of the long-period grating is shown to be nearly line ar over a sufficiently wide range, yielding a linear relationship between t he resultant intensity and applied strain, and a high resolution achieved b y standard lock-in techniques.