Fiber-Bragg-grating cavity sensor interrogated with a self-seeded fabry-Perot laser diode

We propose a low-cost general-purpose fiber Bragg grating (FBG) cavity sensing technique, where short pulses generated from a self-seeded Fabry-Perot laser diode are used to interrogate a fiber cavity formed with two chirped FBGs and the optical loss in the cavity is determined from the power ratio of the first two pulses reflected from the cavity. This technique does not require intensity referencing and the measurement is insensitive to drifts in the center wavelengths of the FBGs. We demonstrate this technique experimentally with a long-period fiber grating placed in the fiber cavity as a refractive-index sensor.