Fiber-optic physical and biochemical sensing based on transient and traveling long-period gratings

A fiber-optic sensing platform based on a transient and traveling long-period grating (LPG) in a single-mode optical fiber has been proposed and demonstrated. The LPG is generated by pulsed acoustic waves that propagate along the fiber. First, we demonstrate the LPG for temperature measurement along the fiber. By coating the fiber with ultrathin ionically self-assembled multilayers, we then show that the LPG is capable of detecting nanometer thickness variations of the fiber. A temperature compensation method is also proposed and demonstrated. Because the acoustically generated LPG travels along the fiber, this advance is expected to yield a highly sensitive fully distributed fiber-optic biochemical sensor.