Extension of sensing distance in a ROTDR with an optimized fiber

A sensing fiber, with a gradually increasing Raman-gain-coefficient (gR/Aeff)along the fiber length, and which can keep the received Raman Stokes power constant in a distributed Raman-based Fiber-optic temperature Sensor, is proposed. This method can be an additional and easy way to further extend the sensing distance of the distributed Raman Fiber-optic temperature Sensor.