Increasing the Measurement Dynamic Range of Rayleigh-Based OFDR Interrogator Using an Amplifying Add-On Module

An add-on amplifying module is presented, capable of significantly extending the measurement dynamic range of fiber-optic distributed strain/temperature interrogators, which are based on Rayleigh backscattering and optical frequency-domain reflectometry. Since Rayleigh backscattering in single-mode optical fibers is very weak, any optical loss along the sensing fiber, originating from bad connectors and/or micro-and macro-bending, especially under embedding, may jeopardize accurate strain measurements due to a deteriorated signal-to-noise ratio. It is shown that adding an optical amplifier between the interrogator output and the sensing fiber, together with an appropriate return path, has improved the one-way tolerable loss by 5 dB. In principle, better results can be obtained with higher optical gains until either optical reflections and backscattering into the interrogator increase its noise floor or other noise sources saturate the available signal-to-noise ratio.