Integrated Auxiliary Interferometer to correct non-linear tuning errors in OFDR

Swept Wavelength Interferometry (SWI) based on Tunable Laser Source (TLS) has various applications in optical measurement and imaging. Nonlinear tuning of the TLS is always a problem in SWI and require proper correction to enhance the spatial resolution and SNR of the signal. Typically, nonlinear tuning correction requires an extra (auxiliary) interferometer. A new type of Optical Frequency Domain Reflectometry (OFDR) arrangement was proposed in which auxiliary interferometer was integrated with the main interferometer and only a single detection channel was used instead of two. This new hardware design eliminated the need for an extra photodetector and an acquisition channel for the auxiliary interferometer. Single trace having beating signal from auxiliary and Rayleigh backscattering from the main interferometer was acquired in a single detection channel. Then the beating signal of the auxiliary interferometer was used to correct nonlinear tuning effects from Rayleigh backscattered signal of the main interferometer. The feasibility of new hardware design is demonstrated by correcting nonlinear tuning effects in a 50 meters long optical fiber and performing distributed strain and temperature sensing in the OFDR technique. Furthermore, an extension of the proposed new design is also described in this paper in which the auxiliary interferometer is replaced by a high reflection event inside the Fiber Under Test (FUT) created by femtosecond laser which makes the overall system design more compact and simpler.