Self-correction of nonlinear sweep of tunable laser source in OFDR

Abstract

Nonlinear laser wavelength tuning effects appear as phase noise in wavelength swept interferometry. A new method is proposed to compensate tuning nonlinear effects in optical frequency domain reflectometry (OFDR). The proposed method is simpler in configuration, and unlike conventional nonlinear compensation methods, it does not require separate auxiliary interferometer detection, which eliminates the need for an extra photo detector and an acquisition channel for the auxiliary interferometer. In the proposed method, an intentional beating signal is introduced in the beginning of the OFDR spectrum which is treated as an auxiliary interferometer to acquire tunable laser phase information for post signal processing. The proposed method can reduce overall OFDR system cost, reduce the data acquisition time and computational load by half, and make system configuration simpler by eliminating the need for extra components. Feasibility of the proposed method was demonstrated by compensating for tuning nonlinearity effects in an optical fiber approximately 35 m long with a measured spatial resolution of ~30 μm. To confirm performance of the proposed method, a comparison was carried out with a conventional nonlinear tuning compensation method, which requires the separate auxiliary interferometer. Moreover, distributed sensing using the proposed method was also demonstrated in an optical fiber approximately 35 m in length by performing strain sensing with 3 cm sensing resolution.