Significant dynamic range and precision improvements for FMF mode-coupling measurements by utilizing adaptive wavelet threshold denoising

In this paper, we propose and experimentally demonstrate a measurement method of mode coupling in few-mode fiber (FMF) based on adaptive wavelet threshold denoising. A nondestructive measurement system of mode coupling along an FMF is established to verify the performance of our proposed method. The system consists of a mode transverter (Photonic Lantern A), a mode demultiplexer (Photonic Lantern B), an FMF circulator and so on Experimental results show that, compared with the results obtained by the average time/number denoising of traditional optical time domain reflectometry (OTDR), the dynamic ranges of backscattered power of the excitation mode LP01, LP11a and LP11b are respectively increased by 3.72 dB, 3.43 dB and 3.37 dB with adaptive wavelet threshold denoising, and correspond to the dynamic ranges of the non-excitation mode are also improved. Moreover, the proposed technique effectively reduce the amplitude fluctuation of the backscattered power distribution of LP01, LP11a and LP11b modes, and thus the measurement accuracy of mode coupling coefficients are averagely raised by 2.62 dB/km between LP01 and LP11a, and 1.51 dB/km between LP01 and LP11b, respectively. We confirm that the dynamic range and measurement precision of mode-coupling are effectively improved.