Fig. 1. Illustration of original Brillouin spectrum

Fig. 2. Fitted by the cross-correlation-LM method. (a) Before and (b) after removing intrinsic signals

Fig. 3. Bimodal fitting.(a) Correlation-LM method; (b) bimodal fitting algorithm

Fig. 4. Comparison of different algorithms for fitting simulation data with the central frequency 10.75 GHz. (a) Correlation-LM method; (b) PSO method; (c) traditional LM method; (d) correlation method

Fig. 5. Schematic of bimodal fitting. (a) Bimodal distance 0.2 GHz, second peak height of 0.4; (b) bimodal distance 0.075 GHz, second peak height of 0.7

Fig. 6. Adapted transformer windings

Fig. 7. Optical diagram of transformer winding deformation detection

Fig. 8. Comparison of experimental data fitting. (a) Correlation-LM method; (b) PSO method; (c) traditional LM method; (d) correlation method

Fig. 9. Brillouin central frequency of original winding

Fig. 10. Comparison of the Brillouin central frequency between the deformed and original winding