Dispersion compensation method based on focus definition evaluation functions for high-resolution laser frequency scanning interference measurement

We study dispersion mismatches and compensation in high-resolution frequency scanning interference measurements. Compared to semiconductor lasers, external cavity lasers can, in theory, provide wideband frequency modulation and high-resolution measurements. However, experiments indicate that the dispersion mismatch cannot be ignored in measurement systems containing wideband tuning lasers. Fibre auxiliary interferometer external clock sampling results indicate that the beat frequency of measurement signals exhibits linear chirp. In turn, the frequency spectrum of the measurement signal broadens, thus lowering the measurement resolution and limiting the measurement distance. We present a dispersion mismatch model and analyse the associated measurement effects. We also propose a dispersion compensation method based on a focused definition evaluation function. By studying the relationship between the compensation coefficient and evaluation function, the optimal compensation coefficient can be determined quickly and accurately. Our experiments demonstrate that within a tuning bandwidth of 40 nm, the peak full width at half maximum (FWHM) after dispersion compensation is 32.2 µm at a distance of 3.8931671 m, which is close to the theoretical resolution. Our method provides a technical approach to realizing large, high-resolution distance measurements for broadband laser frequency scanning interferometers.