Fig. 1. (a) Schematic diagram of two-step wavelength detection: the signal to be measured is located to the rough wavelength unit through the inner product correlation operation, and the fine wavelength value is further determined by the principal component analysis algorithm; (b) Further illustration: the working bandwidth is divided into m coarse wavelength units, and each unit is sub-divided into n fine wavelengths

Fig. 2. (a) Experimental diagram of wavelength detection based on tapered multimode fiber; (b) Radiation images of tapered fiber in different regions and incident wavelengths, scale bar: 100 μm; Plots of transmission mode number with respect to (c) fiber diameters and (d) incident wavelengths

Fig. 3. The intensity distribution patterns are extracted along the axis of the fiber with different taper diameters (a) 40 μm, (b) 50 μm and (c) 60 μm

Fig. 4. The relationship between the inner product and (a) diameter and (b) length of the tapered fiber at the wavelength of 635 nm

Fig. 5. (a) Detection of two separate monochromatic light signals; (b) spectral resolution of 20 pm; (c) plot of the detected wavelength versus calibrated wavelength; (d) statistical histogram of wavelength detection results

Fig. 6. Variation of inner product bandwidth with time