Fig. 1. (a) The structural diagram of spectroscopy detection based on the multimode fiber; (b) the multimode interference patterns at different wavelengths.

Fig. 2. The detecting principle of the spectrometer based on a multimode fiber.

Fig. 3. (a) The reconstruction of two narrow lines, indicating the resolution is 20 pm; (b) The reconstruction error as a function of noise threshold.

Fig. 4. (a) and (b) are spectral reconstructions of the fiber-based spectrometer under different LED-source combinations.

Fig. 5. (a) The infrared spectrometer based on a multimode fiber; (b) The spectrometer based on a planar multimode waveguide; (c) A portable spectrometer integrated with a smart phone.