Spacing-adjustable and switchable multi-wavelength erbium-doped fiber laser using the filter of MMF–PMF–MMF based on PHB

A spacing-adjustable and switchable multi-wavelength erbium-doped fiber laser is proposed and analyzed based on the polarization hole burning (PHB) effect. The comb filter consists of multimode fiber–polarization maintaining fiber–multimode fiber (MMF–PMF–MMF). Here the filter is used as the polarization-dependent element to induce the polarization hole burning (PHB) effect. The filter is placed in the laser cavity or embedded into the Sagnac loop. By adjusting the polarization controller (PC) in the cavity, when the filter is placed in the laser cavity, the output wavelengths can be switched from single-wavelength to sextuple-wavelength, and dual-, triple-, quad-, quintuple- and sextuple-wavelength with adjustable wavelength spacing can be obtained. The dual-wavelength has a substantial amount of wavelength spacing adjustability with the range of 3.32 nm to 30.16 nm. When the filter is embedded into the Sagnac loop, the wavelength tuning ranges for single-, dual-, triple- and quad-wavelength are 28.42 nm, 28.10 nm, 18.21 nm and 14.58 nm, respectively. The proposed erbium-doped fiber laser (EDFL) provides a wide range of wavelengths and adjustable spacing, which is suitable for a variety of applications such as optical communication, optical detection and optical signal processing.