Individually Switchable and Widely Tunable Multiwavelength Erbium-Doped Fiber Laser Based on Cascaded Mismatching Long-Period Fiber Gratings

A novel concept of individually switchable and widely tunable erbium-doped multiwavelength fiber laser (MWFL) is proposed and experimentally demonstrated. The key component of the laser is a channel transmissivity individually variable comb filter composed of two cascaded different-length long-period fiber gratings (LPFGs), named cascaded mismatching LPFGs. When inserted into the laser cavity, this polarization-dependent comb filter functions as the wavelength selector and switching filter simultaneously. By properly adjusting the polarization controllers (PCs) in the laser cavity and in the high birefringence Sagnac loop mirror (HiBi-SLM), eleven individually switchable wavelengths with different flexible lasing states, including successively tunable adjacent single-, dual- and triple- wavelength outputs, nonadjacent dual- and triple- wavelength outputs, as well as quadruple- and quintuple-wavelength outputs, have been achieved. This MWFL may be useful in optical fiber sensing or other fields desiring very flexible optical source.