A switchable and tunable erbium-doped fiber laser with a linear cavity based on fiber Bragg gratings embedded in Sagnac rings is proposed and experimentally verified. Due to the stress birefringence effect and the polarized hole burning effect, which are introduced into the single-mode fiber in the polarization controllers (PCs) by the PCs, the designed laser can achieve seven kinds of laser-states output including three kinds of single-wavelength laser states, three kinds of dual-wavelength laser states and one kind of triple-wavelength laser state. The optical signal-to-noise ratios of the output wavelengths are all higher than 52 dB, and the wavelength shifts are all less than 0.04 nm. Furthermore, the temperature tuning of the wavelength range is also researched, which is about 1.2 nm. Due to advantages, such as low cost, simple structure, easy switching and multiple laser states, the designed laser has great application potential in laser radar, optical fiber sensing and so on.

In this paper, a new type of widely tunable and switchable multi-wavelength erbium-doped fiber laser based on a Sagnac-like loop embedded in Lyot filter is proposed. The nonlinear polarization rotation effect is obtained by adjusting two polarization controllers (PCs). The polarization-dependent isolator and the Sagnac-like loop are used as the basic structure to realize the wide tuning and wavelength switching in C-band. Compared with the traditional Lyot filter, the Sagnac-like loop is used to replace the segment of polarization-maintaining fiber, and a more uniform comb spectrum can be obtained by this filter. The tunable and switchable wavelengths can be achieved by adjusting the PCs based on the nonlinear effect of the loop. The laser can emit single-, dual-, triple-, quad- and quintuple-wavelengths. The optical signal-to-noise ratios all exceed 43 dB. It can also be adjusted to partial wavelength intervals for quad-wavelength and quintuple-wavelength. The tuning range can reach the full range of the C-band, and the laser efficiency can reach the practical application standard. It can be applied to some precision instruments and equipment.

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A multi-wavelength erbium-doped fiber laser using tungsten disulfide (WS2) as a nonlinear saturable absorber is proposed. The laser structure consists of a Lyot filter and a WS2 film in a ring cavity. The WS2 film attached to the end of the fiber jumper can suppress the mode competition phenomenon caused by erbium-doped fiber due to its good nonlinear optical properties. In addition, it can suppress mode contention and stabilize multi-wavelength output. The number of wavelengths can be tuned by adjusting the length of the polarization-maintaining fiber (PMF). In the Lyot filter, the PMF of 4, 8 and 12 m excite 5, 9 and 13 wavelengths with 1.38, 0.7 and 0.42 nm intervals, respectively. The experimental results show that in the range of 1528–1536 nm, the side-mode suppression ratio is 42 dB. After 60 min of continuous excitation, the output wavelength of the structure remains stabilization. It can be used as a light source in distributed sensing and wavelength division multiplexing systems.