Stable dual-wavelength erbium-doped fiber ring laser with switchable spacing employing controllable channel loss

A switchable and wavelength-spacing tunable single-frequency and single-polarization dual-wavelength erbium-doped fiber laser based on a compound-cavity structure

“…Dual-wavelength single-frequency erbium-doped fiber (EDF) lasers (EDFLs) have attracted great interest in recent years because of their potential advantages in applications such as fiber sensing, optical signal processing, radio-over-fiber communication systems, radar systems and photonic generation of microwave signals [1][2][3][4][5][6][7][8][9][10]. Single-frequency dual-wavelength EDFLs, with tunable wavelength spacing, have been considered a valuable source of microwave or millimeter-wave generation, and even for terahertz-wave radiation [3,4,[8][9][10].…”

“…In recent years, researchers have proposed many useful dual-wavelength EDFLs with different techniques. Feng et al used a chirped moiré fiber Bragg grating (FBG), combined with a common chirped FBG, to select the longitudinal mode to achieve stable dual-wavelength lasing for the first time and obtained a microwave signal at 17.682 GHz by beating the laser output [8]; Tan et al presented a dual-wavelength ring-cavity fiber laser with a wavelength spacing of 8.53 nm by using a superimposed FBG and an in-line two-taper Mach-Zehnder interferometer (MZI) [4]; Feng et al reported a single-frequency dual-wavelength ring EDFL with a wavelength spacing of 0.182 nm based on a polarization maintaining FBG combined with an unpumped EDF saturable absorber and used this EDFL to generate a microwave signal at 22.807 GHz [9]; Sulaiman et al demonstrated a compact and low noise dual-wavelength fiber laser with a wavelength-spacing of 13.7 nm using a 70 cm EDF loop attached to a microfiber coupler [5]; Moon et al reported two types of dual-wavelength EDFLs with stable and uniform intensity laser outputs by using four-mixing of dispersion shifted fibers to suppress the homogeneous broadening of EDF [6]; Using a pair of FBGs with different center wavelengths and a segment of unpumped polarization maintaining EDF, combined with the polarization controller (PC), Wang et al fabricated a single-frequency dual-wavelength ring EDFL to generate a microwave signal at 26.44 GHz [10]; Wang et al proposed and demonstrated a single-frequency dual-wavelength fiber laser by incorporating a reconfigurable dual-pass MZI filter and achieved microwave signal generation by beating the laser output [11]. However, all of these techniques cannot give dual-wavelength lasing with continuously tunable wavelength spacing.…”