Multiwavelength erbium-doped fiber lasers with active coupling cavities

Abstract

Erbium-doped fiber (EDF) lasers with active coupling cavities have recently shown to enable the production of multiwavelength oscillations with various novel functions. This paper reviews the advances of such lasers. The lasers may be designed to produce multiwavelength oscillations in both C and L bands, either as a combined band or as two separate bands. In the C band, the laser can operate in a multiwavelength regime with controllable output powers and tunable wavelengths for any one individual lasing line. Wavelength-switching is also possible; switching responses of about 100 Hz are typical. In the L band, the laser exhibits multiwavelength bistable phenomena. The bistable hysterisis behaviors for a dual-wavelength laser evolve in antiphase with respect to each other. The width of the bistable region can be controlled; it could be designed to be as wide as a few hundred milliwatts. The two wavelengths can be switched from one to the other, with typical switching times of 4 to 15 ms. By suitably controlling the bistability, simultaneous multiwavelength oscillations in the L band alone, or in combination with the C band, can be obtained. A new wavelength-tuning and switching mechanism can be achieved by using such bistabilities. With this scheme, widely tunable and switchable lasers in fiber ring and linear configurations have been constructed with two commercially available tunable ordinary fiber Bragg gratings (FBGs). The lasers can be tuned over the whole L-band although the tunable range of each of the FBGs is only about 15 nm.