Wideband tunable Erbium-doped fiber ring laser using switchable parallel fiber Bragg gratings

A wideband wavelength tunable Erbium-doped fiber laser using a unidirectional traveling-wave fiber ring combined with a novel switchable fiber Bragg grating (FBG) array is presented. The switchable FBG array consists of a 1x3 optical switch and three parallel discrete FBGs. The central reflection wavelengths of these three discrete FBGs are 1534 nm, 1549.15 nm and 1559.4 nm, respectively. The corresponding reflectivities are 90%, 99% and 99.8%, respectively. The wavelength of each grating can be continuously tuned in a range of over 16 nm by stretching (7 nm) and compressing (8 nm) the FBG. Therefore a fiber ring laser with a very large wavelength tuning range has been successfully demonstrated. In our experiment, the wavelength tuning range of the Erbium-doped fiber ring laser is 38 nm, from 1527 nm to 1565 nm. Within this tuning range, the total output power is about 7-8 dBm, the 3-dB linewidth is 0.01 nm, and the side mode suppression ratio is more than 48 dB. This tunable fiber ring laser can also work in the mode-locking mode when an amplitude modulator is inserted in the cavity. By applying the driving frequency matching the round-trip frequency or its multiples to the modulator, active mode-locking is realized. The highest harmonic order achieved is 125, the repetition rate and pulse-width of the mode-locked pulses are 1.00475 GHz and 539 ps, respectively.