Fig. 1. Schematic of the synchronized multi-color Q-switched EDF laser with a PI-FBG. Insets: reflection spectrum, schematic illustration, and micrograph of the PI-FBG with two parallel-inscribed FBGs. LD, laser diode; WDM, wavelength division multiplexer; EDF, erbium-doped fiber; PI-FBG, parallel-integrated fiber Bragg grating; PC, polarization controller; CNT-SA, carbon nanotube saturable absorber; SMF, single-mode fiber.

Fig. 2. Synchronized dual-color Q-switched pulse at pump of 80 mW: (a) spectra, (b) pulse trains, (c) RF spectra, and (d) pulse profiles.

Fig. 3. Evolutions of the synchronized dual-color Q-switched pulse versus pump power: (a) pulse duration, (b) repetition rate, (c) average output power, and (d) pulse energy.

Fig. 4. Dependence of the intracavity self-synchronization on the GDD between the dual-color pulses: (a) spectra, (b) average output power, and (c) repetition rate as a function of the GDD. Inset: schematic diagram of the relative temporal walk-off (τ_d).

Fig. 5. Starting dynamics of the synchronized dual-color Q-switched pulse as a function of the pump power: (a) spectra, (b) pulse profile, (c) spectra at transition points (I: 11.8 mW, II: 12.6 mW, III: 14.4 mW, IV: 15.0 mW), (d) pulse duration, and (e) repetition rate.

Fig. 6. Synchronized triple-color Q-switched pulse using a PI-FBG with three parallel-inscribed FBGs: (a) spectra and (b) pulse trains. Black dashed curve: the reflection spectrum of the PI-FBG. Inset: the distribution of three FBGs on the cross-section of the PI-FBG.