Fig. 1. Schematic diagram of the (a) LPFG and (b) polarization-dependent spectral measurement system.

Fig. 2. (a) Measured transmission spectrum of the LPFG with a period of 600 µm; (b) measured loss spectrum, orthogonal polarization spectra, and PDL in the wavelength range of 1530–1600 nm.

Fig. 3. (a) Transmission spectra and (b) PDL spectra of the LPFG as temperature increases; (c) resonance wavelength shift and (d) maximum PDL of the LPFG as a function of temperature.

Fig. 4. Schematic diagram of the mode-locked fiber laser based on LPFG.

Fig. 5. Output characteristics of the LPFG-based fundamental frequency mode-locked operation of the laser. (a) Optical spectrum; (b) output pulse train; (c) repetition rate; (d) AC trace.

Fig. 6. Output characteristics of the LPFG-based harmonic mode-locked operation of the laser. (a) Output pulse train with different orders; (b) optical spectrum; (c) repetition rate; (d) AC trace of the 40th-order harmonic mode locking.

Fig. 7. (a) Spectral evolution of the mode-locked fiber laser when the temperature on grating changes from 25°C to 105°C; (b) central wavelength and output power; (c) 3 dB-spectral width and pulse duration of the laser exhibit changes in response to variations in temperature.