All-fiber dual-wavelength Q-switched and mode-locked EDFL by SMF-THDF-SMF structure as a saturable absorber

Abstract

We demonstrate all-fiber dual-wavelength Q-switched and mode-locked erbium-doped fiber laser (EDFL) by utilizing the thulium-holmium-doped fiber (THDF) as a fiber saturable absorber (SA) and also a Mach-Zehnder interferometer (MZI) element. The 19cm long THDF has a core diameter of 11.5µm, refractive index difference of 0.005, and cutoff wavelength of 1810nm. Stable dual-wavelength Q-switching operation was generated at 1555.14nm and 1557.64nm with free spectral range (FSR) of 2.5nm. The repetition rate of 14.45–78.49kHz was obtained between 12 and 100mW pump power. At maximum pump power, the maximum output power and pulse energy were 2.58mW and 32.87 nJ, respectively. By adding 195cm long SMF in the same cavity, the stable dual-wavelength mode-locking operation was started at 166mW and continue stable to 201mW pump power. This mode-locking operation produced stable dual-wavelength pulses at 1530.34nm and 1532.84nm with a repetition rate of 1MHz with a pulse duration of 128ns and signal-to-noise ratio (SNR) of 62dB. It shares the same value of FSR in Q-switching operation. The highest output power of 1.57 nJ corresponds to the maximum output power of 1.57mW was obtained. Our results validate the linear absorption characteristic at C-band region and multimode fiber effect of THDF can be utilized as SA to generate stable all-fiber dual-wavelength pulsed lasers. Remarkably, these findings expand a fiber gain medium application in short pulse generation.