High-repetition-rate ultrafast fiber lasers

Multi-gigahertz fundamental repetition rate, tunable repetition rate and wavelength, ultrafast fiber lasers at wavelengths of 1.0, 1.5, and 2.0 µm are experimentally demonstrated and summarized. At the wavelength of 1.0 µm, the laser wavelength is tuned in the range of 1040.1-1042.9 nm and the repetition rate is shifted by 226 kHz in a 3-cm-long all-fiber laser by controlling the temperature of the resonator. Compared with a previous work where the maximum average power was 0.8 mW, the power in this study is significantly improved to 57 mW under a launched pump power of 213 mW, thus achieving an optical-to-optical efficiency of 27%. For comparison, a similar temperature-tuning technique is implemented in a Tm³⁺-doped ultrafast oscillator but, as expected, it results in a broader tunable range of 14.1 nm (1974.1-1988.2 nm) in wavelength as compared with the value of 1.8 nm for the wavelength of 1.0 µm. The repetition rate in the process is shifted by 294 kHz. For the high-frequency range from 100 kHz to 10 MHz, the value of integrated timing jitter gradually increases with an increase in temperature. Finally, to the best of our knowledge, for the first time, a new method for tuning wavelength and repetition rate is proposed and demonstrated for a femtosecond fiber laser at the wavelength of 1.5 µm. Through fine rotation of the alignment angle between the Er/Yb:glass fiber and a semiconductor saturable absorption mirror, the peak wavelength can be tuned in the range of 1591.4-1586.1 nm and the repetition rate is shifted by 60 kHz.