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We present a low noise single-frequency and single-polarization distributed Bragg reflector fiber laser at 1083 nm by using a 1.8 cm long newly developed ytterbium-doped phosphate single mode glass fiber. The maximum output power is more than 100 mW with a slope efficiency of $>29.6\%$. The signal to noise ratio is higher than 61 dB and the laser linewidth of less than 2 kHz is estimated. The obtained relative intensity noise for frequencies of over 4.0 MHz is less than $-150\mathrm{dB}/\mathrm{Hz}$, which approaches the shot noise limit. The achieved linear polarization extinction ratio is more than 30 dB.

An all-optical frequency and intensity noise suppression technique of a single-frequency fiber laser is demonstrated. By exploiting the recursive noise reduction effect of a semiconductor optical amplifier (SOA) in a self-injection locked fiber laser, the frequency and intensity noise of the laser are remarkably suppressed in a significantly wide frequency range. In addition to the linewidth suppression from 3.5 kHz to 700 Hz, the frequency noise has been reduced by $\sim 25\mathrm{dB}$. After suppression, the relative intensity noise (RIN) is within 5 dB of the shot noise limit at frequencies from 1.5 to 3 MHz, and the frequency range of the suppression reaches about 30 MHz. The relaxation oscillation peak is observed to shift to lower frequencies and is reduced by about 35 dB from $-90\mathrm{dB}/\mathrm{Hz}$ to $-125\mathrm{dB}/\mathrm{Hz}$. It is believed that the achieved low noise makes the fiber laser a promising candidate in applications such as ultra-long haul coherent optical communication and LIDAR.

We proposed a short-linear-cavity (SLC) fiber laser based on a virtual-folded-ring (VFR) resonator and a fiber Bragg grating Fabry–Perot filter. Spatial hole burning effect was reduced by retarding the polarization state of the counter-propagating light waves utilizing the VFR structure. The photon lifetime of the resonator was extended due to the multi-reflection inside the FBG FP, which increased the intra-cavity power and relatively suppressed the contribution of phase diffusion from spontaneous emission. The relaxation oscillation frequency is around 160 kHz due to the slow light effect. The linewidth of the SLC fiber laser was measured to be less than 600 Hz.

An all-fiber high-power linearly polarized chirped pulse amplification (CPA) system is experimentally demonstrated. Through stretching the pulse duration to a full width of approximately 2 ns with two cascaded chirped fiber Bragg gratings (CFBGs), a maximum average output power of 612 W is achieved from a high-gain Yb-doped fiber that has a core diameter of 20 μm with a slope efficiency of approximately 68% at the repetition rate of 80 MHz. At the maximum output power, the polarization degree is 92.5% and the M² factor of the output beam quality is approximately 1.29; the slight performance degradations are attributed to the thermal effects in the main amplifier. By optimizing the B-integral of the amplifier and finely adjusting the higher-order dispersion of one of the CFBGs, the pulse width is compressed to 863 fs at the highest power with a compression efficiency of 72%, corresponding to a maximum compressed average power of 440.6 W, single pulse energy of 5.5 μJ and peak power of about 4.67 MW. To the best of our knowledge, this is the highest average power of a femtosecond laser directly generated from an all-fiber linearly polarized CPA system.

A high-energy Mamyshev oscillator was experimentally demonstrated with an all polarization-maintaining 10/125 fiber configuration, which is initiated by an external pulse radiation. A maximum output power of 787.3 mW with the single pulse energy of 83.5 nJ was achieved at a repetition rate of 9.43 MHz. The pulse width was compressed to 56 fs with a grating pair, corresponding to a peak power of 1.15 MW considering the insertion loss of the grating pair. The evolution of the pulse properties versus the enhancement of the energy was examined and an excellent long-time stability was verified. It is believed that such a compact all-fiber ultrafast oscillator could be a promising source for practical applications such as material processing, medicine, nonlinear microscopy and so on.