Handing Xia

Single-frequency fiber lasers (SFFLs) are essential for applications such as gravitational wave detection, high-precision spectroscopy, and inertial confinement fusion, requiring narrow linewidth, low noise, and high output power. Here, we present a comparative study of 1 μm waveband distributed Bragg reflector (DBR) SFFLs with varying cavity parameters. Numerically, we investigate the effects of key cavity parameters on laser performance by plotting contour maps of output power versus grating reflectivity and lasing wavelength. We also simulate intensity noise transfer functions from pump fluctuations. Increasing pump power shifts the relaxation oscillation peak to higher frequency and reduces its amplitude, which originates from the higher intracavity photon density that speeds up the damping of perturbations. Experimentally, we construct two lasers using 6.5 mm and 10.5 mm YDFs spliced between FBG pairs. These lasers employ low-reflectivity FBGs centered at 1053 nm and 1064 nm, with reflectivities of 74% and 55%, respectively. The corresponding maximum output powers are 29.7 mW and 197 mW. The 1053 nm SFFL exhibits a relative intensity noise (RIN) of −102 dBc/Hz at 2.07 MHz, a linewidth of 12.52 kHz, and a mode-hop-free tuning range of 0.64 nm. Although increasing the pump power suppresses the relaxation oscillation peak, it broadens the linewidth due to laser phase noise degradation caused by pump noise-induced temperature fluctuations in the gain fiber. For SFFLs, the output powers should be selected according to the specific application, as a higher output power inherently leads to a broader linewidth. These insights are essential for optimizing such lasers and underscore their strong potential for future applications.

We demonstrate an all-polarization-maintaining (PM) dispersion-managed mode-locked ytterbium-doped fiber oscillator based on a nonlinear amplifying loop mirror (NALM). Experimentally, three mode-locking regimes with distinct tailored spectra are achieved with carefully designed cavity setup and adjusted pump power. Using the dispersive Fourier transformation (DFT) technique, the real-time transition dynamics among these regimes are observed as the pump power decreases. It is revealed that the intracavity gain does not decrease continuously during the relaxation period of the gain fiber. Instead, it decreases first and then increases, ultimately leading to the overdriving of NALM. This is attributed to the increase in the population inversion rate of gain fiber under the remaining pump. The dynamic evolution of intracavity gain and non-monotonic transmission properties of NALM collectively induce chaotic pulsation during the transformation. This work not only provides a new perspective for the design and development of novel spectrum-tailored laser sources, but also deepens the understanding of the transient dynamics of ultrafast fiber lasers.

We demonstrate an all-PM Er-doped soliton mode-locked fiber oscillator based on the figure-9 configuration with a compact adjustable reflection-type non-reciprocal phase shifter. An analytical model based on the Jones matrix is established to simulate the wavelength tuning phenomenon. Experimentally, it is observed that the increase in pump power results in a significant redshift in the spectrum of output pulses. When the angle of the half-wave plate is rotated in one direction, the output spectrum is redshifted and then blueshifted successively. Good qualitative agreement is presented between the simulations and the experimental results. It is shown that the increase in pump power changes the nonlinear phase shift, which causes the redshift of the transmittance curves at the laser output port. In contrast, the rotation of wave plates not only changes the nonlinear phase shift difference, but also causes variations in linear phase bias and modulation depth. The changes in these parameters lead to the redshift and blueshift of the transmission curves, which enables wavelength tuning.