  Despite the wide applications for high-repetition-rate mode-locked fiber
lasers, challenges persist in shortening the cavity length and coupling the
fiber collimators for most existing techniques. Here, we introduce a novel
collimator alignment method and demonstrate an all-polarization-maintaining
erbium-doped fiber laser that contains a nonlinear amplifying loop mirror with
a repetition rate of 213 MHz. Compared to the conventional method, we achieve
in-situ alignment of the collimators in a simplified two-step process. Besides,
through a comparison of the spectra from the output ports of the laser, we
assess their quality and establish the spectral evolution relationships among
these ports. It is found that, in addition to the widely believed large
nonlinear effects, spectral interference also plays a significant role in
spectral distortion. Moreover, a transition between different stability states
is observed from the power variation of the single pulse.
