In this work, the full emission spectrum of Tm-doped fiber (1700 nm – 2000 nm) is employed for tunable noise-like pulse operation. By using an Acousto-Optic Tunable Filter (AOTF), the operation wavelength can be electrically tuned within the 300 nm wavelength range. Based on an all-anomalous dispersion cavity and hybrid mode-locking technique, noise-like pulse operations at different wavelengths are obtained with a 10-dB spectral width ranging from 22 nm to 37 nm and output average power from 25.9 mW to 104 mW. The cavity repetition is 35 MHz. Additionally, when the laser operates in the water absorption region, we observe giant pulses with intensity several times higher than average pulse intensity are generated in the output pulse train.
We demonstrated a high accuracy prediction of the fiber laser output parameters by using a feed-forward neural network. We explored both the gain and spectral filter parameters to test the prediction performance of the neural network and realized the mapping between cavity parameters and laser output performance. We also investigated how the number of hidden layers could influence the accuracy of prediction. Based on the results, the output spectrum and temporal pulse profiles can be predicted with high accuracy in various fiber laser designs. Our work paves the way to intelligent laser design with ultimate autonomy.
In this work, we realized broadly tunable mode-locking operation from 1730 nm to 1815 nm in normal dispersion regime employing an acousto-optic tunable fiber (AOTF) in a Tm-doped dispersion-managed fiber laser. The AOTF worked as a multifunctional component in laser cavity suppressing undesired wavelength lasing and introducing a frequency shifting, which improved the stability of laser operation. The hybrid mode-locking incorporated by nonlinear polarization rotation (NPR) effect and frequency shifting effect ensured self-starting stable pulsed operation. The pulse spectral widths ranged from 17 nm to 25 nm. The stretching-free direct amplification in two-cascaded fiber amplifier enabled power scaling up to 310 mW and pulse energy of 19 nJ. Pulse duration was compressed down to 282 fs by a pair of gratings. The seed laser is further optimized. The optimized seed laser enhances output power about 5 times. The laser system was designed for multiphoton imaging of bladder cancer in the third biological window to demonstrate the recently discovered nonlinear effect resulting in improvement of signal contrast at the deeper tissue level.
Apart from the classical nonlinear polarization rotation (NPR) mechanism, we incorporate an additional stabilization mechanism of frequency shifting in a Yb-doped all-normal-dispersion fiber laser oscillator. The similariton pulse with a pulse duration of 7.8 ps and a spectrum width of 20.5 nm is generated. By using a grating pair, the pulse duration can be compressed to be 140 fs. By employing time-stretch dispersion Fourier transform (TS-DFT) technique, the mode-locking pulse buildup process is investigated. The use of frequency shifting as a stabilization technique opens a new route towards reliable laser oscillator fabrication for the industrial-grade system.
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