研究目的
To demonstrate the generation of noise-like pulses in an all-normal-dispersion ytterbium-doped fiber laser using nonlinear multimodal interference as a saturable absorber for the first time, and to study the effects of multimode fiber length on performance and high-power generation.
研究成果
The study successfully demonstrates the first all-fiber integrated NLP mode-locking laser using nonlinear multimodal interference as a saturable absorber. It shows that optimizing the length of the graded-index multimode fiber can regulate mode-locking threshold, spectral bandwidth, and pulse width. High average power of 279 mW was achieved with good stability, indicating potential for further applications in ultrafast lasers.
研究不足
The spectral bandwidth obtained (up to 9.5 nm at 3 dB) is narrower compared to other techniques using multimode pumping or free-space dispersion management, which can achieve over 100 nm. The experiment relies on specific fiber lengths and bending, which may limit scalability and require precise control.
1：Experimental Design and Method Selection:
The experiment uses a passively mode-locked all-fiber ring laser cavity with nonlinear multimodal interference as a saturable absorber. The design includes optimization of intra-cavity birefringence and control of multimode fiber curvature to initiate and maintain NLP operation.
2：Sample Selection and Data Sources:
The laser cavity components are fusion spliced, including ytterbium-doped active fiber, multimode fibers (SIMMF and GIMMF), and other standard fiber optics. Data is collected from spectral and temporal measurements using an autocorrelator and power meters.
3：List of Experimental Equipment and Materials:
Equipment includes laser diodes, polarization beam combiner, wavelength-division multiplexer, ytterbium-doped fiber, coupler, polarization-independent isolator, polarization controllers, and a commercial intensity autocorrelator. Materials include single-mode fibers, step-index multimode fiber (105 μm core diameter), graded-index multimode fiber (
4：5 μm core diameter), and fusion splicing tools. Experimental Procedures and Operational Workflow:
The setup involves splicing fibers to form a compound fiber structure, pumping with laser diodes, adjusting polarization controllers, and bending the multimode fiber to optimize mode-locking. Output is characterized through spectral analysis and autocorrelation measurements.
5：Data Analysis Methods:
Data is analyzed using spectral bandwidth calculations, autocorrelation trace fitting with sech2 pulse shape assumptions, and statistical analysis of power stability (RMS fluctuations).
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laser diode
single-mode LD with PM fiber pigtails
Pumping the ytterbium-doped gain fiber to provide optical gain for the laser cavity.
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polarization beam combiner
PBC
Combining the pump power from two laser diodes efficiently.
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wavelength-division multiplexer
WDM
Coupling pump laser into the gain fiber and separating wavelengths.
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ytterbium-doped fiber
Active gain medium for the laser, providing amplification at 1030 nm.
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fiber coupler
90:10 coupler
Directing a portion of the signal laser out of the cavity for output.
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polarization-independent isolator
PI-ISO
Ensuring unidirectional propagation of light in the cavity to prevent feedback and enable mode-locking.
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polarization controller
PC
Adjusting the polarization state of light to optimize mode-locking conditions.
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step-index multimode fiber
SIMMF
Part of the saturable absorber structure, relieving restrictions on GIMMF length.
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graded-index multimode fiber
GIMMF
Core component for nonlinear multimodal interference, acting as a saturable absorber and spectral shaper.
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intensity autocorrelator
commercial intensity autocorrelator
Measuring the autocorrelation trace of the generated pulses to characterize temporal properties.
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