Abstract
We present a novel approach to study continuous-wave mode-locking in a waveguide laser in the presence of a gain profile with complex features. We introduce a new simulation approach where we separate the role of gain, nonlinearity, dispersion and saturable absorption elements to provide a better understanding of the interplay between these elements. In particular, we use the simulation to explain synchronised dual-wavelength mode-locking. The results show that despite the existence of dispersion which tends to form separate pulse trains in the laser cavity, the saturable absorber plays a critical role in keeping the different wavelength components synchronised. This work, for the first time, provides insight into existing experimental results. It also demonstrates new methods for studying lasers, especially mode-locking laser, with short laser cavities.
Highlights
Mode locked waveguide lasers, including fiber lasers, are the most commonly used ultra-short pulse sources due to their high beam quality, high efficiency, and robustness, as well as easy operation
Single pulse dual wavelength mode locking has only been observed recently[17], reporting an erbium-doped ZBLAN glass chip based waveguide laser showing two peaks around 1530 and 1555 nm in the output spectrum when the laser is mode-locked while the RF spectrum of the output indicates single pulse operation
The large diameter of the ZBLAN waveguide (∼50 μm) and short length (∼15 mm) indicates no significant contribution of nonlinear effects that could lead to spectral modulation that looks like the measured dual wavelength spectrum, which suggested that the pulse spectrum can only due to the profile of the gain
Summary
The simulation of the mode locking laser is based on the well-known Ginzburg-Landau equation. Unless careful dispersion compensation is applied in the cavity design, synchronous mode locking for dual wavelength are not expected to be achieved. We investigate numerically the impact of group velocity dispersion and nonlinearity on dual-wavelength mode locking. When dispersion increases in both negative or positive directions, the spectral width of the output pulse narrows for all N values and ΔN become smaller until the dual-wavelength mode-locking behaviour ceases to occur. MI provides a maximum gain of 2γP0 at a frequency shift of ±
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