How to evaluate the repetition rate of a ultrashort pulse laser?

[Shen Kaiyuan]

In optisystem, here is a program in the example library named ultrashort fiber laser. As the optisystem tutorials says, this fiber laser is based on the passive mode locking.
Theoretically speaking, in a passively mode-locked fiber laser, the generated pulses are emitted after cycling once in the cavity. Observed in time, the laser will generate a pulse sequence with a stable repetition frequency, whose repetition frequency is inversely proportional to the cavity length.
But in the ultrashort fiber laser program, no matter how long I extend the time window, even if it has a length of 1s, I can only see a single pulse on the visualizer. Why is that？
Thanks

• This topic was modified 4 years, 1 month ago by Shen Kaiyuan. Reason: forgot to add the figure

[Ahmad Atieh]

Dear Shen,
The issue here, it is too difficult to get stable pulses in passive mode-locking. There is a huge competition between the pulses due to the fiber design, nonlinearity, flatness of the EDF, etc… If you go through the index of the visualizer and view the progress of the pulses after each propagation in the ring (sweep), you would see the competition between the pulses.
You may get stable pulse train if you have all conditions perfectly set.

Do you have a reference showing the realization of stable output? you may use the parameters in their design to simulate.

My recommendation is to use active mode-locking.

Regards,
Ahmad

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