Optical linewidth of a passively mode-locked semiconductor laser

Area of Science:

• Quantum optics
• Semiconductor laser physics

Background:

• Passively mode-locked quantum dot lasers are crucial for advanced photonic applications.
• Understanding laser linewidth is essential for characterizing laser performance and stability.

Purpose of the Study:

• To investigate the optical linewidth dependence on optical frequency in passively mode-locked quantum dot lasers.
• To establish a correlation between modal linewidth and radio frequency (RF) linewidth for timing jitter measurement.

Main Methods:

• Experimental measurement of optical linewidths for a passively mode-locked quantum dot laser.
• Analysis of the modal linewidth's dependence on mode optical frequency.
• Comparison of experimental results with theoretical predictions.

Main Results:

• The modal linewidth exhibits a parabolic dependence on the mode optical frequency, matching theoretical predictions.
• The minimum linewidth follows Schawlow-Townes behavior, with rebroadening at higher optical power.
• The slope of the parabolic linewidth dependence is directly proportional to the laser's RF linewidth.

Conclusions:

• The parabolic dependence of modal linewidth provides a novel method for directly measuring timing jitter.
• This technique is particularly valuable for fast repetition rate mode-locked semiconductor lasers where RF linewidth measurement is challenging.