Widely tunable narrow-linewidth mode-locked fiber laser via inter-cavity field interference.

Area of Science:

• Photonics
• Laser Physics
• Materials Science

Background:

• Mode-locked fiber lasers are crucial for various applications.
• Achieving narrow linewidths and broad pulse duration tunability simultaneously presents a challenge.
• Microresonators offer potential for precise optical filtering.

Purpose of the Study:

• To develop a widely and continuously tunable narrow-linewidth mode-locked fiber laser.
• To achieve a record pulse-duration tuning range.
• To demonstrate a novel mechanism for spectral linewidth narrowing using a microresonator.

Main Methods:

• Mode-locking a fiber laser intra-cavity coupled to a high-Q aluminum-nitride microresonator.
• Utilizing inter-cavity field interference within the microresonator to act as an active filter.
• Controlling the spectral linewidth by adjusting the microresonator's filtering properties.

Main Results:

• Achieved a record pulse-duration tuning range from 342 ps to 4.02 ns.
• Demonstrated tunable spectral linewidth from 1.34 GHz to 122 MHz.
• Compressed laser linewidth of 122 MHz, which is narrower than the microresonator's intrinsic resonance bandwidth.

Conclusions:

• A novel approach for linewidth narrowing in mode-locked fiber lasers was presented.
• The developed laser offers large and continuous tuning ranges for both linewidth and pulse duration.
• Potential applications exist in LiDAR, spectroscopy, and quantum optics.