Modelocking of a frequency-shifted feedback laser triggered by amplitude modulation

Area of Science:

• Laser Physics
• Nonlinear Optics
• Photonics

Background:

• Frequency-shifted feedback (FSF) lasers utilize an intracavity modulator to shift the optical spectrum per round trip.
• Initiating stable modelocking (ML) in FSF lasers, particularly at desired frequencies, has been a challenge.

Purpose of the Study:

• To develop and demonstrate a novel experimental technique for reliably triggering modelocking (ML) emission in FSF lasers.
• To investigate the role of amplitude modulation (AM) in initiating ML and explore its impact on threshold characteristics.

Main Methods:

• Employing a dual radio frequency (RF) tone drive for the intracavity modulator in an FSF laser.
• One RF tone provides the standard frequency shift, while a second tone matches the cavity's free spectral range (FSR) frequency.
• Utilizing numerical simulations to analyze the pulse formation dynamics and the influence of AM and Kerr effect.

Main Results:

• The dual-tone method successfully induces ML emission in FSF lasers.
• A weak amplitude modulation (AM) synchronized with the cavity round trip time is generated, acting as a seed for ML.
• ML emission is achieved at arbitrary frequency shifts with lower initiation thresholds compared to spontaneous FSF laser ML.
• Simulations confirm AM triggers pulse formation, while the Kerr effect drives the primary pulse buildup mechanism.

Conclusions:

• A practical and effective experimental technique for triggering ML in FSF lasers has been established.
• The method leverages synchronized amplitude modulation to overcome previous limitations in initiating ML.
• This approach offers a new pathway for controlled ML initiation in FSF laser systems.