Phase-lock control considerations for coherently combined lasers

Area of Science:

• Laser physics
• Control systems engineering
• Optical engineering

Background:

• Coherent combination of laser outputs is crucial for applications like laser arrays.
• Phase-lock control loops are essential for maintaining the precise phase relationship between lasers.
• Understanding performance limitations is key to optimizing these systems.

Purpose of the Study:

• To present fundamental performance limitations of a phase-lock control loop for coherent laser combination.
• To derive loop equations and analyze phase error variance.
• To optimize loop parameters for minimizing phase error and discuss implications for laser arrays.

Main Methods:

• Utilized an optical heterodyne configuration to measure differential laser phase.
• Developed an integro-differential loop equation for the linear operating range.
• Analyzed phase error variance in relation to closed-loop noise equivalent bandwidth (W(H)).

Main Results:

• Derived an expression for phase error variance based on W(H).
• Determined the optimal W(H) to minimize phase error variance.
• Examined steady-state and dynamic performance for various loop filters and modulation formats.

Conclusions:

• The study provides a framework for understanding and optimizing phase-lock control loops for coherent laser combination.
• Identified key parameters influencing phase error and methods for minimization.
• Results have implications for the design and performance of coherent laser arrays.