Active phase locking of fiber amplifiers using sine-cosine single-frequency dithering technique

Area of Science:

• Optics and Photonics
• Laser Technology
• Fiber Optics

Background:

• Active phase locking is crucial for coherent beam combination of fiber amplifiers.
• Existing dithering techniques face limitations in phase control speed.
• Phased arrays of fiber amplifiers require precise phase synchronization for high-power output.

Purpose of the Study:

• To introduce and validate the sine-cosine single-frequency dithering technique for active phase locking.
• To demonstrate enhanced phase control speed compared to previous methods.
• To improve the performance of a 3x3 fiber amplifier array.

Main Methods:

• Theoretical development of the sine-cosine single-frequency dithering algorithm.
• Experimental implementation using a signal processor based on a field-programmable gate array (FPGA).
• Testing on a 3x3 array of nine 10 W fiber amplifiers, achieving approximately 100 W total output power.

Main Results:

• The sine-cosine technique achieves twice the phase control speed of the single-frequency dithering method.
• Closed-loop operation significantly improved fringe contrast by over 90% (from 21% in open loop).
• Residual phase error was reduced to less than λ/20.

Conclusions:

• The sine-cosine single-frequency dithering technique is a highly effective method for active phase locking of fiber amplifiers.
• This technique offers substantial improvements in speed and accuracy for phased array systems.
• The experimental validation confirms the practical applicability and performance benefits.