Active phase locking of thirty fiber channels using multilevel phase dithering method.

Area of Science:

• Optics and Photonics
• Laser Physics
• Fiber Optics

Background:

• Active phase locking is crucial for coherent beam combination in large-scale fiber arrays.
• Phase noise in fiber amplifiers degrades beam quality and limits scalability.
• Existing phase dithering techniques often require complex demodulation circuits.

Purpose of the Study:

• To experimentally demonstrate active phase locking of a large-scale, 30-channel fiber array.
• To evaluate a novel multi-level phase dithering algorithm for phase control.
• To assess the efficiency and potential scalability of the proposed technique.

Main Methods:

• Utilized thirty phase controllers for noise compensation and thirty phase modulators for introducing controlled phase distortions.
• Implemented a multi-level phase dithering algorithm with dual-level rectangular-wave phase modulation and time division multiplexing.
• Avoided the need for a coherent demodulation circuit.

Main Results:

• Achieved high phase locking efficiencies of 98.68% (no distortion), 97.82% (±1 rad distortion), and 96.50% (±2 rad distortion).
• Observed root-mean-square phase errors of λ/54, λ/43, and λ/34 for the respective distortion levels.
• Attained a coherent combined beam profile contrast of approximately 89%.

Conclusions:

• The multi-level phase dithering technique effectively achieves active phase locking in a 30-channel fiber array.
• This method offers comparable phase control to existing techniques without requiring a coherent demodulation circuit.
• The demonstrated technique shows significant potential for scaling to large numbers of laser beams for advanced optical applications.