Modeling, analysis, and loop optimization of the Pound-Drever-Hall loop for ultra-stable lasers

Area of Science:

• Physics
• Optical Engineering
• Laser Technology

Background:

• Ultra-stable lasers are crucial for scientific advancements, with current systems achieving 10^-17 fractional frequency stability.
• Reaching the 10^-18 level necessitates frequency stabilization servo controllers with enhanced noise suppression over a wider bandwidth.
• External-cavity semiconductor lasers commonly use combined current and PZT frequency modulation for stabilization.

Purpose of the Study:

• To investigate and improve the performance limitations of dual feedback loop stabilization systems for ultra-stable lasers.
• To enhance noise suppression capabilities, particularly below 10 kHz, for achieving 10^-18 level frequency stability.
• To adapt and apply the developed methods to newer semiconductor laser stabilization techniques.

Main Methods:

• Utilized a dedicated loop analyzer and IQ demodulation for detailed transfer function measurements of individual stages and the closed-loop system.
• Focused on analyzing performance limitations within the 10 kHz frequency range.
• Optimized the feedback path of the dual feedback loop.

Main Results:

• Achieved a three-orders-of-magnitude improvement in laser noise suppression at 1 kHz.
• Reduced the contribution of residual laser frequency noise below 10 kHz to 4.4×10^-19 fractional frequency stability at one second.
• Demonstrated the applicability of the method to semiconductor lasers using solely current frequency modulation.

Conclusions:

• The optimized feedback path significantly enhances noise suppression, paving the way for 10^-18 level ultra-stable lasers.
• The developed measurement and optimization techniques are valuable for advancing laser frequency stabilization.
• The proposed method offers a pathway for improving stability in various semiconductor laser systems.