An open and flexible digital phase-locked loop for optical metrology

Area of Science:

• Physics
• Optical Engineering
• Electrical Engineering

Background:

• Laser stabilization systems require precise control to mitigate environmental noise.
• Existing digital phase-locked loops can be expensive or lack flexibility.
• Field-Programmable Gate Array (FPGA) platforms offer a customizable hardware solution.

Purpose of the Study:

• To present an open and flexible digital phase-locked loop (DPLL) optimized for laser stabilization.
• To implement the DPLL on an accessible FPGA platform (Red Pitaya) with open-source firmware.
• To demonstrate the platform's performance in a practical application, such as fiber noise cancellation.

Main Methods:

• Implementation of a DPLL on a Red Pitaya FPGA board.
• Development of a PC-based software interface for remote control and parameter optimization.
• Integration of measurement tools for rapid data acquisition.
• Construction and testing of a fiber noise canceller utilizing the DPLL.

Main Results:

• Successful implementation of an open and flexible DPLL on an FPGA.
• Demonstrated fiber noise cancellation over a 400 m fiber link with a 30 kHz bandwidth.
• Measured platform latency of 565 ns.
• Identified actuator and fiber propagation delays as primary bandwidth limitations.

Conclusions:

• The developed FPGA-based DPLL is a cost-effective and versatile solution for laser stabilization.
• The system shows significant potential for high-bandwidth noise cancellation in optical systems.
• Further improvements in actuator and system design could enhance the achievable control bandwidth.