Low-latency FPGA-based TDC phase detection scheme for optical frequency comb locking.

Area of Science:

• Physics
• Optical Engineering
• Electrical Engineering

Background:

• Precise phase locking of optical frequency combs is crucial for suppressing fast phase noise.
• High-bandwidth feedback systems are essential for achieving stable phase locking.

Purpose of the Study:

• To present a novel low-latency digital phase detection scheme for optical frequency comb phase locking.
• To demonstrate the effectiveness of a field-programmable gate array (FPGA)-based time-to-digital converter (TDC) for this application.

Main Methods:

• Implementation of a high-resolution time-to-digital converter (TDC) on a field-programmable gate array (FPGA).
• Direct conversion of signal arrival time to phase error, achieving a total system latency of 115 nanoseconds (ns).
• Development of a digital servo system for voltage-controlled oscillator (VCO) locking with a 1 MHz control bandwidth.

Main Results:

• The FPGA-based TDC phase detection scheme achieved a low latency of 115 ns.
• The digital servo system demonstrated a 1 MHz control bandwidth for VCO locking.
• Application to an erbium-doped fiber frequency comb resulted in an f_beat locking bandwidth of 500 kHz and a modified Allan deviation of 6.97×10^-18 at 1 s.

Conclusions:

• FPGA-based TDC phase detection is a viable method for high-bandwidth optical frequency comb phase locking.
• The proposed scheme enables stable and precise phase locking, overcoming limitations of previous methods.
• This technology paves the way for advancements in optical frequency metrology and applications requiring highly stable frequency combs.