On the Development of an RFSoC-Based Ultra-Fast Phasemeter With GHz Bandwidth

Abstract

Precise measurements of the frequency and phase of an electrical or optical signal play a key role in various branches of science and engineering. Tracking changing laser frequencies is especially demanding when the lasers themselves are noisy or if the frequencies rapidly change because they encode highly dynamic signals in, e.g., Doppler-ranging or dynamic cavity readout. Here, to address these and other possible applications, we report the development of a high signal bandwidth (> 2 GHz) and high tracking bandwidth (2 MHz) multi-channel Phasemeter. The implementation utilizes an all-digital phase-locked loop realized within the field programmable gate array (FPGA) part of a radio frequency system-on-chip (RFSoC), the programmable logic (PL). The new features of the phasemeter are obtained by operating the PL at its timing limits and introducing a multi-demodulation and phase accumulation scheme. We present performance measurements, discuss the role of the high tracking bandwidth for tracking highly dynamic signals, and demonstrate ultra-stable phase locking of a beat note between two widely tunable external cavity diode lasers. We achieve a phase-noise floor in the sub-milli radian regime when comparing two signals, even for GHz frequencies, and demonstrate stable tracking of signals with a frequency change rate of 240 GHz/s.