FPGA-based, High-speed Phasemeter for Heterodyne Interferometry

Phasemeter setup for testing a fiber delivered interferometer.

The goal of this project is to develop a high-speed, FPGA-based detection and signal processing system specifically for interferometric phasemeter measurements. A phasemeter is an instrument based on phase demodulation techniques for measuring the difference in phase of two alternating electrical or optical signals. The phasemeter’s primary function is to provide a high accuracy measurement of the phase of the input signals for science measurements. Current commercially available phasemeters are not suitable for low-cost applications because they have a high cost per channel and unfriendly I/O interface. The main motivation of this project is to design a high-performance, economical, user-friendly phasemeter system.

The phasemeter system in this project is based on In-phase/Quadrature method for Displacement Measuring Interferometers (DMIs), which consists of several parts, including quadrant photodiodes detection circuit and its analog signal processing circuit, FPGA and its periphery for high-speed digital signal processing, Ethernet interface for measurement data transmission. At the present stage, the prototype of phasemeter has been implemented, could be operated at 70 kHz split frequency, and can achieve sub-nanometer precision. This system will be improved to be compatible with 5 MHz split frequency, and expanded to four channels for displacement, tip and tilt measurement.