Extending the PZT bandwidth of an optical interferometer by suppressing resonance using a high dimensional IIR filter implemented on an FPGA

TL;DR

This paper demonstrates how FPGA-implemented high-dimensional IIR filters can suppress resonances in piezoelectric transducers, significantly extending the bandwidth and improving stability in optical interferometry systems.

Contribution

It introduces a 24th-order IIR filter on FPGA to suppress resonances, enabling nearly-flat response control of piezoelectric transducers in optical interferometers.

Findings

Extended the usable bandwidth of PZT transducers

Achieved stable closed-loop control with improved bandwidth

Implemented a reproducible digital control scheme

Abstract

This paper considers the application of FPGA-based IIR filtering to increase the usable bandwidth of a piezoelectric transducer used in optical phase locking. We experimentally perform system identification of the interferometer system with the cross-correlation method integrated on the controller hardware. Our model is then used to implement an inverse filter designed to suppress the low frequency resonant modes of the piezo-electric transducer. This filter is realized as an 24th-order IIR filter on the FPGA, while the total input-output delay is kept at 350ns. The combination of the inverse filter and the piezo-electric transducer works as a nearly-flat response position actuator, allowing us to use PI control in order to achieve stability of the closed-loop system with significant improvements over non filtered PI control. Finally, because this controller is completely digital, it is straight forward to reproduce. Our control scheme is suitable for many experiments which require highly accurate control of flexible structures.