Simplified Doppler frequency shift measurement enabled by Serrodyne optical frequency translation

TL;DR

This paper introduces a simplified method for Doppler frequency shift measurement using Serrodyne optical frequency translation, enabling precise, stable, and simultaneous determination of frequency shift magnitude and direction in microwave signals.

Contribution

The paper presents a novel optical frequency translation technique with a Mach-Zehnder modulator for accurate Doppler shift measurement, improving simplicity and precision over existing methods.

Findings

Measured DFS from -100 to 100 kHz with less than 0.03 Hz error

Applicable to microwave signals from 6 to 17 GHz

Achieved measurement stability of 0.015 Hz over 30 minutes

Abstract

A simplified Doppler frequency shift measurement approach based on Serrodyne optical frequency translation is reported. A sawtooth wave with an appropriate amplitude is sent to one phase modulation arm of a Mach-Zehnder modulator in conjunction with the transmitted signal to implement the Serrodyne optical frequency transition, as well as the optical phase modulation of the transmitted signal on the frequency-shifted optical carrier. The echo signal is applied to the other phase modulation arm of the Mach-Zehnder modulator. The optical signals from the two arms are combined in the Mach-Zehnder modulator, whose lower optical sidebands are selected by an optical bandpass filter and then detected in a photodetector. By simply measuring the frequency of the output low-frequency signal, the value and direction of DFS can be determined simultaneously. An experiment is performed. DFS from -100 to 100 kHz is measured for microwave signals from 6 to 17 GHz with a measurement error of less than 0.03 Hz and a measurement stability of 0.015 Hz in 30 minutes when a 500-kHz sawtooth wave is used as the reference.