An Optical Fibre Pulse Rate Multiplier for Ultra-low Phase-noise Signal Generation

TL;DR

This paper presents an all-optical fibre method to generate ultra-low phase-noise microwave signals by using a cascade of fibre interferometers for repetition rate multiplication, achieving near shot-noise-limited performance.

Contribution

It introduces a novel fibre-based pulse rate multiplier that significantly enhances microwave signal quality and reduces phase noise close to fundamental shot noise limits.

Findings

Repetition rate multiplication increases signal level by 18 dB.

Achieved phase noise of -118 dBc/Hz at 1 Hz offset.

System noise floor near -164 dBc/Hz, close to shot noise limit.

Abstract

In this letter we report on an all optical-fibre approach to the synthesis of ultra-low noise microwave signals by photodetection of femtosecond laser pulses. We use a cascade of Mach-Zehnder fibre interferometers to realize stable and efficient repetition rate multiplication. This technique increases the signal level of the photodetected microwave signal by close to 18 dB, that in turn, allows us to demonstrate a phase noise level of 118 dBc/Hz at 1 Hz and -160 dBc/Hz at 10 MHz from 12 GHz signal. The noise floor of the fiber multiplier and photodetection system alone is around -164 dBc/Hz at the same offset frequency, which is very close to the fundamental shot noise floor