Noise floor reduction of an Er:fiber laser-based photonic microwave generator

TL;DR

This paper demonstrates significant reduction in phase noise floor of a photonic microwave generator by multiplying the pulse repetition rate using fiber-based techniques, improving signal quality at 10 GHz.

Contribution

It introduces and compares two methods for repetition rate multiplication in Er:fiber lasers to reduce phase noise in microwave generation.

Findings

Achieved 10-15 dB reduction in phase noise floor at 10 GHz.

Repetition rate multiplication techniques lowered phase noise to -158 dBc/Hz and -162 dBc/Hz.

Methods improve microwave signal quality by mitigating photodetection noise.

Abstract

The generation of microwaves from optical signals suffers from thermal and shot noise inherent in the photodetection process. This problem is more acute at lower pulse repetition rates where photodiode saturation limits the achievable signal-to-noise ratio. In this paper, we demonstrate a 10-15 dB reduction in the 10 GHz phase noise floor by multiplication of the pulse repetition rate. Starting with a 250 MHz fundamentally mode-locked erbium(Er):fiber laser, we compare two different approaches to repetition rate multiplication: Fabry-Perot cavity filtering and a cascaded, unbalanced Mach-Zehnder fiber-based interferometer. These techniques reduce the phase noise floor on the 10 GHz photodetected harmonic to -158 dBc/Hz and -162 dBc/Hz, respectively, for Fourier frequencies higher than 100 kHz.