Coherent artifact and time-dependent polarization in amplified ultrafast erbium-doped fibre lasers

Miguel López-Ripa,Benjamín Alonso,Sebastián Jarabo,Francisco J Salgado-Remacha,Juan Carlos Aguado,Íñigo J Sola

doi:10.1016/j.optlastec.2021.107018

Miguel López-Ripa, Benjamín Alonso + Show 4 more

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https://doi.org/10.1016/j.optlastec.2021.107018

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Abstract

Mode-locked erbium-doped fibre lasers are ultrashort pulsed sources widely studied due to their versatility and multiple applications in the near infrared range. Here we present the experimental study of the emission of a passive mode-locked erbium-doped fibre laser with an amplification stage outside the cavity by means of Frequency Resolved Optical Gating (FROG) and spectral interferometry. Due to shot-to-shot instabilities, the FROG traces can be understood as the combination of two different traces, corresponding to the coherent artifact and the average pulse characteristics. We have modified a Principal Components Generalized Projections Algorithm, in order to make it able to retrieve efficiently both the coherent artifact and the average pulse. In addition, we study the temporal dependence of the polarization, showing that the pulses present time-dependent polarization with a stable spectral relative phase between the horizontal and vertical projections. Up to our knowledge, this is the first experimental study that shows the FROG measurements of unstable pulse trains associated with the coherent artifact and analyses the time-dependent polarization in ultrafast fibre lasers.

Highlights

Erbium-doped fibre lasers (EDFLs) have been studied for many de cades due to their great versatility and multiple applications in the nearinfrared range such as telecommunication, optical sensing or micro processing [1,2]
Following the idea presented by Escoto et al [17] and based on the Principal Compo nents Generalized Projections Algorithm (PCGPA) (Principal Components Generalized Projections Algorithm) of [34], we have developed a modified PCGPA that models the CA Fre quency Resolved Optical Gating (FROG) traces produced by an unstable pulse train as the combination of two different traces, the coherent artifact (CA) trace and the average pulse trace (“ave”), as given by IFROG(ω, τ) = ΓICA(ω, τ) + (1 − Γ)Iave(ω, τ) where IFROG,ICA and Iave are respectively the FROG trace of the experimental measurement, the coherent artifact and the average pulse, all of them with the maximum normalized to unity
In this work we have studied a passive mode-locked erbium doped fibre laser with an amplification stage exhibiting an unstable emission in the time domain

Summary

Introduction

Erbium-doped fibre lasers (EDFLs) have been studied for many de cades due to their great versatility and multiple applications in the nearinfrared range such as telecommunication, optical sensing or micro processing [1,2] These lasers can operate in continuous emission or pulsed emission with interesting characteristics. Due to the high repetition rate of these lasers (usually around the MHz range) and the low energy of the pulses, usually it is necessary to average the detected signal over multiple pulses even in the case of single-shot techniques These lasers are usually characterized by multi-shot techniques such as autocorrelation, FROG (Frequency Resolved Optical Gating) or D-scan (Dispersion Scan) [10,11]

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