Sub-100 fs pulses from an all-polarization maintaining Yb-fiber oscillator with an anomalous dispersion higher-order-mode fiber.

A.J Verhoef,W Kautek,S Møller Israelsen,A Unterhuber,L Grüner-Nielsen,K Rottwitt,A Baltuška,L Zhu,A Fernández

doi:10.1364/oe.23.026139

Abstract

We present an Yb-fiber oscillator with an all-polarization-maintaining cavity with a higher-order-mode fiber for dispersion compensation. The polarization maintaining higher order mode fiber introduces not only negative second order dispersion but also negative third order dispersion in the cavity, in contrast to dispersion compensation schemes used in previous demonstrations of all-polarization maintaining Yb-fiber oscillators. The performance of the saturable absorber mirror modelocked oscillator, that employs a free space scheme for coupling onto the saturable absorber mirror and output coupling, was investigated for different settings of the intracavity dispersion. When the cavity is operated with close to zero net dispersion, highly stable 0.5-nJ pulses externally compressed to sub-100-fs are generated. These are to our knowledge the shortest pulses generated from an all-polarization-maintaining Yb-fiber oscillator. The spectral phase of the output pulses is well behaved and can be compensated such that wing-free Fourier transform limited pulses can be obtained. Further reduction of the net intracavity third order dispersion will allow generating broader output spectra and consequently shorter pulses, without sacrificing pulse fidelity.

Highlights

Femtosecond Yb-doped fiber lasers are very attractive sources for ultrafast optical applications because they are intrinsically associated with reduced sensitivity to alignment, compact design and low production costs
In an attempt to reduce pulse duration without compromising pulse quality, we have previously demonstrated a 61 fs Ybfiber oscillator in which dispersion compensation was realized with a higher order mode (HOM) fiber [5], but this scheme was based on non-polarization maintaining (non-PM) fibers with the modelocking mechanism relying on nonlinear polarization evolution and pulse shaping based on spectral filtering
Summarizing, we demonstrated for the first time an all-PM Yb-fiber oscillator that uses a PM-HOM fiber for intracavity dispersion management

Summary

Introduction

Femtosecond Yb-doped fiber lasers are very attractive sources for ultrafast optical applications because they are intrinsically associated with reduced sensitivity to alignment, compact design and low production costs. In non-polarization maintaining (non-PM) fibers, temperature changes, fiber bending and other mechanical perturbations, can influence the birefringence properties of the fibers which can result in degradation of device performance and eventually losing of modelocking. Since environmental instabilities in fiber lasers mainly arise from induced changes in the birefringence of non-PM fibers, the straightforward approach to make the laser robust against them is to use PM fibers with light polarized only along the slow axis [1,2]. A major challenge to develop operational and environmentally stable fiber lasers delivering short-high fidelity femtosecond pulses at 1 μm wavelength is to realize good higher order dispersion compensation [3,4] and to manage intracavity nonlinearities. In non-PM oscillator cavities careful control of the intracavity dispersion has resulted in high quality pulses and the generation of transformed limited wing-free pulses [3,5]

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