Noise-Like Pulse Generation Using Polarization Maintaining Mode-Locked Thulium-Doped Fiber Laser With Nonlinear Amplifying Loop Mirror

Maria Michalska,Jacek Swiderski

doi:10.1109/jphot.2019.2943709

Maria Michalska, Jacek Swiderski

Open Access

https://doi.org/10.1109/jphot.2019.2943709

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Abstract

We investigate noise-like pulse (NLP) generation in a mode-locked thulium-doped fiber laser with nonlinear amplifying loop mirror (NALM) and different net anomalous dispersions. The all-polarization maintaining (PM) fiber oscillator generates pulse trains with a frequency adjustable in the range of 4.06-20.4 MHz by utilizing different lengths of PM passive fiber in the NALM loop. An NLP with a coherence spike width of 232 fs was generated at 1993.6 nm with a 3-dB spectral width of 32.6 nm when the net cavity dispersion was -0.711 ps <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

Highlights

Over the last decade, the mode-locked fiber lasers operating in the 2-μm spectral region have been intensively developed and investigated owing to their wide range of potential applications including various medical applications, optical sensing, free-space laser communications and spectroscopy [1]–[4]
The signal-to-noise ratio (SNR) of the fundamental frequency is as high as 59 dB, which is a good result for an noise-like pulse (NLP) thulium-doped fiber laser (TDFL), and it indicates a quite low noise level of the amplitude of the inner pulses in the NLP bunch, and the existence of a fluctuation in the pulse duration
The full width at half maximum (FWHM) of the laser spectrum first increase with the pump power from 24.1 nm for the lowest pump power in NLP mode-locking operation (1.9 W), but for a pump power beyond 2.7 W it remains constant at a bandwidth of 26.4 nm and it has a small variation of ±0.1 nm

Summary

Introduction

The mode-locked fiber lasers operating in the 2-μm spectral region have been intensively developed and investigated owing to their wide range of potential applications including various medical applications, optical sensing, free-space laser communications and spectroscopy [1]–[4]. Under high pump power conditions, mode-locked fiber lasers tend to generate NLP with a characteristic smooth and broad optical spectrum and autocorrelation trace with a coherence spike [1]. The first demonstration of NLP generation in a fiber laser was reported in 1997 in Er-doped ring fiber laser, where a wide and smooth optical spectrum of a bandwidth of 44 nm and an autocorrelation spike of 190 fs were presented [13]. NLP generation in the 2 μm spectral region have been presented in fiber oscillators with different mode-locking mechanisms incorporating material (graphene [14], carbon nanotubes [15], MoS2 [16], and semiconductor saturable absorber mirror (SESAM) [17]), as well as artificial saturable absorbers (SA), such as nonlinear optical loop mirror (NOLM), nonlinear amplifying loop mirror (NALM), and nonlinear polarization rotation (NPR) [18]–[23]. Ultrafast lasers with these SAs are usually very sensitive to mechanical disturbance and can exhibit a degradation of their optical properties over

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