Passively Q-Switched and Mode-Locked Er3+-Doped Ring Fiber Laser with Pulse Width of Hundreds of Picoseconds

Ji Wang,Tianrun Zhang,Wenwu Zhang

doi:10.3390/photonics8120560

Ji Wang, Tianrun Zhang + Show 1 more

Open Access

https://doi.org/10.3390/photonics8120560

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Journal: Photonics	Publication Date: Dec 8, 2021
Citations: 2	License type: CC BY 4.0

Affiliation: Ningbo Institute of Industrial Technology

Abstract

Greatly improving the energy of a single mode-locked pulse while ensuring the acquisition of the width of short pulses will contribute to the application of mode-locked pulse in basic research, such as precision machining. This report has investigated a Q-switched and mode-locked (QML) erbium doped ring fiber laser based on the nonlinear polarization rotation (NPR) technology and a mechanical Q-switched device. Without the working of the mechanical Q-switched device, the fiber laser exported the continuous-wave mode-locked (CWML) pulse, with a width of 212.5 ps, and a repetition frequency of 81.97 MHz. For the CWML operation, the maximum output average power is 25.7 mW, and the energy is only 0.31 nJ. For the QML operation, 18.03 mW average power is achieved at the Q-switching frequency of 100 Hz. The energy of the QML pulse is increased by over 1100 times to 360.6 nJ. The width of the QML pulse is 203.1 ps measured by an autocorrelation curve, with the time-band product (TBP) being 0.598. The power instability is 0.5% (RMS) and 0.7% (RMS), respectively, for CWML and QML operation within 120 min. Furthermore, the spectral signal-to-noise ratio is about 60 dB. For the QML operation, the power instability is 0.48% (RMS) within 60 s and 0.37% (RMS) within 10 s. After frequency stabilization, the frequency fluctuation is ±100 Hz in the long-term of 1200 s, with the frequency stability (FS) calculated to be 2.44 × 10−6. It indicates that the QML fiber laser has good power stability and frequency stability.

Highlights

The introduction should briefly place the study in a broad context and highlight why it is important
Based on the combination of the nonlinear polarization rotation effect and mechanical Q-switched device, two output operations of continuous-wave mode-locked (CWML) and Q-switched and mode-locked (QML) are realized in this paper
The polarization state in the ring cavity is adjusted by PC1 and PC2 to realize continuous-wave mode-locked output

Summary

Introduction

The introduction should briefly place the study in a broad context and highlight why it is important. Narrow pulse fiber lasers of hundreds of picoseconds have been widely used in many important fields, such as optical fiber sensing [1], atmospheric optics [2,3], micro-machining [4,5], ultra-fast spectroscopy [6], optical fiber communication [7,8], and medicine [9,10]. Based on the nonlinear polarization rotation characteristics, the self-started mode-locked fiber lasers have been extensively investigated, attributed to their advantages of in-line all-fiber structures, low repetition frequencies, ultra-broadband spectra, and high energies [11–14]. The fiber nonlinear Kerr effect and the formation of fiber dissipative solitons are the intrinsic mechanisms for the self-started nonlinear polarization rotation mode-locked lasers [15,16]. With respect to mode-locked fiber lasers, Q-switched fiber lasers have higher energy optical pulses, but a larger pulse width [17–19]. Combining the advantages of both Q-switched and mode-locked laser technology, the fiber laser can have the superior performance of higher pulse energy and narrower pulse width, compared to ordinary QML fiber lasers [20,21]

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