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Author

Lei Liao

Bio: Lei Liao is an academic researcher from Huazhong University of Science and Technology. The author has contributed to research in topics: Fiber laser & Optical fiber. The author has an hindex of 9, co-authored 54 publications receiving 225 citations.

Papers published on a yearly basis

Papers
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Journal ArticleDOI
TL;DR: Results have confirmed that MCVD-fabricated gain-tailored Yb/Ce codoped aluminosilicate fibers have great potential in power scaling and output stability of high-power fiber lasers and amplifiers.
Abstract: A gain-tailored Ge-free Yb/Ce codoped aluminosilicate fiber is fabricated by MCVD combined with solution doping technique. Through regulating the temperature in the tube and designing the solution doping process, the refractive index profile of this fiber is close to a step-index without any center dip. The laser performance of this fiber is proved through contrast experiments with conventional fiber in a kW-level MOPA setup. The gain-tailored fiber amplifier presents a beam quality of M2 ~1.43 at 1.2 kW. Its MI threshold is 1.25 kW, about 1.74 times as much as that of the conventional fiber amplifier. The laser slope efficiency of the gain-tailored fiber amplifier is 86.75%. Stabilized at an output power of 1.1 kW for 15 hours, the MI threshold does not decrease after this long-term operation, demonstrating a strong resistance to photodarkening effect. These results have confirmed that MCVD-fabricated gain-tailored Yb/Ce codoped aluminosilicate fibers have great potential in power scaling and output stability of high-power fiber lasers and amplifiers.

24 citations

Journal ArticleDOI
TL;DR: It was found that simultaneously Pumping the fiber with 915 and 793 nm LDs can suppress about 80% PD loss, compared with pumping the fiber only with 914 nm LD, and repeatable processes of PD and photo-bleaching were observed when alternately pumped with 913 and 915 nm LD.
Abstract: We report on the strong photo-bleaching of the photo-darkening (PD) induced loss under the cladding pump of a 793 nm laser diode (LD) in double clad Yb-doped fibers. Up to 68% PD loss at 810 nm was bleached. The bleaching rates under different powers show that the higher pump power corresponds to the more bleached loss within the same time. Moreover, repeatable processes of PD and photo-bleaching were observed when alternately pumped with 915 and 793 nm LDs. Furthermore, it was found that simultaneously pumping the fiber with 915 and 793 nm LDs can suppress about 80% PD loss, compared with pumping the fiber only with 915 nm LD. The mechanism of photo-bleaching under 793 nm pump was also discussed.

22 citations

Journal ArticleDOI
TL;DR: It is suggested that the glass phase-separation technology shows great potential for realizing active fibers with larger core and complex fiber designs.
Abstract: We report on the preparation and optical characteristics of an Yb(3+)-doped large core silica fiber with the active core prepared from nanoporous silica rod by the glass phase-separation technology. The measurements show that the fiber has an Yb(3+) concentration of 9811 ppm by weight, a low background attenuation of 0.02 dB/m, and absorption from Yb(3+) about 5.5 dB/m at 976 nm. The laser performance presents a high slope efficiency of 72.8% for laser emission at 1071 nm and a low laser threshold of 3 W within only 2.3 m fiber length. It is suggested that the glass phase-separation technology shows great potential for realizing active fibers with larger core and complex fiber designs.

20 citations

Journal ArticleDOI
TL;DR: In this article, the authors describe the requirements of high-power fiber lasers, such as larger fiber core/higher homogeneity and higher doping level/lower numerical number of numerical parameters.
Abstract: Recent advances in high-power fiber lasers have imposed several pairs of higher requirements on fiber materials, such as larger fiber core/higher homogeneity and higher doping level/lower numerical...

18 citations

Journal ArticleDOI
TL;DR: It is found that the confined-doped fiber with a core of 35 μm and 0.07 numerical aperture could achieve single-mode output and improve the beam quality from 2.8 to 1.5 in the fiber laser, suggesting that it may be the key material for a high-power fiber laser with excellent beam quality.
Abstract: A confined-doped fiber was fabricated by a modified chemical vapor deposition (MCVD) process based on refractive index matching technology. With theory and experiments, we compared the confined-doped fiber and normal-doped fiber. We found that the confined-doped fiber with a core of 35 μm and 0.07 numerical aperture could achieve single-mode output and improve the beam quality from 2.8 to 1.5 in the fiber laser. Meanwhile, it still possesses high laser efficiency and has good stability of beam quality with the increase in pump power. It suggests that the confined-doped fiber with a MCVD process may be the key material for a high-power fiber laser with excellent beam quality.

17 citations


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Journal ArticleDOI
TL;DR: The state of the art regarding the knowledge of radiation effects on the performance of fiber-based technologies, from the microscopic effects observed in the amorphous silica glass used to design fiber cores and cladding, to the macroscopic response of fibers and systems are described.
Abstract: In this topical review, the recent progress on radiation-hardened fiber-based technologies is detailed, focusing on examples for space applications. In the first part of the review, we introduce the operational principles of the various fiber-based technologies considered for use in radiation environments: passive optical fibers for data links, diagnostics, active optical fibers for amplifiers and laser sources as well as the different classes of point and distributed fiber sensors: gyroscopes, Bragg gratings, Rayleigh, Raman or Brillouin-based distributed sensors. Second, we describe the state of the art regarding our knowledge of radiation effects on the performance of these devices, from the microscopic effects observed in the amorphous silica glass used to design fiber cores and cladding, to the macroscopic response of fiber-based devices and systems. Third, we present the recent advances regarding the hardening (improvement of the radiation tolerance) of these technologies acting on the material, device or system levels. From the review, the potential of fiber-based technologies for operation in radiation environments is demonstrated and the future challenges to be overcome in the coming years are presented.

133 citations

Journal ArticleDOI
01 May 2017
TL;DR: In this paper, the authors review the recent advances in the Ln3+ activated inorganic micro-sized UC materials from the perspective of tailoring UC emission color and intensity for plastic recycling applications.
Abstract: The demand for more efficient and complete sorting techniques for plastic waste is growing, and one possible solution isbased on fluorescent labeling. Novel fluorescent labels based on trivalent lanthanide (Ln3+) activated inorganic up-conversion (UC) materials offer a promising technological solution for plastic recycling. UC is a nonlinear, anti-Stokes process of combining two or more low energy near-infrared (NIR) photons to obtain the emission of a single higher energy photon. While Ln3+ based UC materials possess one key disadvantage –low quantum yield, they also exhibit many unique features, such as high signal/noise ratio, tailored emission color, long photo-luminescent lifetime, and low toxicity. These unique features endear them for a diverse range of applications and offer many new opportunities. Herein, we review the recent advances in the Ln3+ activated inorganic micro-sized UC materials from the perspective of tailoring UC emission color and intensity for plastic recycling applications.

63 citations

Journal ArticleDOI
TL;DR: In this article, the spectroscopic properties of Tm3+ -doped silica are first detailed, revealing complex processes and large variations among published measurements, with outputs ranging from 1908 to 2130 nm.
Abstract: Thulium-doped fiber lasers (TDFLs) have had the second highest growth in average output power next to ytterbium-doped fiber lasers. This has been enabled by access to high power, high brightness ∼790-nm pump diodes in conjunction with the cross-relaxation process that improves laser efficiency. While numerous high power TDFLs have been recently demonstrated, a 1-kW result from 2010 remains the highest output power system reported to date. This paper reviews these systems and the concepts behind high power TDFLs. The spectroscopic properties of Tm3+ -doped silica are first detailed, revealing complex processes and large variations among published measurements. Notable multi-100 W TDFLs are then summarized, with outputs ranging from 1908 to 2130 nm. Another route for power scaling is to in-band pump with another TDFL to enable >90% efficiencies. Both 790- and 1900-nm pumped TDFL architectures are theoretically modeled based on currently available systems. Hindered by high background losses and available pump sources, achieving >4 kW like ytterbium-fiber systems will be a substantial challenge.

62 citations

Journal ArticleDOI
TL;DR: A high power single frequency 1030 nm fiber laser with near-diffraction-limited beam quality based on a polarization-maintaining tapered Yb-doped fiber (T-YDF), which is the highest output power of all-fiberized single frequency fiber amplifiers.
Abstract: In this paper, we report a high power single frequency 1030 nm fiber laser with near-diffraction-limited beam quality based on a polarization-maintaining tapered Yb-doped fiber (T-YDF). The T-YDF has advantages of effectively suppressing stimulated Brillouin scattering (SBS) while maintaining good beam quality. As a result, a record output power of 379 W single frequency, linearly polarized, nearly single-mode fiber amplifier operating at 1030 nm is demonstrated. The polarization extinction ratio is as high as 16.3 dB, and the M2 is measured to be 1.12. Further, the dependence of the thermal-induced mode instability (TMI) threshold on the polarization state of an input signal laser is investigated for the first time. By changing the polarization state of the injected seed laser, the output power can increase to 550 W while the beam quality can be maintained well (M2=1.47). The slope efficiency of the whole amplifier is about 80%. No sign of SBS appears even at the highest output power and the further brightness scaling of both situations is limited by the TMI effect. To the best of our knowledge, this result is the highest output power of all-fiberized single frequency fiber amplifiers.

45 citations

Journal ArticleDOI
TL;DR: This work comprehensively studied the up-conversion (UC) properties of BaMgF4:Yb3+,Tb3+ phosphor for the first time and is expected to provide an approach for better understanding ET mechanisms in many Yb3/Tb 3+ codoped UC phosphors.
Abstract: In this work we have comprehensively studied the up-conversion (UC) properties of BaMgF4:Yb3+,Tb3+ phosphor for the first time. BaMgF4:Yb3+,Tb3+ phosphors were prepared by a simple and low cost precipitation method. To determine the influence of dopant concentration on luminescence properties, the corresponding UC luminescence spectra of BaMgF4:Yb3+,Tb3+ phosphors were studied under NIR excitation. Emission spectra under NIR excitation reveal the vital role of Tb3+ concentration in spectral tuning from the blue to green region. The UC decay curves were also studied to explore the possible energy transfer (ET) mechanisms between Yb3+ and Tb3+. The results reported here are expected to provide an approach for better understanding ET mechanisms in many Yb3+/Tb3+ codoped UC phosphors. This study will be helpful in applications where precisely defined optical transitions is an essential criterion.

43 citations