High-power narrow-linewidth linearly-polarized Tm-doped fiber lasers operating at 2.0μm have attracted extensive interest in both scientific and industrial fields such as free space communication, remote laser sensing, coherent Doppler lidar wind detection, and gravitational wave detection. In this work, an output power of 160 W narrow-linewidth linearly polarized fiber laser operating at 2007.6 nm was realized by employing a homemade polarization-maintaining Thulium-doped fiber (PMTDF), corresponding to a slope efficiency of 45% and a 3 dB linewidth of 73 pm. The PMTDF was manufactured by modified chemical vapor deposition (MCVD) method combined with solution doping technology, with core and cladding sizes of 25 μm and 400 μm, respectively. The numerical aperture (NA) of the PMTDF is 0.1 and the cladding absorption is 4 dB/m at 793 nm. During the power scaling, the polarization extinction ratio (PER) maintained higher than 16.5 dB, indicating an excellent polarization maintaining performance of the manufactured fiber. The stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS) effects were well-suppressed. This work could provide a good reference for the further power scaling of narrow-linewidth linearly polarized fiber lasers operating at 2.0 μm.
In this paper, the ytterbium-doped tapered fiber with core/inner cladding diameter varying from 31/250 μm to 62/500 μm was designed and prepared by the improved chemical vapor deposition and solution doping technology. An all-fiber nanosecond pulse amplifier was built based on the ytterbium-doped tapered fiber, and the influence of the longitudinal structure on the output characteristics of nanosecond pulsed laser was investigated. A nanosecond pulsed laser output with a central wavelength of 1064 nm, an average power of 832 W, a single pulse energy of 8.32 mJ and a peak power of 24.8 kW at a repetition rape of 100 kHz was achieved based on the ytterbium-doped tapered fiber with a large diameter uniform region length ratio of 62.5%. Compared with 50/400 μm uniform fiber, the ytterbium-doped tapered fiber showed obvious suppression effect on stimulated Raman scattering and beam degradation at a similar output power.
In order to enhance the irradiation resistance of erbium-ytterbium co-doped optical fibers for long-range space communication applications, a Radiation-Resistant Erbium-Ytterbium co-doped Fiber (RREYDF) was fabricated by Modified Chemical Vapor Deposition (MCVD). The RREYDFs were irradiated at 300 Gy and 1000 Gy with an average dose rate of 0.2 Gy/s at room temperature using a Co60 irradiation source. The Radiation-Induced Absorption (RIA) at 940 nm and 1550 nm were 0.10 dB/m and 0.22 dB/m at 300 Gy and 0.47 dB/m and 0.36 dB/m at 1000 Gy, respectively. An Erbium-Ytterbium co-doped Fiber Amplifier (EYDFA) with a 1550 nm signal and a 940 nm pump source was built for gain testing. The Radiation-Induced Gain Variation (RIGV) was 0.1 dB (300 Gy) and 1.0 dB (1000 Gy) at a pump power of 7.3 W.
Three kinds of Polarization Maintaining Yb-Doped Fibers (PMYDFs) were manufactured by a Modified Chemical Vapor Deposition (MCVD) process combined with Solution Doping Technique (SDT). The laser performance of the PMYDFs were investigated by systematic experiments and a highest output power of 1812 W was achieved, corresponding to a slope efficiency of 79%. The PMYDF-3’s beam quality factor of M2x and M2y are 1.22 and 1.22 respectively at 1615 W. Through comparative experiments, the lower NA PMYDF performed a better TMI threshold.
Yb-doped fiber (YDF) lasers and amplifiers have been widely employed to industrial processing, medical treatment, 3D printing, and military defense owing to the high conversion efficiency, efficient heat dissipation, compactness, and good beam quality [1-3] . However, their outstanding evolution is interrupted by stimulated Raman scattering (SRS) [4] and transverse mode instability (TMI) [5] effects. It is effective to suppress both of them by concentrating on the large mode area (LMA) YDF design. Specially designed fibers, such as constant-cladding tapered-core fiber [6] , spindle-shaped fiber [7] , low-NA fiber [8] , and gain-tailored fiber [9] , have been fabricated and demonstrated to suppress those nonlinear effects (NLEs) with effect. Hereon, we proposed a novel low-numerical-aperture (NA) confined-doped long-tapered fiber, which was fabricated by a modified chemical vapor deposition (MCVD) process combined with solution doping technique (SDT). As described in Fig. 1 (a), the core and inner cladding diameter were 25μm and 400 μm at both ends and 37.5 µm and 600 μm in the middle, respectively. The numerical aperture (NA) of fiber core was ~0.05, as shown in Fig. 1(b). Additionally, the gain dopant was restrictedly distributed in smaller area in fiber core, whose diameter ratio was 70%.
High power ytterbium doped fiber laser has become the most popular laser source in metal cutting, metal welding and other material processing fields[1]. Single mode fiber lasers with excellent beam quality are expected to achieve high aspect ratio and ultrafast processing speed[2]. While the drawbacks of traditional optical transmission fibers such as nonlinear optical effects and the low material’s laser induced damage threshold have hindered the further growing of the high output power[3]. Hollow-core fibers (HCFs) would replace traditional fiber to be an ideal medium for ultra-high-power laser transmission with the advantages of lower nonlinearity, and high damage threshold[4,5]. The simplified negative-curvature hollow-core fibers (NC-HCFs) with simpler structure, lower loss, as wall as great advantages in bandwidth have attracted much attentions in recent year[6–9]. In this work, we propose a novel negative-curvature hollow-core fiber structure with double trigonal-symmetrical anti-resonant elements implementing single-mode or polarization-maintaining transmission for high-power laser delivery at 1μm wavelength window. The single-mode performance with a higher-order modes extinction ratio (HOMER) as high as 4.65*104 is achieved, and it remains >1*104 within a large range of tubes sizes, which can increase the flexibility of fiber fabrication. Fig. 1 shows the cross-section of the proposed NC-HCF. The cladding is constituted of 3 small tubes with diameter of d1, and 9 large tubes with diameter of d2. The 3 small tubes and 3 large tubes are arranged in a staggered pattern in the inner layer to form double trigonal-symmetrical anti-resonant elements, while the other 6 large tubes are connected to the jacket tube in the outer layer.
Er-doped fibers amplifiers (EDFAs) have widely used in many fields, such as optical fiber communication and
inertial research [1]. However, the erbium-doped fibers (EDFs), as the key component of EDFA, are extremely sensitive to
various cosmic rays (X-rays, gamma rays and protons). The fabrication of conventional EDFs add the co-dopants such as
aluminum, phosphorus and germanium for increasing the solubility of erbium ions and weakening the cluster effect [2]. As
a consequence when the erbium-doped fibers are irradiated to a certain dose, the color centers (AlE’, P1 and Ge-NBOHC,
etc.) will be generated which causes radiation-induced attenuation (RIA) and reduces EDFA amplification performance [3].
In this work, the lab-built radiation-resistant Er-doped fibers (RREDF) with the size of 9/125μm (core/cladding) were
manufactured by Modified Chemical Vapor Deposition (MCVD).The Cerium and Lanthanum were doped in fibers for
improving radiation resistance and amplification efficient [2]. Considering the radiation dose in actual space environment is
102~105Gy [3], the Er-doped fibers were irradiated by Co60 radiation source with 1500Gy dose and 0.2Gy/s dose rate at RT.
The RIA of RREDF and radiation-induced gain variation (RIGV) of RREDFA were tested, and a conventional Er-doped
fiber with the same dimension as RREDF was also fabricated for comparison. The characteristic of two EDFs are shown in
Table 1.
A high power short-cavity random fiber laser employing the gain mechanism of the Yb-doped fiber and the half-open cavity structure and the temporal optical rogue waves (RWs) behavior are observed and investigated in the paper. The record output power without the stimulated Raman scattering (SRS) is promoted to 26.6 W in the YDRFL with the GDF length of 120 m. The stochastic pulses and temporal optical RWs are observed and demonstrated in the short cavity YDRFL for the first time. It is found that the proportion of RWs depends on the GDF length which can also affect the stability of output lasing. The research results reveal that achieving the relative stable output power requires the greater pump power for the shorter GDF length, although decreasing the GDF length will promote the maximum output power of the YDRFL without the SRS.
KEYWORDS: Oscillators, Fiber lasers, Cladding, High power lasers, Diodes, Ytterbium, Fabrication, Doping, Laser damage threshold, High power fiber lasers
In this work, deuterium loaded Yb-doped fiber has been proposed to mitigate mode instability in laser oscillator. Experimental results reveal that mode instability threshold power rises from ~459W to ~533W and ~622W at the condition of pristine fiber and fiber loaded with deuterium for 2 weeks and 4 weeks respectively. Mode instability threshold power is raised by more than 16% and 35% after 2 and 4 weeks deuterium loading compared to pristine fiber respectively, and laser slope efficiency is not affected by deuterium loading. The experimental results indicate that deuterium loading is effective in mode instability mitigation and showing potentials in further power scaling of high power fiber lasers.
We have demonstrated a kW continuous-wave ytterbium-doped all-fiber laser oscillator with 7×1 fused fiber bundle combiner, fiber Bragg grating (FBG) and double-clad gain fiber fabricated by corresponding technologies. The results of experiment that the oscillator had operated at 1079.48nm with 80.94% slope efficiency without the influence of temperature and non-linear effects indicate that fiber components and gain fiber were suitable to high power environment. No evidence of the signal power roll-over showed that this oscillator possess the capacity to highest output with available pump power.
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