Blue diode-pumped Pr:YLF laser with planar resonator optics

The one-end-pumped Yb³⁺-doped gain guided and index antiguided (GG+IAG) fiber laser is analyzed with a rate equation model. By solving propagation rate equations, the pump and signal, the gain coefficients and other characteristics are obtained. Computation results show that a properly designed Yb³⁺-doped GG+IAG fiber laser can provide a large-mode laser with a short length. The most important issue addressed is the way of controlling the fiber laser length.     

Threshold characteristics of linear cavity Yb-doped double-clad fiber laser

The threshold characteristics of linear cavity Yb³⁺-doped double-clad fiber laser have been studied theoretically and experimentally. By solving rate equations, the expression for threshold pump power is obtained. The effects of fiber length, mirror reflectivity, pump wavelength, laser wavelength and Yb³⁺ concentration on threshold pump power are discussed. Then, the Yb³⁺-doped double-clad fiber laser with linear cavity is developed. By using various output couplers, threshold pump power has been measured. The experimental results are in accord with theory.     

Comparison of end-pumped and multi-point pumped Yb3+-doped gain guided and index antiguided fiber laser

End-pumped and multi-point pumped Yb³⁺-doped gain guided and index antiguided (GG+IAG) fiber laser are analyzed by solving the rate equations and 3-D thermal conduction equations. Simulation results show that the multi-point pumped scheme can provide lower operating temperature and better temperature uniformity. Meanwhile, fabrication complexity, loss resulted from pump point should be taken into consideration in the practical design.     

Novel shooting method with simple control strategy for fiber lasers

A novel shooting method with excellent simple control strategy is developed for solving the failure to convergence of the traditional shooting methods themselves in fiber lasers model. Compared with the published literature, the novel shooting method provides a clear physical understanding method for getting the threshold pump power and the exact results with given random functions in Yb³⁺-doped fiber lasers and Er³⁺-doped fiber lasers. Then, the results in Er³⁺-doped fiber lasers and Yb³⁺-doped fiber lasers demonstrate that the solutions using the novel shooting method has high accuracy of 10⁻⁸ W with several iteration steps, which have extended the applicable range of the end-pumped power even lower than 1 mW pump power. Furthermore, compared with 1480 nm pump for the threshold and slope efficiencies of the Er³⁺-doped fiber lasers, 978 nm fiber lasers can extend wider scope of application and be pump source in the coming future. Finally, the lower threshold and higher slope efficiency at 975 nm than those of 910 nm pump in Yb³⁺-doped fiber lasers, 975 nm pump laser provides for broad band excellent cladding pump source.     

全光纤超短脉冲掺Yb3+光纤环形激光器

讨论了自启动被动锁模掺Yb³⁺光纤环形激光器产生短脉冲的机理，并研制出全光纤结构超短脉冲掺Yb³⁺光纤环形激光器.采用两个976nm半导体激光器级联抽运作为抽运源，高掺杂浓度掺Yb³⁺光纤作为增益介质，利用光纤的非线性偏振旋转效应，得到自启动、十分稳定的ps量级锁模光脉冲.激光器锁模阈值功率260mW，输出功率25mW，锁模光脉冲中心波长1056nm，3dB带宽11.7nm，重复频率20MHz.与其他结构光纤激光器相比，这种全光纤结构具有更高的效率和更好的稳定性. 关键词： 环形光纤激光器 3+光纤')" href="#">高掺杂浓度掺Yb³⁺光纤 自启动 被动锁模     

The optimum length of linear cavity Yb-doped double-clad fiber laser

In order to improve the performance of the double-clad fiber laser, the optimum laser length needs to be estimated prior to the experiment. Previous expressions for the optimum length of fiber laser have been established under some assumptions, such as the output power without laser scattering loss and the pump power without reflection in the output-end. In this work, the issue of optimum laser length has been analyzed theoretically based on the strongly pumped fiber laser model. An extended expression for the optimum length of the linear cavity Yb³⁺-doped double-clad fiber laser is obtained. The respective effects of the laser scattering loss, the pump power, the Yb³⁺ dopant concentration, and the pump reflection on the optimum laser length are identified.     

Optimization of Yb3+-doped double-clad fiber lasers using a new approximate analytical solution

We investigated the properties of continuous wave (CW) Yb³⁺-doped double-clad fiber lasers (DCFLs) with linear-cavities theoretically and numerically using the rate equations. Under steady-state conditions, a new approximate analytical solution for CW Yb³⁺-doped double-clad fiber lasers (DCFLs) with consideration of the scattering losses were deduced. Good agreement between the proposed solution and the numerical simulation was demonstrated. Compared with the known approximate solutions published in the literature, the proposed solution has a briefer expression, higher accuracy and wider scope of application, which extends the applicable range of the analytical result to low reflective feedback mirror configurations. The solution provides a clear physical understanding of the optimal design of the CW Yb³⁺-doped DCFLs and can be applied to different pump and output configurations. Using the proposed solution, the optimal design of the CW Yb³⁺-doped DCFLs was discussed. If cavity reflectivities are given in advance, the optimal fiber length is found to be independent of the pump power. When the pump power and reflectivity of the feedback end are known in advance, the results show that the optimal fiber length increases and the optimal reflectivity of output mirror decreases with increase in pump power. Furthermore, when the feedback mirror is highly reflective, there exists a certain tolerance of the optimal parameters, in which the conversion efficiency decreases only slightly. But the conversion efficiency is sensitive to reflectivity of output mirror if feedback mirror has low reflectivity.     

Numerical analysis of stimulated Brillouin scattering in high-power double-clad fiber lasers

A theoretical analysis of stimulated Brillouin scattering (SBS) in linear cavity Yb³⁺-doped double-clad fiber lasers is presented by solving the steady-state rate equations with the SBS. The effects of cavity length, fiber core diameter, input mirror reflectivity at Stokes wavelength, Yb³⁺ concentration and laser linewidth on the SBS are discussed. Numerical results show that the SBS threshold power can be improved by shortening the cavity length, using large mode area fiber, reducing the input mirror reflectivity at Stokes wavelength, lowering the Yb³⁺ concentration and broadening the laser linewidth, and the influence of the laser linewidth on the SBS threshold power is more noticeable than other system parameters.     

高浓度镱铒共掺磷酸盐光纤放大器增益特性

在忽略高能级的自发辐射和光纤损耗的情况下，利用速率方程和传输方程理论研究了高浓度Er³⁺/Yb³⁺共掺磷酸盐玻璃光纤放大器的增益特性，讨论了Er³⁺浓度、Yb³⁺浓度、抽运光功率、信号光功率、光纤长度对放大器增益的影响，并与单掺铒光纤放大器进行了比较.由于Yb³⁺的敏化作用降低了铒离子的团簇效应，减少了离子间相互作用，共掺光纤的增益和效率明显高于单掺光纤.数值计算表明，3.2cm长Er³⁺/Yb³⁺共掺光纤在980nm的20dBm(100mW)抽运功率下，1532nm处的增益可达10dB. 关键词： 镱铒共掺光纤放大器 速率方程 传输方程 高浓度     

A global design of high power Nd-Yb co-doped fiber lasers

A global optimization method - niche hybrid genetic algorithm (NHGA) based on fitness sharing and elite replacement is applied to optimize Nd³⁺-Yb³⁺ co-doped fiber lasers (NYDFLs) for obtaining maximum signal output power. With a objective function and different pumping powers, five critical parameters (the fiber length, L; the proportion of pump power for pumping Nd³⁺, η; Nd³⁺ and Yb³⁺ concentrations, N_Nd and N_Yb and output mirror reflectivity, R_out) of the given NYDFLs are optimized by solving the rate and power propagation equations. Results show that dividing equally the input pump power among 808 nm (Nd³⁺) and 940 nm (Yb³⁺) is not an optimal choice and the pump power of Nd³⁺ ions should be kept around 10-13.78% of the total pump power. Three optimal schemes are obtained by NHGA and the highest slope efficiency of the laser is able to reach 80.1%.     

7-GHz high-repetition-rate mode-locked pulse generation using short-cavity phosphate glass fiber laser

A compact short-cavity high-repetition-frequency mode-locked fiber laser configured with Er³⁺/Yb³⁺ highly co-doped phosphate glass fiber and a graphene optical deposited film as saturable absorber is proposed and analyzed experimentally. The laser operates in stable mode-locked regime with fundamental repetition rate of 7.02 GHz. The output power is measured to be 1.2 mW with pump power around 80 mW, and the optical spectrum is centered about 1533.768 nm with mode spacing of 0.056 nm. As the pump power increases, the laser operates in multi-wavelength mode-locking emission state with the same longitude mode spacing. Moreover, the measure results show that different wavelength emission operates in different polarization states.     

Linear polarization Yb<Superscript>3+</Superscript>-doped fiber laser with novel innerclad structures

Results on high radiance Yb³⁺-doped fiber lasers with novel double innerclad structures (double-D clad and four hole) and polarized output at ≈1090 nm are presented. We have demonstrated >40% of the total output power being polarized, making the fiber laser suitable for LIDAR and second-harmonic generation (SHG) applications. It also showed a 10-nm tuning range with low (less than 10 mW) average power variations. The narrow linewidth source was pumped with a low cost, low brightness laser diode, and exhibited a relatively low slope efficiency, which gives room for improvement by using a 976-nm pump source where Yb³⁺ has a narrower linewidth and at least five times higher absorption.     

Spectroscopic properties and diode-pumped 1594 nm laser performance of Er:Yb:Li6Y(BO3)3 crystal

An Er³⁺/Yb³⁺-codoped Li₆Y(BO₃)₃ crystal was grown by the Czochralski method. The polarized absorption spectra and the fluorescence decay curve were recorded. The efficiency of energy transfer from Yb³⁺ to Er³⁺ ions was estimated. Quasi-continuous-wave output power of 325 mW at 1594 nm was realized under the absorbed pump power of 10.4 W in a hemispherical cavity. The absorbed pump threshold and slope efficiency of the laser are 6.0 W and 7.2%, respectively. PACS 42.55.Xi; 42.70.Hj     

Nonlinear transmission coefficient of ytterbium-holmium fiber at the wavelength 978 nm

An experimental and theoretical investigation of the nonlinear transmission coefficient of ytterbium-holmium codoped silica fiber (YHF) at continuous-wave 978-nm pumping is reported. An analysis of the fiber absorption and luminescence spectra under 978-nm pumping reveals a variety of processes participating in the mixed (Yb³⁺, Ho³⁺) system: the energy transfer Yb³⁺ → Ho³⁺, the up-conversion and excited-state absorption in Ho³⁺, and the luminescence quenching due to the presence of Yb³⁺-Yb³⁺ ion pairs. These processes are shown to notably affect the transmission coefficient of YHF, which is reflected in a pronounced modification of its dependences on pump power, fiber length, and dopant concentrations, in comparison with the case of purely ytterbium-doped fiber (YF). A modeling of the experimentally measured dependences of the YHF transmission coefficient on pump power and fiber length allows us to obtain the coefficients addressing the energy transfer process Yb³⁺ → Ho³⁺ in YHF. A comparison of YHF and YF at the same pumping conditions reveals that, in YHF, a considerable part of the pump power absorbed in the Yb³⁺ subsystem is transferred into the Ho³⁺ subsystem; this results in an effective population of its ⁵ I ₇ state and makes YHF promising for 2-μm lasing and amplifying.     

Diode-pumped monolithic Er3+:Yb3+:YAl3(BO3)4 micro-laser at 1.6 μm

Efficient eye-safe 1.6 μm monolithic laser was realized in a c-cut, 0.7-mm-thick Er³⁺:Yb³⁺:YAl₃(BO₃)₄ microchip end-pumped by a quasi-continuous-wave 970 nm diode laser. At incident pump peak power of 20.4 W, a maximum output peak power of 2.6 W with a slope efficiency of 19% was obtained when the waist radius of pump laser beam was 220 μm. The spectra and profiles of output beam of the Er³⁺:Yb³⁺:YAl₃(BO₃)₄ monolithic laser were measured. The influences of the waist radius of pump laser beam on the slope efficiency and threshold of the monolithic laser were also investigated.     

利用光谱滤波器实现自启动的全光纤超短脉冲掺Yb3+光纤激光器

讨论了利用光谱滤波器实现自启动的被动锁模掺Yb³⁺光纤环形激光器的锁模机理,并研制出全光纤结构超短脉冲掺Yb³⁺光纤环形激光器.使用980 nm二极管激光器作为抽运源,高掺杂浓度掺Yb³⁺光纤作为增益介质.在净群速度色散为正的环形腔中加入光谱滤波器,抑制Yb³⁺离子在1030 nm强发射峰的同时,通过对啁啾脉冲的光谱滤波实现脉冲压缩.光谱滤波器与光纤非线性偏振旋转效应相结合,实现了激光器在1053 nm可自启动、十分稳定的锁模运转.激光器锁模阈值功率300 mW,平均斜率效率18.3%,最大输出功率53.07 mW,对应最大输出脉冲能量3.2 nJ.锁模光脉冲中心波长1053.6 nm,3 dB带宽10.84 nm,重复频率16.45 MHz.锁模脉冲宽度为皮秒量级,经腔外光栅对压缩至188 fs. 关键词： 3+光纤激光器')" href="#">掺Yb³⁺光纤激光器 自启动锁模 全光纤     

Investigations of Yb-doped optical fiber using selective laser excitation

The method of tunable site-selective laser excitation was used for a study of the spectral and fluorescence characteristics of Yb³⁺ optical centers in laser optical fiber. Decay curves and positions of fluorescence spectra maxima at different wavelengths of selective laser excitation and positions of excitation spectra maxima at different fluorescence selective registration provide new information on lifetimes and Stark energy distribution among inhomogeneously broadened Yb³⁺ lines. The obtained Stark splitting energy distribution diagram demonstrates the tuneability of Yb³⁺ laser oscillation wavelength under tunable excitation of a pump laser.     

Wavelength tunable linear cavity cladding pump Er<Superscript>3+</Superscript>/Yb<Superscript>3+</Superscript>co-doped fiber laser operating in L-band

We have demonstrated a novel tunable linear cavity Er³⁺/Yb³⁺ co-doped fiber laser, which utilizes amplified spontaneous emission as a secondary pump source so that it can operate in L-band. The tuning wavelength range can be up to 34 nm, from 1588.6 to 1622.6 nm, and the output power excursion of the laser at different wavelengths can be less than 0.4 dB by using a two sections of high-birefringence fiber loop mirror as the wavelength filter. The high output power of 200 mW is realized by using the cladding-pump.     

ANALYSIS OF LASING PERFORMANCES OF Yb3+-DOPED YAG, FAP, KYW CRYSTALS

The Yb³⁺ laser emitting at a 1.03μm wavelength has been evoking strong interest recently due to its advantages of long fluorescence lifetime, broad absorption band and the fact that it never shows concentration quenching. On the other hand, as a laser of three-level system it has, in general, a relatively high threshold power, which makes it important to seek some suitable host crystals to reduce this. Here, we present a comparison of the lasing performances of Yb³⁺-doped YAG [Y₃Al₅O₁₂], FAP [Ca₅(PO₄)₃F] and KYW [KY(WO₄)₂] crystals, including threshold power and slope efficiency, with those of the Nd:YAG laser based on the threshold formula of three-and four-level systems deduced by the authors. The results show that the Yb³⁺ laser can output a power larger than the Nd:YAG laser does in the case of comparably higher pumping power, if the length of the lasing rod and the concentration of the active ions satisfy some conditions. The theoretical results are also close to the experimental results reported.