自由耦合输出的大模场面积光子晶体光纤锁模激光器

对一种基于高增益掺Yb³⁺大模场面积光子晶体光纤（PCF）的锁模激光器进行了简化线型腔结构的实验和理论研究.实验中直接使用塌陷打磨为0°角的光纤端面作为一端腔镜,利用其端面反馈获得了激光振荡,并进一步利用半导体可饱和吸收镜（SESAM）和光栅对的滤波作用实现了稳定的锁模运转.通过调节滤波程度,使激光器实现了从宽带滤波锁模到窄带滤波锁模的连续可调谐.在宽带滤波锁模的条件下,得到了最大平均输出功率2.2 W,单脉冲能量29.3 nJ,脉冲宽度367 fs的锁模脉冲输出;在窄带滤波锁模的条 关键词： 飞秒激光 光纤激光器 光子晶体光纤 大模场面积光纤     

Theoretical study and optimization of a high power mid-infrared erbium-doped ZBLAN fibre laser

Based on the rate equations describing the erbium-doped fluoride glass(ZBLAN) fibre lasers with different pumping configurations being taken into account,this paper presents theoretical calculations related to the dynamic population density and the operation performance of a high power mid-infrared all-fibre erbium-doped ZBLAN fibre laser.It shows that the ground-state absorption,excited-state absorption and energy-transfer-upconversion processes co-exist and produce a population balance,causing the laser to operate stably at a continuous wave state.A good agreement between the theoretical results and recent experimental measurement is obtained.Furthermore,the laser structure parameters including fibre length,reflectance of output fibre Bragg grating and pumping configurations are quantitatively optimised to achieve the best performance.The results show,as expected,that the slope efficiency of the fibre laser can be improved significantly through optimisation,which then provides an important guide for the design of high-performance mid-infrared erbium-doped ZBLAN fibre lasers.     

All-normal-dispersion Yb-doped mode-locked fibre laser and its stability analysis

We experimentally demonstrate an all-normal-dispersion Yb-doped mode-locked fibre laser with no intentional spectral filter inserted.Pulses with 1.1 nJ pulse energy at a repetition rate of 20.4 MHz are achieved.A theoretical model of the fibre laser is derived,whose coefficients are explicitly dependent on the orientations of the wave plates and the polarizer.Based on the model,stability diagrams of both the mode-locking and the continuous wave regimes of the laser are presented.The influence of group-velocity dispersion (GVD) and cavity length on the stability of mode-locking is also discussed.     

Bound soliton pulses in a passively mode-locked fibre ring laser

The bound solitons in a passively mode-locked fibre ring laser are observed and their formation mechanism is summarized in this paper. In order to obtain stable bound solitons, a strong CW laser field at the centre of the soliton spectral is necessary to suppress and synchronize the random soliton phase variations.     

Soliton shaping of dispersive waves in a passively mode-locked fibre soliton ring laser

We have studied the mechanism of soliton formation in a passively mode-locked fibre ring laser when the gain is increased. We show experimentally that new soliton pulses in the laser are generated by soliton shaping of dispersive waves. Our observation is further confirmed by numerical simulations where an improved model is used that takes into account explicitly the polarization dispersion effect and discrete saturable absorber effect.     

Transition state to mode locking in a passively mode-locked erbium-doped fibre ring laser

The transition state between the continuous wave region and the mode-locked region in a passively mode-locked erbium-doped fibre ring laser has been experimentally observed by utilizing the nonlinear polarization rotation technique.When the pump power reaches the mode-locked threshold,the metastable pulse train with a tunable repetition rate is obtained in the transition from the continuous wave state to the passive mode-locked state via proper adjustment of the polarization controller.A simple model has been established to explain the experimental observation.     

Efficient frequency upshift of 10fs laser pulsespropagating in a 5-cm length birefringent photonic crystal fibre

This paper reports that a 5-cm length birefringent photonic crystal fibre is used to tune the output frequency of unamplified 10-fs Ti:sapphire pulses. The zero dispersion of the fibre is at 823~nm and 800~nm for slow and fast fundamental modes, respectively. It is demonstrated that efficient upshift of the output frequency can be achieved when the pumped radiation is polarized along the slow axis of the fibre. When the average input power reaches 320~mW, about 60% of the output energy is located in one peak at 600~nm and is accompanied by depletion of the pulse inside the anomalous dispersion region.     

Interaction of a parabolic-shaped pulse pair in a passively mode-locked Yb-doped fiber laser

We numerically investigate the formation and interaction of a parabolic-shaped pulse pair in a passively mode-locked Yb-doped fiber laser. Based on a lumped model, the parabolic-shaped pulse pair is obtained by controlling the intercavity average dispersion and gain saturation energy, Moreover, pulse repulsive and attractive motion are also achieved with different pulse separations. Simulation results show that the phase shift plays an important role in pulse interaction, and the interaction is determined by the inter-cavity average dispersion and gain saturation energy, i.e., the strength of the interaction is proportional to the gain saturation energy, a stronger gain saturation energy will result in a higher interaction intensity. On the contrary, the increase of the inter-cavity dispersion will counterbalance some interaction force. The results also show that the interaction of a parabolic-shaped pulse pair has a larger interaction distance compared to conventional solitons.     

被动锁模光纤激光器多孤子脉冲形成机理

基于非线性耦合薛定谔方程,在非线性偏振技术锁模的掺铒环形光纤激光器中,理论研究多孤子脉冲的形成和演化规律。研究结果表明：随着小信号增益不断增加,光纤激光器的锁模透过率函数影响多脉冲输出,多脉冲产生受色散波和脉冲分裂形成的峰值功率的限制效应和孤子能量量子化的影响,这是增益竞争和非线性偏振旋转引起的损耗之间动态平衡的最终结果。     

Interaction of parabolic-shaped pulse pair in a passively mode-locked Yb-doped fiber laser

We numerically investigate the formation and interaction of parabolic-shaped pulse pair in a passively mode-locked Yb-doped fiber laser. Based on a lumped model, the parabolic-shaped pulse pair is obtained by controlling the inter-cavity average dispersion and gain saturation energy, Moreover, pulse repulsive and attractive motion are also achieved with different pulse separations. Simulation results show that the phase shift plays an important role in pulse interaction, and the interaction is determined by the inter-cavity average dispersion and gain saturation energy, i.e., the strength of the interaction is proportional to the gain saturation energy, the stronger gain saturation energy will result in higher interaction intensity. On the contrary, the increase of the inter-cavity dispersion will counterbalance some interaction force. The results also show that the interaction of a parabolic-shaped pulse pair has a larger interaction distance compare to the conventional solitons.     

Influence of the bias current on the output characteristics of a mode-locked fiber ring laser consisting of two SOAs

In this paper, after obtaining the mode-locked pulse shape with self-reproduction theory, the influence of the bias current on the output characteristics of a backward-optical-injection harmonic mode-locked fiber ring laser consisting of two semiconductor optical amplifiers (SOAs) has been numerically investigated. The results show that the mode-locked pulse with high peak power and narrow width can be obtained through reasonably adjusting the bias currents of the two SOAs.     

Raman oscillation with intracavity pumping of a fibre laser

We introduce the concept of cascaded resonant Raman pumping of fibre lasers. The pump scheme utilises the relatively large intracavity Stokes field that is generated within a Raman fibre laser to excite a lanthanide ion that is doped within the core of the fibre providing the Raman gain. In order to illustrate the general characteristics of the pump method and, to establish the design parameters necessary for the realisation of the pump scheme, calculations from a theoretical model that is used to simulate the generation of laser output from a fibre laser that is resonantly pumped with first Stokes radiation is presented. Specifically, the 2.1 μm output from a Ho³⁺-doped silica fibre laser that is pumped with 1.15 μm first Stokes radiation is calculated with the use of a relatively simple numerical model. For a launched pump power of 20 W at 1.07 μm, a fibre laser output of 3 W is predicted for a nominal intrinsic loss of 1.5 dB/km at 2.1 μm, however, this low value of the intrinsic loss at 2.1 μm can be significantly relaxed when the length of the Ho³⁺-doped silica fibre laser resonator is made considerably shorter than the Stokes resonator.     

振幅和相位涨落对锁模脉冲列特性的影响

用傅里叶变换的方法分析了锁模激光器中模式间的相位和振幅涨落对锁模脉冲列特性的影响。将锁模激光器中各模式的相位和振幅涨落作傅里叶展开,再通过增益谱抽样的傅里叶变化得到其时域行为。分析结果表明振幅系统涨落及随机涨落均不引起脉宽的明显变化,只引起脉冲间背景的加大,但相位涨落随机会使脉冲列强度产生波动。所用物理图像简明,结果对获得稳定的锁模脉冲列的实验研究有参考意义。     

振幅和相位涨落对锁模脉冲列特性的影响

 用傅里叶变换的方法分析了锁模激光器中模式间的相位和振幅涨落对锁模脉冲列特性的影响。将锁模激光器中各模式的相位和振幅涨落作傅里叶展开，再通过增益谱抽样的傅里叶变化得到其时域行为。分析结果表明振幅系统涨落及随机涨落均不引起脉宽的明显变化，只引起脉冲间背景的加大，但相位涨落随机会使脉冲列强度产生波动。所用物理图像简明，结果对获得稳定的锁模脉冲列的实验研究有参考意义。     

高功率TEA CO2激光器两波长激光切换输出技术

 以TEA CO₂激光器通常采用的平-凹光学稳定腔为基础,提出了一种新的波长选支方法——输出窗口镀膜选支方法。利用一台高平均功率TEA CO₂激光器进行了选支实验研究,结合现有光学镀膜技术,得到了中心波长为9.3 μm的激光单谱线输出,其单脉冲能量及平均功率与激光器原中心波长10.6 μm单谱线输出的相应参数基本相当。研究发现,以相同单脉冲能量激光照射热敏纸时,中心波长9.3 μm激光光斑与中心波长10.6 μm的明显不同。同时,还设计出两波长窗口密闭免调切换装置,在一台激光器上实现了10.6,9.3 μm两个中心波长激光同等功率水平的免调切换输出,切换位置误差小于5″,密封性能满足使用要求。     

Improved design of a DFB Raman fibre laser

A Raman fibre laser based on phase shifted DFB structures is modelled for the first time. Using parameters of realistic devices, the model predicts low-threshold and highly-efficient laser output. The change of position and width of the phase shift were found to have a substantial impact on laser performance.     

大激活体积高功率CO_2激光器环状输出稳定腔的研究

本文从理论和实验上研究了具有环状耦合、工作在稳定腔边缘的凹-凸型高功率激光稳定腔.在一台大激活体积万瓦级模流CO_2激光器上进行实验,获得了具有良好方向性的均匀的环状分布近场花样的7kw激光输出.     

Design and fabrication of triangular inner cladding double-clad ytterbium doped fibre for high power lasers

To improve the performance of double clad high power fibre lasers, inner cladding design plays a significant role. A triangular inner cladding and silica structure second cladding with large air holes go acquire high inner cladding numerical aperture are designed. Single mode and high power output of the fibre lasers need the double clad Yb doped fibre with large core. A fibre with annular refractive index distribution core and low numerical aperture to acquire a large mode area fibre core is designed and fabricated. Furthermore co-doping with aluminium （A1） has been used to improve the solubility of ytterbium （Yb） into silicate network, and the core absorption coefficients of two Yb doped fibres are compared with different A1 concentration experimentally.     

高功率半导体泵浦固体激光器输出特性的研究

通过实验详细测量了水温、工作电流对二极管激光器发射波长的影响;采用光线追踪法模拟计算出在不同泵浦参数下半导体泵浦光在NdYAG棒内的分布情况,得到了圆周上泵浦模块的个数,泵浦光发散角等因素对泵浦光分布均匀性的影响.采用直接泵浦方式,分别设计了二种不同功率水平的半导体泵浦的NdYAG固体激光器聚光腔,得到了170和800 W的输出功率,并对激光器的输出特性进行详细测量,最大光-光转换效率达37%,电-光转换效率约为16%.