基于受激布里渊散射的波长间隔可变多波长光纤激光器

提出了一个基于自激发受激布里渊散射的波长间隔可变多波长光纤激光器.利用单模光纤中自激发产生的非线性布里渊增益和掺铒光纤的线性增益组成混合增益光纤激光器,从而使光纤激光器在室温下产生稳定的多波长输出.改变双折射光纤环镜滤波器中保偏光纤的长度,可以实现波长间隔可变多波长激光产生,提高了多波长光纤激光器操作的灵活性和实用性.实验实现了波长间隔从0.8 nm至0.076 nm可变的多波长激光产生,波长数随波长间隔减小而增加,间隔为0.08 nm的激光波长数达86.     

0.16 nm spaced multi-wavelength Brillouin fiber laser in a figure-of-eight configuration

A stable and compact multi-wavelength Brillouin fiber laser (BFL) operating at room temperature is experimentally demonstrated using a 100 m long photonic crystal fiber (PCF) in conjunction with a figure-of-eight configuration. At a Brillouin pump (BP) level of 15.3 dBm, 7 simultaneous lines with 20 GHz or 0.16 nm line spacing is achieved by removing the odd-order Stokes lines. The anti-Stokes lines are also generated via four wave mixing process in the laser cavity. Compared with the Erbium-based multi-wavelength laser, this BFL has advantages in term of channel spacing and flexibility in the choice of operating wavelength. The output spectrum of the proposed BFL can be tuned by 80 nm, dependent on the availability of an appropriate BP source. The multi-wavelength BFL shows a good stability with power fluctuations of less than 0.5 dB over more than 3 h.     

Effects of output coupler reflectivity on the performance of a linear cavity Brillouin/erbium fiber laser

The effect of output coupler reflectivity (or output coupling ratio) on the performance of a linear cavity Brillouin/erbium fiber laser (BEFL) is demonstrated. The operating wavelength, output laser power and number of channels vary with changes in the coupling ratio in the linear cavity system. The optimum BEFL operation is obtained with an output coupling of 40%, i.e., 60% of the laser power is allowed to oscillate in the cavity. A stable laser comb consisting of up to 40 channels with line spacings of approximately 0.09 nm are obtained at the Brillouin pump and 980 nm pump with powers of 2.5 mW and 100 mW, respectively. The linear cavity BEFL has the potential to be used in inexpensive wavelength division multiplexing system.      

Stimulated Brillouin scattering of Q-switched laser pulses in large-core optical fibres

Q-switched Nd : glass laser pulses of 60 ns duration are transmitted through multimode fused-silica fibres of 0.4–1 mm core diam and lengths of up to 20 m. For laser radiation with narrow spectral width, stimulated Brillouin scattering (SBS) is observed for energies well below the threshold energy of fibre damage. The SBS threshold is shifted beyond the threshold of fibre damage through increasing the spectral width of the laser radiation. The SBS threshold energies of step-index and gradient-index fibres are measured for various fibre and laser parameters.     

Photonic crystal fibre Brillouin laser based on Bragg grating Fabry-Perot cavity

A photonic crystal fibre Brillouin laser based on fibre Bragg grating Fabr-Perot cavity is presented. A highly nonlinear photonic crystal fibre 25 m in length is used as Brillouin gain medium and fibre Bragg grating Fabry-Perot cavity is chosen in order to enhance the laser conversion efficiency and suppress the higher-order Stokes waves. The laser reaches the threshold at input power of 35 mW, and the experimental laser conversion efficiency achieves 18% of the input power of 140 mW and does not show higher-order Stokes waves. A photonic crystal fibre Brillouin laser with shorter fibre length and lower threshold is experimentally realized.     

Multiwavelength self-seeded Brillouin-erbium fiber laser with 45-nm tunable range

We have demonstrated a tunable multiwavelength self-seeded Brillouin-erbium fiber laser (BEFL) without externally Brillouin pumping. In this scheme, the stable multiwavelength comb can be produced within a ∼45-nm wavelength tuning range through adjusting the polarization controllers (PCs) in a high-birefringent Sagnac loop mirror. The generation of ∼200-line Stokes comb has been achieved by adjusting PCs under bidirectional pumping of two laser diodes, which is the largest wavelength number to the best of our knowledge. The effect of 980 nm pump power on the multiwavelength generation was also investigated.     

Simple tunable multiwavelength Brillouin/Erbium fiber laser utilizing short-length photonic crystal fiber

We have demonstrated a simple ring cavity tunable multiwavelength Brillouin/Erbium fiber laser (MWBEFL), in which 70 m highly nonlinear photonic crystal fiber (HNL-PCF) is used as the Brillouin gain medium. The fiber laser utilizes recycling mechanism to enhance stimulated Brillouin scattering (SBS). The configuration that consists of only 3 optical components is easy to be integrated and improves the practicality. At the maximum 1480 nm pump power of 110 mW and the Brillouin pump power of 3 dBm, 10 stable output channels with more than 10 dB optical signal to noise ratio (OSNR) and 0.078 nm channel spacing could achieve 10 nm tuning ranges.     

Multi-wavelength generation using a bismuth-based EDF and Brillouin effect in a linear cavity configuration

The generation of a multiple wavelength source using a bismuth-based erbium-doped fiber (Bi-EDF) in a linear cavity configuration is demonstrated. The configuration uses a pair of optical circulators at the input and output ends of the cavity to form a resonator for multi-wavelength generation in conjunction with optical couplers to inject the Brillouin pump (BP) and to tap the output at the two ends. The Brillouin erbium fiber laser (BEFL) comb with a 2.15 m of Bi-EDF has a wavelength spacing of 0.09 nm and operates in long-wavelength (L-) band region. A stable output laser comb of 50 lines is obtained at a BP of 1568.2 nm and 5 dBm and two 1480 nm pumps at 120 mW. The injected BP wavelength and power as well as the 1480 nm pump powers have a great effect on the number of lines and output power of the BEFL. This configuration is compact due to the use of the significantly shorter Bi-EDF as the linear gain medium, and can be made more compact by replacing the single-mode fiber with highly non-linear fibers such as holey fibers.     

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.     

Stable room-temperature multi-wavelength lasing oscillations in a Brillouin–Raman fiber ring laser

A stable room-temperature multi-wavelength Brillouin–Raman fiber laser with a ring cavity configuration was proposed and experimentally investigated. An obvious suppressant effect for unstable mode hopping of multi-wavelength lasing oscillations induced by deeply saturated effect was observed in the ring cavity configuration. Stable room-temperature multi-wavelength lasing oscillations with more than 30 lasing lines and wavelength spacing of 0.076 nm were obtained with only 250 mW Raman pump power and a section of high nonlinear fiber with a length of 1.5 km. The lasing output is so stable that the maximum power fluctuations for the foremost three Stokes lines over more than 20 min of observation were less than 0.30 dB. The lasing stability of the laser was also compared with a linear cavity configuration with the same gain components and pump conditions. While using the linear laser cavity configuration, obvious mode hopping was observed. The minimum value of the maximum power fluctuations at all lasing lines over more than 10 min of observation was more than 0.90 dB.     

Millimeter wave carrier generation based on Brillouin fiber laser with improved tuning capability

An all-optically generated millimeter wave carrier at 21.7 GHz, 43 GHz and 64.45 GHz are experimentally achieved. These frequencies are realized by generating two consecutively laser wavelengths and are detecting on the 70 GHz high-speed photo detector (HSPD). The initial mixing between the Brillouin pump and the second-order Stokes wavelengths is spaced by 0.178 nm. This spacing, which is doubled from an inherently generated Stokes shift, is accomplished through an isolated circulation of the first order Stokes wave in the double Brillouin Stokes shifter (DSBS) built with 25-km single mode fiber. The generated millimeter carrier is measured at 21.7 GHz, 43 GHz and 64.4 GHz achieved with BP power of 11 mW, 30 mW and 47 mW, respectively.     

对受激布里渊散射激光进行组束的数值模拟及方案设计

 提出了时间上串行的多路激光脉冲通过受激布里渊散射(SBS)池进行组束的方法,并对其进行了数值模拟研究。利用6束每束能量为45J的KrF激光进行组束, 可获得能量为141.89J,脉宽为670ps的Stokes输出光。根据模拟结果设计出了时间上串行的SBS激光组束的两个方案, 对其进行了讨论。数值模拟还发现在介质的增益系数更大、声子寿命更短的情况下,输出激光脉冲的脉宽可以压缩得更窄。     

An Efficient Photonic Crystal Fiber-Based Brillouin Erbium Fiber Laser Using a Fiber Bragg Grating for Multi-Wavelength Generation

Abstract

An efficient multi-wavelength Brillouin erbium fiber laser is demonstrated using an improved configuration with a broadband fiber Bragg grating and a piece of photonic crystal fiber. The laser generates more than 55 lines of optical comb with a line spacing of approximately 0.09 nm in a 1,565-5 nm region using pump powers of 3 dBm and 150 mW for the Brillouin and 980-nm pumps, respectively. The Brillouin erbium fiber laser with a fiber Bragg grating's reflectivity of 50% obtained a higher number of comb lines compared to that of 99% reflectivity.     

Application of a phase conjugate Brillouin cavity for the generation of a train of short laser pulses

Summary An oscillator and a regenerative amplifier have been realized using a phase conjugate mirror in the amplifier laser cavity. The phase conjugate mirror, via stimulated Brillouin scattering, acts as a modulator owing to its time-depending reflectivity. A pulse-forming network applied to the amplifier increases the discharging time which contributes to get an output beam formed by a train having four short pulses. The shortest pulse was 2 ns FWHM long.     

Spacing-adjustable and wavelength-tunable multiwavelength fibre laser with nonlinear Brillouin gain and birefringence fibre loop mirror

This paper demonstrates a room-temperature multiwavelength fibre laser with spacing-adjustability and wavelength-tunability. The nonlinear gain of self-excited stimulated Brillouin scattering can suppress mode competition induced by homogeneous broadening of Erbium-doped fibre. With the use of a birefringence fibre loop filter, the wavelength spacing can be adjusted by changing the length of the used birefringence fibre, and the lasing wavelengths can be finely tuned through modifying the filtering profile of the birefringence filter. Multiwavelength output with spectral spacing as small as 0.076~nm and a wavelength number of more than 80 has been successfully produced.     

激光聚变中受激布里渊散射的混合模拟研究

在激光等离子体相互作用中, 受激布里渊散射的模拟耗时较长. 为缩短模拟时间, 对电子采用Boltzmann描述, 开发了一维混合Vlasov程序, 利用离子束双流不稳定性理论结果对程序进行了考核.在此基础上对激光聚变中的受激布里渊散射进行了研究, 结果表明程序正确, 模拟结果可信.     

Investigation of stimulated Brillouin scattering for broadband KrF laser

Stimulated Brillouin scattering (SBS) numerical mode for broadband multimode KrF laser pump with optical breakdown has been built up in this paper. The basic premises of the model are that KrF spectrum is composed of an umber of lines and SBS arises from these lines with coupling to some extent. The broadband SBS threshold strongly depends on pump bandwidth. SBS and optical breakdown occur nearly simultaneously when broadband SBS and breakdown have the same threshold. The decrease of saturation reflectivity for broadband pump radiation is explained with this model. Experimental results agree well with the model.     

KrF激光受激布里渊散射反射率稳定性的研究

实验研究发现抽运功率密度（或抽运能量）的波动引起的受激布里渊散射(SBS)反射率的不稳定程度受实验参数（抽运能量、介质气压和透镜焦距）的影响.当抽运能量、介质气压和透镜焦距这三个参数同时满足下列条件时可以获得稳定的输出：抽运能量超过5倍的SBS阈值，介质气压在16×105Pa和透镜焦距在15—50cm的范围内；同时还发现当改变实验参数时SBS反射率与稳定性的变化规律完全一致，反射率越高稳定性越好.通过理论分析得到 SBS反射率的相对稳定度实际上是受GIL因子的影响，理论计算与实验符合得很好. 关键词： KrF激光 受激布里渊散射 反射率 稳定度     

多模光纤受激布里渊散射非相干组束的机理及理论模型

 基于布里渊散射耦合强度方程,分析了多模光纤受激布里渊散射非相干组束的机理,建立了其非相干组束的理论模型,并依据模型进行了理论计算。结果表明：在较长的多模光纤中,受激布里渊散射产生的Stokes光以LP­­₀₁模传输;其非相干组束过程是混合光分解成线偏振光的逆过程;计算的组束功率与T.H.Russel等人的实验结果相一致。最后,分析了组束光强的分布,表明了组束光强对模场尺寸的依赖关系,证明提高组束光强的有效措施是减小组束光的模场半径。     

Ge-codoped fibers for mitigating stimulated Brillouin scattering in high power fiber amplifiers

Rare-earth doped fibers for high power fiber amplifiers normally have a small refractive index difference between the core and inner cladding, but have a larger core diameter than conventional telecom fibers. We take advantage of this feature as well as the difference between the optical and acoustic waveguides and proposed several fiber designs to mitigate Stimulated Brillouin scattering (SBS) to produce higher output powers. The numerical modeling shows that an increase in SBS threshold by 3-6 dB can be achieved using Ge-codopant while maintaining diffraction limited beam quality. The key parameters that can affect the SBS performance are specified and optimal parameters for SBS suppression are obtained. The study also highlights the need to take into account the effects of minor refractive index profile variation in evaluating SBS performance.