Low-repetition-rate, all-polarization-maintaining Yb-doped fiber laser mode-locked by a semiconductor saturable absorber

A low-repetition-rate, all-polarization-maintaining（PM）-fiber sub-nanosecond oscillator is presented, which is simple and low-cost, composed of standard components. The ring cavity is elongated by 114-m-long standard PM fiber, and passively mode-locked by a fiber pigtailed semiconductor saturable absorber. Linearly polarized pulses with 1.66 MHz repetition rate and 22 dB polarization extinction ratio are generated at a wavelength of 1030 nm, which is determined by an intracavity filter. In addition, to demonstrate that the oscillator is a good seed for high energy pulse generation, an all-fiber master oscillator power amplifier is built and amplified pulses with energy about 2 μJ are obtained.

Microstructure and properties of novel polarization maintaining fiber

An improved type of elliptical jacket polarization maintaining fiber was developed by using a modified chemical vapor deposition method with special treatment. Different from conventional elliptical jacket, the shape of the stress jacket was transmuted. The cross-section of fiber consists of 5 layers: substrate, outer cladding, stress jacket, inner cladding and core. The cross sectional component distribution was investigated by electron probe microscopy and energy dispersive spectrum. The finite element method was used to calculate the stress birefringence. Based on the analyses of the microstructure, the technological process is improved. The temperature cycling test of the fiber wound into gyroscope coils was performed. The results show that the fiber possesses superior performance at high and low temperatures compared with other fibers. The high homogeneity is achieved by well-controlled modified chemical vapor deposition process. A homogeneous length of 8 km fiber is obtained. With advantages in homogeneity and length, the fiber has great potential in applications such as fiber gyroscopes, fiber hydrophone and other optical fiber sensors.

A tunable comb filter using single-mode/multimode/polarization-maintaining-fiber-based Sagnac fiber loop

A novel tunable comb filter composed of a single-mode/multimode/polarization-maintaining-fiber-based Sagnac fiber loop is proposed and experimentally demonstrated. The filter tunability is achieved by rotating the polarization controller. The spectral shift is dependent on rotation direction and the position of the polarization controller. In addition, the adjustable range achieved by rotating the half-wave-plate polarization controller is twice higher than that of the quarter-wave-plate one.

Coupling Character of Polarization Maintaining Optical Fiber Under the Condition of Bend

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Generation of a mid-infrared broadband polarized supercontinuum in As_2Se_3 photonic crystal fibers

A simplified structure of birefringent chalcogenide As 2 Se 3 photonic crystal fiber（PCF） is designed.Properties of birefringence,polarization extinction ratio,chromatic dispersion,nonlinear coefficient,and transmission are studied by using the multipole method,the finite-difference beam propagation method,and the adaptive split-step Fourier method.Considering that the zero dispersion wavelength of our proposed fiber is about 4 μm,we have analysed the mechanism of spectral broadening in PCFs with different pitches in detail,with femtosecond pulses at a wavelength of 4 μm as the pump pulses.Especially,mid-infrared broadband polarized supercontinuums are obtained in a 3-cm PCF with an optimal pitch of 2 μm.Their spectral width at 20 dB reaches up to 12 μm.In the birefringent PCF,we find that the supercontinuum generation changes with the pump alignment angle.Research results show that no coupling between eigenpolarization modes are observed at the maximum average power（i.e.,37 mW）,which indicates that the polarization state is well maintained.

保偏光纤制备及其参数测试原理

为了研制工作波长为1310 nm的保偏光纤,采用改进的化学气相沉积工艺制备了保偏光纤预制捧和应力棒,经加工、拼接、清洗、拉丝工艺后,得到几何尺寸精确的高质量保偏光纤;同时搭建了高效测试系统,采用折射近场法、远场扫描法、视频灰度技术(传输近场),分别测量了预制棒的折射率分布和几何尺寸,保偏光纤模场直径、数值孔径、几何尺寸等关键参数。结果表明,此标准化测试系统操作流程简单、结果精确;模场直径为6.26μm,数值孔径为0.23,包涂直径80μm/135μm/165μm(精度±0.7μm);终检测试合格的光纤成品随机抽样16.25%,高低温老化实验后拍长、串音变化小。所研制的保偏光纤性能稳定,几何尺寸精确、结构均匀、损耗低,具有优良保偏性能,已广泛应用于实际生产中。

High-Sensitivity Temperature Sensor Based on Polarization Maintaining Fiber Sagnac Loop

A high-sensitivity all-fiber temperature sensor based on a Sagnac interferometer is demonstrated by splicing a section of polarization maintaining fiber(PMF)between two sections of standard single mode fibers(SMFs).In this sensor,the SMF-PMF-SMF structure in the Sagnac loop is bent into a circle to enhance the sensitivity.The length and curvature of the PMF in the loop are investigated and can be optimized to further increase the temperature sensitivity of the sensor. Results show that the radius of the circle has an important effect upon temperature sensitivity due to the bend-induced birefringence variation of the PMF.The SMF-PMF-SMF structure bent into a circle with a radius of 30mm exhibits a high-sensitivity temperature of 1.73nm/℃.The sensor is provided with the advantages of easy fabrication,low-insertion loss,and high sensitivity,which may find potential applications in the field of high precision temperature measurement.

All-fiber high-power linearly polarized supercontinuum generation from polarization-maintaining photonic crystal fibers

We demonstrate an all-fiber high-power linearly polarized supercontinuum source with polarization-maintaining photonic crystal fibers(PM-PCFs)as the nonlinear medium.The source exhibits an average output power of 3.8 W with a flat spectrum from 480 nm to 2100 nm at the-10 dB level,except for the residual pump peak.The polarization extinction ratio(PER)is measured to be greater than 20 dB at selected sample wavelength points(532 nm,1064 nm and 1550 nm)at the highest pump power level and greater than 20 dB at all wavelengths from 800 nm to 1500 nm at the low pump power level.We also experimentally study the spectral properties when the pump light propagates along different axes of the PM-PCF.The results show that propagating parallel to the slow axis enables a broader spectrum in the PM-PCF in this case,probably due to matching of the dispersion properties with the pump light,which is qualitatively in accordance with the numerical simulation.To our best knowledge,this is the first demonstration of a watt-level linearly polarized supercontinuum source generated from PM-PCFs in an all-fiber structure.

Refractive index and temperature sensing characteristics of an optical fiber sensor based on a tapered single mode fiber/polarization maintaining fiber

An evanescent field optical fiber sensor based on a short section of polarization maintaining fiber spliced with a tapered single mode fiber is proposed and experimentally investigated. We mainly focus on the refractive index （RI） and temperature sensing characteristics of this compact device. The transmission spectrum of the resonance wavelength, induced by the interference between the excited low order cladding modes and core modes, shows the quadratic function relationships with RI and linear relationships with temperature. Thus, the proposal of this simple-to-fabricate, compact, and low cost sensor shows its possible potential in the sensitive detection field.

Low Loss Polarization Maintaining Photonic Crystal Fiber

A low loss polarization maintaining photonic crystal fiber has been fabricated. The fiber loss was 1.3 dB/km at 1550 nm. The polarization crosstalk for a 100-m fiber was -35 dB at 1550 nm.

结构调制型长周期光纤光栅温度传感器研究

燃油系统的温度监测对于飞行器的安全、性能和可靠性至关重要。本文提出并测试了一种基于激光蚀刻法在保偏光纤上制备的长周期光纤光栅温度传感器,有望用于飞机内部液体温度监测。通过解调该种光纤光栅谐振峰的波长变化,可以实现对环境温度的精准测量。试验结果表明,该传感器具有83.1pm/℃的温度灵敏度和0.32 pm/με的低应变响应。由于光纤具有耐腐蚀、抗电磁干扰,不易产生电火花等特性,在替代电学传感器使用时可以提升飞行器的安全性。

检偏器对轴角度误差对光纤环偏振耦合测量的影响研究

为了分析检偏器偏振轴与光纤偏振主轴间的对轴角度误差对光纤环偏振耦合强度测量结果的影响,从理论上分析了采用光相干域偏振检测(OCDP)技术测试光纤环偏振耦合强度的基本原理,建立了光纤环中偏振耦合点耦合强度与检偏器对轴角度间的关系模型。根据模型仿真分析了耦合点偏振耦合强度测量值随检偏器对轴角度的变化规律。仿真结果表明:当检偏器偏振轴与光纤环偏振轴夹角为45°时测量误差最小,夹角偏离45°越大,产生的强度测量误差越大。当检偏器偏振轴与光纤环偏振轴的对轴误差为0.6°时,对轴误差引起的偏振耦合强度测量误差为0.18 dB。将对轴误差控制在3°以内,可使得偏振轴对轴误差引起的偏振耦合强度测量误差<1 dB。

基于双层孔结构的850nm超细径保偏光子晶体光纤

光子晶体光纤由高纯度石英玻璃制备而成,具备弯曲损耗小、环境适应性强等优点,尤其适用于恶劣应用环境下的高稳定光纤陀螺。传统光子晶体光纤内部微孔占据了较大的空间,导致光纤直径大,并且主要工作波段为1550nm,无法满足小型化、高精度光纤陀螺需求。提出了双层空气孔结构缩小光纤直径,通过微孔尺寸调节降低光纤损耗,并使光纤限制损耗具有偏振相关性,从而实现超细径保偏光子晶体光纤设计。采用“堆积拉制”法制备了Φ60/100μm光子晶体光纤样品,经截断法测试光纤损耗为6.5dB/km@850nm,偏振串音-15dB@100m。

双芯介电手性圆保偏光纤分束器

目前,由线偏振分束器和1/4波片所组成圆偏振保持的分束器应用在光纤系统中具有难以避免的对准误差。本文提出了一种基于双芯介电手性光子晶体光纤的圆保偏光纤分束器,仿真结果表明,在弱手性背景(δ=27.6°/mm)下,该偏振分束器在中心波长为1.55μm时的长度可低至57.46 mm,中心波段的消光比ER=41.25 dB并且在ER>20 dB的光谱宽度为14 nm,该分束器可以应用于光学集成、光纤通信和光纤传感等领域。

基于PMF-Sagnac环结构的光纤压力传感特性研究

提出了一种基于熊猫保偏光纤(PMF)-Sagnac环结构的光纤压力传感系统。利用PMF对外界环境的双折射敏感且可进行窄带滤波特性,搭建了压力传感系统,并对该传感系统进行了解调。系统结构简单,成本低,易操作。理论分析表明:当传感单元固定,随着压力的增加,传感系统干涉光的波长漂移呈线性变化。实验验证了传感头分别为1 m和2 m的传感器的压力传感特性。结果显示:随着压力的升高,该传感系统干涉光的波长呈线性变化,线性度分别为0.998和0.995;灵敏度分别为0.258 nm/N和0.133 nm/N;且随着传感光纤长度的增加,透射谱波谷的3 d B带宽不会改变。

Self-starting all-fiber PM Er:laser mode locked by a biased nonlinear amplifying loop mirror

A compact all-fiber polarization-maintaining Er:laser using a nonlinear amplifying loop mirror is reported. Fundamental single-pulse mode-locking operation can always self start, with a cavity round-trip decreased from ~ 4.7 m to~ 1.7 m. When the pulse repetition rate is 121.0328 MHz, output pulse is measured to have a center wavelength/3-d B spectral bandwidth/radio frequency signal to noise ratio(SNR)/pulse width of 1571.65 nm/18.70 nm/80 d B/477 fs, respectively. Besides, three states including the exponential growth, damping state, and steady state are investigated through the build-up process both experimentally and numerically. Excellent stability of this compact Er:laser is further evaluated,demonstrating that it can be an easy-fabrication maintenance-free ultrafast candidate for the scientific area of this kind.

陀螺用超细径保偏光纤机械强度评估方法

针对陀螺应用场景下超细径保偏光纤机械强度评估需求,提出一种基于可拉伸骨架的超细径保偏光纤强度评估方法,超细径保偏光纤绕制于可拉伸骨架之上形成光纤环圈可模拟出成环应力过程,采用该光纤环圈构建光纤陀螺,环圈骨架内的压电堆栈可驱动骨架带动超细径保偏光纤周期性拉伸,对超细径保偏光纤起到应力激励施加效果可激发光纤疲劳以实现光纤强度快速评估与筛选,同时在超细径保偏光纤内形成相位调制功能以实现陀螺偏置调制,陀螺信号长期输出变化情况可表征超细径保偏光纤力学特性优劣。该方法能够体现出超细径保偏光纤成环应力施加的复杂性和陀螺应用光纤长期张紧、弯曲等条件下应力长期演变性,有助于陀螺用超细径保偏光纤强度评估与筛选。

高灵敏保偏光纤模式干涉温度传感研究

该文介绍了一种灵敏度较高的Mach-Zehender干涉温度传感器,在单模光纤之间嵌入一段保偏光纤,并通过重叠挤压放电方式形成反向凸起锥,形成单模光纤-保偏凸锥形光纤-单模光纤结构的传感器,凸锥结构增加了包层模式的能量,提高了传感器透射谱对比度。实验证明,当保偏光纤长度为2.5 cm时,在30~70℃内温度灵敏度达到最大值126.45 pm/℃。此外,该文通过计算不同偏振模式及相应的模式传播常数,分析得到参与模式干涉的主要成分,从而验证了温度灵敏度测试的精准度。此结构的传感器具有结构紧凑、尺寸小、制作工艺简单的特点,可被应用于温度传感测量。

Figure-9腔锁模全保偏掺铒光纤飞秒激光器

针对特殊应用领域对高可靠性、轻量化、输出功率大于100 mW、重频大于50 MHz的飞秒激光器的需求,设计了一种Figure-9腔锁模全保偏掺铒光纤飞秒激光器,通过在腔锁模振荡器中引入π/2相移偏置,降低了振荡器的自启动锁模阈值。实验结果表明:当泵浦功率为130 mW时,振荡器可获得平均功率为12 mW、重频为85.89 MHz、脉冲宽度为249 fs的稳定锁模脉冲序列输出;采用一级正色后向泵浦散掺铒增益光纤放大器进行放大后,最终可获得平均功率为113 mW、脉冲宽度为107 fs的飞秒脉冲序列输出。

1.06μm结构参数最优化非保偏锁模光纤激光器

采用半导体可饱和吸收镜的锁模光纤激光器是构建皮秒脉冲光纤放大器的热门候选种子光源之一。本文利用非线性薛定谔方程从理论上分析了单模传输光纤和单模增益光纤的模场半径、增益光纤的光纤长度、光纤布拉格光栅的反射率、半导体可饱和吸收镜的调制深度、非饱和损耗和饱和通量对输出脉冲特性的影响。对输出激光的脉冲和光谱特性也进行了理论研究。根据仿真结果,搭建了基于非保偏线型腔和SESAM的掺镱锁模光纤激光器系统。在没有任何腔内色散补偿和外部偏振控制的情况下,获得了中心波长为1.06μm、脉冲宽度小于12.51 ps、光谱宽度为0.32 nm、重复频率为37 MHz、输出功率为2 mW的稳定锁模脉冲激光输出。在我们的实验中,激光脉冲的光谱边缘平滑,光谱分布非常接近高斯线型。最后,通过系统的仿真,近红外锁模光纤激光器的整体结构得到了优化。本文介绍的锁模光纤激光器具有紧凑的非保偏光纤结构、精简的腔内配置和较少的元器件、高质量的输出脉冲相关特性,有望为下一代皮秒脉冲光纤激光器提供性能优异的实用化种子光源。