A convenient field-installable antireflection coating for optical fiber connectors and other components

Disc-shaped pellicles 15 microns thick are antireflection coated and cemented to the polished ends of optical fiber connectors. Excess loss due to increased fiber separation is a maximum of 10% (.46 dB), typically 3.8% (.16 dB) in graded index fibers; Fresnel back-reflections are reduced by a factor of more than 10.     

基于无芯光纤强度调制型液位传感器的设计与性能

利用强度调制型光纤传感器容易解调的优势,提出了一种强度调制型光纤液位传感器.传感器由三根无芯光纤组成,其中,无芯光纤1与无芯光纤2串联构成测量臂,无芯光纤3构成参考臂.仿真分析得出,无芯光纤长度每缩短1mm,透射峰波长增加25.46nm.在0~50mm小液位范围内,实验测得传感器在水、5%NaCl、10%NaCl和15%NaCl水溶液四种液体环境中的液位灵敏度分别为0.069 5dB/mm、0.074 73dB/mm、0.077 49dB/mm及0.082 71dB/mm,线性度分别为0.998 25、0.998 49、0.988 11及0.995 13,线性度较高.该传感器可较好地消除光源光功率波动与环境温度变化带来的影响,重复性较好,在石油化工领域有一定的应用潜力.     

变纤芯直径传能光纤中受激拉曼散射传输特性的理论研究

锥形光纤纤芯直径沿着光纤长度方向均匀增大,在抑制非线性效应方面有着独特的优势。理论对比了单横模高斯光束输入时,输入纤芯直径均为50 μm、纤芯直径沿着光纤长度方向恒定、线性增大和非线性增大的变纤芯直径传能光纤的输出光谱演化和拉曼光特性。在相同条件下,输入功率10 kW时,恒定型传能光纤的输出光谱中,拉曼抑制比（定义为输出光谱中信号光峰值强度分贝值与拉曼光峰值强度分贝值之差）为33.1 dB,线性增大和非线性增大型的输出拉曼抑制比分别为47.0,48.6 dB,分别优于恒定型传能光纤13.9,15.5 dB;输入功率达17.5 kW时,恒定型传能光纤中有81.6%的输入能量被耗散或转移到其他波长,线性增大和非线性增大型仅不到2%,其输出的信号光波段能量占总输入能量的98.1%,98.9%。结果表明,使用线性增大型或非线性增大型传能光纤代替恒定型常规光纤,可以有效提高受激拉曼散射阈值,相关研究可以为大功率光纤合束器和光纤端帽的设计提供有益参考。     

短腔Er/Yb光纤光栅激光器

报道采用光敏Ｅｒ／Ｙｂ 光纤制作短腔Ｅｒ／Ｙｂ 光纤光栅激光器的实验结果。激光谐振腔由一对直接写在３０ ｍ ｍ 长的Ｅｒ／Ｙｂ 光纤上、长度分别为６ ｍ ｍ 及１０ ｍ ｍ 、反射率分别为９０％ 及９８．６％ 、３ ｄＢ带宽分别为０．２８ ｎｍ 及０．２６ ｎｍ 的光纤布拉格光栅组成, 激光器的泵浦阈值为８ｍ Ｗ, 斜效率约１４％ , 输出光的信噪比为６１ ｄＢ, 偏振模抑制比为３０ ｄＢ。     

Grating-Outcoupled Radiation in Second-Order Fiber Bragg Gratings

Abstract

The experimental results of the radiation for second-order fiber Bragg gratings, which are made of a single-mode photosensitive fiber (PS-1500; Fiber-Core Corp.) and a single-mode fiber (SMF-28; Corning Inc.), by a phase mask writing fabrication technique are explored. For PS-1500 fiber Bragg gratings, the maximum radiation efficiency of ?23.5 dB at resonance λ = 1,539.34 nm with a very narrow bandwidth (about 0.02 nm) are measured from a 10-mm-diameter photo-detector, while for SMF-28 fiber Bragg gratings, the maximum radiation efficiency is ?34.6 dB (λ = 1,538.03 nm) with a bandwidth of 0.06 nm. The total efficiencies of the radiation are about ?16.8 dB for PS-1500 fiber Bragg gratings and ?28.1 dB for SMF-28 fiber Bragg gratings.     

Nonlinear-optical modulator for high-power fiber lasers

We propose a novel nonlinear-optical fiber modulator for high-power (>1-W) single-mode fiber lasers. The device is based on transferring the amplitude modulation from a low-power signal at the Stokes frequency onto a high-power beam through stimulated Raman scattering. The efficiency and limitations of the Raman modulator when highly Ge-doped fiber is used is considered. An insertion loss of less than 0.4 dB and an extinction ratio of 20 dB are predicted for modulation of a 10-W single-mode Nd-doped fiber laser.     

Frequency noise reduction in erbium-doped fiber distributed-feedback lasers by electronic feedback

A novel technique for suppressing frequency noise in an erbium-doped fiber distributed-feedback laser incorporated into a master-oscillator-power-amplifier configuration by an electronic feedback technique is presented. The frequency noise is suppressed by locking of the laser emission to a fiber interferometer. The frequency noise spectral density of the laser is reduced by as much as 20 dB over the frequency range 1 Hz-10 kHz to 1.5 Hz/Hz(1/2) +/-25% at 1 kHz with a relative intensity noise spectral density below -120 dB/Hz over the frequency range 10 Hz-1 kHz. These lasers will have applications as sources for fiber-optic interferometry, high-resolution spectroscopy, and high-bandwidth communications.     

Stable and spacing-adjustable multiwavelength Raman fiber laser based on mixed-cascaded phosphosilicate fiber Raman linear cavity

A novel multiwavelength Raman fiber laser based on the mixed-cascaded Stokes effects of phosphosilicate fiber is proposed and demonstrated experimentally. By using stimulated Raman scattering of both P(2)O(5) and SiO(2) along 1 km phosphosilicate fiber pumped with a 1064 nm double-clad fiber laser, the mixed-cascaded Raman linear cavity is formed by a pair of fiber Bragg gratings at 1239 nm, a polarization-maintaining fiber (PMF) Sagnac loop filter, and a conventional optical loop mirror. Up to 15-wavelength stable oscillations around 1320 nm are obtained with a wavelength spacing of 0.44 nm and power nonuniformity of less than 4 dB. By changing the length of the PMF in the Sagnac loop filter from 10 to 5.5 m, the wavelength spacing is adjustable from 0.44 to 0.8 nm. The extinction ratio of the laser is more than 30 dB. Excellent stability is also observed with a peak power fluctuation of less than 0.8 dB in 1 h.     

分布反馈式光纤激光水听器拖曳线列阵实验研究

为了进一步增大光纤拖曳阵的探测距离,研制了缆径为16mm的32元分布反馈式光纤激光水听器拖曳线列阵.阵元在10~2 000Hz频率范围内的平均声压灵敏度为-142.7dB(re 1rad/μPa),波动幅度小于±2dB.基于声光调制器的时分、波分联合复用技术实现了32元光纤激光水听器的多路复用,各个阵元之间以及各个通道之间的串扰均小于-40dB,并完成了静态和动态拖曳湖上实验.实验结果表明,研制的32元分布反馈式光纤激光水听器拖曳线列阵无论是在静态,还是在6~16节的动态拖曳状态,都能对目标形成稳定的波束指向,与GPS轨迹记录完全一致,展现了分布反馈式光纤激光水听器拖曳线列阵在工程上的应用前景.     

Optical fiber coupling to single-mode silica-based planar lightwave circuits with fiber-guiding grooves

To enable alignmentfree optical fiber coupling to single-mode silica-based waveguides, fiber-guiding grooves are fabricated in the same substrate as waveguide circuits.These grooves are used successfully to couple optical fiber to Waveguides. An average, fiber-to-waveguide coupling loss of 0.6 dB per interface is obtained with eight arrayedguiding grooves, and it is expected that this will further be reduced to 0.2 dB per interface. The coupling loss varies by ±0.3 dB during thermal cycling between -10°C and +60°C.     

用于10Gb/s传输系统的电吸收调制器与分布反馈激光器集成光源

采用超低压(22×１０^２Pa)选择区域生长(selective area growth, SAG)金属有机化学气相沉积(metal-organic chemical vapor deposition, MOCVD)技术成功制备了应变型InGaAsP/InGaAsP电吸收调制器(electroabsorption modulator, EAM)与分布反馈激光器(distribute feedback laser, DFB)单片集成光源的新型光电器件.实验结果表明，采用该技术制备的集成器件表现出了良好的性能：激射阈值为19 mA，出光功率接近7 mW，边模抑制比(side-mode suppression ratio, SMSR)大于40 dB，将该集成器件出射光耦合进普通单模光纤后进行测量，获得了16 dB的消光比，器件3 dB响应带宽达到了10 GHz以上.将该集成器件完全封装后成功进行了10 Gb/s非归零码(non-return zero, NRZ)的传输实验：在误码率为10^-10的传输条件下于普通单模光纤中传输了53.3 km，色散代价小于1.5 dB，动态消光比大于8 dB，且眼图清晰张开. 关键词： 超低压 选择区域生长 集成光电子器件 10 Gb/s     

Polarization-insensitive nonlinear optical loop mirror demultiplexer with twisted fiber

We experimentally demonstrate reduction of the polarization sensitivity of a nonlinear optical loop mirror (NOLM) from 5 to 0.5 dB by use of 550 m of twisted dispersion-shifted fiber with a twist rate of 8 turns/m (24 turns/beat length). The twisting of the fiber induces circular birefringence and equates the parallel-and the orthogonal-polarization nonlinear phase-shift terms. Experimental results show that the polarization sensitivity monotonically decreases from 5 dB for nontwisted fiber to 0.5 dB for fiber that is twisted at a rate of 8 turns/m, and the twist rate should be more than 4 turns/m (>10 turns/beat length) for emulation of circularly polarized fiber. The minimum polarization sensitivity occurs when the control-pulse polarization is aligned with one of the eigenmodes of the twisted fiber. With the fiber twisted at a rate of 8 turns/m in the NOLM, the nonlinear transmission is 23% at a switching energy of 4 pJ/pulse. Simulations confirm the observed behavior and show that the remaining polarization sensitivity results from energy transfer between orthogonal modes of the signal pulse.     

Amplification effect on SBS and Rayleigh scattering in the backward pumped distributed fiber Raman amplifier

The amplification effect on stimulated Brillouin scattering （SBS） and Rayleigh scattering in the backward pumped G652 fiber Raman amplifier （FRA） is studied. The pump source is a 1427.2-nm fiber Raman laser whose power is tunable between 0 - 1200 mW, and the signal source is a tunable narrow spectral bandwidth （〈 10 MHz） external cavity laser （ECL）. The Rayleigh scattering lines are amplified by the FRA and Stokes SBS lines are amplified by the FRA and the fiber Brillouin amplifier. The total gain of SBS lines is the production of the gain of Raman amplifier and that of Brillouin amplifier. In experiment, the SBS gain is about 42 dB and the saturation gain of 25-km G652 backward FRA is about 25 dB, so the gain of fiber Brillouin amplifier is about 17 dB.     

简单MOPA结构窄线宽激光突破5 kW近单模输出

高功率窄线宽光纤激光器在非线性频率转换、光谱合成以及相干合成等领域有着重要的应用前景。本文基于自研的复合腔结构窄线宽振荡器作为种子,采用单级主振荡功率放大技术（MOPA）,实现了5 kW高效率的近单模窄谱激光输出。通过优化振荡器的时序特性和放大级结构,受激拉曼散射、光谱展宽和热致模式不稳定效应得到综合抑制。在最高功率时,信号光的3 dB和20 dB线宽分别为0.48 nm和2.1 nm,放大器的斜率效率约为86.1%,拉曼抑制比为28.3 dB,光束质量M2约1.35。本研究工作对于高功率窄线宽光纤激光的发展和研究具有重要的指导意义。     

Large-scale interferometric fiber sensor arrays with multiple optical amplifiers

We report what we believe to be the first laboratory prototype of a fiber sensor array using multiple low-gain (5dB) remotely pumped amplifiers in a 10-rung ladder structure. Incorporating amplifiers improves the system noise figure to less than 20dB, compared with 32dB in an optimized passive array of the same size. Scalability to more than 300sensors per fiber pair while a high dynamic range (1microrad/ sensitivity) is maintained is demonstrated.     

Numerical analysis and experimental results of output performance for Nd-doped double-clad fiber lasers

Numerical analysis is investigated for the high-power double-clad fiber lasers and experimental results using different microscope objectives for focusing into a Nd-doped rectangular double-clad fiber also performed. The numerical analysis includes dependence of output power on output mirror reflectivity, absorbed pump power, loss, and fiber length and pump power distribution for the cases of one-end and two-end pumps with 20 dB/km loss. Calculated conversion efficiencies are 76.36%, 69.73%, and 63.84% for lossless, two-end pump, and one-end pump fiber lasers, respectively. Slope efficiencies from absorbed pump power/output powers measured using microscope objectives are 16.8%/182 mW, 53.8%/351 mW, 24.9%/1240 mW, and 13.9%/649 mW for magnifications of 5×, 10×, 20×, and 40×, respectively.     

A Novel Fabrication for Method Long PeriodFiber Grating

A new method of fabricating all-fiber broadband-rejection filter based on long period fiber grating (LPFG) is proposed. The principle in the method is to make periodic asymmetrical deformation in the core of fiber without microbends by electrode discharging so as to induce periodic refractive index changes. Two kinds of filters whose rejection peak wavelength at 1550 nm and 1310 nm are obtained. The insertion loss is less than 0.6 dB and 1.4 dB respectively. The 20 dB bandwidth ranges from 10 nm to 39 nm. The backward reflection loss is extremely small (less than - 70 dB). Such devices can be used as isolation filters in 1310/1550 nm WDM system and other fields.     

400 mW ultrashort cavity low-noise single-frequency Yb³⁺-doped phosphate fiber laser

A compact, low-noise, single-frequency fiber laser by using a newly developed Yb3? heavily doped single-mode phosphate glass fiber has been demonstrated. Over 400 mW stable continuous wave single transverse and longitudinal mode laser at 1.06 μm was achieved from a 0.8 cm long active fiber. The measured slope efficiency and estimated quantum efficiency of laser emission are 72.7% and 93%, respectively. The signal-to-noise ratio is higher than 72 dB, and the linewidth of the fiber laser is less than 7 kHz, while the measured relative intensity noise is less than -130 dB/Hz at frequencies of over 1.5 MHz.     

A Novel Fabrication for Method Long Period Fiber Grating

A new method of fabricating all-fiber broadband-rejection filter based on long period fiber grating (LPFG) is proposed. The principle in the method is to make periodic asymmetrical deformation in the core of fiber without microbends by electrode discharging so as to induce periodic refractive index changes. Two kinds of filters whose rejection peak wavelength at 1550 nm and 1310 nm are obtained. The insertion loss is less than 0.6 dB and 1.4 dB respectively. The 20 dB bandwidth ranges from 10 nm to 39 nm. The backward reflection loss is extremely small (less than -70 dB). Such devices can be used as isolation filters in 1310/1550 nm WDM system and other fields.     

Chirped pulse amplification with a nonlinearly chirped fiber Bragg grating matched to the Treacy compressor

We demonstrate a fiber chirped pulse amplification system that uses an engineered nonlinearly chirped fiber Bragg grating stretcher dispersion matched to the Treacy compressor. The seed pulses at 1558 nm are stretched to 720 ps, amplified by more than 50 dB to 6.5-microJ energy, and recompressed to 940 fs. After almost 1000 times compression the pulses are within 30% of the bandwidth limit and have a contrast ratio of better than 30 dB.