非对称光纤反射镜的可调谐光纤激光器

提出一种非对称窄带光纤环形反射镜结构的可调谐掺铒光纤激光器。980nm泵浦光对掺铒有源光纤进行抽运,高双折射光纤、偏振控制器（PC）和光纤耦合器构成窄带光纤反射镜,窄带光纤反射镜和普通光纤反射镜组成激光谐振腔,利用窄带光纤反射镜工作带宽纳米量级的特性得到单纵模激光。调整偏振控制器改变反射镜对不同波长的反射率,实现可变波长的激光输出。实验表明,该激光器的工作带宽为8nm,120mW泵浦光条件下最大输出功率为4mW,3dB带宽（脉冲的半高宽度）小于0．2nm,边模抑制比为20dB以上,在1527nm～1535nm的波长范围内观察到稳定激光输出。     

利用挤压光纤双折射效应的自适应偏振控制器

报导了利用光纤应力双折射效应研制的1．55μm波长的自适应偏振控制 器,该控制器具有自动搜索、跟踪和精确控制光纤输出偏振态的功能。经初步检测,当偏振态变化3π/s时,输出偏振光强度为给定偏振方向分量总光强的92％,平均偏差小于2％。     

偏振成像在目标探测中的应用

针对偏振度编码成像在目标探测识别中的优点,本文分析了偏振探测的消偏振机理,以及表面散射和体散射对目标偏振度的影响.利用808 nm半导体激光器照明,目标的后向散射光由卡塞格林望远镜接收,经过偏振分光棱镜成像在两个CCD上,通过一次测量获得偏振状态相互垂直的两幅图像,然后计算出目标的强度和偏振度,分别利用强度和偏振度编码成像.实验结果表明,在目标的反射率相近时,强度图像不能区分不同材料的目标,偏振度图像可以区分,融合强度和偏振度图像进行HSI伪彩色编码,可以达到目标探测、分类等目的.     

金属板热红外偏振的方向特性研究

热红外偏振探测有利于从背景中识别金属目标.通过分析热红外偏振探测方法,根据现有条件研制了一种热红外成像偏振探测仪.利用该系统,研究了金属板热红外偏振度和观测角之间的关系.实验中采用的金属板分别为铝质和钢质,表面都进行了抛光处理.实验结果表明,金属目标板热红外偏振度和其自身的热辐射亮温值没有直接的关系.在观测角大于20°时,随着观测角度的增大,金属目标板热红外偏振度的数值也增大.但在观测角小于20°时测量,金属目标板热红外偏振度和观测角之间的关系并不遵循上述原则.     

基于Hilbert-Huang变换的轴流泵流动诱导振动试验

对不同叶片角度下轴流泵站机组正常运行和开机状态进行振动试验,对比分析振动信号特征,探寻叶片角度在正常运行和开机状态下对机组振动的影响规律,为保证机组安全稳定运行提供参考。得到以下结论:正常运行工况下,随叶片角度从-8°增大到+8°,外筒体和下机架的振动幅值整体表现出逐渐升高的趋势,主轴摆度的幅值基本不变,满足无限制长期运行要求;沿来流方向监测的振动信号主要频率成分包括2.5 Hz和10 Hz;垂直来流方向及轴向的振动信号主要频率成分包括2.5 Hz,10 Hz和20 Hz,与水泵的转频2.5 Hz成倍数关系;随着叶片角度从2°增大到8°,部分测点振动峰峰值逐渐超出50μm,进入C区域,说明水泵不宜在大角度下长期持续运行。     

基于干涉解调技术的光纤激光器水声传感系统

分析了基于Michelson干涉解调技术的光纤激光器水声传感的原理,在一段掺铒光纤中写入具有π相移的光纤光栅构成光纤激光器,水声压力作用在激光器上引起激光工作波长的变化;采用基于3×3耦合器的偏振无关的非平衡光纤Michelson干涉仪将激光波长变化转化为干涉仪的相位变化;干涉仪的输出由光电探测器转换后使用DSP进行信号解调.针对3×3耦合器分光比不对称的问题,本文提出利用实时调整幅度的2路干涉信号进行解调的方案,该方案不需要3×3耦合器有严格的分光比,消除了外界环境对解调输出的非线性影响.水声探测实验表明,光纤激光器水声传感系统的声压灵敏度为-166.5 dB(参考值1 rad/μPa),解调结果与水声信号具有良好的线性关系.     

一种新型偏振分光棱镜的设计和应用

一种新型的偏振分光棱镜结构,实现了将偏振态相互垂直的光以不同的角度输入后合为一 束的功能,尤其能与双光纤准直器配合使用。通过计算说明二者角度可相互匹配,并分析了在准直器的角度加工出现小的偏差时,通过微量调节输入光束的方向能予以补偿。实验将该棱镜用于偏振光合束器和光学环行器等无源器件中取得了良好效果。     

一种利用保偏光纤产生圆偏振光的方法

保偏光纤是利用光纤的高双折射特性,使两个偏振模之间不易耦合,维持偏振态稳定的。 利用保偏光纤传输线偏振光时,在出射端将一段保偏光纤扭转,可以改变光的偏振状态。从理论上证明了扭转的光纤长度为1/2拍长,扭转角度为p/2时,出射光变成圆偏振光。实验表明,这种产生圆偏振光的方法是可行的,且比传统方法简单、紧凑。     

半导体激光与高双折射光纤基模的耦合

在双模干涉型光纤传感器中,为了消涂光纤引导段的敏感效应,需要选择性地激发光纤的基模,本文对半导体激光器(简称LD)与光纤基模的耦合进行了理论上的分析。在高斯分布漠场假设的基础上,给出了激光束腰半径和光纤基模模场半径的表达式,以及利用透镜进行两模式匹配的具体光学计算公式。据此进行的LD与高双折射光纤偏振模(基模的一个偏振分量)的耦合实验得到了28％ 耦合效率。文章最后讨论了半导体激光器的椭圆性和固有象散以及光反射对耦合造成的影响。     

激光损伤的光散射法判别研究

在激光损伤测量系统中,利用光散射法判别激光薄膜损伤,需要寻求光源和探测器之间的最佳位置。为此,在不同损伤激光脉冲能量、不同测量入射角度(0°,30°,45°,60°)和不同探测器距离(200,250 mm)条件下,研究了损伤点散射光能量的角分布。获得结果如下:在相同的探测角度上,散射光能量随着损伤面积和测试光入射角度增加而增加。在探测角度小于反射角度时,随着探测角度增加散射光能量逐渐变强;当探测角度大于反射角度后,随着散射角度增加散射光能量逐渐变弱。散射光相对能量在反射光方向附近出现极大值;在60°入射时,散射光相对能量具有最大值;探测距离在200 mm时,最大散射光相对能量大于探测距离在250 mm时。根据以上结论,可以确定在利用光散射判别损伤的测量系统中,探测器应放置在反射光方向的两侧,并且尽量增加测试光入射角度和缩小探测器与样片间距离。     

Multibeam scanning optics with single laser source for full-color printers

In the novel optical system described here, four-color toners can be developed in one rotation of the photoconductor, and the color control information is given when the intensities of the laser power levels are changed and the two polarization directions are switched. A polarizing beam splitter between the common scanning optics and the photoconductor enables the laser beam to pass through a common scanning system and to illuminate two positions on the photoconductive material. The laser beam polarization direction is controlled by an electro-optical device immediately behind the laser. In each illuminated position, two-color toners are developed by a three-level (trilevel) photographic process. This simplified optical system eliminates the registration errors that occur with four-color information items and can be useful in high-speed printing systems.     

Optical rectification effect in nanocarbon films

When a nanocarbon film obtained by plasmachemical deposition is fixed between two parallel electrodes and exposed to the pulsed radiation of a Q-switched neodymium laser, a pulsed electric voltage appears between the electrodes, with the pulse shape repeating the laser pulse envelope. It is shown that the amplitude and polarity of the pulsed voltage strongly depend on the angle of incidence and polarization of laser beam and on the spatial orientation of a carbon film with electrodes relative to the laser beam. The observed phenomenon exhibits all features characteristic of the optical rectification effect. For the optimum spatial orientation of a film, the factor of conversion of the laser pulse power into electric voltage amounted to 500 mV/MW, which is many times greater than the values observed in the case of optical rectification in well-known dielectric nonlinear optical crystals.     

Angular dependence of polarizing beam-splitter cubes

The field-of-view dependence of polarizing beam-splitter cubes has been studied to characterize their behavior in imaging systems such as optical computers and optical correlators and in other applications that involve noncollimated light. Significant polarization aberration is present in polarizing beamsplitter cubes for two reasons: (1) the s- and p-component orientations, which define the polarizing axes, at the beam-splitting interface vary with the direction of propagation, and (2) the performance of the coating is a function of the angle of incidence. We describe the polarization aberration of a polarizing beam-splitter cube in terms of its diattenuation (polarizing efficiency). We use an imaging polarimeter to measure six figures of merit for three polarizing beam-splitter cubes demonstrating typical polarization aberrations. Finally, we derive the Mueller matrix for a polarizing beam-splitter cube in terms of the s and p transmittance and reflectance and the phase retardances, the parameters generally calculated with thin-film analysis programs.     

Near-field thermal transport in a nanotip under laser irradiation

We report on a systematic study of highly enhanced optical field and its induced thermal transport in nanotips under laser irradiation. The effects on electric field distribution caused by curvature radius, tip aspect ratio, and polarization angle of the incident laser are studied. Our Poynting vectors' study clearly shows that when a laser interacts with a metal tip, it is bent around the tip and concentrated under the apex, where extremely high field enhancement appears. This phenomenon is more like a liquid flow being forced/squeezed to go through a narrow channel. As the tip-substrate distance increases, the peak field enhancement decreases exponentially. A shift of field peak position away from the tip axis is observed. For the incident light, only its component along the tip axis direction has a contribution to the electric field enhancement under the tip apex. The optimum tip apex radius for field enhancement is about 9 nm when the half taper angle is 10°. For a tip with a fixed radius of 30 nm, field enhancement increases with the half taper angle when it is less than 25°. The thermal transport inside the nanoscale tungsten tips due to absorption of incident laser light is explored using the finite element method. A small fraction of light penetrates into the tip. As the polarization angle or apex radius increases, the peak apex temperature decreases. The peak apex temperature goes down as the half taper angle increases, even though the mean laser intensity inside the tip increases, revealing a very strong effect of the taper angle on thermal transport.     

Generation of inhomogeneously polarized laser beams by use of a Sagnac interferometer

A principal scheme for an external cavity technique for changing the polarization of a laser beam based on a modified Sagnac interferometer is proposed. The modified Sagnac interferometer includes standard optical components: a displacement polarizing beam splitter, an angle reflector, and a Dove prism. The radially polarized beams, obtained with the help of the developed scheme, allow the generation of a longitudinally polarized electric field by sharp focusing. The phase correction of radially polarized modes of higher orders leads to increasing the longitudinal field in the focus of the beam.     

SOA-based multi-wavelength source

A simple fiber laser configuration based on a semiconductor optical amplifier (SOA) is proposed for obtaining multi-wavelength oscillation at room temperature, in which a Sagnac loop mirror is used as the wavelength selective component. The SOA has a flat gain of approximately 23dB within a bandwidth of 12 nm at a small input signal power. The loop mirror was constructed using a 3dB coupler and polarization maintaining fiber (PMF). The output spectrum of the proposed laser can be adjusted by controlling the bias current of the SOA and is quite stable at room temperature. At a bias current of 150 mA, six lines are obtained with at least ?40 dBm output power and 25dB signal-to-noise ratio (SNR). The channel spacing and number of lines is determined by the length of polarization maintaining fiber (PMF) used in the loop mirror. The channel spacing of the proposed laser is 1.49 nm with a PMF 3 m. The multi-wavelength comb output can also be tuned by adjusting the operating temperature of the SOA. The multi-wavelength laser has the advantage of a simple configuration, stability at room temperature, a broad wavelength band, and no need for optical pump lasers.     

纤维含量及排列方向对单向纤维复合材料介电性能的影响

本文着重研究了纤维含量和排列方向对环氧/单向玻璃纤维复合层板介电性能的影响.结果表明,纤维与施加电场方向的改变,将导致复合层板电击穿强度发生变化,其夹角越大层板承受电击穿强度越高.纤维含量增加,其单向纤维复合层板的介电性能下降.本文对单向纤维复合层板建立了亚微观介电模型,且在此基础上,对其电击穿强度,介电常数与纤维方向和纤维含量的关系进行了理论预测,其理论值与实验值有较好的吻合性.     

光纤水听器调制激光光源的一种实现方法

在干涉型光纤水听器的信号检测技术中,采用相位载波零差检测方式,直接调制激光光源,具有明显的优越性。提出了一种实现方法,通过产生高频正弦波,对激光光源(多量子阱分布反馈激光器),进行直接驱动调制。光源调制输出波形精确多样(正弦波、三角波(包括锯齿波)和方波),输出频率大范围(0～20MHz),连续可调。实验表明达到了水听器对光源的要求。此调制技术也可在光纤通信等其它领域得以应用。