Relay lens-free birefringence-customized stackable beam-steering modules for optical interconnects

A previously suggested birefringence-customized modular optical interconnect technique is extended for lens-free relay operation. Various lens-free relay imaging models are developed. We claim that the lens-free relay system is important in simplifying an optical interconnect system whenever the imaging conditions permit. To verify the validity of various proposed concepts, we experimentally implemented some 8 x 8 optical permutation modules. High-power efficiency and low channel cross talk were experimentally observed. In general, the larger the channel spacing, the less the cross talk. A quantitative cross-talk measurement of the lens-free relay system shows that, for a fixed channel width of 0.5 mm and channel spacings of 0.5, 1, and 2 mm, a less than -20-dB cross-talk performance can be guaranteed for lens-free relay distances of 40, 280, and 430 mm, respectively. (C) 1998 Optical Society of America.

提高能量密度的超衍射极限激光光束相位补偿技术

定义了激光光束衍射远场光斑压缩前后的能量比以及能量密度比来衡量超衍射极限激光光束的质量。通过利用反向传递算法设计了合适的补偿相位板，不但对准直放大的单一横模激光光束进行小于光学衍射极限的发散度的压缩，同时又保证光束能量集中于压缩后的远场衍射主瓣中，使压缩后的远场衍射光斑的能量密度增加。给出了相应的实例。这一结论不但解决了光学超分辨中光束压缩与能量损失不可避免这一矛盾，而且为发散度小且能量密度高的超衍射极限激光光束的实验工作以及该类光束的实际应用提供了理论基础。

Coherence measurement of a Ti:sapphire femtosecond pulsed laser

The interference patterns produced by Gaussian-shaped broad-bandwidth femtosecond pulsed laser sources are derived. The interference pattern contains both spatial and temporal properties of laser beam. Interference intensity dependent on the bandwidth of femtosecond laser are given. We demonstrate experimentally both the spatial and the temporal coherence properties of a Ti:sapphire femtosecond pulse laser, as well as its power spectrum by using a pinhole pair.

Measurement of thermal rise-time of a laser diode based on spectrally resolved waveforms

Thermal resistance and thermal rise-time are two basic parameters that affect most of the performances of a laser diode greatly. By measuring waveforms received after a spectroscope at wavelengths varied step-by-step, the spectrally resolved waveforms can be converted to calculate the thermal rise-time. Basic formulas for the spectrum variation of a laser diode and the measurement set-up by using a Boxcar are described in the paper. As an example, the thermal rise-time of a p-side up packaged short-pulse laser diode was measured by the method to be 390 mu s. The method will be useful in characterizing diode lasers and LID modules in high-power applications. (c) 2005 Elsevier B.V. All rights reserved.

Wavefront measurement of double-clad pulsed ytterbium fiber laser

Because of high efficiencies, compact structure, and excellent heat dissipation, high-power fiber lasers are extremely useful for applications such as cutting, welding, precision drilling, trimming, sensing, optical transmitter, material processing, micromachining, and so on. However, the wavefront of the double clad fiber laser doped with ytterbium is still unknown. In this paper, wavefront of a fiber laser is measured and the traditional Hartmann-shack wavefront sensing method is adopted. We measured a double clad fiber laser doped with ytterbium which produces pulse wave output at infrared wavelength. The wavefront shape and contour are reconstructed and the result shows that wavefront is slightly focused and not an ideal plane wavefront. Wavefront measurement of fiber laser will be useful to improving the lasers' performance and developing the coherent technique for its applications.

Modal fields and bending loss analyses of three-layer large flattened mode fibers

Theoretical method to analyze three-layer large flattened mode (LFM) fibers is presented. The modal fields, including the fundamental and higher order modes, and bending loss of the fiber are analyzed. The reason forming the different modal fields is explained and the feasibility to filter out the higher order modes via bending to realize high power, high beam quality fiber laser is given. Comparisons are made with the standard step-index fiber. (c) 2006 Elsevier B.V. All rights reserved.

"神光-Ⅱ"装置第九路靶场终端光学组件的研制

针对“神光-Ⅱ”装置第九路系统主激光瞄准精度小于等于30μm和大焦斑辐照均匀性优于10％的要求，提出了靶场终端光学组件的设计结构。应用有限元法对组件关键机械元件和ICF靶室整体进行动静态分析，优化了设计参数。同时与聚焦透镜配合进行数值分析列阵透镜，确定了单元数、曲率和厚度以及单元长和宽等参数。经过实验测试，主激光瞄准精度达到28．9μm，大焦斑辐照的形状为1000μm×500μm，均匀性为12．0％。

梯度补偿法控温晶体的高功率绿光激光器

研究了平均功率超过30 W的稳定高效全固态绿光激光器,分析得出影响全固态腔内倍频激光器倍频效率和输出稳定性的主要因素是倍频晶体局部温升造成的相位失配和热透镜效应,采用温度梯度补偿控温法对大尺寸倍频晶体进行温度控制,降低激光器工作中倍频晶体内外温度梯度从而有效地克服因晶体局部温升造成的倍频相位匹配角失配和热透镜效应。采用三条60 W的半导体激光二极管阵列板条侧面抽运Nd:YAG激光增益介质棒,采用声光调Q,平凹直腔和腔内倍频结构配合温度梯度补偿控温法对大尺寸倍频晶体进行温度控制,得到了稳定高效的532 nm

Write-once medium with Fe-Doped BiOx thin films for blue laser recording

Fe:BiOx films are fabricated on K9 glass substrates by rf-magnetron sputtering of a BiFeO target under argon atmosphere with increasing sputtering power from 80 to 200 W at room temperature. It is found that the thin films grown at the sputtering power of 160W can be formed at an appropriate deposition rate and have an improved surface morphology. The XPS result reveals that the films investigated are comprised of Bi, Fe and O elements. A typical XRD pattern shows that no phase transition occurs in the films up to 400 degrees C. The results of the blue laser recording test demonstrate that the Fe:BiOx films have good writing sensitivity for blue laser beam (406.7 nm) and good stability after reading 10000 times. The recording marks of 200nm or less are obtained. These results indicate that the introduction of Fe into BiOx films can reduce the mark size and improve the stability of the films.

The origin of the super-resolution via a nonlinear thin film

In laser applications, resolutions beyond the diffraction limit can be obtained with a thin film of strong optical nonlinear effect. The optical index of the silicon thin film is modified with the incident laser beam as a function of the local field intensity n(r) similar to E-2(r). For ultrathin films of thickness d << lambda the transmitted light through the film forms a profile of annular rings. Therefore, the device can be related to the realization of super-resolution with annular pupils. Theoretical analysis shows that the focused light spot appears significantly reduced in comparison with the diffraction limit that is determined by the laser wavelength and the numerical aperture of the converging lens. Analysis on the additional optical transfer function due to the thin film confirms that the resolving power is improved in the high spatial frequency region. (C) 2007 Published by Elsevier B.V.

激光束质量实时测量技术

提出一种新型光束质量实时测量技术, 该技术主要基于由平板反射镜组成的多平面成像系统, 一次性将激光束腰附近2倍瑞利距离内的多个光斑成像在同一个平面上, 用CCD相机获取这些光斑的光强分布图样。通过图像处理获知接收到的光斑的光强分布。采用远场发散角、焦点尺寸、桶中功率比和M2因子四种光束质量评价标准对激光光束质量进行评价。利用该方法实时测量了高能钕玻璃双板条激光器的输出光束。

高重复率半导体激光抽运Nd：YAG放大器激光特性的实验研究

实验研究了高重复率、大功率半导体激光二极管阵列（LDA）侧面环绕抽运的Nd：YAG激光放大器的放大特性、热焦距变化和热致双折射效应引起的退偏特性。偏振光绎千赫兹高功率单通激光放大器，获得约3倍的光脉冲能量放大，脉冲宽度基本保持不变，其输出的P分量与S分量的能量比趋于常数3：1，实验测得的能量放大倍率及放大光束的椭圆偏振度与理论预期吻合很好。

新一代大功率固体板条激光器的技术进展

介绍了固体板条激光器为了获得大功率和高光束质量而采用的新技术, 阐述了新一代大功率固体板条激光器的最新进展, 分析了新一代大功率固体板条激光器的技术特点, 并对其应用前景进行了展望。

基于正交频率变换的高功率蓝绿全固态激光器

对多横模全固态激光器使用正交频率变换进行了分析,计算了频率转换效率与激光发散角的关系。使用双KTP晶体正交倍频的方法,对Nd∶YAG激光器输出的含有高阶横模的激光进行倍频实验研究。在1064 nm Nd∶YAG激光基波功率密度为121 MW/cm2时,其谐波转换效率达到75.5%。研究表明,对于光束质量较差的基波激光,采用正交频率变换的方式,适当选择晶体参数,同样可以获得较高效率的二次谐波输出。

多模光纤激光器实现高功率低阶模输出

采用光纤缠绕的方法，来抑制大模场面积（LMA）双包层光纤激光器中的高阶模振荡。将光纤缠绕至两种不同半径，实验测量了相应条件下激光器的输出功率和光束质量因子M2。缠绕半径为165mm时，输出功率为217W，M2为2.96；缠绕半径为52mm时，输出功率为160W，M2为1.38。光纤激光器相应的斜率效率分别为60％和48％。光纤缠绕半径较小时，虽然激光器输出功率减小，但其亮度是大缠绕半径时对应值的3.4倍。