Z-切Ti:LiNbO3平面波导模式数量的色散特性

对于在流动干氩气中扩散而形成的Z-切Ti:LiNbO₃平面波导,用Fouchet等人提出的钛感应折射率增量在0.6～1.6μm波长范围内的色散关系,推得与扩散参数有显函数关系的模式数量的色散公式。在若干重要波长,用这些色散公式,画出模式数量和扩散参数的关系曲线,可用来控制相应波导和器件的模式数量。     

Quasi-phase-matched difference-frequency generation in periodically poled Ti:LiNbO(3) channel waveguides

Mid-infrared radiation near 2.8 mum was generated by difference-frequency generation in an 80-mm-long periodically poled Ti:LiNbO(3) channel waveguide by pump radiation near 1.55 mum (tunable external-cavity laser) and a signal radiation of 3.391 mum (HeNe laser). We obtained a normalized conversion efficiency of 105% W(-1) , which is to our knowledge the highest value ever reported.     

Continuous-wave singly resonant optical parametric oscillator based on periodically poled RbTiOAsO(4)

We report a continuous-wave optical parametric oscillator (OPO) based on periodically poled RbTiOAsO(4) (PPRTA). The singly resonant OPO, which is located within a Ti:sapphire laser, has a high-finesse signal cavity and delivers a maximum output power of 270 mW to the nonresonant idler wave at 2.92mum , through a 4.5-mm PPRTA crystal. For room-temperature operation and a crystal with a 30-mu;m grating period, pump tuning over 838-848 nm results in OPO tuning over 1.13-1.27mum (signal) and 2.53-3.26mum (idler), limited by the bandwidth of optical coatings. PPRTA exhibits thermal properties superior to those of periodically poled LiNbO(3) .     

Ti∶LiNbO_3二维渐变折射率光波导传播常数的计算

从Ti∶LiNbO3波导截面折射率分布的特点出发，得出一套计算传播常数简单而精确的方法。文中对该法进行了分析，并应用该方法计算了钛扩散波导的色散关系。该方法为钛扩散光波导集成光学器件的设计提供了一种较可靠的理论手段。     

High-repetition-rate ultrashort-pulse optical parametric oscillator continuously tunable from 2.8 to 6.8 mum

We describe a synchronously pumped femtosecond optical parametric oscillator based on periodically poled LiNbO(3) that is broadly tunable in the mid infrared. A transmission window of periodically poled lithium niobate beyond the conventionally accepted infrared absorption edge of 5.4 mum has been exploited to produce idler pulses that are tunable across a wavelength range of 4 mum , with milliwatt-level output powers at wavelengths as long as 6.8 mum . We also present experimental tuning results that are in good agreement with the theoretical phase matching predicted from published infrared-corrected Sellmeier equations for LiNbO(3) .     

1.5μm Ti:LiNbO_3光波导TE_0模偏振器

在1.523μm波长He-Ne激光,对于Z切Ti扩散LiNbO_3光波导及其带有金属包覆/介质缓冲层的偏振器结构,理论上计算了单模波导的工艺参数和基模的吸收损耗系数.文中用TM_0模的共振吸收效应,在1.5μm波长首次研制成Ti:LiNbO_3光波导TE_0模偏振器.当器件长度为2mm和9mm时,其消光比分别为20dB和25dB.     

Broadband and highly efficient quadratic interactions in double-slot lithium niobate waveguides through phase matching

We propose and study in detail a phase-matched quadratic optical interaction in a realizable 2D double-slot lithium niobate (LN) waveguide. As opposed to the single-slot waveguide, the field can be well confined in the nanometric nonlinear material, and it is also more flexible for birefringence and dispersion design. The proposed compact double-slot structure could not only achieve form birefringence phase matching but also effectively enhance the modal overlap integral and expand the working wavelength. The calculated results on second harmonic generation show an extremely large bandwidth of ~40 nm. The modal overlap integral up to 0.035 W(3/2)/V can be realized by optimizing the waveguide geometry, and it is much better than previous results on single-slot waveguides. Its temperature dependence is low--around 25 °C. The geometry is practical considering the current micromachining technique of LN.     

LiNbO(3) platforms for optical fiber alignment

A technique for incorporating a groove into a LiNbO(3) substrate is described. Both V grooves for fiber alignment and vertical grooves for waveguide end-face formation can be fabricated with this technique. The proposed fabrication method is based on an excimer-laser ablation and a high-speed rotation saw cut for LiNbO(3) . The former process provides a variety of cross-sectional groove shapes by changing the ablation mask shape of LiNbO(3) , and the latter provides an optical-quality cutting face. The proposed fabrication method is simple and provides low-cost optical platforms not only for LiNbO(3) but also for glasses, polymers, and semiconductors.     

Zero-birefringence photosensitive polyimides for optical waveguides

Zero-birefringence (delta n < 1 x 10(-6)) photosensitive fluorinated polyimides are synthesized for use in polymer optical waveguides. To obtain zero birefringence, the UV exposure time and copolymer content of photosensitive polyimides are controlled. Zero birefringence combined with photoprocessing of the material has excellent potential for applications in high-performance wavelength division multiplexing components such as polarization-independent arrayed waveguide gratings and Bragg wavelength filters.     

集成光学电光调制干涉光谱仪的模式谱分析

基于钛扩散铌酸锂(Ti∶LiNbO3)波导的集成光学电光调制技术的干涉光谱仪是Ti∶LiNbO3调制器的一种崭新应用,一般应用的探测光谱区间是在波导的单模区间。为拓宽探测波长范围至多模传输范围,以x向切割,y向传输。以共面对称电极的Ti∶LiNbO3波导电光调制干涉器(器件长度60mm)为例,模拟了多模传输时电光调制系数的模式色散现象。数值模拟中采用了有限差分方法(FDM)。分析表明,在多模传输情况下,光的各阶模式的光场分布差异导致了电光调制系数的模式色散;在对经线性扫描电压调制后的干涉输出数据进行傅里叶变换谱分析后,可发现对应波长的各阶传输模式谱。实验采用0.808μm单模偏振光源,在激励起准TE多模式和激励起混合模两种情况下,验证了数值模拟和分析的结果。     

Fidelity of an optical memory based on stimulated photon echoes

We investigated the preservation of information encoded into the relative phase and amplitudes of optical pulses during storage and retrieval in an optical memory based on stimulated photon echo. By interfering photon echoes produced in a single-mode Ti:Er:LiNbO(3) waveguide, we found that decoherence in the medium translates only as loss and not as degradation of information. We measured a visibility for interfering echoes close to 100%. These results may have important implications for future long-distance quantum communication protocols.     

31%-efficient blue second-harmonic generation in a periodically poled MgO:LiNbO3 waveguide by frequency doubling of an AlGaAs laser diode

We present a method of controlling the shape of the domain-inverted structure in an off-cut MgO:LiNbO(3) crystal by utilizing a two-dimensional high-voltage application. With this technique a periodically domain-inverted structure with a period of 3.2mum and a thickness of 2.0mum was fabricated over a 10-mm interaction length. This structure has made possible sufficient overlaps between propagation modes and domain inversion in the waveguide. Using this structure, we demonstrated cw blue second-harmonic generation of 17.3 mW of power at a wavelength of 426 nm with single-pass 55-mW cw AlGaAs laser diode input, which corresponded to 31% power-conversion efficiency.     

Ti：LiNbO3光波导导模的场分布

给出了Ti扩散LiNbO_3条波导任意阶导模场分布的试探解.通过变分法分析,不但可以合理地确定其中的待定参数,而且也得到了相应导模传播常数的近似值.与扩展的有效折射率方法比较:这种解不但在函数形式上简单,待定常数确定方便,而且具有精度高的优点.还可以得到等效一维波导折射率分布的解析表达式.     

用有效折射率/有限元法设计1.55μmTi:LiNbO3单模条波导及其方向耦合器

应用有效折射率/有限元法(EI-FEM),考虑到LiNbO3晶体和Ti扩散的各向异性,折射率增量与寻常光、非寻常光及波长色散的关系,设计了1.55μm光波长下工作的z切y传播Ti:LiNbO3单模条波导的制备参数,计算和分析了其单模特性、模式场分布及其变化规律.扩展了EI-FEM,将其用于求解耦合波导系统,确定了方向耦合器的耦合长度及其波长色散特性.     

Refractive index measurement of optical waveguides using modified end-fire coupling method

We present a modified end-fire coupling method to reconstruct two-dimensional index profiles of optical waveguides. The reconstruction is based on the measured differential optical fields and an inverse algorithm for the Helmholtz equation. The differential fields are obtained from spatially perturbed images recorded by a CCD camera. A closed-loop piezoelectric stage given a sinusoidal wave and an oil-immersion objective lens for high-resolution images are used in the measurement. A single-mode fiber and a Ti:LiNbO(3) waveguide with known index profile at 632.8 nm are measured for demonstration. The measured index profiles agree quite well with core regions of known index profiles.     

Singly resonant continuous-wave optical parametric oscillator pumped by a diode laser

We report on what is believed to be the first singly resonant cw optical parametric oscillator (SRO) that is directly pumped by a diode laser. The SRO consists of a 38-mm-long periodically poled LiNbO(3) crystal in a four-mirror signal-resonant ring cavity. Pumped by 2.5 W of 925-nm diode-laser radiation, the SRO generates 480 mW of single-frequency idler radiation at 2.1mum . The wavelengths of the signal and the idler output are tuned in the ranges of 1.55 to 1.70mum and 2.03 to 2.29mum, respectively, by tuning the wavelength of the diode laser from 924.0 to 925.4 nm.     

High-energy, broadly tunable, narrow-bandwidth mid-infrared optical parametric system pumped by quasi-phase-matched devices

We have developed a tunable, narrow-bandwidth (<2 cm(-1)) mid-infrared (MIR) optical parametric system with a large-aperture periodically poled Mg-doped LiNbO(3) (LA-PPMgLN)-based high-energy pump source. The system has a continuously tunable tuning range from 4.6 to 11.2 mum and produces a maximum output energy of 2.0 mJ at 5.1 mum. Practical use of the MIR source is demonstrated by MIR-UV double-resonance spectroscopy of jet-cooled acetanilide.     

微结构聚合物光纤中高双折射可调效应研究

通过在纤芯附近引入两个直径较大的空气孔诱导纤芯局部双折射,在包层减小x方向的孔间隔诱导包层双折射,设计实现了一种高双折射随波长可调效应的微结构光纤.采用全矢量平面波方法,以聚合物甲基丙烯酸甲酯为基材,对其偏振特性和基模模场进行了研究.结果发现,该光纤基模双折射在光通信波段呈现两个最大值,且最大双折射大小和位置随光纤结构和波长的变化可以进行调节.通过调节光纤结构参数,模拟得到了该光纤具有高双折射和零偏振模色散的最佳设计参数. 关键词： 导波与光纤光学 双折射可调 聚合物 全矢量平面波法     

Continuous-wave 4.3-mum intracavity difference frequency generation in an optical parametric oscillator

We have achieved 150 mW of cw output at 4.3mum, using difference frequency mixing in a singly resonant optical parametric oscillator (OPO). We pumped the OPO cavity, which contains periodically poled LiNbO(3) (PPLN), with a 14-W 1.06-mum Nd:YAG laser to generate a signal at 1.7 mum and an idler at 2.8 mum. Mixing of the two waves at the same crystal temperature and grating spacing yielded emission in the mid IR. This technique avoids the mid-IR absorption-high-threshold problem, which has limited the cw performance of PPLN OPO's at wavelengths beyond 4 mum. Provided that tunability is not required, this method is a simple alternative to multiple-crystal configurations.     

Design and Fabrication of Integrated-Optic Disk Pickup on LiNbO_3 Substrate

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