电光聚合物波导中的锥形结构

提出并设计了一种基于电光聚合物的锥形波导,可用于单模光纤与电光聚合物波导器件之间的连接.锥形波导中采用了宽度锥形和折射率锥形结构.宽度锥形采用劈形形状,通过宽度和折射率的缓慢变化实现模场转换.劈形形状的宽度锥形具有较小的损耗且易于制作,折射率锥形可采用灰度掩膜光刻技术制作.研究了锥形波导的传输损耗与锥形波导的长度、波导宽度和厚度、材料吸收损耗等参数的关系及其优化,分析了锥形波导中的功率传输、模场分布与模式转换效率.结果显示锥形波导的传输损耗小于0.37 dB,光纤-波导-光纤的连接损耗优于1.62 dB,对插入损耗的改善达到8.78 dB,模场转换效率达到了83.7%.     

阵列波导光栅平坦化的研究

阵列波导光栅的平坦化在实际应用中有很重要的意义.本文系统地研究了阵列波导光栅的平坦化.在输入波导、输出波导、阵列波导输入端与输出端上分别引入了指数型锥形波导.通过改变锥形波导的形状和尺寸来实现平坦化的优化.本文首先从理论上论述了引入指数型锥形波导的输出光谱特性,给出了结构参量的关系表达式,阐明了输入波导处的锥形波导是影响输出光谱平坦化的主要因素,阵列波导和输出波导处的锥形波导对输出光谱的平坦化有一定的影响.其次采用数值模拟的方法模拟了输出光谱,优化了结构参量,总结出了指数型锥形波导对平坦化影响的趋势和规律.模拟结果显示,输出光谱1 dB带宽大于通道间隔的50%,插入损耗从5.2 dB减小到了4.0 dB,串扰小于-30 dB.最后,本文给出了实验结果,插入损耗减小了0.87 dB,串扰减小了3.67 dB,1 dB带宽增加0.1 nm,增加了54.7%.实验结果表明引入指数型锥形波导提高了阵列波导光栅器件的光谱性能.     

A taper coupler for integrated optics formed by ion-exchange under a non-uniform electric field

A method for the formation of gradient index tapered optical waveguides with predicted shape is proposed and described analytically. The method is applicable for structures fabricated by electric-field assisted ion-exchange in glass. The technique is based on the control of the taper shape by applying a non-uniform electrical field during the waveguide formation process. For experimental verification optical waveguides with tapers were formed by electrically induced migration of K⁺ ions. An optical coupler based on such a tapered waveguide has demonstrated 1.2° outcoupled beam divergence. The method proposed can be used to form different integrated optical elements, e.g. mode filters, horn structures etc.     

High efficient Tm3+ doped double cladding silica fiber laser with an intracavity biconical taper

A high efficient LD (laser diode) pumped Tm³⁺ doped double clad silica fiber laser with an intravacity biconical taper was reported. A biconical taper located ～3 cm from the output end of the fiber laser was fabricated by heating and stretching method with a length 1.5 cm and waist diameter ～20 µm. The slope efficiency was 49.8% with respected to the launched pump power, and the maximum output power was 1.97 W. Pre and post output laser power ratio was ～10. This fiber laser was compared with other three biconical tapered fiber lasers (the same fiber with different tapers) and a uniform geometry fiber laser. With intracavity biconical tapers, fiber lasers’ thresholds were ～1 W higher than the fiber laser without the taper (1.97 W). The pump end’s slope efficiencies of fiber lasers with tapers were 3–5% in contrast with 37.6% of the uniform one. After tapered, the pre and post laser power ratios were much higher than the un-tapered one’s, but not changed much with the launched pump power.     

Ultrafast laser machining of tapered microchannels in glass and PDMS

The ability to fabricate tapered microchannels with customizable cross sections in a variety of materials is highly desirable for microfluidic applications. This article examines ultrafast laser machining of tapered microchannel trenches in both hard (soda-lime and borosilicate glasses) and soft (PDMS elastomer) transparent solids. A simple model for channel width and depth as a function of processing parameters and threshold fluence is presented. Estimated channel sizes from the model are in good agreement with experimental results. We also show that the channel depth is a linear function of the number of laser pulses per channel width. All measurement data are found to collapse onto a single curve, which can serve as a useful guide for micromachining of tapered channels in transparent materials.     

Composite optical waveguide composed of a tapered film of bromothymol blue evaporated onto a potassium ion-exchanged waveguide and its application as a guided wave absorption-based ammonia-gas sensor

For what is the first time to our knowledge, we have successfully evaporated a tapered film of bromothymol blue (BTB) onto a potassium ion-exchanged (PIE) waveguide to form a composite optical waveguide (COWG) for trace-ammonia detection. The BTB film has a high refractive index (1.69) and a smooth surface and is transparent to a 633-nm laser beam in air. In the COWG structure, the BTB film serves as a single-mode waveguide, and adiabatic transition of the TE(0) mode was realized between the BTB waveguide and the PIE waveguide with both BTB tapers. In the presence of ammonia, the BTB film changes color from yellow to blue, which causes absorption of the 633-nm guided wave. Our experimental results demonstrate that such a guided wave absorption-based ammonia-gas sensor is much more sensitive than one based on evanescent-wave absorption. A detection limit of part in 10(9) of ammonia has been realized for a BTB film-PIE glass COWG.     

Efficient couplers for photonic crystal waveguides

We use two-dimensional simulations to study the design of tapers to provide efficient, low reflection coupling between a waveguide in a two-dimensional photonic crystal (PC) and free space. We find that, largely independent of the PC parameters, or of the length and width of the tapered region, the same type of concave, horn-shaped tapering profile is optimal for coupling from the waveguide into free space, and significantly out-performs the widely used linear taper. We also find that optimal tapers can radiate nearly Gaussian beams, and therefore they can also provide efficient coupling of Gaussian beams from free space into the PC waveguide. These properties are better exhibited by rod-type PCs with E_z polarization than by hole-type PCs with H_z polarization. This study of taper couplers exemplifies a design strategy for photonic circuits which optimizes positioning of the cylinders immediately surrounding the light path, and then builds the rest of the crystal structure around these cylinders.     

气源MBE外延自组装GeSi量子点光致荧光研究

利用气源分子束外延设备（MBE）制作了GeSi自组装量子点样品。利用原子力显微镜（AFM）和光致荧光（PL）光谱研究了量子点的形貌和光学性质。气源MBE在较低温度下生长的量子点材料具有较高的量子点覆盖度。200K以下载流子以局域激子形式束缚在量子点中,激子束缚能约为17meV。升温至200K,载流子的输运过程发生变化。对量子点PL积分强度与温度关系曲线进行拟合得到量子点中空穴跃迁至浸润层的热激活能为129meV。     

掺半导体玻璃波导的导波功率限制

首次利用阳极氧化法在掺半导体玻璃上制备了两端带有抛物耦合喇叭的4微米条宽沟道波导,用光栅耦合器将波长0.532微米的YAG倍频激光耦合进波导中,实现了输出光的功率限制.     

850nm高亮度锥形半导体激光器的光电特性

采用激射波长为850 rm的AlGaInAs/AlGaAs梯度折射率波导分别限制增益量子阱结构的外延片,设计并制备了具有条形结构和锥形结构的半导体激光器.在输出功率同为1 W时,锥形激光器的发散角、光束传播因子和亮度分别为4°、2.8和9.9 MW·cm-2·sr-1,远好于条形激光器的6°、9.2和3.0 MW·cm...     

Tapered hollow waveguide for focusing infrared laser beams

A tapered hollow waveguide that can focus a laser beam into a small beam spot is proposed for medical and dental applications. We fabricated hollow tapered optics by using a traveling torch, and the shape was formed as a precise linear taper. For a hollow taper tip with input and output diameters of 700 and 200 microm, respectively, the insertion loss is as small as 0.7 dB in a 10 mm long taper. The hollow taper optic producing a 200 microm spot withstands input energy of 100 mJ. Because a focusing lens is unnecessary at the output end, the laser beam can be introduced into a deep and narrow spot with these tapered optics.     

锥形半导体激光芯片的光刻工艺研究

针对锥形半导体激光器中的脊形波导区宽度较小的问题,对半导体激光芯片制造中的刻蚀标记及刻蚀方法进行了研究。提出对于锥形半导体刻蚀中的脊型区域和锥形区域,采用不同精度的双标记刻蚀方法,细化对脊形波导和锥形波导的刻蚀中的对准问题,并使光刻标在不同的光刻版上相错位排列,在相应光刻版中相互遮挡,反复刻蚀中保证相应的光刻标清晰、完整。刻蚀后的芯片在电流为7 A时获得了中心波长963nm、连续功率4.026 W、慢轴方向和快轴方向激光光束参数乘积分别为1.593 mm·mrad和0.668 mm·mrad的激光输出。     

An analysis of optical waveguide tapers

The characteristics of slab waveguide tapers with finite-thickness cladding are investigated by approximating the tapered section as a series of uniform five-layer waveguides with successive changes in the core and cladding thickness. The behaviour of multimode coupling and transmission characteristics for typical tapers are studied in detail by computer simulation, employing parameter values appropriate for practical systems. Strong coupling and efficient conversion between core and cladding modes are demonstrated. In addition, it is shown that for tapers of moderate slopes, the nearest-neighbour coupling approximation is quite adequate for the calculation of the individual mode amplitudes. For steeper tapers, however, additional neighbouring modes have to be taken into account, and the modal energy tends to spread further towards the higher-order modes. It is also demonstrated that relatively large step-size can be used in the iterative numerical calculations. This, in conjunction with the choice of an appropriate coupling scheme (e.g., the nearest-neighbour approximation for mild tapers), makes it possible to reduce the cost of computer simulation. The relevance of the present analysis to fiber tapers is also discussed. Supported in part by the Department of Communications of Canada     

Analysis of Semi-conductor Laser Diode with Two-dimension Nonlinearly Tapered Waveguide

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锥形脊结构半导体光放大器的有限元分析

为提高半导体光放大器与单模光纤耦合效率，建立了半导体放大器的锥形脊结构模型。在该模型下利用有限元数值模拟方法分析，计算了波导区折射率、锥尖宽度、条形波导尺寸、渐变折射率波导层对锥形脊结构模式扩展的影响。通过完善锥形脊结构参量的设计，获得了锥形脊结构半导体光放大器与单模光纤95％的耦合效率。     

Analysis of Semi-conductor Laser Diode with Two-dimension Nonlinearly Tapered Waveguide

A novel semiconductor laser diode with a two-dimension nonlinearly tapered waveguide is proposed and its property is studied by Fourier expanding method. It is shown that coupling loss between the semiconductor laser diode and a single mode fiber is reduced effectively, the reduction role of the nonlinearly tapered waveguide is more apparent than that of a linearly tapered waveguide , the minimum coupling loss is 0.36 dB, and the far field divergence is decreased. The reduction mechanism is discussed.     

Thinnest optical waveguide: experimental test

A thin dielectric waveguide with a subwavelength diameter can exhibit very small transmission loss only if its diameter is greater than a threshold value, while for smaller diameters, waveguide loss grows dramatically. The threshold diameter of transition between these waveguiding and nonwaveguiding regimes is primarily determined by the wavelength of propagating light and, to a much lesser degree, by the characteristic length of the waveguide's long-range nonuniformity. For this reason, the transmission spectrum of a thin waveguide allows immediate and quite accurate determination of its thickness. An experimental test of these facts is performed for a tapered microfiber. Good agreement with the recently developed theory of adiabatic microfiber tapers is demonstrated.     

斜波导喇曼振荡器

 采用斜波导的喇曼氢气池, 使泵浦激光束在波导内部传播, 增大了受激喇曼散射的作用区域。在传播过程中光束截面逐渐被压缩, 补偿因波导内壁的反射损耗而引起的功率密度下降。在一定气压范围内提高了喇曼转换的效率, 并利用波导对激光束的均匀作用, 使输出的一阶斯托克斯光光强的均匀性获得改善。     

Efficiency improvement of multimode Tm3+ doped double cladding silica fiber laser by in-line biconical tapers

Efficiencies improvement of LD (laser diode) pumped multimode large mode area (LMA) Tm³⁺ doped double cladding silica fiber lasers with different in-line biconial tapers were reported. Two types of multimode Tm³⁺ doped fiber were used in this experiment. Each type of fiber was made into three fiber lasers, a uniform geometry fiber laser and two tapered fiber lasers with different taper parameters. Biconical tapers located several centimeters from the output end of the multimode fiber lasers were made by heating and stretching method. Although the threshold of the best tapered fiber laser was added 200 mW, the slope efficiency (25.3%) and the maximum output power (1.31 W) of the fiber laser increased by 10.3% and 350 mW respectively, in comparison with the un-tapered one. Pre and post output laser power ratio was 6.3–15.6. Simultaneously, the laser spectrum moved to shorter wavelengths. The same trends of these characteristics were also observed in the other three tapered fiber lasers.     

Horn structures for integrated optics

The results of an experimental study of linear and shaped horns for integrated optics in Ti-diffused LiNbO₃ waveguide structures are reported. The single mode to single mode coupling efficiencies for various tapers are measured with greater than 90% throughput for shaped horns. The use of tapered horn structures in an optical switch design is discussed.