飞秒激光直写透明光学材料光波导的研究进展

综述了飞秒激光直写光波导的加工过程和表征方法、可直写形成光波导的不同透明光学材料以及直写光波导应用的进展。总结了飞秒激光直写引起的折射率变化与材料有关,同时还依赖于加工的脉冲能量、脉冲宽度、偏振以及扫描速度等。指出飞秒激光微加工在光子器件领域的有很好的应用前景。     

激光直写法制备条形光波导中的功率密度阈值

采用溶胶-凝胶法(sol-gel)在Si基SiO2衬底上制备了SiO2-TiO2芯层薄膜,构成了以SiO2为下包层,空气为上包层的平面光波导。利用光纤激光器对平面波导的芯层进行直写,结合后续的化学腐蚀工艺得到了SiO2-TiO2条形光波导,并着重研究了激光直写波导过程中存在的功率密度阈值以及阈值随薄膜预热处理温度的变化关系。研究结果表明,激光直写SiO2-TiO2波导存在起始收缩阈值和烧蚀损伤阈值;随着薄膜热处理温度的提高,两个阈值同时增大,其中损伤阈值的增大趋势要大于收缩阈值;因而薄膜可承受的直写光斑直径变小,所得波导宽度显著减小。最后对直写制得条形光波导的导光性能作了测试分析,验证了波导的三维导光性。     

激光直写技术制备SiO2-TiO2条形光波导工艺研究

为了研究激光直写技术在光波导制备中的应用,采用波长为1.07μm的连续光纤激光器制备了硅基SiO2-TiO2条形光波导。探讨了激光直写技术制备条形光波导的原理,研究了激光参数对条形光波导宽度的影响,最后测试了光波导的通光模场以及光传输损耗。结果表明,条形光波导的宽度随着激光功率密度的增加而增大。当激光扫描速率在0.1mm/s~1mm/s范围内变化时,条形光波导的宽度随着激光扫描速率的增加而降低;高于1mm/s时对波导宽度无明显影响。在优化的工艺参数下,激光直写得到的条形波导的厚度约为0.4μm,宽度为120μm,整条波导非常均匀、准直性很好,对于1550nm波长的光呈多模传输,最小传输损耗为1.7dB/cm。     

Light propagation studies on laser modified waveguides usingscanning near-field optical microscopy

By means of direct laser writing on Al, a new method to locally modify optical waveguides is proposed. This technique has been applied to silicon nitride waveguides, allowing modifications of the optical propagation along the guide. To study the formed structures, a scanning near-field optical microscope (SNOM) has been used. The laser modifications locally changes the optical properties of the waveguide. The change in the effective refractive index is attributed to a TE to TM mode conversion. Thus, the laser modification might be a new way to fabricate optical mode converters     

Waveguide Interconnection in Silica-Based Planar Lightwave Circuit Using Femtosecond Laser

The interconnection of waveguides inside a silica- based planar lightwave circuit (PLC) is demonstrated both two- and three-dimensionally by using a femtosecond laser. The waveguides written with a femtosecond laser can be successfully connected to waveguides inside a PLC with low loss. Unlike previous work on the direct writing of 2-D and 3-D waveguides in bulk glass, the waveguide must be written a few tens of micrometers beneath the surface of a PLC composed of multilayers of different glasses. To realize a low-loss waveguide, we studied the sensitivity difference for femtosecond pulses in each layer in detail and developed a multiple-scanning technique with a femtosecond laser for writing waveguides. In addition, we investigated a mode-field (MF) diameter control technique to allow us to achieve the low-loss interconnection of PLC and written waveguides. We also studied particular problems caused by nonlinear optical effects, such as the positional displacement of written waveguides from the focal point. As a result, we achieved a low-loss waveguide with almost the same MF diameter as a PLC waveguide and performed the first demonstration of interconnection between PLC waveguides. The excess losses at 1550 nm were 1.4 and 2.3 dB for 2-D and 3-D interconnection, respectively.      

Determination of Refractive Indices From the Mode Profiles of UV-Written Channel Waveguides in ${hbox {LiNbO}}_{3}$-Crystals for Optimization of Writing Conditions

We report on a method for the simultaneous determination of refractive index profiles and mode indices from the measured near-field intensity profiles of optical waveguides. This method has been applied to UV-written single-mode optical waveguides in ${hbox {LiNbO}}_{3}$ for the optimization of the writing conditions. The results for the waveguides written with light of the wavelengths 275, 300.3, 302, and 305 nm for different writing powers and scan speeds reveal that for optimum writing conditions a maximum possible refractive index change of $sim$0.0026 can be achieved at a value of 632.8 nm transmitting wavelength. The computation process used in the presented technique may also become useful to extract absolute refractive index values of any slowly varying graded index waveguide.      

Fabrication and characterization of integrated optical waveguidesin sulfide chalcogenide glasses

This paper reports on the fabrication process of As-S-(Se)-based chalcogenide glass optical waveguides using three techniques: photolithography, laser beam writing, and ion implantation. The fabrication method of the bulk sulfide glasses and the processing of integrated devices are described and assessed in light of the propagation characteristics and optical losses in each case     

Group-delay ripple reduction in step-chirped fiber Bragg gratingsby using laser-beam written step-chirped phase masks

Step-chirped phase masks for step-chirped fiber Bragg gratings (FBGs) were fabricated by employing a new writing strategy, in which the beam is able to scan a step-chirped pattern all at once or continuously. This new writing strategy was realized by using a raster scan-type laser-beam writing system. Linearly and nonlinearly step-chirped FBGs, fabricated by using these masks, show very low group-delay ripple characteristics, which means that the masks have fewer stitching errors than conventional step-chirped masks     

Optical channel waveguide in chalcogenide (Ga:La:S) glass

A novel method for fabricating optical channel waveguides in Ga:La:S chalcogenide glass, through continuous wave direct UV laser writing (λ=244 nm) is reported. Well-formed single-mode channel structures, with low propagation losses of 0.38±0.05 dB/cm at 1.3 μm, were engineered using this technique     

Stable-phase microwave-signal transmission channels and simulation synthesis of wave beams performed on the basis of beam waveguides

The prominent contribution of Academician V.A. Kotel’nikov to creation of an underground testing ground formed from a periodic sequence of phase equalizers (lenses and reflectors) is reported. A series of experiments that were performed on this unique facility and that involved laser-beam transmission with low loss over a line of a highly stable electric length are described. It is shown that the experience in investigations dealing with beam waveguides initiated research aimed at formation of wave beams with unique properties.     

Thermal Aging Reliability of Package-Level Polymer Optical Waveguides

Polymer optical waveguides are viewed as a potential interconnect solution in board-level optoelectronic systems. In this paper, the optical loss changes in siloxane polymer waveguides during thermal aging conditions are studied for the wavelengths of 850 and 1310 nm. The optical loss in waveguides during intended operation and temperature exposure can increase due to factors such as oxidation of waveguides, increased absorption, and scattering. In addition to these inherent changes in the optical properties of the waveguides, physical failures such as delamination and cracking of waveguides will also increase the optical loss. This paper focuses on the first set of parameters that affects the optical loss and as a first step; the optical absorption of the polymer material is characterized through spectroscopy experiments. The thermal-aging dependent optical loss is determined for waveguide samples at several different accelerated temperature conditions. The temperature contours in a polymer waveguide with an embedded laser are determined from experiments as well as finite-element modeling. Using experimental data, analytical models have been developed that relate the optical loss with temperature and time, and provide a practical way of determining the reliability of the optical waveguides during field-use conditions.     

Impact of Temporary Link Blockage on Ergodic Capacity of FSO System

Free-space optical (FSO) systems have attracted much attention from both research and application perspectives owing to their many benefits, such as license-free operation, low-cost, and high data rates. This paper investigates the ergodic capacity of FSO systems, which is an important metric of system performance. The stochastic temporary laser-beam blockage, pointing errors, and atmospheric turbulence are simultaneously considered. The results illustrate that the link blockage causes a decreased ergodic capacity. We show that to maximize the ergodic capacity, there is an optimal value of the laser-beam radius at the waist, which largely depends on pointing errors; however, it is independent of the atmospheric turbulence and the probability of link blockage.     

弯曲光波导端面修饰的设计方法

光波导的弯曲损耗一直是集成光学中一个值得人们重视的问题,为有效地减小光波导弯曲损耗,弯曲光波导的设计成为集成光学波导设计中的一个重要内容.本文在弯曲光波导保形变换方法的基础上,应用几何光学分析方法给出了波导弯曲损耗产生的简洁的物理图像,从而深入地分析了弯曲损耗产生的根本原因,并由此提出了弯曲光波导端面修饰的设计方法.理论分析表明,与传统的弯曲的光波导设计相比,该种设计方法可以有效地减小导波的模式泄漏,从而减小波导弯曲损耗.尤其是在弯曲光波导曲率半径、材料折射率等参数被设定的情况下,该种设计方法成为一种有效的设计方法.     

Nonreciprocal Magnetooptic Waveguides

The longitudinal magnetooptic effect can be used in a unique way to mix TE and TM modes of a planar dielectric waveguide where the strength of mixing is dependent upon propagation direction (forwards or reverse). A detailed study of Faraday effect circulators in optical dielectric waveguides is presented and accurate design data for a practical version are offered. At this writing, experimental confirmation has been hampered by lack of success optically contacting two dissimilar materials.     

TM-pass polymer modulators with poling-induced waveguides and self-aligned electrodes

Transverse magnetic (TM) mode selective polymer Mach-Zehnder modulators with self-aligned electrodes were fabricated for the first time in the electro-optic polymer material APC-CPW1 by employing a poling-induced (PI) writing method. The waveguides support only a TM polarisation, when an arbitrarily polarised optical source is incident. Modulators with a single 3 cm long driving electrode show a V/sub /spl pi// of 3.5 V at 1.55 /spl mu/m.     

Low-loss three-dimensional waveguide crossings using adiabatic interlayer coupling

The silica-based planar lightwave circuit (PLC) is a promising technology for application to a reconfigurable optical add/drop multiplexer (ROADM), which contains arrayed waveguide gratings (DEMUX/MUX), variable optical attenuators (VOAs), switches (SWs), and tap monitors (TAPs) as shown in Fig. 1. Specifically, single-chip integration with higher delta (D) contrast waveguides, which allow a small bending radius, enables us to realise compact and low-cost ROADM modules [1]. The critical problem with regards to single-chip integration is the large excess loss caused by conventional two-dimensional (2D) waveguide crossings as shown by the broken line in Fig. 1, because a large channel number of more than 40 ch is strongly required in ROADMsystems, and the crossing loss will accumulate in proportion to the channel number. On the other hand, three-dimensional (3D) waveguide crossings are attractive because they are fundamentally lossless [2, 3]. The most important technical aspect with regards to 3D waveguide crossings is to find a way to interconnect between vertically stacked waveguides. Various approaches have been proposed for realising interlayer coupling. One approach is direct writing using a femtosecond laser [2]. The problem with this approach is that the writing process time increases in proportion to the number of channels. Another approach involves using vertical directional couplers to realise interlayer coupling of the double waveguide structures [3, 4]. In this case, a severe fabrication tolerance is required if we are to form a directional coupler with 100% coupling. To overcome these problems, we propose and demonstrate 3D waveguide crossings based on a triple waveguide layer structure and adiabatic double/stacked-core modefield (MF) converters. By adopting simple mode conversion with the middle waveguide layer, we can provide stable low-loss interlayer coupling between vertically stacked upper and lower waveguides.     

硅包层质子交换条形光波导的频率响应

退火质子交换工艺已成为一种制备低损耗铌酸锂光波导的重要技术.但目前对该类光波导传输特性的研究还不多.利用半矢量光束传播法,对硅包层X切退火质子交换铌酸锂条形光波导的频率响应特性进行了数值分析.给出了几种波导结构参数下的计算结果.结果表明,波导传输模式的衰减特性与波长相关.波导的衰减特性,可以通过调整波导表面中心处折射率增量,硅包层厚度,及缓冲层的折射率和厚度来控制.硅包层光波导可以用来制作光频滤波器.     

光纤合束器的研制与应用

光纤合束器是一种先进的将泵浦光耦合进双包层光纤的器件.介绍了这种器件的结构和优点,以及它在大功率光纤激光器和光纤放大器中的应用,并对它的研制过程进行了探讨.     

Discrete Out-of-Plane Coupling Components for Printed Circuit Board-Level Optical Interconnections

We propose discrete out-of-plane coupling components as a versatile alternative to current approaches used to couple light in and out of the propagation plane in waveguide-based printed circuit board (PCB)-level optical interconnections. The out-of-plane couplers feature a 45deg micromirror and are fabricated using deep proton writing as a rapid prototyping technology. Their fabrication is compatible with replication techniques and shows all the potential of low-cost mass fabrication. In a first configuration, we use the component in a fiber-to-fiber coupling scheme. Coupling losses as small as 0.77 dB were achieved. In a second configuration, the out-of-plane coupler is plugged into a laser ablated cavity in optical waveguides integrated on a PCB. Here a total link loss between out-of-plane fiber and in-plane fiber of 3.00 dB was achieved when using it at the transmitter side and 5.69 dB when using it at the receiver side.     

离散谱折射率法优化设计深刻蚀、单模GaAs/GaAlAs脊形光波导

采用离散谱折射率法对深刻蚀GaAs/GaAlAs多层脊形光波导的特性作了详细的理论分析,并对所获得的较大截面、低损耗的单模脊形光波导的制作容差性作了进一步的分析．计算表明,用离散谱折射率法获得的单模脊形光波导具有较大的制作容差性．