【作者】 谭杨；

【导师】 陈峰；

【作者基本信息】 山东大学 ， 凝聚态物理， 2011， 博士

【摘要】 从上个世纪末开始迅速发展的集成光学技术,可将多个光学元件集成在同一块基片材料上,形成结构相对复杂的多功能小型/微型器件,以实现一种或多种光学功能,在信息传输/通信、环境检测、生物和化学传感等领域都有广泛的应用。光波导是集成光学最基本的元件,波导结构中的光密度与体材料相比大大增强,同时进行光信号传输和转换,直接决定了集成光学元件的性能和作用。低损耗的光波导制备以及波导的各种光学性质研究,一直是集成光学重要的研究课题。光波导有多种制备方法,例如离子注入、聚焦质子束直写、快重离子辐照、飞秒激光直写、离子交换、扩散和薄膜沉积等。其中,离子注入和飞秒激光直写技术可以适用于多种光学材料,是目前适用范围最广的两种波导制备方法。在离子注入过程中,注入离子通过与材料的相互作用遗失自己的能量,造成核能量损伤和电子能量损伤。这些能量损伤将会导致衬底材料的结构畸变,引起材料注入区折射率的变化,在离子注入末端折射率降低的光位垒,或者注入诱导产生的折射率增强势阱。通过光位垒和增强势阱对光传输进行限制,形成波导结构。以MeV氧离子注入铌酸锂晶体为例,在离子注入末端,由于核能量损伤的影响会形成一个折射率降低的光位垒；同时由于电子能量损伤的影响,在光位垒和空气之间,材料的异常光折射率上升形成增强势阱,通过光位垒、增强势阱和空气对光的共同限制,形成波导结构。飞秒激光导致的材料折射率变化,依赖于激光与材料之间的相互作用,这个过程包含很多复杂的物理过程,例如离子重排、晶格压缩、热积累等等。折射率的变化可以分成两类：(1)通过非线性作用在焦点处使材料折射率升高形成波导；(2)焦点处折射率降低,焦点周围的折射率间接的升高,在晶体中写入多条径迹,径迹之间形成波导。波导的结构依赖于各种制备手段对材料折射率的调制。这种调制有时会改变材料的光学性质,这些性质的变化直接影响到集成器件的应用价值。因此,研究光波导内各项光学性质的变化,具有重要的意义。从另一方面来讲,波导结构与体材料相比具有独特的性质。在波导结构中,光被限制在一个很小的空间内,光的能量密度在很低的入射能量下就可以达到很高的量级。因此体材料中的某些光学性质,例如非线性效应、激光性能,在波导中可以得到一定程度的加强。对波导性质的研究在集成光学元件的设计和应用上都具有重要作用。本文主要研究离子注入和飞秒激光直写技术在钕掺杂钒酸钇(Nd:YVO4)晶体、钕掺杂钒酸钆(Nd:GdVO4)晶体、钕掺杂钇铝石榴石(Nd:YAG)陶瓷、铌酸锂(LiNbO3)晶体、铌酸锶钡(SBN)晶体、钕掺杂铌酸钙钡(Nd:CBN)晶体、钕掺杂氟化钇锂(Nd:YLiF4)晶体等光学材料上波导的形成方法；测量波导的传输模式、损耗,通过退火处理优化波导的性质；用共聚焦显微镜、二波混频等技术手段研究波导的光学性质(例如光折变、荧光性质、热光性质等),对波导性质变化机理进行探讨；在离子注入和飞秒激光直写波导中实现激光输出,通过测量泵浦阈值、斜率效率等多个激光参数,讨论波导激光性能优化的方法；根据对波导腐蚀性质和光折变性质的研究,发明一种脊型波导制备方法和一种光诱导波导阵列制备方法；制作二元波导阵列,研究该阵列中的带隙光孤子。主要结果如下：钕离子掺杂钒酸钇(Nd:YVO4)晶体是一种应用广泛的固体激光器增益介质,因为它具有出色的荧光性质,例如大发射截面、宽吸收带、优良的机械性质等。本文用飞秒激光直写地方法在Nd:YVO4晶体内部写入条形波导。实验表明Nd:YVO4晶体条形波导的损耗为,～1dB/cm;晶体的荧光性质在波导中被很好的保留下来。基于该波导实现了波长为1.06μmm的单波长波导激光和波长为1.06μm和1.34μm的双波长波导激光输出。波导激光的最高斜率效率为～60%,最低泵浦阈值为～17mW。钕离子掺杂钒酸钆(Nd:GdVO4)晶体与Nd:YVO4晶体性质相似,也是一种优良的激光介质,具有出色的荧光性能。与Nd:YVO4晶体相比,它具有高热导率、高损伤阈值等特点。在中高功率二极管泵浦固体激光器中,有极大的应用前景。本文用飞秒激光直写的方法,在该晶体内制备条形波导。飞秒激光的写入速度高达17mm/s,而制备的波导损耗仅仅为～0.5dB/cm。利用808nm激光泵浦,实现波长为1.06μm的波导激光输出,波导激光的阂值为52mW,斜率效率为～70%,接近理论极限。钕离子掺杂钇铝石榴石(Nd:YAG)透明陶瓷是近几年出现的一种优良的激光材料。与Nd:YAG晶体相比它更容易进行加工和生产,可以进行高浓度掺杂。本文用离子注入的方法在Nd:YAG透明陶瓷表面形成平面波导,研究波导的荧光性质。实验发现轻离子注入后,波导内发生了荧光焠灭现象；重离子注入后,波导内荧光性质基本不变。在对波导荧光性质研究的基础上,实现平面波导激光输出,激光的斜率效率为～11%；泵浦阈值为～19.5mW。铌酸锂(LiNbO3)晶体是集成光学中应用最多的一种晶体材料。本文研究离子注入铌酸锂波导中,电子阻止本领对LiNbO3晶体热光性质的影响。研究发现电子阻止本领对热光性质的影响存在一个阈值(-2.2keV/nm),当低于此阈值时,晶体的热光性质被很好的保留在波导中；当高于这个阈值时,晶格结构受到破坏,热光性质在波导中发生变化。研究了氢离子(质子)注入LiNbO3波导的腐蚀性质,实验结果表明离子注入后晶体的腐蚀性质基本不变。基于该研究结果,本文提出一种脊型波导制备方法,选择性的对氢离子注入z切LiNbO3晶体进行腐蚀,依靠空气和光位垒对光进行限制形成脊型波导。经过400℃、30min退火,脊型波导的损耗降至～0.9dB/cm。用端面耦合和FD-BPM模拟的方法,研究波导的传输模式。稀土元素掺杂LiNbO3晶体既具有稀土元素的荧光性质,又具有LiNbO3晶体的电光和非线性性质,可以制备多种光学和电光器件,例如调Q、自倍频激光等。本文用离子注入的方法,在稀土元素掺杂LiNbO3晶体表面,制备平面和条形波导。对样品进行退火处理,并测量波导的传输损耗,实验结果表明退火后光波导损耗可以保持在一个较低的水平(～1dB/cm)。使用共聚焦显微镜对波导的荧光性质进行研究,发现晶体材料的荧光性质,在波导中被很好的保留下来。Fe:LiNbO3晶体是一种优秀的光折变晶体,在很低的入射光强下就可以产生较大的折射率改变,在全息存储和光通信等方面有着重要的应用。本文用二波混频的方法研究离子注入Fe:LiNbO3晶体波导中的光折变性质；对体材料和波导的增益系数和光电导系数进行对比,发现Fe:LiNbO3晶体的光折变性质在氧离子注入波导中没有发生变化。同时,研究发现在相同的入射光强下,波导中光折变效应的响应时间要比体材料中低一个数量级。铌酸钡(SBN)晶体是一种著名的光折变晶体,在光信号放大、全息存储等方面有着重要应用。铌酸钙钡(CBN)晶体与SBN晶体相比,居里温度更高(～280％),具有更广阔的应用前景。钕离子掺杂氟化钇锂(Nd:YLiF4)晶体具有折射率温度系数小、荧光线宽大等特点,适合制备低阈值连续激光器、锁模激光器。本文研究Nd:YLiF4、Nd:CBN和SBN晶体中平面及条形波导的制备和光学性质,使用端面耦合和模拟计算分析波导中的传输模式；使用共聚焦显微镜研究波导的荧光性质。更多还原

【Abstract】 The integrated photonics, which refers to the fabrication and integration of several photonic components on a common planar substrate, is a swiftly developing and synthesized technical domain ever since the end of last century. Based on the combination of photonic components, complex miniature devices with a wide range of functions could be realized and have been used as optical communication, environmental monitoring, biological and chemical sensing, etc. Waveguides are fundamental and key elements of integrated photonics that perform guiding, coupling, switching, splitting and multiplexing of optical signals. And the quality of integrated devices is determined by the performance and optical property of waveguide. Hence, the fabrication of low loss waveguides and the investigation of optical properties of waveguide are a continuous interesting topic in integrated optics.At present, several techniques have been developed to fabricate waveguides in optical materials, including ion implantation, proton beam focusing, swift ions irradiation, ultrafast direct laser writing (DLW), ions exchange, diffusion and film deposition etc. Ion implantation and DLW are two widely used methods for waveguide fabrication, due to their non-sensitivity of the structure of substrate materials. During ion implantation, the losses of incident ions include two different kinds of physical mechanisms called nuclear energy deposition and electronic energy deposition. Those energy depositions would cause the lattice distortion of the substrate material near the surface region and induce the variation of refractive index. At the end of the ion range, an optical barrier with a relatively low refractive index compared with the substrate is formed by the nuclear energy deposition. Meanwhile, refractive index would increase or be slightly disturbed between the air and the optical barrier, which is mainly decided by electronic energy deposition. The propagation light would be well confined by air and optical barrier in optical waveguide. For DLW, femtosecond lasers are used for buried three-dimensional waveguide fabrication due to nonlinear absorption of focused pulsed laser beam. The technique for writing waveguides can be sorted into two strategies. One relies on the direct refractive-index increase at the laser focus, and another one causes the refractive index decrease at the laser focus while indirectly increases on its surroundings. Both processes depend on the material and on the writing conditions and have a complex physical origin which involve several processes, such as ionic rearrangement, lattice stress, heat accumulation, etc. Although kinds of waveguide structures have been formed in masses of optical materials(such as optical crystals, glass, semiconductors etc), fabrication of waveguide with high quality in new materials is still a focus in integrated optics according to the benefit of wide applications of ion implantation and DLW.Waveguide structure formation is based on the modification of refractive index of bulk materials by fabrication techniques. The modification would change properties on the bulk, which are of great importance to the practical applications. Hence, investigation of property modification in waveguide is significant. On the other side, the waveguide is designed in micrometers and confines light diffraction in one or two dimensions. The specialties in the waveguide structure lead to the unique features of waveguide compared with bulk material. In such structure, the light is confined within a small volume and optical density could reaches a high level with low input power. As a result, the corresponding features of the bulks, such as nonlinear response or ability for laser generation, may be improved to some extent within waveguides. Based on the investigation of fabrication and properties, waveguide could be appropriately designed for integrated photonics devices with different functions in various research fields.In this dissertation, we report fabrication, characterization and application of waveguide. Ion implantation and DLW were used to fabricate channel, planar and ridged waveguides in variety of materials, which include SBN, KTP, Nd:CBN, Nd:YVO4, Nd:GdVO4, Nd:YLiF4, rare earth doped LiNbO3, Nd:YAG ceramics and Er3+/Yb3+ co-doped phosphate glass. Prism coupling method was introduced to investigate the refractive index distribution of waveguides. The propagation modes in waveguide were analyzed by end-facet coupling method. A confocal microscope was applied to study the fluorescence properties in rare-earth doped waveguides. Photorefractive property in waveguide was investigated by two-wave mixing method. Besides, we analyze the thermo-optic and etching properties in implanted waveguide. According to previous work, kinds of waveguide laser were generated, such as single-wavelength laser and simulated dual-wavelength laser. A new method was developed to form reconfigurable optical waveguide array. And we analyzed binary gap solitons in the waveguide array formed by this method. We also found a new method to fabricate ridged waveguide by wet etching.Neodymium-doped yttrium orthovanadate Nd:YV04 is one of most used gain media for solid state laser generation owing to its outstanding features high emission cross section, broad absorption bands, good mechanical and thermal properties. We fabricate the channel waveguides in Nd:YVO4 crystal by ultrafast direct laser writing method. The confocal fluorescence images revealed that the waveguide is constituted by a locally compressed area in which the original fluorescence of the Nd:YV04 system are preserved. Waveguide laser was generated at 1064nm with pumping at 808nm. Through the well design of input and output mirrors, dual-wavelength laser at 1.06μm and 1.34μm were also found in the channel waveguide.Neodymium doped gadolinium vanadate (Nd:GdVO4) is a well known crystal that is of special relevance for the development of compact near-infrared solid state lasers, which is owing to its excellent spectroscopic properties, high thermal conductivity, high damage threshold, high Raman gain. We report high efficiency continuous wave laser oscillations at～1.06μm from an ultrafast laser written Nd3+:GdVO4 channel waveguide under the 808 nm optical excitation. A record 17 mm/s writing speed was used while the low propagation loss of the waveguide (-0.5 dB/cm) enabled laser performance with a threshold pump power as low as 52 mW and a near to quantum defect limited laser slope efficiency of 70%.Neodymium-doped yttrium aluminum garnet (Nd:Y3Al5O12 or Nd:YAG) ceramics have emerged during the last years as an outstanding laser material capable of providing serious competition to the traditional single crystals. Indeed Nd:YAG ceramics show several advantages over their crystalline partners while retaining the outstanding fluorescence properties of neodymium ions. We report on the generation of continuous wave lasers at a wavelength of～1.06μm in a Nd:YAG ceramic waveguide at room temperature. The waveguide was fabricated by using 6 MeV carbon ion implantation at a fluence of 3×1014 ions/cm2. Laser operation has been realized with a slope efficiency as high as～11%. The pump threshold of an 808-nm laser beam for the waveguide laser oscillation is 19.5 mW.The rare-earth doped LiNbO3 system combines the excellent laser features of rare-earth with the electro-optical and nonlinear properties of LiNbO3, allowing the fabrication of many attractive devices for optical and photonic applications, such as Q-switched and self-doubling-frequency lasers. We report on rare-earth doped LiNbO3 active planar waveguides produced by ion implantation. The extraordinary refractive index of the sample surface experiences positive alternations constructing enhanced-well confined waveguide structures. After the implantation, the sample was annealed to reduce loss of waveguide The propagation loss of the waveguide was measured to be less than 2 dB/cm, which means acceptable quality for further guide-wave applications. The micro-luminescence spectra of the waveguide show fairly good potentials for laser action.Lithium niobate (LiNbO3) is one of the most favorite materials for integrated optical applications owing to its combination of many intriguing features, e.g., excellent thermo-optic, electro-optic and nonlinear optical properties. The thermo-optic (TO) properties of the lithium niobate waveguide fabricated by oxygen ion implantation at three different energies (2,3 and 6MeV) have been investigated. It is found that, as the electronic stopping power (Se) of the O ions is below a threshold of 2.2 keVnm-1, the TO features are well preserved in the waveguide regions. When Se is above this value, the TO coefficients of the waveguides are considerably modified, which is attributed to the increased defect generation in the crystal.We report on a new, simple method to fabricate optical ridge waveguides in a z-cut LiNbO3 wafer by using proton implantation and selective wet etching. The measured modal field is well confined in the ridge waveguide region, which is also confirmed by the numerical simulation. With thermal annealing treatment at 400℃, the propagation loss of the ridge waveguides is determined to be as low as～0.9 dB/cm. In addition, the measured thermo-optic coefficients of the waveguides are in good agreement with those of the bulk, suggesting potential applications in integrated photonics.Photorefractive (PR) materials, in which rather large light-induced refractive index changes can be obtained at low optical power levels, have attracted great attention for their potential applications in holographic storage and optical communications. The photorefractive properties of optical planar waveguides in Fe:LiNbO3 crystals fabricated by ion implantation are investigated. Two-wave mixing experiments are carried out for both the waveguide and the bulk. The results show that the measured gain coefficients are almost identical for the waveguiding layer and the substrate. In the waveguide, the response time could be reduced by one order of magnitude, with respect to the bulk, at the same power level of the incident light.Photovoltaic photorefractive binary waveguide arrays are fabricated by implantation and selective light illumination on top of an iron-doped near stoichiometric lithium niobate crystal. Linear discrete diffraction and nonlinear formation of gap solitons were investigated by single-channel excitation using Gaussian light beams coupled into either wide or narrow waveguide channels. The results show that, at low power, linear light propagation leads to discrete diffraction, whilst for higher input power the focusing mechanism dominates, finally leading to the formation of gap solitons in the binary waveguide arrays. Our simulation of light propagation based on a nonlinear beam propagation method confirms the experimental findings.Neodymium-doped yttrium lithium fluoride (Nd:YLiF4) is an excellent candidate for low-threshold continuous-wave (CW), mode-locked laser operation due to its many advantages, such as low thermal lensing, large fluorescence linewidth, and natural birefringence. Commercial lasers based on Nd:YLiF4 crystals have been available at wavelength of both 1047 and 1053 nm. Strontium barium niobate (SBN) is a well-known photorefractive crystal that has been successfully used to realize optical amplification, holographic storage, and self-pumped phase conjugation, and also exhibits promising potential applications for optical information processing and optical computing. Recently, another crystal from the same family, calcium barium niobate (CBN) with higher a Curie temperature 280℃has attracted rapidly growing attention for its outstanding ferroelectric and optical properties. We report on the fabrication and characterization of waveguides in Nd:YLiF4, Nd:CBN and SBN crystals by ion implantation. The guided-mode profiles are analyzed by the end-coupling method and numerical simulations. Room-temperature microluminescence investigations reveal the features of waveguides.更多还原