Scattering characteristics of a beam mode in dielectric-slab optical waveguide

Scattering of the light beam propagating through a dielectric-slab optical waveguide occurs due to refractive index inhomogeneities of the thin film region and due to boundary irregularities of the filmsubstrate and the film-air interfaces. The quantity and direction of the scattered light are evaluated by means of a perturbation method together with the use of a stationary phase method, for a variety of correlation lengths and variances and the thin film thicknesses. The results show that for a slab waveguide of t/=10.0,t and being the thickness of thin film and the wavelength of light, the effect of refractive index inhomogeneities is pronounced in comparison with that of waveguide wall irregularities. In this case, therefore, the scattering pattern is determined mainly by the correlation length of refractive index inhomogeneities.     

Interferometric optical isolator with Si guiding layer fabricated by wafer bonding

An interferometric optical isolator, with a Si guiding layer, employing a nonreciprocal phase shift was studied. The optical isolator was comprised of a magneto-optic waveguide with a magnetic garnet/Si/SiO₂ structure, which was fabricated by wafer bonding technique. The nonreciprocal phase shift in the magneto-optic waveguide with the Si guiding layer was calculated at a wavelength of 1.55 μm. Several kinds of layer structures in the magneto-optic waveguide were discussed.     

Control of the refractive index change in fused silica glasses induced by a loosely focused femtosecond laser

We demonstrate waveguide fabrication using of a loosely focused femtosecond laser that induces both nonlinear ionization and nonlinear propagation in silica glasses without any scanning process. The numerical aperture is chosen to be 0.007 to avoid spatial splitting of the laser pulses during the nonlinear propagation of the femtosecond laser pulses inside the fused silica glass. It also enables a uniform cylindrical refractive index change, which acts as an optical waveguide, to be induced. We found that the induction of irregular refractive index changes is related to the free electron density of the focused area and is controlled by decreasing the NA. The length, position, and core diameter of the fabricated waveguide can be controlled by the pulse-width, energy, and irradiation time of the incident laser. By using this technique, we varied the length of the fabricated waveguides between 20 m and 6 mm, while keeping the core diameter at around 5 m. PACS 42.70.Ce; 42.82.Et; 61.80.Ba     

光波导技术同步测量棱镜及波导薄膜参数

依据全反射理论和棱镜耦合原理,实现了对棱镜折射率及波导薄膜材料折射率和厚度的同步测量。使用高准直半导体激光器激光入射到棱镜内部与波导膜的分界面上,逐步旋转棱镜或改变棱镜的入射角,得到棱镜耦合M线,曲线前面几组的波谷为波导模激发,在M线左侧收尾处有一个不完整波峰,其反射光强随入射角迅速衰减,为全反射时的临界点,由此可实现棱镜及波导薄膜参数的同步测量;用此法测量了棱镜耦合一体化平面波导棱镜的折射率和聚甲基丙烯酸甲酯(PMMA)聚合物波导薄膜的折射率和厚度。测量棱镜折射率精度为±1.9×10-4,波导薄膜折射率和厚度的精度分别为±6.2×10-4 μm和±1.6×10-2 μm。     

利用泄漏波导测量低折射率薄膜的折射率和厚度

根据泄漏波导原理对K_9玻璃基板上的冰晶石薄膜进行折射率测量,达到的精度为1×10~(-4),与真实波导的情况相似。文中讨论了利用添加高折射率薄层减小待测薄膜的最小厚度的可能性。文中还利用光电方法观察反射光中暗条纹的方法判别波导的激发,并测出了冰晶石薄膜在4500到6500范围内的折射率。     

A spectroscopic prism coupler for measuring the refractive indices and thicknesses of dielectric films

A spectroscopic prism coupler is created for measuring refractive indices n_f and thicknesses H_f of dielectric films. The operating principle of the device is based on the simultaneous resonance excitation of several waveguide modes in a film by a focused TE or TM polarized light beam in the geometry of frustrated total internal reflection. Calculations of n_f and H_f are performed using measured angular positions θ_m of dark m-lines in the cross section of the specularly reflected beam. Using obtained angles θ_m, we can calculate effective refractive indices β_m of modes. By solving a set of nonlinear dispersion equations for the modes of a planar waveguide, we can calculate refractive index n_f and thickness H_f of a film. The proposed prism coupler has no moving parts and allows us to measure the optical parameters of films 0.5–10 μm thick in the 400–1100 nm range of wavelengths. The device can also be used as a spectroscopic refractometer for measuring the refractive indices of bulk media. The device is used to measure refractive index and thickness of a SiO film and the refractive index of TF4 glass.     

Design and optimisation of high-brightness 980 nm laser diodes with distributed phase correction

Designs for 980 nm Al _x Ga_1–x As/In_0.2Ga_0.8As/GaAs high-power, high-brightness semiconductor lasers/amplifiers with distributed phase correction and short-cavity lengths (i.e. cavity lengths 560–1040 m) are presented. The proposed lasers/amplifiers employ a single mode feed waveguide coupled to a power amplifier with a laterally graded effective refractive index (GRIN) profile to control the lateral mode shape and phase. The lateral index of the power amplifier has a hyperbolic secant (HYSEC) profile, which can be approximately realised by tailoring the effective refractive index of the amplifier using a series of discrete etches. The epitaxial and structure designs of the laterally discretised GRIN lasers/amplifiers are presented. Finally, a method for improving the effective refractive index discretisation is described.     

InP阵列波导光栅的误差分析

在InP阵列波导光栅的制作过程中会引入不同的误差,从而影响器件的性能.为了最大限度地控制误差,提高半导体器件性能,本文采用传输函数法对InP基阵列波导光栅的系统误差和随机误差分别进行了分析.从系统误差的模拟结果中可以得到如下结论:深脊型波导的有效折射率n_c平均每偏移+0.000 1,中心波长偏移+0.05nm.相邻阵列波导长度差ΔL每偏移+0.01 μm,中心波长将偏移+0.44 nm.n_c和ΔL仅仅会影响到传输谱中心通道及其他各通道对应的波长,使得传输谱发生整体漂移,而信道间隔及串扰不会改变.罗兰圆半径R偏移不会影响器件的中心通道对应的波长,但会使其它通道对应的波长发生变化,最终使得信道间隔改变,R增加50 μm,信道间隔减小0.03 nm.从随机误差模拟结果中,得出:波导芯区折射率、上包层折射率、衬底折射率、波导宽度和波导芯层厚度的随机波动会对阵列波导光栅的串扰产生较大的影响.根据以上分析,可以通过控制不同参量来调节器件的中心波长以及信道间隔等来优化阵列波导光栅的光学性能.     

Experimental analysis of metal coated dielectric waveguides

This paper concerns the experimental characteristics of metal coated dielectric waveguides with a rectangular surface corrugation. Waveguide are designed to operate at a second Bragg frequency of 90 GHz. The period, height and the duty cycle of a rectangular grating were calculated using the chosen frequency. A metallic layer of aluminum is sputtered on one side of the slab waveguide. The purpose of the metallic layer is to simulate a layer of high density plasma on the surface of the waveguide similar to that obtained by optical excitation of semiconductor structures. Experiments were performed to examine the far field radiation pattern, attenuation constant and the dispersion relation. Due to the presence of the plasma layer there will be an angular shift in the far field radiation pattern. We have observed angular shifts of about 20 in the radiation pattern of the waveguide before and after coating. Measurements are made in the frequency range of 88–95 GHz. This waveguide structure can be used to design an electronically steerable antenna and an electronic phase shifter operating in the millimeter-wave frequency band.Supported in part by the Army Research Office.     

Guide/antiguide optical intensity modulator

An electrorefractive index-controllable guide/antiguide optical intensity modulator has been created and characterized. The operating mechanism, beam propagation method simulation, device design and fabrication, and calculated and experimental results of this guide/antiguide modulator are given. The operational principle of the modulator is based on the field-induced waveguide (FIG) concept; that is, electric-field-induced refractive index changes cause the waveguide to be turned on and off electrically. The modulator is formed with a central narrow FIG electrode sandwiched between two antiguide electrodes. The electrooptic effects, along with carrier effects, have been exploited to adjust the refractive index under the guide and adjacent antiguide electrodes by changing reverse biases applied to them. The modulation is determined mainly by changing the lateral refractive index profiles. In the on state, a waveguide is formed under the central electrode, and the input light propagates along this waveguide. To realize the best off state, an antiguide situation is created that causes the light to diffract out of the central guide rapidly. An on/off ratio larger than 23 dB, a propagation loss 1 dB, and a record optical bandwidth from 1.0 to 1.55 m have been obtained for this modulator.     

Polymeric optical waveguides using direct ultraviolet photolithography process

Single-mode polymeric channel waveguides were fabricated using simple direct ultraviolet photolithography process. A cross-linkable negative tone epoxy NANO^TM SU-8 2000 polymer was used. Once exposed to ultraviolet light through a photomask, the waveguide stripes were obtained upon development. The polymer has many desirable properties, such as high refractive index, good adhesion to substrate, optical transparency in the infrared wavelength region, and high glass transition and high thermal decomposition temperatures. Properties of the optical waveguides were characterized, and there is an excellent agreement between measured data and theory. The values of dn/dT and waveguide birefringence are -1.87×10^-4 /°C and 10^-4, respectively, and are comparable to those of halogenated acrylate polymers. With an overcladding layer, the propagation losses measured are 0.25 and 0.28 dB/cm at 0.8 m, 0.62 and 0.77 dB/cm at 1.31 m, and 1.25 and 1.71 dB/cm at 1.55 m for TE and TM polarizations, respectively. PACS 42.70.Jk; 42.79.Gn; 42.82.Et; 42.82.-m     

光栅-液晶复合结构太赫兹移相器

随着太赫兹技术及其应用的快速发展,各类太赫兹控制器件需求也随之增加,作为太赫兹系统重要器件之一,太赫兹波移相器成为当前研究热点。已有移相器存在着尺寸较大、结构复杂、相移量较小等问题,为克服上述缺陷,提出一种光栅-液晶复合结构太赫兹移相器,该器件结构为石英、石墨烯、液晶盒、光栅结构、石墨烯和石英组成。通过改变石墨烯电极上电压,使液晶折射率发生改变,相移器的相位因折射率改变而发生变化,通过控制外加电压可以实现对太赫兹波相移量有效调控。计算结果表明,该移相器在0.39~0.46 THz频率范围内实现了400°相移量,回波损耗小于-11 dB,在频率0.43 THz处,最大相移量达到422°。太赫兹波入射角在0°~30°范围内变化,移相器的相移量保持不变,而且该器件对入射太赫兹波偏振态不敏感。所设计的太赫兹移相器具有相移量大、结构尺寸小等优点,在未来的太赫兹通信、安检、医疗、传感、成像等领域中具有广阔的应用前景。     

一种新型高功率微波相移器

 研究了一种新型高功率微波相移器同轴插板式相移器,其设计思想为：在同轴波导内插入金属导体板,将同轴波导分为几个扇形截面波导,由于扇形截面波导中传输的TE₁₁模相速度与同轴TEM模的相速度不同,通过改变插入金属板的长度就可以实现相移的调节。设计了中心频率为4 GHz的同轴插板式相移器,并进行了数值模拟验证。结果表明：当相移器同轴波导内半径为2.0 cm,外半径为4.5 cm,相移器总长度为50 cm时,可实现的最大相移量为360°,在3.9~4.1 GHz频率范围内相移器的插入损耗低于0.1 dB。     

Low-n mesoporous silica films: structure and properties

The properties and structure of mesoporous silica films are investigated. Because of their extremely low refractive index (n=1.14), these films are interesting optical waveguide supports. The films have been synthesized by a template-modified sol–gel process using the triblock copolymer Pluronic P123. A significant dependence of the formed structure on the processing conditions has been revealed, allowing an appreciable structure tuning. One set of processing conditions allows the reproducible synthesis of low-n films. They are optically clear, mechanically and chemically resistant, extremely smooth, and sufficiently thick (1 m). Under other processing conditions a novel mesoporous layer structure was synthesized that has very large and well-defined nanoscopic voids. PACS  61.30.Pa; 68.37.Ps; 78.20.Ci     

Beam Steering Type of 1 : 4 Optical Switch Using Thermo-Optic Effect

We propose a beam steering type optical switch employing a phase shifter. It consists of collimating waveguide mirrors, an arrayed-waveguide which has deep trenches incorporating polymer materials, and input/output waveguides. The incident light is guided to the front mirror, where it is then collimated, and input to the arrayed waveguide. The number of trenches filled with polymer linearly increases in order. The refractive index of the polymer can be controlled with temperature, and the propagation direction of the output light from the arrayed waveguide can also be controlled. A switch with 15 waveguides in the array has been fabricated. The chip size is about 2:5 × 9:0 mm², the insertion loss is 10 dB, and the extinction ratio is about 10–13 dB.     

Demonstration of Optical Isolator with CeY2Fe5O12 Guiding Layer Employing Nonreciprocal Phase Shift

A waveguide optical isolator with a CeY2Fe5O12 guiding layer employing a nonreciprocal phase shift was studied.The isolation ratio of more than 12.2 dB was achieved at a wavelength of 1.55 μm.     

TE0导模干涉刻写周期可调亚波长光栅理论研究

通过棱镜耦合激发非对称金属包覆介质波导结构中的TE₀导波模式, 利用两束TE₀模的干涉从理论上实现了周期可调的亚波长光栅刻写. 分析了TE₀模式的色散关系, 刻写亚波长光栅的周期与激发光源、棱镜折射率、光刻胶薄膜厚度及折射率之间的关系. 用有限元方法数值模拟了金属薄膜、光刻胶薄膜和空气多层结构中TE₀导模的干涉场分布. 研究发现, 激发光源波长越短, TE₀ 模干涉刻写的亚波长光栅周期越小; 光刻胶越厚, 刻写的亚波长光栅周期越小; 高折射率光刻胶有利于更小周期亚波长光栅的刻写. 相较于表面等离子体干涉光刻, 基于TE₀ 模的干涉可在厚光刻胶条件下通过改变激发光源、棱镜折射率、光刻胶材料折射率、特别是光刻胶薄膜的厚度等多种方式实现对亚波长光栅周期的有效调控.     

980nm半导体激光器n型波导结构优化

为了提高980nm半导体激光器的输出功率并获得较小的远场发散角,在非对称波导结构的基础上设计了n型波导结构,即在n型波导中引入高折射率的内波导层。采用理论计算和SimLastip软件模拟对常规非对称波导结构和内波导结构进行了研究。利用分子束外延系统生长980nm内波导结构的外延材料,并制作了激光器。对于条宽为100μm、腔长为1000μm的器件,阈值电流为97mA,斜率效率为1.01W/A;当注入电流为500mA时,远场发散角为29°(垂直向)×8°(水平向),与模拟结果相符。理论计算和实验结果表明:较之于常规非对称波导结构,内波导结构可有效降低光场限制因子,提高输出功率,减小远场发散角。     

Formation of channel optical waveguides in polymethylmethacrylate with embedded electro-optic chromophore DR13 by the photoinduced bleaching method

A composite polymeric material based on polymethylmethacrylate (PMMA) with embedded electro- optical (EO) chromophore DR13 is designed. Irradiation with electromagnetic radiation in the visible range leads to a bleaching of the composite and its refractive index n decreases due to the irreversible photodestruction of the chromophore. Changes in the absorption spectrum and refractive index of the composite with the irradiation time are measured. It is shown that the change in n depends on the concentration of DR13 in the polymer matrix and can reach a value of Δn = 0.034 in the telecommunication C-range near a wavelength of 1.55 μm. The rate of bleaching depends on the wavelength of the actinic light and reaches its maximum when the wavelength is near the maximum of chromophore absorption. With the use of the photobleaching method and the PMMA/DR13 composite, channel waveguides and the other elements of the integrated optical devices are fabricated, including waveguide splitters, directional couplers, and Mach–Zehnder interferometers. This simple one-step method does not involve the removal of polymer material by liquidphase or reactive ion etching.     

Design and fabrication of multi-channel photodetector array monolithic with arrayed waveguide grating

We have provided optical simulations of the evanescently coupled waveguide photodiodes integrated with a 13-channels AWGs. The photodiode could exhibit high internal efficiency by appropriate choice of layers geometry and refractive index. Aseamless joint structure has been designed and fabricated for integrating the output waveguides of AWGs with the evanescently coupled waveguide photodiode array. The highest simulation quantum efficiency could achieve 92% when the matching layer thickness of the PD is 120 nm and the insertion length is 2 μm. The fabricated PD with 320-nm-thick matching layer and 2-μm-length insertion matching layer present a responsivity of 0.87 A/W.