Loss Reduction in a Mesh Waveguide Star Coupler

Abstract

A straight mixing waveguide has been introduced into a mesh waveguide star coupler for the purpose of reducing its excess loss. A preferable structure for a 4 × 4 star coupler has been found by a ray-tracing method. Loss reduction by 3·5 dB compared with a previous structure is demonstrated in an ion-diffused waveguide.     

全息光聚合法制备聚合物波导光栅耦合器

在光通信及集成光学中,光波耦合器是关键器件之一。本文中选择树脂CN960E60单体作为聚合体系,采用自由基型对532nm波长敏感的单光子引发剂,利用全息光聚合法制备出聚合物波导光栅耦合器。在进行聚合实验之前,首先测定了聚合材料的透射光谱。实验观测结果证实了用光全息聚合方法制作波导光栅耦合器的可行性。     

导波器件的宽带声光叉指换能器

研制了一种用于导波器件的宽带声光Ｂｒａｇｇ偏转叉指换能器，并给出了在Ｙ切Ｔｉ：ＬｉＮｂＯ３光波导上的实验结果。     

宽带太赫兹非对称十字孔矩形波导定向耦合器的设计

根据波导定向耦合器原理,设计了一种太赫兹频段,采用非对称十字形孔耦合的矩形波导定向耦合器。通过优化波导结构和十字形耦合孔参数,在WR4波导频段内,实现了稳定的耦合平坦度、良好的方向性和工作带宽。仿真结果表明该型波导定向耦合器耦合度稳定在-19.9d B~-22.0d B之间,方向性优于32d B,相对工作带宽为40%。     

Recording and Analysis of the Radiation Spectrum in the Infrared Band by Means of Bragg Waveguide Gratings

A method of spatial separation of the spectral components of electromagnetic radiation based on the use of waveguide diffraction gratings is proposed. Optimization of the parameters of the detecting part of a spectrum recorder that employs the proposed method is realized by means of numerical simulation.__________Translated from Izmeritel’naya Tekhnika, No. 4, pp. 37–39, April, 2005.     

光栅衍射特性的耦合波分析、计算与讨论

本文从麦克斯韦方程组及电磁场边界条件出发,推导了广泛应用于各类光栅衍射问题的矢量分析方法--严格的耦合波分析方法.针对光栅的衍射特性,编写了基于严格的耦合波分析方法的计算程序,并以TE模情形为例对光栅的衍射效率和收敛性作了数值计算.结果表明,当谐波数不断增加,即便对于厚光栅(d/λ>10)情形,光栅的衍射效率仍将收敛于某一确定值.     

Nonlinearity Compensation of the Fiber Bragg Grating Interrogation System Based on an Arrayed Waveguide Grating

In this paper, we report on nonlinearity compensation for a solid-state fiber bragg grating (FBG) sensor interrogation system based on an arrayed waveguide grating (AWG) device. A lookup table with calibration data is used to improve system linearity. A reduction in the absolute value of the measurement error from 120 mustrain or 15degC to 4.8 mustrain or 0.6degC, respectively, is experimentally demonstrated.     

铁路货车钩缓装置钩尾扁销螺栓断裂原因分析

铁路货车钩缓装置中的钩尾销螺栓在螺杆近方头一侧根部位置发生断裂。采用微观分析方法分析了该螺柱断裂原因。综合分析表明：该断裂螺栓方头一侧可能仅局部加热后锻打成四方头,并发生过热,造成在方头一侧的螺柱根部形成马氏体组织和魏氏体组织过渡的U型区域。不良组织的存在增大了钢的脆性,冷加工性能大大降低,在U型区域和螺柱表面交界处萌生了微细裂纹。当钩尾扁销螺栓在列车运行过程中受到过大的冲击时,该螺栓上的微细裂纹在螺栓靠近方头一侧存在的沿轴向的拉应力和螺栓正常紧固力的合力联合作用下张开并迅速扩展,造成螺栓断裂。     

硅太赫兹波导配置及性能分析

针对现有太赫兹辐射源在输出频率可调性及输出功率方面的局限性。本文从非线性介质的Maxwell方程入手对非线性聚合物的光学性质进行理论分析,建立硅波导配置的数学模型。利用硅材料的高折射率,设计了硅太赫兹波导。分析了太赫兹波导模式图,讨论了硅太赫兹波导模式的有效折射率、波导损耗、连续波输出功率与输出频率的关系,实验结果表明:硅太赫兹波导产生的太赫兹波连续可调,输出太赫兹波频率范围宽至0.1THz到15THz,输出功率可达到微瓦级。     

Polarization Splitting Coupler with Metal Intermediate Layer Theoretical Analysis

Abstract

An analytical model of the polarization splitting coupler with a metal intermediate layer is presented. Fields and propagation constants of the coupler modes are found assuming some specific form of the mode fields. Attenuation characteristics of the coupler are calculated in terms of the local normal mode method.     

Analysis of the reflective-matched fiber Bragg grating sensing interrogation scheme

A technique for the demodulation of fiber Bragg grating (FBG) sensors based on the use of a second wavelength-matched FBG receiver to track wavelength shifts from the FBG sensor is analyzed, particularly regarding its sensitivity as determined by primary noise sources. Numerical and experimental results show that there is an optimum Bragg wavelength difference between the two FBG's that maximizes the sensitivity for this demodulation technique.     

低损耗离子交换玻璃基光波导制备与分析

考虑到离子交换和离子扩散工艺的特殊要求, 设计并熔制了适合于离子交换工艺的硅酸盐玻璃材料SiO₂-B₂O₃-Al₂O₃-R’O-R₂O（R’=Ca, Mg; R=Na, K）. 采用Ag⁺/Na⁺熔盐离子交换和电场辅助离子扩散工艺在这种玻璃材料基片上获得了掩埋式条形光波导. 光学显微镜和电子探针分析表明高折射率的Ag⁺扩散区位于玻璃基片表面以下约10μm处, 形成光波导的芯部. 光波导芯部尺寸约为8μm×8μm, 与单模光纤芯径尺寸相当, 保证了较低的光纤耦合损耗. 对光波导的测量结果得出：在波长为1.5μm处条形光波导的传输损耗约为0.1dB/cm, 与单模光纤的耦合损耗约为0.2~0.3dB. 条形光波导的传输损耗与材料本身的损耗接近, 表现出掩埋式光波导的低损耗特征. 分析表明, 经过进一步优化, 这种光波导制备技术可用于低损耗光波导器件的制作.     

Analysis of nonuniformities of sampled fiber Bragg gratings

We have analyzed the effects of various normally distributed nonuniformities of sampled fiber Bragg gratings on the reflective spectra and group time delay. Through numerical simulations we have drawn the following conclusions: (1) the magnitude of nonuniformity with normal distribution of the fiber's average refractive-index modulation deltaneff greatly influences the characteristics of both reflective spectra and group time delay, whose suggested precision varies from 20% to 10%; (2) the nonuniformities of sampling periods P and sampling lengths L are important factors that influence the characteristics of the group time delay, and the accepted tolerance of dimensional precision of both P and L are +/- 4 microm; and (3) the tolerance of nonuniformity of the sampling period's chirp coefficient is high, and its precision can be as great as 100% with few adverse effects.     

Analysis of chirped-sampled and sampled-chirped fiber Bragg gratings

We analyze sampled fiber Bragg gratings that have chirp in the grating period, in the sampling function, or in both. In the last-named case the sampling period can be chirped, the sample length can be chirped, or both. We explain the features in the spectral and group-delay (dispersion) responses for gratings that have a single chirp parameter. We then show how the response of sampled gratings that have multiple chirp parameters can be explained in terms of the single-chirp parameter cases.     

Analysis of Bragg reflectors by lateral photoluminescence spectroscopy

Abstract

A new method for the rapid determination of layer thicknesses in semiconductor Bragg mirrors for vertical cavity surface emitting lasers (VCSEL) has been developed. The photoluminescence spectrum of a complete VCSEL structure for a wavelength of 980 nm is measured in the wafer plane at room temperature with the excitation being normal to the specimen. In the spectrum from 850 to 1000 nm three regions can be distinguished; the long wavelength part of the spectrum (λ > 950 nm) gives iriformation about the quantum well emission, the shorter part (λ > 850 nm) stems from luminescence of heavily doped p type GaAs. A pronounced structure in the range from 900 to 950 nm arises from constructive interference of light generated in the GaAs layers and leaving the specimen parallel to the surface near the angle of total reflection. From the wavelength of these peaks the layer thicknesses within the Bragg mirror can be calculated with high precision.     

Effect of fabrication errors in channel waveguide Bragg gratings

The spectral performances of nonideal rectangular Bragg gratings, integrated in a rib waveguide, are analyzed by a multilayer approach based on the effective-index method. The effects of errors on the photolithographic definition of the grating, that is, period and shape, and of errors on the control of etching depth are investigated. Also the influence of the stitching error, which is unavoidable when the grating is realized by means of electron-beam photolithography, is addressed. A novel analytical approach that extends coupled-mode theory to the analysis of real gratings is also presented.     

Analysis of Rotation Errors of a Waveguide Rotary-Vane Attenuator

In the Microwave Calibration Services Section of the NBS Radio Standards Laboratory, Boulder, Colo., and analysis of calibration data obtained from measurements made on a rotary-vane type attenuator reveals that the vane alignment produces an inherent vane-angle error. It is found that the standard deviation of the measured values of attenuation is correlated with the vane-angle error. Approximately two-thirds of the attenuators calibrated were in error by less than 50 per cent of the manufacturer's stated specifications of accuracy. The treatment of the errors of a rotary vane attenuator is extended to cover the vane-angle error, resettability error, and mismatch error. The method of analysis is applicable to all attenuation values and vane-angle errors of this sample. Graphs are used to estimate the limits of these errors. Several representative cases are given using the deviation from the "estimated vane-angle error" to establish limits in the correction of vane-angle error. A modified rotary-vane attenuator with a resolution equal to 30 times the resolution of the attenuators comprising the sample was used to verify calculated vane-angle error at various values of attenuation. Inherent vane-angle error can be reduced by increasing the dial resolution and by a technique of precise vane alignment at zero dial setting.     

Analysis of Waveguide Ring Lasers with Nonlinear Directional Outcoupler

Abstract

The waveguide ring laser with the light outcoupled through the nonlinear directional coupler is analysed theoretically. The influence of the characteristic system parameters on the laser radiation for two configurations of the laser is presented. In particular, the stability of the laser radiation is studied in details.     

Analysis of SHG in a Planar Double Waveguide Structure

The possibility of second harmonic generation (SHG) has been analysed for a system of two planar waveguides separated by a barrier. The system has been modelled for ion implanted planar waveguides in quartz. For this system the phase-matching condition can be met for the mode conversions TE y₀ M TE₂ y₂ and TE y₀M TE ₂ y₃. The efficiencies of SHG for the double structure are evaluated by calculating the normalized spatial coupling between the fundamental and harmonic field distributions. We show that the two parallel waveguide system increases the phase-matching possibilities, and depending on the dimensions of the system, it is possible to obtain at least 40% more SH power compared with that from a single well phase match. The influence on the nonlinear response of the barrier is discussed; since in principle, a double well structure with an active barrier could increase the SH power by 400% relative to the single well example.