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在前两篇论文中,作者提出了一种求解缓变系数一阶常微分方程组的数学方法——“缓变系数法”,从而建立了多波型波导本地简正波的广义理论。但是,该文所提的理论没有考虑到波导参数突然变化的情形,而这在任何实际的传输系统中是不可避免的。本文的目的是从耦合简正波理论的观点来研究波导特性的突变。这样,就使本地简正波的概念能够用来描述更多的波导传输问题。 相似文献
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对曲折圆形槽波导新型慢波系统的高频特性进行了研究,通过理论分析和数值计算,得到了它的色散曲线和耦合阻抗表达式,并分析了结构参数变化对色散特性和耦合阻抗的影响。研究表明:当周期变小时色散减弱,耦合阻抗增加;而增大直波导长度时色散变弱,但同时耦合阻抗也会下降。因此较小的周期有利于改善曲折圆形槽波导慢波电路的高频特性。鉴于这种电路的耦合阻抗较低,可以适当地减小直波导长度来提高耦合阻抗。曲折槽波导结合了曲折波导散热能力强、色散特性好、容易加工和槽波导单模工作、低损耗、大尺寸等优点,在毫米波及亚毫米波段的行波管中具有较好的发展前景。 相似文献
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在本文中作者提出了耦合本地正规波型的广义理论;它建立在作者在另一篇论文中提出的数学方法——“缓变系数法”的基础上。为了说明这种方法的应用,依次解出了考虑两个及三个耦合波型的缓变曲率波导弯曲问题。在两个耦合波型的情形下,所得结果与Louisell及Unger已得结果相符合。三个耦合波型的问题在以前的文献中尚未讨论过。本文讨论了所提出的理论及数学方法在其它方面的应用。 相似文献
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本文将无源的不规则波导看作有源的理想波导,求等效极化电流电场,直接得到单一光波导模间耦合和辐射损耗问题的解。用这个方法计算了阶跃单模光纤折射率轴向不均匀变化的损耗。这种方法完全脱离了耦合波的概念,它不但物理意义明确,而且求解问题的方法简洁。最后以单模光纤弯曲和微弯损耗为例,说明等效电流方法还适用于广义耦合波理论才能求解的问题。 相似文献
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根据耦合波理论,推导出轴对称渐变波导中, 考虑波导壁损耗时的多模传输时域耦合波方程组,并给出该方程组中各模式间耦合系数的具体表达式。据此编写了渐变波导中多模传输特性数值模拟程序。利用该程序计算了在THz波段圆波导中的模式衰减,在THz波段研究波导中的多模传输特性时,必须考虑波导壁的阻抗损耗影响。数值分析了直波导中的模式耦合问题,从而证实了波导壁有限电导率能产生模式耦合这一耦合机制。介绍了利用该程序数值分析波导耦合器和过渡器中多模传输特性的两个例子,利用该程序可对波导耦合器和过渡器中的多模传输特性进行数值模拟分析,进而对结构进行设计和优化。 相似文献
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第十三章集成光学和纤维光学 13.1.4 波能的耦合光从一元件传输到另一元件是通过辐射耦合方式完成的。当光从辐射源进入光波导和从光波导输入到探测器时,就会出现耦合问题,当光从一波导输入另一波导的时候,在这两个光波导之间也会出现这个问题。实现这种耦合可以采用多种机理。 相似文献
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This paper proposes a cutoff waveguide Ion-Cyclotron Range of Frequencies (ICRF) coupler in heatings of fusion plasma for large tokamaks. Structures of tokamaks do not permit enough aperture areas for using cylindrical waveguides in the propagative region. However, if the power source to excite the coupler is located near its aperture, electromagnetic power is expected to pass through the cutoff region as a tunnel effect and radiate into the fusion plasma. We calculate characteristics of the normalized radiation power and the input impedance for this cutoff waveguide coupler, regarding its aperture as a slot. Numerical results show that the cutoff waveguide coupler has a few million watts handling power when the effective dielectric constant of the plasma is between 60 and 100. Experiments for a one-tenth model of actual size are performed using air and water instead of the fusion plasma. Measured input impedance showed a fine agreement with the theory for typical ones. Furthermore, experiments verify that its input impedance can be controlled by the location of a short-circuiting plunger. All these results suggest that the cutoff waveguide coupler is very attractive for ICRF heating. 相似文献
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For development of complementary metal–oxide–semiconductor (CMOS)-compatible integrated optical circuits, vertical directional coupling between a hybrid plasmonic slot waveguide and a Si waveguide is theoretically investigated in detail. To determine the vertical separation gap and efficient coupling length, we investigate the characteristics of the even and odd supermodes at a wavelength of 1.55 μm. The vertical coupler transfers 90% of the power carried by the Si waveguide to the hybrid plasmonic slot waveguide after normalizing to reference waveguides when the gap is 60 nm and the coupling length is 2.6 μm. Because of the lossy hybrid guided mode in the plasmonic waveguide, the transmitted power exhibits damped sinusoidal behavior depending on the overlapping length. The proposed vertical coupler shows more efficient light coupling between a dielectric and plasmonic waveguide in comparison to the other types of hybrid coupler, and can be exploited further for on-chip integrated opto-electronic circuits. 相似文献
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The design of a vertical directional coupler between a three-dimensional plasmonic slot waveguide and a silicon waveguide is theoretically investigated in detail. It consists of two steps: the design of isolated plasmonic slot waveguide and silicon waveguide and the determination of the gap between the two waveguides and the length of a coupling region. The designed structure transfers 70.8% of the power carried by the silicon waveguide mode to the plasmonic slot waveguide mode when the gap is 150 nm and the coupling length is 2.14 μm. The wavelength dependence of our vertical directional coupler is also studied. The analysis shows that the amount of the transferred power changes slightly over a very wide wavelength range between 1.40 μm and 1.61 μm. Moreover, if we employ the fabrication technology for silicon photonics, it is quite tolerant to the variation of the length of its coupling section. Finally, the vertical directional coupler is considered for a polarizer. 相似文献
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用两段式波导模型研究3dB宽带光纤耦合器 总被引:1,自引:0,他引:1
报道了用两段式组合波导模型分析研究3dB宽频带熔锥型单模光纤耦合器。根据文献[1]用两根阶跃型单模光纤,使其中一根光纤的熔锥区腐蚀变细,熔融拉锥成两段式的准双锥体组合波导,分别用变分理论和传统的耦合波理论分析横截面近似不变的腰部区域和横截面随从向距离变化的梯度区域内的耦合行为,耦合器的耦合功率是这两段区域耦合功率的叠加。从而得到了耦合器中任意点的耦合功率表达式。用光纤参数和适当的组合波导横截面尺寸 相似文献
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Optical sensing by silicon slot-based directional couplers 总被引:1,自引:0,他引:1
A theoretical investigation of an optical liquid sensor, based on asymmetric directional coupler employing slot optical waveguides, is carried out. The sensing principle is based on the shift in the waveguide transmitted spectrum induced by analyte refractive index change. Silicon-on-insulator technology has been assumed in sensor design, and sensor modelling is carried out by using the coupled modes theory and the finite element method. The influence of geometrical parameters on the sensor characteristics has been investigated. A minimum detectable refractive index change of the order of 10?6 can be theoretically predicted. 相似文献
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Zhefu Zhong 《International Journal of Infrared and Millimeter Waves》1995,16(10):1837-1844
The numerical analysis for millimeter wave slot type coupler of overmode waveguide cavity is studied by mode-matching taking account of the thickness of the plate on which the slot is cut. It is found that the higher modes in cavity can be suppressed by proper thickness of the plat and proper dimension of the output waveguide. 相似文献
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The scope of the spectral index method for solving general planar waveguiding problems is analysed by first showing how simple it is to set up a closed-form transcendental equation whose solution is very accurate; the solution is so fast that the method can be used as a subroutine, making it possible to solve many two-dimensional problems fully, even for coupled rib waveguides, without using effective index approximations. The method is then extended to the uniformly buried waveguide of rectangular cross-section, and the corresponding coupler, thereby unifying the effective index, transverse resonance and spectral index methods for the first time, and giving an asymptotic expression for the coupling length without using overlap integrals. Finally, sample numerical results and optical field profiles are given for the rib waveguide and rib waveguide coupler. 相似文献
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In this Letter, we propose general optimization methods to design broadband high-efficiency grating couplers for planar waveguides. We attribute the coupling bandwidth to the mismatch of effective indices between the diffracted beam and the actual grating structure around the operation wavelength for fiber to waveguide excitation. The coupling bandwidth formula is deduced. A simple parameter-separate optimization procedure is proposed for general layered grating couplers for high coupling efficiency. Using our principle, we optimized a grating coupler for a horizontal slot waveguide operating at wavelength 1.55 μm for TM polarization. The grating coupler has 1 dB bandwidth of 60 nm and coupling efficiency of 65% with incident light from single-mode optical fiber (SMF) at 8°. 相似文献