增加表面等离子体波导中慢光的传播长度研究

因为金属内部的吸收损耗,表面等离子体波导的应用受到了阻碍.通过在电介质芯中引入非线性材料,提出了参量增益机制来补偿纳米尺寸金属-绝缘体-金属(MIM)波导中的传输损耗.有限差分时域法( FDTD)进行仿真结果表明,使用此方法群速度为0.005c的慢光的传播长度显著增加到为原来的四倍.     

Characterization of Silver/Polystyrene (PS)-Coated Hollow Glass Waveguides at THz Frequency

Finite-element analysis based on the full-vectorial H-field formulation has been established as one of the most powerful and accurate modal solution approaches for optical guided-wave devices. Among the available optical waveguides, those incorporating thin metal layers supporting the surface plasmon modes (SPMs) and coupling of these modes to dielectric modes have recently been proven to be attractive for many applications. In this paper, the H-field approach incorporating the perturbation technique is used in calculating the complex propagation characteristics of silver/polystyrene (PS)-coated hollow glass waveguides for terahertz frequency radiation. The propagation and attenuation characteristics of the SPMs at the metal/dielectric interfaces are presented. The formation of the coupled supermodes and the effect of the PS coating thickness on the attenuation characteristics of these waveguides are also investigated and shown to be critical to their design optimization.     

Circular Bends in Dielectric Frame Beam Waveguides (Short Papers)

An investigation is described on circular bends in beam waveguides constituted by dielectric frames. A uniform bending of the guide axis is obtained by tilting each frame by a small angle; however, due to the phase correction performed by the dielectric frame, the losses introduced by the bending can be made lower than those of an analogously bent iris waveguide. A numerical analysis is performed on the basis of the analogy between beam waveguides and open resonators which permits the assessment, in a number of cases, of the maximum permissible amount of tilting and the corresponding optimum frame dimensions in view of acceptable losses. The losses due to mode conversion are also evaluated when considering the connection between a straight and a curved section of the waveguide.     

Planarization properties of hydrogen silsesquioxane (HSQ) influence on CMP

Low dielectric constant materials are now required as intermetallic dielectrics to reduce RC delay in advanced technologies. Hydrogen silsesquioxane (HSQ) is a spin-on dielectric with a dielectric constant around 3. Local planarization of HSQ and its impact on the global planarization due to CMP process was studied. Local planarization of HSQ and its impact on the global planarization due to CMP process was studied. When lines and spaces are equal, HSQ shows a good planarization for lines smaller than 20 μm. In this case, the HSQ thickness on metal line is equal to 2500 Å, which is the minimum which can be obtained for this metal thickness and HSQ deposited. For various environments of the metal line HSQ planarizes better for small lines in a dense zone created by an array of lines or plates of metal. For the CMP process the planarization is good for small lines, as for HSQ but in an array of lines only. Plates must be totally prohibited for CMP process. Finally, for an intermetal dielectric including HSQ the goal of CMP is no more a local planarization as for gap fill but a large scale intra-die planarization.     

Flexible,Low-loss Waveguide Designs for Efficient Coupling to Quantum Cascade Lasers in the Far-infrared

We coupled linearly polarized and azimuthally polarized Terahertz quantum cascade lasers (QCLs) to the low-loss optical modes of hollow core waveguides having a sequence of different metallic or dielectric inner coatings. The latter waveguides have been specifically designed to force the propagation of a dominant optical mode once the thickness (d) of the inner dielectric coating is properly chosen. Our results demonstrate that both the TE01 and the TE11 modes can be easily converted to a hybrid one when d > 6 μm allowing the propagation of THz QCL beams with transmission losses as low as 1.5 dB/m, bending losses < 1.1 dB and reasonably high coupling efficiencies (87%).     

Transmission characteristics of germanium thin-film-coated metallichollow waveguides for high-powered CO2 laser light

Various losses such as straight waveguide losses, coupling losses from a CO₂ laser, and bending losses are studied. The authors studied the fact that high-powered CO₂ laser light could be transmitted through germanium-coated waveguides and investigated beam profiles from straight or bent waveguides. To ascertain the application of the waveguide in wavelengths other than 10.6 μm, the authors investigated the wavelength-dependent losses of the waveguide excited by incoherent IR light. As a result, the thickness of the deposited germanium layer can be very precisely obtained     

MDM光波导激发高阶SPP模的传输特性

研究了金属-介质-金属(MDM)型表面等离子体激元(SPP)光波导的电磁特性。理论计算结果表明,对于633nm的TM偏振入射光,当介质膜层厚度小于85nm时,波导中只能激发产生一阶SPP模(基模),其余高阶模全部截止。随着介质膜厚度增加,高阶SPP模逐渐被激发产生。当介质膜层厚度较小时,SPP模的有效折射率的实部随阶数的增加而减小,而虚部则随阶数的增加而增加,SPP基模具有最大传输距离。然而,当MDM波导中的介质层厚度超过0.555μm时,由于三阶SPP模的电磁场主要集中在离金属层相对较远的介质层中,其有效折射率的虚部具有最小值,具有最大的传输距离,而非基模。当入射光波长为633nm介质层厚度为0.9μm时,Ag/SiO2/Ag光波导中三阶SPP模的传输距离达到约150μm。     

Proton-exchanged optical waveguides in Z-cut LiNbO3 using phosphoric acid

Proton-exchanged Z-cut LiNbO₃ planar waveguides formed using phosphoric acid were characterized optically. The refractive index profile and the diffusion parameters were studied systematically. These waveguides have propagation losses of less than 1 dB/cm and exhibit properties that are different from those obtained using benzoic acid. The index profile is not a simple step function and can be modeled accurately by a polynomial expression. A maximum surface index increase of 0.145 was measured at a 0.633-μm wavelength. The diffusion constant D₀ and the activation energy Q for the proton-exchange process using this acid were found to be 6.43×10⁸ μm²/h and 82.91 kJ/mol, respectively. The annealing properties of these waveguides were also established, and the effects of annealing on surface index change and waveguide depth increase were found to follow a power-law relationship     

Losses in Dielectric Image Lines

The dipole mode in a dielectric rod permits an image system in which half the dielectric and its surrounding field are replaced by a metal sheet. If the field is allowed to extend many wavelengths outside the rod, the resulting line has very low losses. The contribution of the image surface to line loss is calculated, and shown to be generally less than the dielectric loss. Radiation from obstacles along the line is also discussed. Such obstacles in closed single-mode waveguides are useful for matching purposes. Although matching elements are easily constructed for the image line, radiation loss proves difficult to control.     

Metal–Dielectric Slot-Waveguide Structures for the Propagation of Surface Plasmon Polaritons at 1.55 μm

We present a deep-subwavelength-size metal slot-waveguide structure which can efficiently propagate surface plasmon polaritons (SPPs) at 1.55 mum within a high-index material. Through a systematic design analysis, we investigate the intrinsic tradeoffs and suggest solutions to substantially increase the propagation length of SPPs combining high-index dielectrics and metal structures. By studying several metal/dielectric geometries, we have found that the slot-waveguide size can be significantly decreased by the use of high-index materials without compromising the overall propagation losses. Our analysis also indicates that the device size-scaling is ultimately limited by a cutoff thickness for the metal film in which the slot is defined. For film thicknesses below cutoff, radiation modes exist which leak out of the guiding region. For certain operating frequencies, the radiant energy leaks out into both free space modes as well as surface plasmons guided along the top/bottom metal surfaces of the device. We have shown that, by using a silicon filling, the cutoff thickness of a 100-nm-wide slot waveguide can be as small as 90 nm, compared with 750 nm for the unfilled reference structures. In addition, we have demonstrated that by the use of SiO₂ gap regions surrounding the Si dielectric core in a 200times400-nm silver slot region (partially filled metal slot), we can considerably reduce the overall propagation losses to less than 0.14 dB/mum, corresponding to a propagation length of approximately 50 mum     

基于SPP的1550纳米光波导的超长传输特性

采用严格电磁理论研究了介质-金属-介质型光波导激发表面等离子激元(SPPs)的电磁特性,对比分析了SPP波在SiO2/Ag/SiO2和Si/Ag/Si光波导的传输距离。研究表明,对于1550nm光通信波长入射光及10nm厚的金属银膜层,SiO2/Ag/SiO2光波导中非对称SPP的传输距离可达40cm,明显高于对称SPP波的传输距离,也显著高于非对称SPP波在Si/Ag/Si波导中的传输距离,具有超长传输距离;随着金属层厚度的增加SPP波的传输距离明显减小,当银层厚度超过50nm后,非对称的SPP在SiO2/Ag/SiO2及Si/Ag/Si波导中的传输距离趋于一致,约为200nm;此时银层厚度变化对SPP波传输距离的影响明显减弱。     

A Combined Method for Dielectric Waveguides Using the Finite-Element Technique and the Surface Integral Equations Method

A combined method employing a finite-element technique in the H/sub x/ - H/sub y/ formulation and the surface integral equations method is proposed to treat the propagation characteristics of inhomogeneous waveguides with single or multiple claddings. The significant features of this combined method are that it does not suffer from any kind of spurious modes, which have been troublesome in applying the finite-element technique to waveguides and it is also capable of treating the cutoff frequencies of arbitrarily shaped, inhomogeneous dielectric waveguides with a single cladding, which is perhaps original. Furthermore, the proposed method is convenient in treating propagation constants close to cutoff and in handling coupled waveguides. Numerical results of inhomogeneous elliptical waveguides, diffusion waveguides, and the corresponding directional couplers are presented, including the cutoff frequencies of the elliptical waveguides.     

Calculation of bending losses in dielectric waveguides usingeigenmode expansion and perfectly matched layers

In this letter, we present a different approach to accurately calculate the bending losses in curved dielectric waveguides. It is based on the well-known conformal transformation of the index profile and on vectorial eigenmode expansion, but this time with perfectly matched layer (PML) boundary conditions to accurately model radiation losses. The modal spectrum of these waveguides in the presence of PML is discussed and the method is validated by comparing it to previously published results     

Helix Leaky Waveguide

The propagation characteristics of leaky waves in a helix waveguide covered with a slitted cylinder are presented by a method of transverse network representation. The main interest is in helix waveguides with small pitch angles, characterized by a hybrid mode consisting of TE/sub 01/, and a small amount of TM/sub 01/ modes. The leaky wave discussed in this paper may then be regarded as a perturbation of the TM/sub 01/ wave by the slitted cylinder outside the helix. The radiation, metal, and dielectric losses are calculated numerically at a frequency of 50 GHz. The relation between the radiation loss and aperture angle of slit is very different from that of an ordinary leaky waveguide composed of a slitted cylinder without helix, especially when the distance between the helix and shield cylinder is about a quarter of the radial wavelength. The metal and dielectric losses are the same order as radiation loss, however the dielectric loss decreases as the power factor /spl epsiv/"/ /spl epsiv/' increases. The measured total attenuation constant averages about 5 dB/km, almost twice the theoretical value.     

基于贝塞尔函数数值求解平面光波导的弯曲损耗

为了数值求解平面光波导的弯曲损耗,首先给出了平面弯曲光波导的传输模型。基于这种模型,使用基于求解贝塞尔函数的方法数值求解出平面光波导的弯曲损耗。为了验证该方法的准确性,将计算得到的弯曲损耗结果与以往的实验结果相比较,结果表明,在弯曲半径较大的情况下两者基本吻合。     

GaAs/GaAlAs curved rib waveguides

Curved dielectric optical waveguides suffer from radiation loss due to bending. To minimize the bending loss and reduce the radius of curvature, it is necessary to fabricate guides which provide strong optical confinement. This paper gives a brief review of curved waveguide analysis and presents some experimentally measured loss values for GaAs/GaAlAs curved rib waveguides. The rib waveguides, fabricated using ion beam milling, have a large rib height and are tightly guided structures. When corrected for reflection losses and input coupling efficiency, a minimum loss of approximately 3 dB has been achieved for a multimode 90° curved guide with a radius of curvature of 300 μm, and 8.5 dB for a single-mode curved guide with a radius of curvature of 400 μm. It is believed that most of this residual loss is not radiation loss due to bending, but rather scattering loss due to rib wall imperfections.     

Numerical optimization procedure for low-loss sharp bends in MgOCo-doped Ti:LiNbO3 waveguides

Recent results provided experimental evidence that losses in bent Ti:LiNbO₃ waveguides can be drastically reduced by using additional titanium and magnesium oxide. We determine an optimization procedure for the index profile in curved sections. The beam propagation method indicates that in optimized bends, losses are orders of magnitude below those of conventional bends. Tolerances in mask alignment and in deposited film thickness are estimated to be well compatible with present technology     

Metal-Clad Multilayer Waveguide: Circle-Chain Convergent Method and Two Perturbation Methods

Computer modeling studies for the calculation of the propagation constants and attenuation coefficients of TE mode in an asymmetric metal/ dielectric/dielectric layers structure are presented. Two different perturbation methods, circle chain convergent method and Downhill method are used. The last two methods can be used easily for the waveguides consist of any number of layers with complex refractive index due to gain and loss. The developed programs were run on a personal computer and numerical results are presented.     

Dishing-radius model of copper CMP dishing effects

Copper chemical-mechanical polishing (CMP) dishing concerns semiconductor manufacturing yield in contemporary back-end-of-the-line process. In this work, we first propose and validate a dishing model through first-principle analysis and carefully designed experimentation. This model utilizes the novel concept of dishing radius, a metric that assumes cylindrically shaped post-CMP copper surface and directly captures the extent of metal dishing for a CMP process. Additionally, a dishing-model-based method for extracting the parameterized two-dimensional post-CMP metal profile is developed for damascene structures. The case study utilizing this method shows that the extracted parameters are in good agreement with those from cross-sectional scanning electron microscopy and surface profilers, which confirmed that dishing radius is linewidth-independent for typical metal lines. This method is particularly useful in determining dishing artifacts, which are modeled using the dishing radius concept. The approach is nondestructive, precise, and efficient.     

A Surface Integral Equations Method for Homogeneous Optical Fibers and Coupled Image Lines of Arbitrary Cross Sections

Based on the surface integral equations, a novel method is developed to treat the propagation characteristics of homogeneous optical fibers of arbitrary cross sections in both the rigorous vectorial and the approximate scalar formulations. This method is ready to be generalized to the cases of multiple dielectric waveguides, such as the coupled dielectric image lines used in microwave integrated circuits. Further, Green's function at cutoff is presented so that the corresponding cutoff frequencies can be treated. Numerical results of propagation characteristics of single and double waveguides are presented in both the vector and solar forms.