硅基结构混合等离子激元波导模式特性的数值研究

首先建立了一种由相同宽度的金属带,SiO2间隔层与Si介质脊构成的导体-夹层-硅基结构(Conductor-Gap-Silicon,CGS)的混合等离子激元波导模型,分析了间隔层的厚度以及波导宽度对模式传输特性的影响,提出了模场面积为0.08 m2与430 m传输距离的设计方案.在此基础上,通过增加数值模型中介质脊的宽度而形成硅基板CGS波导结构.数值分析结果表明:硅基板CGS波导可将模式有效折射率增至2.8,同时传输长度能够延长到1.74 mm.并且模场面积可以进一步压缩到0.025 m2.此外,硅基板CGS波导制作更加简便,并可采用现有COMS制作技术完成,进而具有较大的实用前景.     

中红外波段高速硅基电光调制器设计与优化（特邀）

作为中红外波段中最接近O波段和C波段的波段,2 μm波段区域逐渐引起人们的广泛关注。主要对2 μm波段的马赫-增德尔型调制器进行优化设计和仿真,根据2 μm波长下光模场分布的特点,选用具有340 nm厚度顶层硅的SOI衬底,结合实际工艺中240 nm硅刻蚀深度,得到宽度为600 nm以及平板层厚度为100 nm的最优脊波导结构。通过优化掺杂浓度和掺杂区位置获得综合性能最优的调制器器件,在4 V反向偏压下器件光损耗为5.17 dB/cm,调制效率为2.86 V·cm,静态消光比为23.8 dB,3dB EO带宽为27.1 GHz。同时,与220 nm厚度顶层硅器件相比较,器件的综合性能更为优越。研究内容为后续器件实际制作提供了依据,也为后续2 μm波段光收发集成模块所需调制器设计提供了新的方向。     

高速硅基单端推挽驱动狭缝脊波导调制器

针对硅基单端推挽驱动调制器的脊波导pn结部分结电容较大,限制了调制器带宽进一步提高的问题,提出了一种狭缝脊波导pn结结构。通过将脊波导pn结蚀刻一定尺寸的狭缝,降低了pn结电容,实现了带宽的提升。对两种pn结进行了仿真对比,结果表明,在相同电极结构与掺杂条件下,狭缝脊波导调制器比脊波导调制器的电光带宽提升了约8.3 GHz。基于优化的单端推挽驱动狭缝脊波导调制器,仿真实现了90 Gbit/s的OOK信号调制,眼图消光比为14.69 dB。     

Fourier transformation using an electroabsorptive CCD spatial light modulator

The use of a GaAs CCD as a spatial light modulator is described and its application to coherent optical Fourier transformation is analyzed. In this device, the transmission through the two-dimensional buried-channel CCD may be electroabsorption modulated near the GaAs cutoff wavelength since the electric field in each storage well is controlled by the transferred charge. One of the primary advantages of this modulator is the ability to electrically address the device at high speed. Analysis of the two-dimensional modulator with a silicon CCD detector array yields a projected dynamic range approximately equal to the number of modulator array elements. For arrays containing greater than 1000 elements, detector performance and nonuniformities can limit the maximum range to 30-40 dB. The device can also be optically addressed, and in this mode of operation it has a comparable dynamic range to the electrically addressed structure with an optical write energy an order of magnitude lower than liquid crystal or photorefractive light valves. An alternative mode of device operation is a waveguide mode in which the light propagates along an epitaxial layer and is modulated as it passes under a one-dimensional CCD. The detection is done by a second linear CCD. The higher modulation efficiency results in a dynamic range approximately one hundred times the number of elements but is again limited to 30-40 dB because of detector response and nonuniformities.     

Integration of an electrooptic polymer in an integrated opticscircuit on silicon

This paper presents the joining of active nonlinear polymer waveguides with passive silicon nitride waveguides (SiO₂-Si ₃N₄-SiO₂) to form an integrated Mach-Zehnder modulator with a lateral electrode configuration on a silicon substrate. Passive and active waveguides are based on a silicon-nitride-strip guiding structure. In the active waveguide a nonlinear polymer layer is used to obtain an index modulation via the electrooptic effect. Despite the silicon nitride strip based guiding structure, 63% of the energy of the fundamental mode is guided in the nonlinear polymer (provided by Flamel Technology, Venissieux, France). Poling with field strengths up to 75 V/μm applied to the lateral electrodes has been employed to orient the chromophores. A half wave voltage of 35 V has been measured for an electrooptic coefficient of 5.8 pm/V at a wavelength of 1.3 μm. Optical loss measurements have been done on polymer and passive waveguides. The best results have been 1.8 dB/cm for the active and 0.78 dB/cm for the passive waveguides leading to a total loss of 6 dB for a modulator with an interaction length of 2.5 cm. The coupling loss between a laser diode and the passive waveguide structure was measured to be at least 4.6 dB using a microscope objective and piezo-electric displacement elements. Stability tests under atmospheric conditions have shown a decrease of the electrooptic coefficient which might be due to the hygroscopic behavior of the active polymer. The bandwidth of the modulator has been determined to be 4 MHz     

级联槽型腔表面等离子体滤波器

提出一种中心波长随槽型腔腔长线性变化、透射率随耦合距离可调的级联腔表面等离子体滤波器。该滤波器由输入波导、两个级联的介质槽型腔和输出波导组成。通过级联两个相同的槽型腔,共振模被分离从而实现窄带的双通道滤波器;进一步调节输出波导的位置,能够将双通道分离,实现单通道的滤波。通过时域有限差分法和耦合模理论对模型进行仿真分析,结果表明,该滤波器的最小半高宽低至20nm。同基于单槽型腔的滤波器相比,半高宽显著减小。     

Propagation Properties of a Modified Slot Surface Plasmonic Waveguide

In this paper, we present a modified slot surface plasmonic waveguide formed by metallic rod, core dielectric layer, and metallic film on the substrate. Using the finite-difference frequency-domain method, modal field distribution are analyzed firstly. Results show that the fundamental mode could be well confined in the space between the metal rod and the metal film. The dependence of modal field distribution, effective index, and propagation length of the fundamental plasmonic mode without gain on dielectric constant of the core layer, geometrical parameters, and working wavelengths are analyzed and discussed. A kind of available gain dielectric medium was used for the core dielectric layer to extend the propagation length. Results show that the propagation length can be extended observably with the help of the gain dielectric medium. Finally, effect of the thickness of the core dielectric layer on modal field distribution, effective index, and propagation length are analyzed and discussed. Since the modal field distribution, effective index, and propagation length can be controlled by adjusting the geometrical parameters, dielectric constant and gain of the core layer and working wavelengths of the waveguide, this kind of surface plasmonic waveguide can be applied to the field of photonic device integration and sensors.      

A high-drop hole-type photonic crystal add-drop filter

Based on the effect of total internal reflection（TIR）and photonic band gap,a new type of hexagonal-lattice hole-type silicon photonic crystal add-drop filter is proposed with a large circular hole as inner ring.The single mode operation is realized by compressing the two rows of photonic crystal above and below the line defect waveguide.Two-dimensional（2D）finite-difference time-domain（FDTD）method is then applied to investigate the impacts of side length of inner ring and coupling strength on its drop efficiency.It is also fairly compared with the traditional inner ring structure composed of hexagonal-lattice holes.The results show that the proposed structure can offer higher spectral selectivity than the traditional one.Two channel wavelengths of 1.425μm and 1.45μm can be simultaneously dropped at corresponding ports with drop efficiency of more than 90%and quality factor of 900 in the proposed configuration when the width of bus waveguide,the side length of inner ring and the coupling strength are 0.8 3 a,4a and 0,respectively,where a is the lattice constant.     

Low-loss, single-model optical phase modulator in SIMOX material

This paper reports results of the simulation of an optical phase modulator. The proposed modulator consists of an elongated p-i-n structure fabricated in a silicon-on-insulator material such as SIMOX. It utilizes the free-carrier effect to produce the desired refractive index change in a single-mode optical rib waveguide. The MEDICI two-dimensional semiconductor device simulation package has been employed to optimize the overlap between the injected free carriers and the propagating optical guided mode. Although the device is designed to support a single optical guided mode, it measures several micrometers in cross-sectional dimensions, thereby simplifying fabrication and allowing efficient coupling to/from other single-mode devices. Furthermore, the device has an extremely high figure of merit, predicting over 200° of induced phase shift per volt per millimeter, as well as a low drive current of less than 10 mA. This is approximately an order of magnitude lower than most other reported devices in silicon     

Mode coupling between dielectric and semiconductor planar waveguides

Computer modeling studies on four-layer silicon-clad planar dielectric waveguides indicate that the attenuation and mode index behave as exponentially damped sinusoids when the silicon thickness is increased. This effect can be explained as a periodic coupling between the guided modes of the lossless structure and the lossy modes supported by the high refractive index silicon. Furthermore, the attenuation and mode index are significantly altered by conductivity changes in the silicon. An amplitude modulator and phase modulator have been proposed using these results. Predicted high attenuations in the device may be reduced significantly with a silicon dioxide buffer layer.     

混合表面等离子体光子晶体波导

构建了一种金属-绝缘体-半导体混合表面等离子体结构,基于时域有限差分法验证了该结构在归一化频率0.243~0.271 (a/λ) 范围内具有明显的TM模式带隙。在二维光子晶体层移除或改变中间行空气孔半径构成线缺陷,形成混合波导结构1和2。分析表明,入射光频率位于带隙内的光子能量被很好的局域在低折射率层中,且只能沿线缺陷传输。当入射波长为1550nm时,两种波导的传输距离分别为18.41μm和15.70μm,群速度极值分别为0.186c和0.166c,品质因数FoM达到384.74和1042.50。此波导能通过光子晶体层的线缺陷控制低折射率层SPP的传输路径,为波导器件的研究提供了有效的理论基础和依据。     

Ridge Waveguide Electro-Optic Polymer Modulator with a New Kind of Corona Poled Crosslinkable Polyurethane

制备了一种全部以聚合物为波导材料的电光调制器,其中芯层为新型可交联极化聚胺脂电光功能材料．旋涂制备波导薄膜、电晕极化产生非线性、光刻和氧反应离子刻蚀完成脊波导为主要的工艺步骤。1.3μm光源光纤耦合输入脊波导调制器,得到很好的输出端单模近场图及清晰的低频调制信号．     

Bilevel mode converter between a silicon nanowire waveguide and a larger waveguide

A bilevel mode converter is analyzed for providing low-loss coupling between the small fundamental mode of a silicon nanowire waveguide and the larger mode of a conventional silicon-on-insulator (SOI) rib waveguide. The bilevel converter can also be used to improve the coupling efficiency between a lensed fiber and a silicon nanowire waveguide. The mode converter consists of two tapers formed at different levels. The top taper comprises a parabolic and sine taper, which is optimized to improve the mode conversion efficiency. Numerical analyses are given by using a three-dimensional semivectorial beam propagation method. The design has good tolerance against misalignment of the two masks needed for the double etch.     

Non-polarization and high-coupling-efficiency coupler using multilevel grating structure

A multilevel grating coupler based on silicon-on-insulator (SOI) material structure is proposed to realize the coupling between waveguide and waveguide or waveguide and fiber. This coupler is compatible with the current fabrication facilities for complementary metal oxide semiconductor (CMOS) technology with vertical coupling. This structure can realize coupling when the beams with transverse electric (TE) polarization and transverse magnetic (TM) polarization are incident at the same time. The influences of the grating coupler parameters including wavelength, the thickness of waveguide layer, the thickness of SiO₂ layer and the number of steps on the TE mode and TM mode coupling efficiencies are discussed. Theory researches and simulation results indicate that the wavelength range is from 1533 nm to 1580 nm when the TE mode and TM mode coupling efficiencies are both more than 40% as the grating period is 0.99 μm. The coupling efficiencies of the incident TE and TM modes are 49.9% and 49.5% at the wavelength of 1565 nm, respectively, and the difference between them is only 0.4%.     

High-speed silicon electrooptic Modulator design

An electrically driven Mach-Zehnder waveguide modulator based on high-index contrast silicon split-ridge waveguide technology and electronic carrier injection is proposed. The excellent optical and carrier confinement possible in high-index contrast waveguide devices, together with good thermal heat sinking and forward biased operation, enables high-speed modulation with small signal modulation bandwidths beyond 20 GHz, a V/sub /spl pi// times length figure of merit of V/sub /spl pi//L=0.5 V/spl middot/cm and an insertion loss of about 4 dB. The modulator can be fabricated in a complementary metal-oxide-semiconductor compatible way.     

Finite Element Analysis of Lossless Propagation in Surface Plasmon Polariton Waveguides With Nanoscale Spot-Sizes

We present simulation results on the propagation characteristics of active plasmonic waveguides at 1.55 mum wavelength based on semiconductors as the active gain media. Three waveguide structures were investigated: metal rib, metal-semiconductor-metal (MSM), and triangular metal groove. In all three structures, we observed strong plasmon mode confinement with nanoscale spot-sizes and corresponding simulated gain values compatible with existing semiconductor technology. We show the effect of systematic modification of waveguide geometry on the required gain for achieving lossless propagation in all the three plasmonic waveguide structures. We demonstrate that lossless propagation with subwavelength spot sizes well below the diffraction limit of light can be obtained by controlling the geometrical parameters of the proposed waveguides.     

GaAs-on-Si modulator using a buried silicide reflector

A surface-normal GaAs quantum-well absorption modulator has been produced atop a silicon wafer that has been implanted with Co and annealed to form a silicide layer. The silicide layer functions as a mirror allowing reflection mode operation. This substantially reduces the thickness of the modulator compared to devices with AlGaAs-AlAs multilayer reflector stacks. A contrast ratio of 2.5 was obtained with 25 V operation     

TM-pass polarizer based on multilayer graphene polymer waveguide

A TM-pass polarizer based on multilayer graphene polymer waveguide is proposed and theoretically analyzed. The mode properties, the extinction ratio, the insertion loss and the bandwidth are also discussed. The results show that a TM-pass polarizer, which only guides the TM mode, can be achieved by multilayer graphene polymer waveguide. With length of 150 μm, the proposed polarizer can achieve extinction ratio of 33 dB and insertion loss of 0.5 dB at optical wavelength of 1.55 μm. This device has an excellent performance, including large extinction ratio and low insertion loss within the spectral range from 1.45 μm to 1.6 μm.     

Heavily doped silicon:A potential replacement of conventional plasmonic metals

The plasmonic property of heavily doped p-type silicon is studied here.Although most of the plasmonic devices use metal-insulator-metal(MIM)waveguide in order to support the propagation of surface plasmon polaritons(SPPs),metals that possess a number of challenges in loss management,polarization response,nanofabrication etc.On the other hand,heavily doped p-type silicon shows similar plasmonic properties like metals and also enables us to overcome the challenges pos-sessed by metals.For numerical simulation,heavily doped p-silicon is mathematically modeled and the theoretically obtained re-lative permittivity is compared with the experimental value.A waveguide is formed with the p-silicon-air interface instead of the metal-air interface.Formation and propagation of SPPs similar to MIM waveguides are observed.     

Integrated-optic focal-spot intensity modulator using electroopticpolymer waveguide

A novel integrated-optic focal-spot intensity modulator comprising an electrooptic (EO) phase-distribution modulator and a focusing grating coupler (FGC) in an EO polymer planar waveguide on a Si substrate is proposed and demonstrated. The integrated phase-distribution modulator is made up of three-finger top electrodes and a planar bottom electrode sandwiching the waveguide. The electrodes are used for both the poling process and the modulation of the phase distribution of the guided wave. The FGC couples the guided wave to a beam focused on a point in free space. The intensity distribution of the focused spot is modulated by altering the wavefront of the guided wave. The bottom metal electrode is extended to the place under the FGC and serves as a reflection film so that the output coupling occurs only into the direction of the air for increasing the efficiency. The device was designed and fabricated with an active polymer p-NAn-PVA (p-nitroaniline n-polyvinyl alcohol). An extinction ratio of the focal-spot intensity was higher than 3 dB at a modulation voltage of 30 V for 3-mm-long electrodes. The frequency response was measured to be flat over 2 MHz. The EO effect induced by poling showed no significant relaxation over 300 h in an unconditioned room (20-30°C)