Guiding Modes of a Slab Waveguide Composed of Impedance-Matched Single Negative Materials

The properties of guiding modes of a slab waveguide composed of impedance-matched $epsilon $ (permittivity) negative and $mu $ (permeability) negative media were investigated. This special type of waveguide supports only a single mode having polarization degeneracy: transverse-electric (TE)- and transverse-magnetic (TM)-polarized light waves always have the same propagation wavevectors. However, the overall power flow directions of these degenerate TE and TM modes are always opposite to each other.      

Compact Variable ${rm TE}$-${rm TM}$ Polarization Splitter Based on Simplified Coherent Coupling in Lithium Niobate

A compact-sized electrically tunable ${rm TE}$- ${rm TM}$ mode splitter composed of a mode converter and an asymmetric Y-branch structure is presented. The asymmetric Y-branch consists of a straight and a bent waveguides to split two polarization modes based on the mode-sorting effect. To shorten the device length, a simplified coherently coupled-bending structure is utilized for the bent waveguide. Experimental results show that the device length is reduced about 52%, extinction ratios of both ${rm TE}$ and ${rm TM}$ modes are higher than 25 dB, yet the applied voltage is not significantly increased.      

Ultrashort Polarization Splitter Using Two-Mode Interference in Silicon Photonic Wires

An ultrashort polarization splitter based on the zero-gap directional coupler is proposed and realized. Its interference section is 8.8 $mu$m long. It is also shown that the length of the interference section can be reduced to about 2.1 $mu$m. The crosstalk for both transverse-electric (TE) and transverse-magnetic (TM) polarizations is 16 dB at a wavelength of 1.55 $mu$m. The extinction ratios of TE and TM polarizations are 18.2 and 13.7 dB, respectively. The device has 3-dB bandwidth of 43 nm in TE polarization and 50 nm in TM polarization with the center wavelength at 1.55 $mu$ m.      

A polarization independent GaAs-AlGaAs electrooptic modulator

Two designs for polarization independent GaAs-AlGaAs interferometric electrooptic modulators are described. One design uses the linear electrooptic effect to couple degenerate TE/TM eigenmodes of a single-mode waveguide. In the other design the eigenmodes need only be near degenerate. The design using the coupling between near degenerate TE/TM modes utilizes a novel biasing scheme. A novel polarization independent GaAs-AlGaAs interferometric optical modulator based on this design has been fabricated and characterized at 1.3 μm. This modulator is fabricated as a traveling wave modulator incorporating 50 Ω, phase velocity matched, low microwave loss electrodes for maximum electrical bandwidth     

Integrated-Optic Polarization Controlling Devices Using Electro-Optic Polymers

Integrated-optic polarization controlling devices such as polarizers, polarization splitters, and polarization converters, are proposed and demonstrated in nonlinear optic polymers. Poling-induced birefringence in electro-optic polymers is exploited to fabricate the devices. The polymeric waveguide polarizers show low excess losses, and extinction ratios of 20.7 dB and 17.1 dB for TM-pass and TE-pass polarizers, respectively. The polymeric waveguide polarization splitters exhibit TE-TM mode splittings with crosstalk of 14.2 dB and 10.1 dB for TM and TE mode splittings, respectively. The polymeric waveguide polarization converters show successful TE/TM polarization mode conversion with conversion efficiencies of higher than 30 dB. The device employs poling-induced waveguides which have slowly rotating azimuth angle of optic axis along the light propagation direction. The novel polarization converter is insensitive to wavelength and easier to fabricate than the other polarization converters containing periodic structures.     

Incoupling waveguide hologram with reduced polarization sensitivity

An incoupling waveguide hologram (IWGH) with significantly reduced polarization sensitivity was designed and fabricated in InP for 1550 nm wavelength. The IWGH couples the light from an optical fiber, irrespectively of the state of polarization, into the InP waveguide and simultaneously focuses it to a desired position in the waveguide. Conventional IWGHs are strongly polarization sensitive with a measured 19 dB difference in the incoupling efficiency between the TE and TM mode. In contrast, although some design parameters turned out to be slightly in error, the fabricated IWGHs designed for reduced polarization sensitivity exhibited a 3.1 dB difference in the incoupling efficiency between the TE and TM modes     

Design of three-dimensional silica on a silicon single-mode single-polarization waveguide

We present a design of three-dimensional(3D) silica on a silicon single-mode single-polarization waveguide (SMSPW) by taking into consideration the induced birefringence effect of the silica.This can cut off the TM mode and transmit the TE mode.The characteristics of the light propagating across the polarization maintaining waveguide were simulated by 3D beam propagation methods(3D-BPM).The result showed that the SMSPW has a high extinction ratio over 50 dB for the TM mode.Without increasing the complexi...     

硅基二氧化硅单模单偏振光波导的设计

在不增加工艺难度的前提下,利用硅基二氧化硅光波导的双折射效应并结合有效折射率方法, 设计了一种新型单模单偏振波导, 使得两个正交偏振模式中的TM 模式被截止, TE 模式可以通过. 利用三维有限差分光束传输法(3D -BPM ) 进行数值模拟,结果显示,对于TM 模式消光比可高达到50dB 以上.此种结构的光波导可以直接制作偏振器, 同时还易与其他波导器件集成.     

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%.     

交叉型TE/TM模分离器的研制

采用光束传播法（ＢＰＭ）计算了交叉型ＴＥ／ＴＭ模分离器的偏振串音（ｃｒｏｓｔａｌｋ）。通过结构参数的优化，理论计算的偏振串音为－２３．７ｄＢ（ＴＭ）和－２２．８ｄＢ（ＴＥ）。同时制成相应的器件，测试结果表明，理论计算与实验是一致的     

Measurement of depolarization ratio and ultimate limit ofpolarization crosstalk in silica-based waveguides by using a POLCR

A polarization optical low coherence reflectometer (POLCR) is described that enables us to excite only the transverse electric (TE) mode of a test waveguide and to measure its Rayleigh backscatter signal distributions in the TE and transverse magnetic (TM) modes at a spatial resolution of 0.3 mm. The depolarization ratios of silica-based waveguides with relative refractive index differences of Δ=0.45 and 0.75% are obtained as 0.14 and 0.10, respectively, by measuring the bias in the ratio between the distributions in the TM and TE modes of each waveguide. By using the depolarization ratios and the Rayleigh backscatter signal levels, we calculate the ultimate polarization crosstalks to be -53 and -51 dB over 1 km, respectively. The actual polarization crosstalks of previously fabricated waveguides are about 50 dB higher than their ultimate limits for the same length of fiber     

Polymeric waveguide polarization splitter with a buriedbirefringent polymer

A waveguide polarization splitter is demonstrated based on a low-loss polymer waveguide and a birefringent polyimide. Crosslinkable fluorinated polymers with an excellent stability and a low absorption loss are utilized for the device. The polyimide is buried under one branch of the Y-branch waveguide to enhance the birefringence between the TE and TM modes. By the adiabatic mode evolution, the TE mode is coupled to the branch with the polyimide strip, while the TM mode propagates through the other branch without the polyimide. For the device with a branch angle of 1/400 rad, we obtained a crosstalk less than -20 dB and a fiber-to-fiber insertion loss of 3.8 dB     

Scattering at Circular-to-Rectangular Waveguide Junctions

A formally exact solution is given for the problem of scattering at a circular-to-rectangular waveguide junction and at a thick diaphragm, with a centered circular aperture, in a rectangular waveguide. The method uses normal TE and TM mode expansions of the waveguide fields and traditional mode matching of the transverse electric and magnetic fields at the junction boundary. Exact closed-form expressions are obtained for the electric field mode-matching coefficients which couple the TE(TM) modes in the rectangular guide to the TE(TM) and TM(TE) modes in the circular guide. Numerical results are presented for the case of TE/sub 10/ mode propagation in the larger rectangular guide with all other modes cutoff. Convergent numerical results for the equivalent shunt susceptances of such junctions are obtained when about 12 modes (eight TE and four TM) are retained in the circular waveguide or in the circular aperture of the diaphragm. The results are graphically compared with formulas and curves due to the quasi-static theory of Bethe and the variational theory given in the Waveguide Handbook [2].     

New polarization-insensitive antiresonant reflecting opticalwaveguide (ARROW-B)

A type of antiresonant reflecting optical waveguide (ARROW-B) is proposed to reduce the polarization dependence of propagation loss in ARROW. A low-loss propagation (<1 dB/cm) for both transverse electric (TE) and transverse magnetic (TM) modes is demonstrated. The features of the conventional waveguide, ARROW, and ARROW-B are summarized. The conventional ARROW is advantageous in constructing some functional devices such as a waveguide-type polarizer or wavelength demultiplexer. On the other hand, the ARROW-B seems to be suitable for applications requiring a primarily polarization-insensitive function, such as optical interconnection     

对称单负材料平面波导的波导模

基于经典电磁理论建立了芯层为单负材料的对称三层平板波导的导波方程,采用图解法研究了该波导中的TE和TM波导模,分析了TE波导模和TM波导模会受波导参数μ1/μ2和R的影响,给出TE模和TM模解的横向场分布图.结果显示,在单负材料的对称三层平板波导中只存在慢波导模,TE慢波模只能在磁负材料中传播,TM慢波模只能在电负材料...     

Electrooptic polymer modulators operating in both TE and TM modes incorporating a vertically tapered cladding

We propose a modified electrooptic (EO) PMMA polymer waveguide structure supporting both TE and TM modes in spite of the large birefringence induced by the poling. A vertically tapered structure is employed to connect a single-mode rib waveguide and a confinement-enhanced rectangular buried waveguide. This waveguide structure can be easily fabricated by a two-step reactive ion etching (RIE) process with a shadow mask. To demonstrate TE/TM confinement and single-mode operation, Mach-Zehnder intensity modulators are fabricated by incorporating the proposed waveguide structure. The extinction ratio is better than -15 dB, which proves the single-mode operation. Half-wave voltages for TM and TE modes are 6 and 24 V, respectively.     

Integrated optical waveguide polarizer based on photobleaching-induced birefringence in an electrooptic polymer

A TE-pass waveguide polarizer is fabricated by utilizing the photobleaching-induced birefringence at room temperature in an electrooptic polymer. The polarizer consists of the photobleached waveguide supporting only TE mode, which is integrated in the middle of the etched rib waveguide supporting both TE and TM modes. It has a simple structure and requires no high temperature process like poling. The measured polarization extinction ratio is about 21 dB at the wavelengths of 1.3 and 1.55 /spl mu/m, and the estimated excess loss is about 0.4 dB.     

Exact derivation of the coupling coefficient in corrugated waveguides with rectangular tooth shape

An exact analysis, based on local field expansion, is used in order to calculate the coupling coefficient in corrugated waveguide structures having rectangular tooth shape and small tooth height. In particular, the coupling coefficients for TE field polarization and TM field polarization are derived. It is shown that the expression for the TE coupling is identical with previous results based on the coupled wave formalism and on other techniques as well. This is a consequence of the formal validity of the equivalent index method for TE polarized waves. In the case of TM coupling, the equivalent index method does not hold and the expression for the coupling coefficient deviates significantly from the results obtained by the coupled mode formalism.     

Radiation loss coefficients of asymmetric dielectric waveguides with shallow sinusoidal corrugations

Kiselev [10] has solved the boundary equations for an asymmetric slab waveguide with a shallow sinusoidal corrugation, and derived explicit, closed expressions for the TE radiation loss coefficients of various waveguide geometries. For many practical applications in integrated optics, the Rayleigh assumption justifying the boundary-matching procedure and the approximations of linear perturbation analysis employed in this derivation are both satisfied. We have extended this procedure to TM modes and found that the expressions for both TE and TM modes in all of the geometries so treated agree identically with those derived by coupled-mode theory. The dependence of the TM radiation loss coefficient in each waveguide geometry on the grating period, radiation angle, refractive index profile, and mode polarization is illustrated graphically, and compared with its TE counterpart.     

矩形波导中电磁场分布特征研究

波导内电磁场结构复杂,为了解矩形波导中电磁场分布特征,由矩形波导中的TM波和TE波场方程确定波导空间任意时刻、任意位置各分量量值,进而确定空间任意位置电场和磁场矢量的指向,模拟出波导截面和纵剖面的TM11波和TE11波的电磁场分布图。模拟结果得出的结论符合实际,正确地反映了矩形波导中电磁波传播特征,对了解波导中电磁场特性具有重要意义。