Silicon-on-insulator irregular waveguide mode converters

Irregular waveguide elements in a silicon-on-insulator platform that allow new device concepts are introduced. Specific designs are achieved using a multiresolution optimization strategy where the waveguide width is varied in stepwise increments. Simulation results are given for high-efficiency waveguide mode converters, power splitters, and waveguide transitions operating at 1.55 microm. The degrees of freedom available permit these functions and small dimensions, making these devices candidates for optical integrated circuits.     

Polarization mode conversion in YIG rib waveguide

This paper describes the experimental results on the orthogonally polarized mode conversion in a YIG rib channel waveguide, in which a small magnetic field induced around the electrode deposited on the waveguide was used. The dependence of mode conversion efficiency on the coupling length and the effect of a d.c. bias field applied to the waveguide were investigated. The Faraday rotation angle of the fabricated YIG rib channel waveguide was found to be 160° cm^–1, which was a reasonable value compared with that in the YIG planar waveguide reported previously. Furthermore, an increase in conversion efficiency and a decrease in switching time were found in the presence of a d.c. magnetic bias field.     

Polarization mode conversion in an optical microdisk resonator vertically coupled to a waveguide bus

Due to the existence of non-zero, and asymmetrics cross-polarization coupling coefficients between a microdisk and a waveguide bus, high Q (∼10,000) overcoupled microdisks with minimal internal losses and sharp bending curvature (small radii) vertically coupled to a narrow-width ridge waveguide can be engineered as a proper candidate for a narrow-band polarization rotator. A semi-analytical calculation method is presented to realize microdisk-waveguide system as a polarization rotator.     

94 GHz回旋管过模波导模式转换与传输

 在耦合波理论的基础上,研究了94 GHz回旋管内置TE₀₃-TE₀₂-TE₀₁模式转换器和外接的TE₀₁-TE₁₁模式转换器。采用半径渐变微扰和轴线微扰几何结构以及不同的相位重匹配技术进行优化分析,得到了可靠的最优几何参量,设计出了紧凑、高效的94 GHz波纹波导模式转换器和蛇形线模式转换器。回旋管的热测实验中测出的模式样图表明,所设计的内置模式变换器有效地实现了TE₀₃-TE₀₂-TE₀₁的模式转换。     

94 GHz回旋管过模波导模式转换与传输

在耦合波理论的基础上,研究了94 GHz回旋管内置TE03-TE02-TE01模式转换器和外接的TE01-TE11模式转换器。采用半径渐变微扰和轴线微扰几何结构以及不同的相位重匹配技术进行优化分析,得到了可靠的最优几何参量,设计出了紧凑、高效的94 GHz波纹波导模式转换器和蛇形线模式转换器。回旋管的热测实验中测出的模式样图表明,所设计的内置模式变换器有效地实现了TE03-TE02-TE01的模式转换。     

高功率圆波导TE0n-TE11模式变换研究

 在模式耦合理论的基础上，详细讨论了波导轴线弯曲与波导半径渐变的圆波导模式变换，并对TE_0n-TE₁₁模式变换器的几何结构进行了优化分析，采用不同的相位重匹配技术，得到了可靠的最优几何参量。以此数据设计的8mm回旋速调管TE₀₁-TE₁₁模式变换器的转换效率可达98%。     

TE-TM模变换型光波导隔离器的理论研究

利用微扰理论研究了TE-TM模转换型光波导隔离器的自相位补偿. 从相位同步和功率转换解释了这种器件的工作原理, 揭示了两个模转换器相位 失配与模转换比例的关系, 数值仿真结果与理论分析相符, 证实了模转换型 波导隔离器中的自相位补偿理论.     

高功率圆波导TE0n-TE11模式变换研究

在模式耦合理论的基础上,详细讨论了波导轴线弯曲与波导半径渐变的圆波导模式变换,并对TE0n-TE11模式变换器的几何结构进行了优化分析,采用不同的相位重匹配技术,得到了可靠的最优几何参量。以此数据设计的8mm回旋速调管TE01-TE11模式变换器的转换效率可达98%。     

Optical pulse propagation in an irregular waveguide with spatially distributed Kerr-like nonlinearity

A nonstationary two-dimensional problem of propagation of a femtosecond pulse in a planar waveguide comprised of linear and nonlinear sections connected in series is solved using the finite-difference method. The accuracy of the finite-difference techniques is analyzed as applied to solution of stationary and nonstationary two-dimensional quasi-linear equations of light propagation in step-index waveguides. The effects of wave instability on the dynamics of the spatiotemporal pulse distribution in a nonlinear waveguide are studied. It is shown that, due to the retarded nonlinear response of the medium and the dependence of the group velocity of the pulse on its intensity, radiation continuously leaks from the fiber core to the cladding as the pulse propagates along the fiber.     

Simulation of low-frequency sound propagation in an irregular shallow-water waveguide with a fluid bottom

A further development of a previously proposed approach to calculating the sound field in an arbitrarily irregular ocean is presented. The approach is based on solving the first-order causal mode equations, which are equivalent to the boundary-value problem for acoustic wave equations in terms of the cross-section method. For the mode functions depending on the horizontal coordinate, additional terms are introduced in the cross-section equations to allow for the multilayer structure of the medium. A numerical solution to the causal equations is sought using the fundamental matrix equation. For the modes of the discrete spectrum and two fixed low frequencies, calculations are performed for an irregular two-layer waveguide model with fluid sediments, which is close to the actual conditions of low-frequency sound propagation in the coastal zone of the oceanic shelf. The calculated propagation loss curves are used as an example for comparison with results that can be obtained for the given waveguide model with the use of adiabatic and one-way propagation approximations.     

Mode conversion in helix loaded waveguide

Forward coupling of a fast TE-like mode is an interesting and desirable option in the gyro-TWT amplifier. We consider in this paper a mode conversion at the abrupt junction of two infinitely long sheath-helix-loaded waveguides. A helix mode traveling from the left to the right side excites fast TE-like modes are numerically calculated by taking dominant terms in the into TE-like modes are numerically calculated by taking dominant terms in the eigenmode-expansion method. The bandwidth (3 dB) for TE-mode-like coupling in the second (right-hand-side) waveguide is found to be over 40$.     

Acoustooptic collinear TE-TM mode conversion in a two-layer Ti-indiffused and proton-exchanged waveguide structure in LiNbO3

Acoustooptic collinear TE-TM mode conversion was investigated in a two-layer Ti-indiffused and proton-exchanged waveguide structure in LiNbO₃. A very narrowband interaction of only 130 kHz (0.31 nm optical bandwidth) was achieved with about 25 mW acoustic power for 96% conversion efficiency. This structure is especially suitable for constructing novel-type acoustooptical gas sensors.     

Spatial structure of the coherence parameter of the sound field in an irregular arctic waveguide

Results of numerical simulation of the total and coherent sound fields and the coherence parameter for a multimode acoustic signal excited by a monochromatic sound source and propagating in an irregular arctic waveguide are presented. Expressions used as the basis for the algorithm of the sound field calculation by the method of coupled normal modes are given. Both regular and stochastic sound scattering by horizontal inhomogeneities of the bottom, water medium, and ice cover are taken into account. It is found that, in the course of sound propagation in an arctic waveguide, an anomalous variation of the energy coherence parameter of the sound field as a function of distance is observed. This variation manifests itself in the form of local peaks of the field coherence parameter. This fact should be taken into account in both the measurements of the ice cover characteristics by acoustic methods and the evaluation of the efficiency of the operation of receiving arrays.     

Mode conversion and absorption in an optical waveguide under cascaded complex modulations

We investigate the mode conversion in a dielectric waveguide under spatially complex modulation, which refers to modulating both the real and imaginary parts of the dielectric permittivity. The complex modulations are applied separately in two distinct regions in the waveguide. The mode conversion can be controlled by adjusting the initial phase difference of the modulations in the two cascaded regions and by varying the phase difference of real and imaginary modulations in each region. The former is analogous to an Aharonov–Bohm (AB) phase and the latter suggests a symmetric propagation phase. Comparing to one modulated region, the cascaded modulations could benefit to realizing laser, coherent perfect absorber, and bidirectional invisibility. The study may contribute to the applications in optical switches and mode converters.     

Interrelation between ray and mode field representations in an acoustic waveguide

Some well-known results obtained by Brekhovskikh, Felsen, Tindle, Guthrie, and other authors during their studies of the interrelation between modes and rays in a plane-layered waveguide are briefly discussed. The relationships that extend these results to the case of a waveguide with large-scale inhomogeneities of the refractive index are analyzed. It is shown that in the presence of inhomogeneities, the groups of the constructively interfering modes, as in the case of a plane-layered waveguide, also form contributions of individual rays. In this case, fluctuations of the amplitudes of normal modes can be described by simple ray formulas, which are the mode analogs of the relationships of geometric optics and the smooth perturbation method.Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 38, Nos. 1–2, pp. 115–121, January–February, 1995.