Stigmatically focusing grating coupler

A grating coupler that couples out a spherical wave (stigmatic beam) from a planar optical waveguide is experimentally demonstrated. This kind of grating coupler is formed ho-lographically using two cylindrical waves with mutually perpendicular focal lines.     

基于表面等离子波耦合的流体波导光栅耦合器

提出了一种由金属光栅和流体光波导结构组成的,基于表面等离子波耦合的光栅耦合器。利用光栅的衍射效应,将金属光栅与介质分界面之间产生的表面等离子波耦合到流体光波导中,并且能够沿着流体光波导稳定地向前传播。通过采用基于有限时域差分算法的FDTD Solutions软件对光栅耦合器进行了参数优化及特性分析,通过优化使该结构在650 nm波长下的耦合效率达到56%。此外,由于该结构对TE偏振光和TM偏振光的选择比达到70∶1,因此具有偏振器的功能。同时由于TE偏振光耦合频谱的频带宽度仅为20 nm,该结构还具有窄带滤波的作用。此外,还研究了光栅结构参数、入射角以及流体折射率对耦合频谱的影响。     

Magnetostatic surface waves in a ferrite/dielectric/metal-strip-grating structure

The dispersion relation for magnetostatic surface waves in a ferrite/dielectric/metal-strip-grating structure is obtained. It is shown that dispersion of magnetostatic surface waves must be qualitatively the same as in a ferrite/dielectric/metal structure, while the slope of the dispersion curve in the region of backward magnetostatic waves existing in a ferrite/dielectric/grating structure (and in a ferrite/grating structure in particular) is considerably higher than the slope of this curve corresponding to a ferrite/dielectric/metal structure. It is found that this phenomenon can be explained by the dependence of the grating’s shielding capability on the wave number of magnetostatic surface waves. A grating shielding parameter is introduced and dependences of this parameter on the wave number that can be used to explain the phenomena observed in the experiment are determined.     

Wavelength-selective coupling between vertically integratedthin-film waveguides via supermode by a pair of grating couplers

Grating coupling between vertically integrated waveguides via supermode was discussed and demonstrated. Two thin-film waveguides with grating couplers were stacked on a substrate. A guided wave in one waveguide is converted by a grating coupler to a supermode propagating contradirectionally, and then converted by another grating coupler to a guided wave in the other waveguide. The coupling shows high wavelength selectivity, and the wavelength-division add/drop multiplexing function can be combined. A demonstrator was designed and fabricated. Theoretically predicted coupling efficiency was almost 100% with wavelength selectivity of 2 nm, while the experimentally obtained value was 40% in the efficiency and 1 nm in the selectivity     

Reflection by a Sinusoidally Modulated Surface Reactance at Oblique Incidence

The reflection characteristics of the TM and the TE surface waves by a weak sinusoidal modulation of the surface reactance are investigated for the oblique incidence in which the wavevectors are not aligned with the grating vector. A superposition of TM and TE wave fields is needed for the fulfillment of the required boundary conditions. For both the TM and the TE surface waves, the Brewster phenomenon of total transmission occurs at the angle of incidence theta=theta/sub B/ = 45°. A modulation in the surface reactance, in general, causes the TE surface waves to be more efficiently reflected than the TM surface waves.     

Application of a variational principle to systems with radiation loss

A variational principle for the frequency of electromagnetic systems with radiation is derived from Maxwell's equations. Expressions for the quality factorQare obtained in three illustrative examples: a leaky transmission line resonator, a grating coupler, and a curved slab waveguide. Extensive numerical results for theQof the grating coupler are presented in normalized form. By optimization of the variational expressions with respect to the amplitudes of the forward and backward waves, coupled-mode equations are derived for a grating structure. The variational formulas agree with results obtained from a perturbational analysis.     

The theory of twisted transverse-wave couplers

The coupled-mode theory of a class of transverse-wave couplers in which the plane of polarization of the electric field rotates along the length of the coupler is described. The synchronism conditions between the circuit wave and the beam that lead to strong interaction with one or more of the transverse beam waves are given and the case of equal interaction with the two cyclotron waves is discussed in detail. It is observed that any two transverse waves of opposite polarization can be excited equally in a twisted coupler, or that coupling to one of two waves with the same phase velocity but opposite polarizations can be achieved.     

掺半导体玻璃波导光栅耦合器及其功率限制作用

本文报导了在掺半导体玻璃波导上用离子刻蚀的方法制备出了表面刻蚀光栅耦合器。观察到了光栅耦合器的耦合效率随着输入激光功率增加而下降的功率限制作用。     

Theory of line-source radiation from a metal-strip gratingdielectric-slab structure

This paper describes the fundamental theory of line source radiation from a source on a dielectric slab backed by a metal-strip grating. A continuous phased-array (CPA) method is applied to treat the analytic and numerical problems of antenna interaction with periodic structures. Both TE and TM mode cases for a one-dimensional strip grating are investigated. It is found that the strip grating on the dielectric surface may result in surface wave elimination and may also be used to support leaky waves. It is shown that high-efficiency and high-gain antennas on a dielectric substrate are possible with such metal-strip gratings     

Effective power input into quasi-optical cavity with travelling wave

The open three-mirror cavity with a travelling wave, and reflecting diffraction grating on one mirror as a coupler was excited by a wave beam at the frequency 140 GHz. The investigation showed the wave power in the cavity to be about 30 times higher than that at the cavity entrance.     

Excitation of Hybrid Space-Surface Waves in Clinotrons with Non-uniform Grating

Excitation of surface (slow), space (fast), and hybrid surface-space waves in BWO-clinotron with periodically non-uniform grating has been studied both theoretically and experimentally. It is shown that an interaction of electron beam with hybrid surface-space wave may be more effective than with surface wave because of higher Q-factor, and than with space wave because of higher impedance. The experimental test results of both 100-GHz CW clinotron with non-uniform three-stage grating and of 130-GHz CW clinotron with four-stage grating showed the excitation of radiation with output power more than 1 W and some specific features of electronic frequency tuning.     

聚合物波导光栅耦合器的衍射场仿真

为了实现横截面尺寸为50 m50 m的聚硅氧烷聚合物光波导的耦合转向问题,设计了一种表面覆盖高折射率包层的多层蚀刻光栅耦合器。首先,分析了影响聚合物波导光栅耦合器耦合效率的结构因素;然后,采用在光栅表面蚀刻高折射率层的方法,提高了聚合物波导光栅耦合器的耦合效率;接着,对不同的周期（范围:100~4 000 nm）和不同的蚀刻深度（范围:0~50 000 nm）进行排列组合,形成不同的光栅结构,基于时域有限差分法编写程序,遍历所有情况,得到不同光栅结构下的光场情况以及其耦合效率,找到使耦合效率最大的周期以及蚀刻深度。最后,设计了多层蚀刻的光栅耦合器,进一步提高耦合效率。当蚀刻深度为5 000 nm,光栅周期为2 600 nm时,带高折射率层的聚硅氧烷聚合物光波导均匀光栅耦合器的耦合效率达到最大,为17.2%。采用多层蚀刻的方式,对结构进行优化,其耦合效率能达到37.4%。为聚硅氧烷聚合物光波导在光互连中的实际应用提供了理论依据。     

Performance implications of wide-band lasers for FSK modulation labeling scheme

Optical labeling via frequency-shift keying (FSK) modulation capability of a grating-assisted codirectional coupler with sampled grating reflector laser is investigated for the first time. FSK modulation can be best implemented with only the phase section current and optical frequency deviation of 20 GHz is achieved. The measured frequency modulation response indicates the limitation of the maximum modulation rate is sufficient for Internet protocol packet optical labeling.     

Improved light coupling efficiency of organic light- emitting diode and polymer optical waveguide integrated device by grating coupler

In this work, the light coupling efficiency of organic light-emitting diode (OLED) and polymer optical waveguide integrated device was improved by the grating coupler. To maximize light coupling efficiency, the grating coupler was optimized by finite-difference time-domain (FDTD) method. Based on the simulation results, the grating coupler was fabricated via laser interference lithography process and an OLED was integrated on the surface of it. Comparing the integrated devices without and with grating coupler, light coupling efficiency of the grating-based integrated device was improved by about 5%. The proposed integrated device has the potential application for low-cost and flexible monolithic optical sensors.     

Dynamics of optical radiation in an optical waveguide with a time- and length-modulated refractive index

The problem of propagation of a double-mode wave packet in a nonstationary optical waveguide is solved analytically. Generalized synchronism conditions for waves propagating in optical waveguides with a realized traveling permittivity-variation wave (TPVW) are considered. The dependence of the velocities of wave-packet envelope maxima on the waveguide parameters and on the characteristics of the realized TPVW is analyzed.     

Reflection of Magnetostatic Forward Volume Waves by a Shallow-Grooved Grating on a YIG Film

The magnetostatic forward volume wave (MSFVW) reflection characteristics of a uniform grating of shallow grooves etched on the planar surface of an epitaxial YIG film are treated using an approach which integrates field theory with the coupled-mode approach. The MSFVW reflectivity per groove is found to be comparable to the reflectivity of magnetostatic surface waves (MSSW's) and thus is found to be significantly large considering that the volume waves are reflected by surface-localized and shallow grooves.     

布拉格光纤光栅内部能量特性研究

基于耦合模理论并结合边界条件,推导出布拉格(Bragg)光纤光栅前向波和后向波的 表达式。以均匀光纤光栅为例,得出光栅内部能量分布是振荡的。在禁带内,前向波、后向波能量单调递减,其相干迭加能量振荡,振荡周期与光纤光栅周期一致;在禁带边缘及外部,前向波、后向波能量是振荡的,二者相干迭加的能量也是振荡的,且呈包络变化,迭加能量的快变周期亦与光栅周期相同;在禁带边缘及外部,前、后向波振荡周期与包络周期一致,都和入射波长有关,入射波长偏离布拉格波长的程度越大,周期越小;在禁带附近存在前向波能量振幅的极大值;能量振幅随光栅长度的增加而增大。     

硅基波导光栅耦合器与波导传输损耗的研究

对硅(Si)基波导光栅耦合器的设计与耦合性能进 行了研究。采用本征模展开法对光栅耦合器进行设计与 优化,通过实验测量了光栅的耦合性能,并对均匀光栅、自聚焦光栅和反射光栅等3种光栅 耦合器的耦合 性能进行了比较,耦合效率分别达到了达到47.86、56. 36和48.98%,自聚焦光栅可以有效改善光纤到 光纤的传输效果,耦合效率提高了8.5%。通过实验测量了基于耦合光 栅技术的Si基条形波导和槽型波导的 传输损耗,结果显示,条形波导和槽型波导的传输损耗分别为2.34d B/cm和6.31dB/mm。     

Characteristics of THz-wave radiation using a monolithic grating coupler on a LiNbO3 crystal

Wide tunable terahertz (THz) wave generation was successfully demonstrated utilizing a grating coupler fabricated on the surface of a LiNbO₃ crystal which was pumped by a Q-switched Nd:YAG laser. In this paper, we report the detailed characteristics of the oscillation and the radiation including tunability, spatial and temporal coherency, directivity, and efficiency. Oscillation using a LiTaO₃ crystal was also performed, in which experimental phasematching condition values agreed well with the calculated one.     

Analysis of two parallel long-period fiber gratings

A wavelength-selective coupler constructed with two parallel identical uniform long-period fiber gratings (LPFGs) is analyzed by the coupled-mode theory. The effects of introducing a longitudinal offset distance between the two gratings on the transmission characteristics of the coupler are discussed and the conditions for achieving a 100% coupling efficiency are highlighted. It is found that 100% coupling can be achieved with a practical grating length by using a proper grating design and a suitable index-matching surrounding medium. The theoretical results agree well with the experimental data.