Compact Focusing Grating Couplers for Silicon-on-Insulator Integrated Circuits

We report experimental results on compact and broadband focusing grating couplers, both in silicon-on-insulator (SOI) and gold on SOI. An eight-fold length reduction of the coupling structure from fiber to photonic wire in SOI, as compared to a linear grating and adiabatic taper, is obtained, without performance penalty. A proof of principle is given for a focusing grating coupler in gold on SOI, with 20% fiber-to-focus efficiency.     

Calculation and experimental verification of two-dimensional focusing grating couplers

A ray tracing method has been performed to calculate the focus spot size of two-dimensional focusing grating couplers that are produced by holographic interferometry of freely propagating wavefronts. The calculations have been used to optimize the constructing optical configuration. Diffraction limited spot diameters of about 2 μm can be achieved for couplers at wavelength 632.8 nm. These spot sizes have been experimentally verified for coupling and focusing TE modes which are guided in sputtered glass films on Si substrates.     

Study of High Efficiency Grating Couplers for Silicon-Based Horizontal Slot Waveguides

Horizontal slot waveguides are becoming a very promising waveguide configuration for silicon photonics nonlinear applications. In this letter, the design of grating couplers for highly efficient coupling between standard single-mode fibers and horizontal slot waveguides is reported. Parameters have been optimized to achieve maximum coupling efficiency for lambda = 1550 nm and transverse magnetic polarization. Maximum coupling efficiencies of 61% and 48% have been achieved for negative and positive detuned grating couplers, respectively, by means of simulations. A 35-nm 1-dB bandwidth spectral response has also been obtained.     

Compact and efficient fibre-to-waveguide grating couplers in InP-membrane

The design and fabrication of compact grating couplers in InP-membrane waveguides for coupling to standard singlemode fibre is presented. A wafer bonding technique is applied to achieve a high vertical index contrast. Coupling efficiencies of 30% were measured on first fabricated couplers.     

Integrated optical elliptic couplers: modeling, design, andapplications

This paper presents the modeling, design, experimental results and applications of integrated optical elliptic couplers. An approximate analytical model is presented and the design procedure is described. Some elliptic focusing and collimating structures have been experimentally tested and the results are in good correspondence with the design. The couplers have low losses, are polarization and lateral index contrast insensitive, compact, and easy to design and fabricate. The potential and limitations of the device are evaluated. Some applications of the elliptic couplers are also presented     

单FBG双波长掺铒光纤激光器的设计与实验研究

为给密集波分复用(DWDM)光纤通信及光纤传感系统提供理想光源,设计了一种双波长环形腔掺铒光纤激光器。该激光器采用单支光纤光栅(FBG)和2个3dB耦合器构成可调谐光滤波器,结合多模光纤的偏振烧孔效应,通过改变系统的偏振态来获得波长可调谐的双波长激光输出。实验结果表明:改变系统的偏振态时,可分别获得单波长和双波长激光输出,双波长光纤激光器的最大波长差为4.692nm。引入多模光纤后,激光跳模现象得到明显抑制。     

Compact and Highly Efficient Grating Couplers Between Optical Fiber and Nanophotonic Waveguides

We present high-efficiency grating couplers for coupling between a single-mode fiber and nanophotonic waveguides, fabricated both in silicon-on-insulator (SOI) and InP membranes using BenzoCycloButene wafer bonding. The coupling efficiency is substantially increased by adding a gold bottom mirror to the structures. The measured coupling efficiency to fiber is 69% for SOI grating couplers and 56% for bonded InP membrane grating couplers     

用闪耀光栅获得并聚焦偏振光

构造了用闪耀光栅分离并聚焦偏振光的模型，用傅里叶光学的方法详细推导出了衍射场强分布公式，分析计算了闪耀光栅对偏振光分离并聚焦的特性。优化设计了两个闪耀光栅。计算结果表明，选用不同的光栅参数，可以实现将o光和e光分离任意角度并聚焦。本文的方法扩展了闪耀光栅的应用范围，对实际制作偏振光分束器有一定的指导意义。     

Analysis of detuned second-order grating output couplers with an integrated superlattice reflector

Analysis is presented of second-order gratings at wavelengths detuned from the reflection bandwidth. These gratings have applications, for example, as surface-emitting output couplers in monolithic integrated master oscillator power amplifier (M-MOPA) configurations. The grating output couplers have reflectivities below 10/sup -4/ at an emission wavelength of 874 nm when the Bragg condition of the second-order grating occurs at 904 nm. When used in conjunction with a superlattice reflector integrated into the substrate, the surface emission can exceed 85% of the radiation incident on a 250 mu m long grating. Consequently, these gratings can act as nearly ideal output couplers in a M-MOPA without introducing undesirable feedback to the amplifier or master oscillator.<>     

Polarization-Controlled Surface Grating VCSELs Under Unpolarized and Polarized Optical Feedback

The polarization control of a surface grating vertical-cavity surface-emitting laser (VCSEL) and of a nominally identical standard VCSEL without a surface grating are compared for unpolarized and polarized optical feedback with different feedback levels in the long external cavity regime. While the polarization of the standard VCSEL is strongly influenced by isotropic feedback with a feedback level of just 1% and can even be controlled by polarized feedback, the surface grating VCSEL remains polarization-stable under isotropic feedback. Its polarization can only be disturbed by optical feedback polarized orthogonal to the polarization of the solitary surface grating VCSEL for feedback levels exceeding 18%.     

倾斜耦合的光栅耦合器研究进展

近年来,片上光子集成技术备受关注并飞速发展,但在光纤与芯片、芯片与芯片上实现高效、高可靠性的光耦合仍是难题。光栅因其制作简单,位置灵活,对准容差大及可实现片上测试等一系列优点而备受研究者的关注。目前在绝缘体上硅(SOI)平台和绝缘体上铌酸锂(LNOI)平台上已开发出大量的光栅耦合器件,并获得较高的耦合效率和大带宽。该文主要介绍光栅耦合器的工作原理和主要性能指标,阐述了均匀光栅、倾斜光栅、闪耀光栅和切趾光栅耦合的特点及现阶段进展,并对具有代表性的一维光栅性能指标进行了比较。结果表明,分布式布喇格反射镜和金属反射镜可有效地提升光栅耦合效率。此外,该文还介绍了基于LNOI平台的几种光栅耦合器,其可帮助研究者们梳理光栅耦合器的发展历程、研究现状及各耦合器的特点,为未来研究提供一定的参考。     

Polarization-Controlled Surface Grating VCSELs Under Externally Induced Anisotropic Strain

The polarization control of surface grating vertical-cavity surface-emitting lasers (VCSELs) is tested under externally applied anisotropic stress and is compared to that of a nominally identical standard VCSEL without a surface grating. This is done by bending the VCSEL chip in a well-defined way. The anisotropic in-plane strain thus induced in the VCSELs leads to a polarization switch of the standard VCSEL for rather moderate strain. In contrast, the polarization of the surface grating VCSELs is fixed by the grating and remains unchanged despite a high strain which causes a wavelength splitting of the two polarization modes of about 130 pm. Such a result is of high practical relevance, since strain is unavoidably induced during VCSEL fabrication and mounting and counteracts any method applied for polarization control.     

Silicon thin‐film solar cells with rectangular‐shaped grating couplers

As an alternative to randomly textured transparent conductive oxides as front contact for thin‐film silicon solar cells the application of transparent grating couplers was studied. The grating couplers were prepared by sputtering of aluminium‐doped zinc oxide (ZnO) on glass substrate, a photolithography and a lift‐off process and were used as periodically textured substrates. The period size and groove depth of these transparent gratings were tuned independently from each other and varied between 1 and 4 μm and 100–600 nm. The optical properties of rectangular‐shaped gratings and the opto‐electronic behaviour of amorphous and microcrystalline silicon solar cells with integrated grating couplers as a function of the grating parameters (period size P and groove depth h_g) are presented. The optical properties of the gratings are discussed with respect to randomly textured substrates and the achieved solar cell results are compared with the opto‐electronic properties of solar cells deposited on untextured (flat) and randomly textured substrates. Copyright © 2005 John Wiley & Sons, Ltd.     

Effects of grating heights on highly efficient unibond SOIwaveguide grating couplers

We report the first successful experimental evaluation of the effect of grating height upon the output efficiency of grating couplers as predicted using perturbation theory. In addition, we have also produced a grating with an output efficiency of 70%, which is the highest efficiency yet reported for a silicon-on-insulator waveguide grating coupler     

平面光栅埋入式介质耦合器导波场严格解

本文给出了当埋置于平面耦合器介质层中的光栅剖面结构为矩形条件下,介质耦合器中导波的严格解.所得的解表明,对这样一种含有平面光栅层的介质耦合器,即使所设计的能量传输的工作点并不满足相位匹配条件,也同样可以获得最佳能量传输.     

Bandwidth of forward and backward coupling directional couplers

This paper deals with the filter properties of directional couplers. Formulas are derived for the bandwidth in wavelength units of couplers consisting of two waveguides that exchange their power either in the direction of the incident wave (forward couplers) or in the opposite direction (backward couplers). Backward couplers require the presence of a diffraction grating on one or both waveguides but they can achieve very much smaller bandwidth than forward couplers and hence are useful for constructing narrow-band optical wavelength filters.     

Polylithic Integration of Electrical and Optical Interconnect Technologies for Gigascale Fiber-to-the-Chip Communication

Polylithic integration of electrical and optical interconnect technologies is presented as a solution for merging silicon CMOS and compound semiconductor optoelectronics. In contrast to monolithic and hybrid integration technologies, polylithic integration allows for the elimination of optoelectronic and integrated optic device-related processing from silicon CMOS manufacturing. Printed wiring board-level and compound semiconductor chip-level waveguides terminated with volume grating couplers facilitate bidirectional optical communication, where fiber-to-board and board-to-chip optical coupling occurs through a two-grating (or grating-to-grating) coupling path. A 27% increase in the electrical signal I/O projected by and 33% increase in the number of substrate-level electrical signal interconnect layers implied by the International Technology Roadmap for Semiconductors (ITRS) projections for the 32-nm technology generation are required to facilitate 10 Tb/s aggregate bidirectional fiber-to-the-chip communication. Buried air-gap channels provide for the routing of chip or board-level encapsulated air-clad waveguides for minimum crosstalk and maximum interconnect density. Optical signals routed on-board communicate with on-chip volume grating couplers embedded as part of a wafer-level batch package technology exhibiting compatible electrical and optical input/output interconnects. Measurements of grating-to-grating coupling reveal 31% coupling efficiency between two slab, nonoptimized, nonfocusing volume grating couplers.     

Photorefractive polarization couplers in elliptical core fibres

Photorefractive polarization couplers written internally in germanium-doped elliptical core fibers at 488, 514, and 532 nm are reported. Complete power transfer between the orthogonal polarization modes of the fiber was achieved for couplers written at 514 and 488 nm, respectively. It is shown that the couplers are nonuniform in length because of the high photoinduced attenuation and also due to two-photon absorption. Polarization coupling of higher order modes is also demonstrated at shorter wavelengths where their polarization beat lengths match the polarization beat length of the fundamental mode at which the coupler was written.<>     

Polarization-dependent coupling in twin-core photonic crystal fibers

The polarization dependence of light coupling in photonic crystal fibers (PCFs) with sixfold symmetric dual cores and highly birefringent dual cores are numerically investigated. The characteristics of PCF-based couplers, such as coupling length, extinction ratio and form birefringence, are examined as functions of the air-hole size and pitch. The silica bridges between air holes take an important role in the energy transfer across the two cores. We believe that the mechanism of light coupling in PCF-based couplers is different from that of conventional waveguide couplers. The polarization dependent coupling can be reduced by adjusting the air holes around the cores of PCFs. On the other hand, the polarization dependent coupling can be enhanced by introducing high birefringence in the two cores.