Low-Loss and Compact Silicon Rib Waveguide Bends

[EN] Waveguide bends support intrinsically leaky propagation modes due to unavoidable radiation losses. It is known that the losses of deep-etched/strip waveguide bends increase inevitably for decreasing radius. Here, we theoretically and experimentally demonstrate that this result is not directly applicable to shallow-etched/rib waveguide bends. Indeed, we show that the total losses caused by the bends reach a local minimum value for a certain range of compact radii and rib waveguide dimensions. Specifically, we predicted the minimum intrinsic losses < 0.1 dB/90 degrees turn within the range of 25-30 mu m bend radii in a 220 nm-thick and 400 nm-wide silicon rib waveguide with 70 nm etching depth. This unexpected outcome, confirmed by experimental evidence, is due to the opposite evolution of radiation (bending) losses and losses caused by the coupling to lateral slab modes (slab leakage) as a function of the bend radius, hence creating an optimum loss region. This result may have important implications for the design of compact and low-loss silicon nanophotonic devices.This work was supported in part by the European STREP Program under Grant FP7-ICT-2013-11-619456-SITOGA and Grant FP7-ICT-2012-10-318240 PhoxTroT and in part by LEOMIS under Grant TEC2012-38540. (Corresponding author: Regis Orobtchouk.)Brimont, ACJ.; Hu, X.; Cueff, S.; Rojo-Romeo, P.; Saint Girons, G.; Griol Barres, A.; Zanzi, A.... (2016). Low-Loss and Compact Silicon Rib Waveguide Bends. IEEE Photonics Technology Letters. 28(3):299-302. https://doi.org/10.1109/LPT.2015.2495230S29930228

Interferometric switches for transparent networks : development and integration

Magneto-optic devices are a potential enabler of better scaling, transparent networks that are bit-rate, protocol and format insensitive. Transparency is critical given the paradigm shift from connection-oriented communications to IP-centric packet switched data traffic driven by the influx of high bandwidth applications. This is made more urgent by the large and growing optical-electronic bandwidth mismatch as well as the rapid approach of device dimensions to the quantum limit. Fiber-based switches utilizing bismuth-substituted iron garnets as Faraday rotators in Mach-Zehnder and Sagnac interferometer configurations are proposed, analyzed and characterized. The issues and limitations of these switches are investigated and efforts are undertaken to model and optimize the field generating coil impedance parameters. While alleviating the concerns associated with free-space switches and being compatible with contemporary optical networks, the performance of the fiber-based interferometric switches is still below theoretical limits and could be improved. Moreover, the discrete components of a fiber-based implementation engender scalability concerns. In keeping with the spirit of Richard Feynman\u27s lectures, the maturity of planar lithographic techniques that are widely used in microelectronics is leveraged to realize integrated versions of the fiber-based interferometric switches. The design, analysis, fabrication and characterization of these integrated switches are detailed herein, including the selection of a suitable material system, design of the waveguide geometry, creation and calibration of a fabrication process based on direct-write scanning electron-beam lithography as well as determination of the switches\u27 fabrication tolerance. While the larger waveguide cross-section of the microphotonic switches enables efficient coupling to fiber and greatly reduces geometrical birefringence, the weak confinement results in longer device lengths. Moreover, the small but finite birefringence induces some polarization dependence in switch performance. Consequently, compact and nominally non-birefringent nanophotonic versions of the interferometric switches are proposed and analyzed in the interest of further improving switch performance and scalability

Application of statistical method to investigate the effects of design parameters on the performance of microring resonator channel dropping filter

Microring resonator (MRR)-based channel dropping filters have been extensively explored because of the high quality factor, compact size, and easy integration of fabrication. In order to design an excellent MRR wavelength filter, optimization of the design parameters are essential. In this paper, the design trade-off ofMRR-based channel dropping filter was statistically studied by employing the Taguchi method. Four control factors considered were width of rings and channels, radii of the microring, upper rib waveguide height, and gap size. The analysis of variancewas adopted to analyze significant trends that occurred on the free spectral range (FSR) and insertion loss (IL) performance under different sets of control factor combinations. The best parametric combination of control factors was identified in order to achieve a balance performance between large FSR and low IL using Finite-Difference Time Domain (FDTD) simulation by RSoft Inc. After optimization, the value of FSR and IL obtained was 17nm and 0.245 dB, respectively. Confirmation tests were carried out to verify the optimized parametric combinations and a new parametric combination considering both outputs were 16nm and 0.215 dB. The optimal combinations were 6 mm ring radius with the separation gap of 50 nm and 350 nm350 nm rib waveguide cross section

Suspended Waveguide Platforms for Mid-Infrared Group IV Photonics

Fecha de lectura de Tesis Doctoral: 4 de noviembre 2019En las últimas décadas, la banda del infrarrojo medio (2-20 µm) ha despertado un gran interés en la comunidad científica dedicada a la fotónica del Grupo IV. Este auge se debe a las múltiples aplicaciones que pueden desarrollarse en este rango del espectro electromagnético, entre las que sobresalen las comunicaciones ópticas por espacio libre y, sobre todo, la espectroscopia infrarroja, que permite identificar inequívocamente las sustancias disueltas en una muestra y cuantificar su concentración. La plataforma de guiado más usada en la banda de comunicaciones, la de silicio sobre aislante, no puede utilizarse fácilmente a longitudes de onda mayores de 4 µm a causa de las elevadas pérdidas que presenta el dióxido de silicio (aislante). Por ello, es necesario encontrar nuevas estructuras que puedan operar por encima de los límites de transparencia impuestos por los materiales de las estructuras tradicionales. Así, en esta tesis se expone el desarrollo de nuevas plataformas fotónicas integradas para la banda del infrarrojo medio. En concreto, se han propuesto las plataformas de guiado de silicio suspendido y de germanio suspendido con rejillas laterales en régimen sublongitud de onda, en las que el dióxido de silicio se elimina con una solución ácida. Entre otros dispositivos, se han diseñado, fabricado y demostrado experimentalmente guías de onda a diferentes longitudes de onda, entre las que destaca la de 7.67 μm, consiguiéndose pérdidas de propagación bajas en torno a 3 dB/cm (silicio suspendido) y 5 dB/cm (germanio suspendido). Asimismo, el problema del acoplo chip-fibra, cuya resolución es imprescindible para la utilización práctica de cualquier plataforma integrada competitiva, se ha abordado mediante el diseño de acopladores chip-fibra superficiales de alta eficiencia y banda ancha, a saber: una microantena de germanio suspendido y un acoplador de rejilla de orden cero

Towards photonic integrated circuits : design and fabrication of passive InP waveguide bends

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2004.Includes bibliographical references (leaf 69).Waveguide bends, in the (In,Ga)(As,P) material system, have been simulated, fabricated and tested. A process is developed for waveguides of 1 [micro]m through 7[micro]m widths. Waveguides containing S-bends of varying bending radii as well as resonator bends were examined. Inconsistent measurement results were obtained. Improved measurement methods have been suggested.by Sarah J. Rodriguez.S.M

Computer modelling of electro-optic modulators

An electro-optic modulator is an essential part of an optical communications system. An ideal modulator would have low drive voltage, large bandwidth, small size, low insertion loss, a very high extinction ratio, very low chirp and low power consumption. However, there is a trade-off between some of these characteristics, and consequently the modulator is designed with a compromise. It is due to these complex devices that computer modelling has become a necessary and integral part of device design, which is made easier and more economically acceptable by the larger capacities of today’s computers. In this work, a finite element method-based approach is used to design and develop computer programs in order to simulate the major characteristics of electro-optic modulators (i.e. low drive voltage, a large bandwidth, small size, low insertion loss) and fabrication variables and combine these separate computer programs into one complete suite to model electro-optic waveguide modulators for a good and complete design process for these devices. The devices examined in this work are the TkLiNbCfi directional coupler-based modulator, the Ti:LiNb03 Mach-Zehnder interferometric modulator and a GaAs/AlGaAs interferometric-based electro-optic modulator. These computer programs give the optical mode for each of the devices examined in this work both before and after application of an electric field, giving exact values for the refractive and any change in refractive index with applied electric field. In this way it is the drive voltage and size of the device that can be adjusted and examined in order to obtain an optimum design. The electrode design is important to modulators particularly bandwidth but is also essential for decreasing optical loss without increasing the drive voltage. A program was designed and developed using a perturbational approach in order to model this optical loss. For the TiiLiNbCfi directional coupler based modulator, the light coupling process between the two adjacent waveguides as well as the power transfer efficiency were also modelled using a FEM LSBR-based approach. However, the directional coupler based devices are slower than their MZI-based counterparts. A TkLiNbCfi MZI-based modulator was also studied with both channel and ridge waveguides. It was found that a ridge waveguide is optimally beneficial only if the FWHM (width and height) of the mode fit into the ridge. The bending waveguides at the input and output of the Ti:TiNb03 MZI-based modulator were modelled using a FEM BPM-based approach. This approach yields accurate results for structures where the cross-section of the device is changing. A computer program was also developed to incorporate the RF characteristics of the device in order to find the bandwidth of the device for perfect velocity and impedance matching conditions. Furthermore, smaller studies were undertaken for a ThLiNbCfi MZI-based modulator for electrical sensing applications as well as for a GaAs/AlGaAs interferomtric-based modulator. The main work of this thesis was to improve these device structures in order to provide optimal results. The suite of computer programs yielded results very close and similar to that examined in the literature. Most importantly, the computer modelling approach to device design yields accurate results for both simple and more complex devices structures and is a cheaper long-term approach to device design