Design of optical metamaterial waveguide structures

Subwavelength gratings (SWGs) are periodic structures with a pitch (Λ) smaller than the wavelength of the propagating wave (λ), so that diffraction effects are suppressed. These structures thus behave as artificial metamaterials where the refractive index and the dispersion profile can be controlled with a proper design of the geometry of the structure. SWG waveguides have found extensive applications in the field of integrated optics, such as efficient fiber-chip couplers, broadband multimode interference (MMI) couplers, polarization beam splitters or evanescent field sensors, among others. From the point of view of nano-fabrication, the subwavelength condition (Λ << λ) is much easier to meet for long, mid-infrared wavelengths than for the comparatively short near-infrared wavelengths. Since most of the integrated devices based on SWGs have been proposed for the near-infrared, the true potential of subwavelength structures has not yet been completely exploited. In this talk we summarize some valuable guidelines for the design of high performance SWG integrated devices. We will start describing some practical aspects of the design, such as the range of application of semi-analytical methods, the rigorous electromagnetic simulation of Floquet modes, the relevance of substrate leakage losses and the effects of the random jitter, inherent to any fabrication process, on the performance of SWG structures. Finally, we will show the possibilities of the design of SWG structures with two different state-of-the-art applications: i) ultra-broadband MMI beam splitters with an operation bandwidth greater than 300nm for telecom wavelengths and ii) a set of suspended waveguides with SWG lateral cladding for mid-infrared applications, including low loss waveguides, MMI couplers and Mach-Zehnder interferometers.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Comparing the fundamental limit of detection for interferometric and resonant biosensors with coherent phase read-out

We compare the limit of detection of coherently interrograted photonic biosensors, using both interferometric and resonant architectures.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Receptor coherente integrado ‘colorless’ de gran margen dinámico basado en un acoplador a 120º

Un receptor ‘colorless’ requerirá en su banda de operación de un elevado rechazo en modo común CMRR para reducir eficientemente la interferencia en banda base ocasionada por los canales colindantes al detectado y conseguir un mayor rango dinámico de operación. La obtención de un elevado CMRR se ve imposibilitada en la práctica en el receptor convencional a 90º (basado aquí en un MMI 2x4) por los inevitables desbalanceos, ya sea por operar lejos de su frecuencia de diseño o por las tolerancias presentes en su proceso de fabricación. En esta contribución se propone como alternativa un esquema coherente basado en un acoplador a 120º (implementado con un MMI 2x3), capaz simultáneamente de demodular sin distorsión las componentes IQ de un canal específico y ofrecer un elevado CMRR en una amplia banda de operación. Esto es posible desde la realización de una sencilla operación lineal desde un circuito analógico calibrado, pudiendo prescindir así de los algoritmos de ortogonalización (GSOP) necesarios en el receptor convencional a 90º para resolver sus desbalanceos. Los resultados numéricos muestran que en un escenario realista de fabricación nuestra propuesta es una interesante alternativa al receptor convencional. Así, específicamente, para una recepción 'colorless' de 80 canales modulados a 56 Gbps bajo 16-QAM, es capaz de ofrecer un rango dinámico de 21 dB frente a los 8 dB del receptor convencional a 90ºUniversidad de Málaga Campus de Excelencia Internacional Andalucía Tech. CEIC de Andalucía (P09-TIC-5268), C.I.C.Y.T. (TEC2009-10152), MIRTHE ICT-2009-5 nº 25798

High performance and small footprint spot size converters based on SWG metamaterial lenses

Spot size converters with high expansion ratio are required in a variety of situations. This is the case of non-focusing Silicon on Insulator (SOI) fiber-to-chip grating couplers, which typically require long adiabatic tapers (Ltaper >100μm) from the narrow single-mode waveguides (WSi-wire ~ 500nm) to the wide grating region (Wgrating ~ 15μm). Here, we explore the potential of subwavelength grating (SWG) dielectric metamaterials to implement integrated GRaded INdex (GRIN) lenses to expand the mode field. Our designs achieve the desired Beam Expansion (BE) with insertion losses below 1dB over a distance of only LBE ~ 17μm.Ministerio de Economía y Competitividad, Programa Estatal de Investigación, Desarrollo e Innovación Orientada a los Retos de la Sociedad (cofinanciado FEDER), (TEC2016-80718-R); Universidad de Málaga. Ministerio de Educación, Cultura y Deporte (MECD) (FPU16/06121); Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Diffractive sidewall grating coupler: towards 2D free-space optics on chip.

Silicon photonics has been the subject of intense research efforts. In order to implement complex integrated silicon photonic devices and systems, a wide range of robust building blocks is needed. Waveguide couplers are fundamental devices in integrated optics, enabling different functionalities such as power dividers, spot-size converters, coherent hybrids and fiber-chip coupling interfaces, to name a few. In this work we propose a new type of nanophotonic coupler based on sidewall grating (SIGRA) concept. SIGRAs have been used in the Bragg regime, for filtering applications, as well as in the sub-wavelength regime in multimode interference (MMI) couplers. However, the use of SIGRAs in the radiation regime has been very limited. Specifically, a coarse wavelength division multiplexer was proposed and experimentally validated. In this work we study the use of SIGRAs in the diffractive regime as a mean to couple the light between a silicon wire waveguide mode and a continuum of slab waveguide modes. We also propose an original technique for designing SIGRA based couplers, enabling the synthesis of arbitrary radiation field profile by Floquet- Bloch analysis of individual diffracting elements while substantially alleviating computational load. Results are further validated by 3D FDTD simulations which confirm that the radiated field profile closely matches the target design field.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

Estudio comparativo de biosensors coherentes basados en estructuras interferométricas y resonantes

La gran mayoría de los biosensores fotónicos de campo evanescente se basan en arquitecturas interferométricas o resonantes. La determinación analítica del límite de detección (LOD) alcanzable con estas arquitecturas es muy importante. Sin embargo, hasta donde los autores conocen, no existe un marco común que permita establecer una comparación justa entre ambas alternativas en términos de su LOD intrínseca. En este artículo desarrollaremos un modelo sistémico para biosensores fotónicos, que incluye las posibles pérdidas ópticas y el ruido térmico, a partir de las cuales se puede comparar el LOD intrínseco de ambas arquitecturas. Los resultados obtenidos muestran que la arquitectura interferométrica debe ser la opción preferente para todos aquellos casos en los que la cantidad disponible de analito no es un recurso limitadoUniversidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. Este trabajo ha sido parcialmente financiado por el proyecto TEC2016-80718-R del Ministerio de Economía y Competitividad (cofinanciado FEDER) y por la acción Marie Skłodowska-Curie 713721

Automatic design of high-performance fiber-chip surface grating couplers based on Floquet-Bloch mode analysis

We propose a new strategy to automatically design highly efficient fiber-chip surface grating couplers. High performance designs are achieved with a substantially reduced computational cost by combining Floquet-Bloch mode analysis with a multi-objective optimization technique (genetic algorithms)

Efficient fiber-to-chip grating coupler for micrometric SOI rib waveguides

Grating couplers are an efficient means for fiber to chip coupling, as they require no facet preparation and enable wafer scale testing. While grating couplers are commonly used in silicon wire waveguides, their application to micrometric silicon-on-insulator rib waveguides is complicated due to the presence of high-order Bloch modes. We study the Bloch modes behavior and their excitation determined by access waveguide design. The latter is implemented to enable single Bloch mode excitation. The use of a design process based on modal analysis is proposed. A grating coupler is proposed in silicon-on-insulator with 1.5 microm thick silicon layer that achieves a coupling efficiency of 65.6% at 1.55 microm. The structure, including interconnection waveguides, access waveguide and grating can be fabricated using a single lithography step

Designing polarization management devices by tilting subwavelength grating structures

Subwavelength gratings (SWG) are periodic structures which behave as controllable homogeneous metamaterials. SWGs are extremely interesting when they are used in platforms with a limited choice of material refractive indices, enabling the design of a myriad of high-performance devices. Here we present a novel technique to gain control over the intrinsic anisotropy of the synthesized metamaterial. We show that tilting the silicon segments in a SWG structure mainly affects the in-plane (TE) modes, with little impact on the out-of-plane (TM) modes. Moreover, we present a methodology to quickly but accurately calculate the modes of a tilted periodic structure modeling the structure as a rotated uniaxial crystal which can be solved with an anisotropic mode solver. Measurements on a set of fabricated tilted SWG waveguides validate our simulation results. By using the presented technique, we design a polarization beam splitter based on a 2x2 multimode interferometer. The design is based on the optimization of the tilting angle to tone the beat length of the TE modes to be a half of the beat length of the TM modes.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech; Ministerio de Economía y Competitividad (MINECO) (IJCI-2016-30484, TEC2015-71127-C2-R, TEC2016-80718-R); Ministerio de Educación, Cultura y Deporte (MECD) (FPU16/06762); European Regional Development Fund (ERDF); Comunidad de Madrid (SINFOTON-CM S2013/MIT-2790); European Association of National Metrology Institutes (EURAMET) (H2020-MSCA-RISE-2015:SENSIBLE, JRP-i22 14IND13 Photind)