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

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)

A review of silicon subwavelength gratings: building break-through devices with anisotropic metamaterials

Abstract Silicon photonics is playing a key role in areas as diverse as high-speed optical communications, neural networks, supercomputing, quantum photonics, and sensing, which demand the development of highly efficient and compact light-processing devices. The lithographic segmentation of silicon waveguides at the subwavelength scale enables the synthesis of artificial materials that significantly expand the design space in silicon photonics. The optical properties of these metamaterials can be controlled by a judicious design of the subwavelength grating geometry, enhancing the performance of nanostructured devices without jeopardizing ease of fabrication and dense integration. Recently, the anisotropic nature of subwavelength gratings has begun to be exploited, yielding unprecedented capabilities and performance such as ultrabroadband behavior, engineered modal confinement, and sophisticated polarization management. Here we provide a comprehensive review of the field of subwavelength metamaterials and their applications in silicon photonics. We first provide an in-depth analysis of how the subwavelength geometry synthesizes the metamaterial and give insight into how properties like refractive index or anisotropy can be tailored. The latest applications are then reviewed in detail, with a clear focus on how subwavelength structures improve device performance. Finally, we illustrate the design of two ground-breaking devices in more detail and discuss the prospects of subwavelength gratings as a tool for the advancement of silicon photonics

Integrated metamaterial surface-emitting antenna for beam steering applications

Integrated optical antennas are relevant devices for the development of next-generation LIDAR systems. Here we experimentally demonstrate a new topology to implement long antennas in silicon-on-insulator platform. The designed 2-millimeter-long antenna presents a measured far-field beam divergence of 0.1° and a wavelength sensitivity of 0.13°/nm.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. HTSN Challenge Program at the NRC of Canada; Junta de Andalucía (P18-RT-1453, P18-RT-793, UMA18-FEDERJA-219); Ministerio de Ciencia, Innovación y Universidades (FPU16/03401, PID2019-106747RBI00)

Customized spectral filters using cladding-modulated Bragg gratings in silicon waveguides.

Funding: Ministerio de Economía y Competitividad (PID2019-106747RB-I00); Ministerio de Educación, Cultura y Deporte (FPU16/03401, FPU16/06762, FPU17/00638); Junta de Andalucía (P18-RT-1453, P18-RT-793, UMA18-FEDERJA-219); Universidad de Málaga; National Research Council Canada (CSTIP grant #HTSN210); Grantová Agentura České Republiky (19-00062S).Waveguide Bragg gratings are expected to play an important role in diverse applications of photonic integrated circuits. Here, we present our latest progress in implementing Bragg filters with a customized spectral response in the silicon-on-insulator platform. Our filter comprises a silicon waveguide with an array of Bragg segments placed aside. The waveguide core is designed to have a reduced mode confinement, which enables an accurate control of the grating strength via modulation of the Bragg segment separation distance and allows for minimum feature sizes compatible with deep-UV lithography (>100 nm). Our design strategy is experimentally validated by demonstrating a filter with 20 non-uniformly spaced notches in the transmittance spectrum. Palabras clave: Silicon photonics, Bragg gratings, spectral filters.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Bricked and evanescently-coupled topologies: expanding the portfolio of subwavelength metamaterial silicon photonic devices

We present two novel topologies of subwavelength grating (SWG) waveguides: the bricked-SWG and the evanescently-coupled-SWG. The bricked topology enables accurate control of waveguide anisotropy while maintaining the index and dispersion engineering advantage intrinsic to SWG waveguides. The evanescently-coupled-SWG allows unprecedented control of the strength of the modal perturbation in waveguide Bragg gratings and nanophotonic antennas. Both topologies leverage a Manhattan-like pattern, with pixel sizes compatible with deep-uv lithography. Our recent results will be discussed, focusing on polarization-independent multimode interference couplers for the O and C bands and a millimeter-long narrow-beam steerable optical antenna array with angular divergence of only 1.8º×0.2º.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Engineering sub-wavelength silicon waveguides for sensing applications in the near-infrared and mid-infrared band

Silicon photonics is one of the most promising candidates to achieve lab-on-a-chip systems. Making use of the evanescent-field sensing principle, it is possible to determine the presence and concentration of substances by simply measuring the variation produced by the light- matter interaction with the real part of the mode effective index (in the near infrared band), or with its imaginary part in a specific range of wavelengths (in the mid-infrared band). Regardless of which is the operating wavelength range, to maximize the device sensitivity it is essential to select the proper sensing waveguide. In this work we will review the potential of diffractionless sub-wavelength grating waveguides (SWG) for sensing applications by demonstrating its powerful capability to engineer the spatial distribution of the mode profile, and thereby to maximize the light-matter interaction. Among other things, we will demonstrate that the SWG waveguide dimensions used until now in the near-infrared are not optimal for sensing applications. In the mid-infrared band, due to the unacceptable losses of silicon dioxide for wavelengths longer than 4 μm, an additional effort is required to provide a more convenient platform for the development of future applications. In this sense, we will also show our recent progresses in the development of a new platform, the suspended silicon waveguide with subwavelength metamaterial cladding. A complete set of elemental building blocks capable of covering the full transparency window of silicon (λ < ∼8.5 μm) will be discussed.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

Subwavelength-engineered metamaterial devices for integrated photonics

The engineering of subwavelength grating metamaterials has become an essential design strategy in silicon photonics. The lithographic segmentation of integrated waveguides at the subwavelength scale enables the synthesis of on-chip metamaterials and provides control over optical properties such as mode delocalization, wavelength dispersion, and anisotropy. At the near-infrared wavelengths of the 1.55-μm telecom band, a range of subwavelength-based devices with unprecedented performance has been demonstrated, including couplers, filters, and polarization-handling structures. In this invited paper, we review the foundations of anisotropic subwavelength grating metamaterials and discuss our latest advances in five new subwavelength-enhanced devices: a millimeter-long optical antenna that is evanescently coupled to diffractive lateral segments, thereby achieving a record far-field beam width of 0.1º in silicon; a multi-line integrated Bragg filter also using lateral loading segments, which produces 20 non-uniformly spaced spectral notches with a 3-dB linewidth as low as 210 pm; a low-loss curved wavelength demultiplexer; a segmented multi-mode interference coupler based on novel bricked subwavelength gratings, yielding a 1-dB bandwidth exceeding 140 nm; and a suspended waveguide platform with low propagation loss at mid-infrared wavelengths.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

Building high-performance integrated optical devices using subwavelength grating metamaterials

Ministerio de Ciencia, Innovación y Universidades (MCIU) (PID2019-106747RB-I00), Consejería de Economía, Conocimiento, Empresas y Universidad (CECEU) (UMA18-FEDERJA-219, P18-RT-1453, P18-RT-793) and National Research Council of Canada (NRC) Collaborative Science, Technology and Innovation Program (CSTIP) (HTSN 209).The use of subwavelength grating structures in silicon waveguides have fuelled the development of integrated optical components with superior performance. By a judicious lithographic pattern of the grating, the optical properties of the synthesized metamaterial can be accurately tailored. In this work, we review our latest advances in subwavelength-grating-engineered silicon and germanium planar devices.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Subwavelength metamaterial for communications and sensing

Silicon photonics is considered a breakthrough technology with strong impact in areas as diverse as data center interconnection, high performance computing, the deployment of 5G future communication systems or lab-on-a-chip sensors. The emergence of sub-wavelength grating waveguides (SWG) has been fundamental to achieve advanced devices with unprecedented performance in integrated optics. In this talk we will focus on our recent progress in designing sub-wavelength engineered devices like ultra-broadband mode (de)multiplexers and converters [1], ultra-narrowband Bragg filters [2], sensing waveguides with enhanced sensitivity [3], or suspended silicon mid-infrared waveguides capable of covering the full transparency window of silicon [4], among other. This work was supported by the Ministerio de Economía y Competitividad, Programa Estatal de Investigación, Desarrollo e Innovación Orientada a los Retos de la Sociedad (Proyecto TEC2016-80718-R), and the Universidad de Málaga (Campus de Excelencia Internacional Andalucía Tech).Universidad de Málaga, Campus de Excelencia Internacional Andalucía Tech