Integrated optical filters play a key role in modern optical systems, finding extensive applications in quantum optics, biosensing, programmable photonics, and telecommunications. Among the most commonly used structures utilized for implementing integrated optical filters are ring resonators and Bragg gratings. Bragg gratings are characterized by a periodically perturbed refractive index profile along the propagation direction. By precisely engineering the strength of the perturbation along the grating length, filters with arbitrary spectral responses can be achieved.
In this work we summarize our recent contributions to integrated Bragg filters in Si-photonics, covering designs for applications ranging from telecommunications to quantum optics.
In this talk we present our recent advances in SWG metamaterial engineering. We will show a 1D-optical phased array composed of 112 evanescent-coupled surface emitting antennas with a length of 1.5 mm and fed by a compact distributed Bragg deflector. The measurements demonstrate a wavelength-steerable collimated beam with a far-field angular divergence of 1.8o × 0.2o. Experimental results of a bricked SWG 2×2 MMI coupler are also shown, achieving polarization agnostic performance in the 1500nm to 1560nm wavelength range. Both devices were fabricated on a standard 220-nm SOI platform using a single full-etch step process, with a minimum feature size of 80 nm, and thus compatible with immersion deep-UV lithography.
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.
Subwavelength grating metamaterials have become an integral design tool in silicon photonics. The lithographic segmentation of integrated waveguides at the subwavelength scale allows us to control optical properties such as mode delocalization, wavelength dispersion, and birefringence. So far, a range of subwavelength-based devices with unprecedented performance has been demonstrated, such as couplers, polarization-handling structures, filters, and input/output chip interfaces. In this invited talk, we will review the anisotropic foundations of subwavelength-grating metamaterial design and will provide an overview of our latest advances in subwavelength-enhanced silicon photonics devices, including optical antennas for beam steering and multi-line Bragg filters for spectral shaping.
Silicon photonic waveguides patterned at the subwavelength level behave as metamaterials whose optical properties, including refractive index, dispersion and anisotropy can be tuned by judiciously designing the subwavelength geometry. Over the past years, the added design freedom afforded by these structures has enabled a wide variety of novel high performance devices, ranging from high efficiency fibre-to-chip couplers, to on-chip polarization and mode management, and ultra-broadband waveguide couplers covering several optical communication bands. In this invited keynote talk we will revisit the physical foundations of these structures, explore some of the latest advances in the field with applications in both telecommunications and sensing, and discuss some of the outstanding challenges to move these structures from research labs to large-scale commercialisation.
Periodic silicon waveguides with a pitch that is below half the effective wavelength of light support diffraction-less Bloch modes. These modes propagate as through a homogeneous, artificial-core metamaterial waveguide whose optical characteristics can be engineered by lithographic patterning. Subwavelength gratings (SWGs) provide designers with unique tools to control the refractive index, dispersion and birefringence of the equivalent metamaterial, yielding improved device performance. Based on this approach many high-performance optical devices have been designed and experimentally demonstrated in the last years. In this paper we will review the fundamentals of SWG engineering and present some of our latest findings.
Silicon photonics has emerged as an intense field of research due to its unique capabilities to integrate photonics and electronics into the same platform using standard semiconductor fabrication facilities. Subwavelength grating (SWG) structures, i.e. periodic nanostructured waveguides with a pitch below half the wavelength of light, allow the lossless propagation of Bloch-Floquet modes which closely resemble propagation through a homogenous waveguide with optical properties (refractive index, dispersion, birefringence) that can be tailored to fulfill specific design goals. SWG engineering is now routinely used for novel and advanced device design. Fiber-chip couplers, polarization and mode multiplexers, multimode interference couplers (MMIs), lenses, and bragg filters have been successfully designed in our group based in these concepts. In this invited talk we will review some of our last advances in the field.
Integrated photonics devices, based in subwavelength grating (SWG) metamaterials, have shown unprecedented performance in a wide variety of situations. Since their proposal and first experimental demonstration in 2010 designers have made use of the new degrees of freedom provided by these structures to design advanced devices with improved capabilities. The extended design space provided by SWG structures has been successfully used to engineer the refractive index, the dispersion and, more recently, the waveguide birefringence, thus allowing novel advanced device design. In this invited talk we will review some of the advances made by our group in the field
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.
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 in the real part of the mode effective index (in the near-infrared band), or in its imaginary part in a specific range of wavelengths (in the mid-infrared band).
Regardless of which is the operating wavelength range, it is essential to select the proper sensing waveguide in order to maximize the device sensitivity. In this work we will review the potential of diffractionless subwavelength grating waveguides (SWG) for sensing applications by demonstrating their 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 regard, we will also show our recent progress 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.
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