Broadband Mid-IR superabsorption with aperiodic polaritonic photonic crystals

We propose an approach for broadband near-perfect absorption with aperiodic-polaritonic photonic crystals (PCs) operating in the phononpolariton gap of the constituent material. In this frequency regime the bulk polaritonic materials are highly reflective due to the extreme permittivity values, and so their absorption capabilities are limited. However, we are able to achieve absorptance of more than 90%  almost across the entire phonon-polariton gap of SiC with a SiC-air aperiodic one-dimensional(1D)-PC with angular bandwidth that covers the range of realistic diffraction-limited sources. We explore two types of aperiodic PC schemes, one in which the thickness of the SiC layer increases linearly, and one in which the filling ratio increases linearly throughout the structure. We find that the former scheme performs better in terms of exhibiting smoother spectra and employing less SiC material. On the other hand, the second scheme performs better in terms of the required total structure size. We analyze the principles underpinning the broadband absorption merit of our proposed designs, and determine that the key protagonists are the properties of the entry building block and the adiabaticity of the aperiodic sequencing scheme. Further investigation with derivative lamellar sequences,–resulting by interchanging or random positioning of the original building blocks–, underline the crucial importance of the building block arrangement in an increasing order of thickness. If we relax the requirement of near-perfect absorption, we show that an averaged absorption enhancement across the SiC phonon-polariton gap of ~10 can be achieved with much shorter designs of the order of two free-space wavelengths. Our findings suggest that our aperiodic polaritonic PC route can be promising to design broadband electromagnetic absorbers across the spectrum

Low-loss, compact, spot-size-converter based vertical couplers for photonic integrated circuits

Funding: (i) European Union Horizon H2020 Programme (H2020-ICT27-2015, COSMICC No. 688516). (ii) European Union Research Council (ERC) starting grant 337508.In recent years, the monolithic integration of new materials such as SiN, Ge and LiNbO3 on silicon (Si) has become important to the Si photonics community due to the possibility of combining the advantages of both material systems. However, efficient coupling between the two different layers is challenging. In this work, we present a spot size converter based on a two-tier taper structure to couple the optical mode adiabatically between Si and SiN. The fabricated devices show a coupling loss as low as 0.058 dB  ±  0.01 dB per transition at 1525 nm. The low coupling loss between the Si to SiN, and vice versa, reveals that this interlayer transition occurs adiabatically for short taper lengths (<200 µm). The high refractive index contrast between the Si and SiN is overcome by matching the optical impedance. The proposed two-tier taper structure provides a new platform for optoelectronic integration and a route towards 3D photonic integrated circuits.PostprintPeer reviewe

Compact photonic-crystal superabsorbers from strongly absorbing media

Copyright © 2013 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Journal of Applied Physics, Volume 114 (3), article 033504, and may be found at http://dx.doi.org/10.1063/1.4811521We present a route to near-perfect absorption in compact photonic-crystal (PC) structures constructed from strongly absorbing media that are typically highly reflective in bulk form. Our analysis suggests that the key underlying mechanism in such PC superabsorbers is the existence of a PC-band-edge reflectionless condition. Although the latter is by default uncharacteristic in photonic crystals, we propose here a clear recipe on how such condition can be met by tuning the structural characteristics of one-dimensional lossy PC structures. Based on this recipe, we constructed a realizable three-layer SiC- BaF2 -SiC PC operating within the Reststrahlen band of SiC. We demonstrate near-perfect absorption in this prototype of total thickness smaller than λ/3 , where more than 90% of the impinging light is absorbed by the top deep-subwavelength layer of thickness ∼λ/1100 . We believe our study will inspire new photonic-crystal-based designs for extreme absorption harnessing across the electromagnetic spectrum.University of Exete

Slow light to reduce the energy dissipation of Mach-Zehnder modulators in silicon photonics

Integrated Mach-Zehnder (MZ) modulators are important components in silicon photonic devices that rely on a reverse-biased p-n junction to modulate the optical signal via a change of the waveguide refractive index. Reducing their energy consumption is a crucial step towards the application of silicon photonics, especially in connection with the growing traffic volumes in data centers. In this work, we combine band-edge slow light structures consisting of silicon grating waveguides with periodic (interlaced) p-n junctions to maximize spatial matching between the optical field mode and the depletion region of the p-n junction. The two effects together will result in an improved modulation efficiency, leading to a strongly reduced energy dissipation per bit

On two problems related to cancellativity

SIGLETIB: RN 7281 (138) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman