Optical pump-rejection filter based on silicon sub-wavelength engineered photonic structures

The high index contrast of the silicon-on-insulator (SOI) platform allows the realization of ultra-compact photonic circuits. However, this high contrast hinders the implementation of narrow-band Bragg filters. These typically require corrugations widths of a few nanometers or double-etch geometries, hampering device fabrication. Here we report, for the first time, on the realization of SOI Bragg filters based on sub-wavelength index engineering in a differential corrugation width configuration. The proposed double periodicity structure allows narrow-band rejection with a single etch step and relaxed width constraints. Based on this concept, we experimentally demonstrate a single-etch, $\mathbf{220\,nm}$ thick, Si Bragg filter featuring a corrugation width of $\mathbf{150\,nm}$, a rejection bandwidth of $\mathbf{1.1\,nm}$ and an extinction ratio exceeding $\mathbf{40\,dB}$. This represents a ten-fold width increase compared to conventional single-periodicity, single-etch counterparts with similar bandwidths

Solutions to Landau equation under Prodi-Serrin's like criteria

In this paper, we introduce Prodi-Serrin like criteria for weak solutions under which it is possible to show existence of classical solutions to the spatially homogeneous Landau equation for all classical potentials and dimensions $d \ge 3$. The physical case of Coulomb interaction in dimension $d=3$ is included in our analysis, which generalizes the work of \cite{silvestre}. The first step consists in establishing instantaneous appearance of $L^{p}$ estimates using the Prodi-Serrin criteria. Then, we introduce a new $L^{p}$ to $L^{\infty}$ framework, using a suitable De Giorgi's argument reminiscent of the one found in \cite{ricardo}, which provides appearance of pointwise bounds for such solutions. Our approach is quantitative and does not require a preliminary knowledge of elaborate tools for nonlinear parabolic equations

Identification and characterization of novel factors that act in the nonsense-mediated mRNA decay pathway in nematodes, flies and mammals

Nonsense-mediated mRNA decay (NMD) is a surveillance mechanism that degrades mRNAs harboring premature termination codons (PTCs). We have conducted a genome-wide RNAi screen in Caenorhabditis elegans that resulted in the identification of five novel NMD genes that are conserved throughout evolution. Two of their human homologs, GNL2 (ngp-1) and SEC13 (npp-20), are also required for NMD in human cells. We also show that the C. elegans gene noah-2, which is present in Drosophila melanogaster but absent in humans, is an NMD factor in fruit flies. Altogether, these data identify novel NMD factors that are conserved throughout evolution, highlighting the complexity of the NMD pathway and suggesting that yet uncovered novel factors may act to regulate this process

A general approach for robust integrated polarization rotators

Integrated polarization rotators suffer from very high sensitivity to fabrication errors. A polarization rotator scheme that substantially increases fabrication tolerances is proposed. In the proposed scheme, two tunable polarization phase shifters are used to connect three rotator waveguide sections. By means of properly setting the polarization phase shifters, fabrication errors are compensated and perfect polarization rotation is achieved. Analytical conditions are shown that determine the maximum deviation that can be corrected with the proposed scheme. A design example is discussed, where the thermo-optic effect is used to provide the required tunable polarization phase shifting. Calculated 40dB extinction ratio is shown in presence of fabrication errors that would yield a 4dB extinction ratio in the conventional approach. © (2013) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.The authors want to aknowledge Universidad de Málaga alaga, Campus de Excelencia Internacional Andalucia Tech for their support

Combining Higher-Order Wavelets and Discontinuity Meshing: a Compact Representation for Radiosity

Colloque avec actes et comité de lecture. internationale.International audienceThe radiosity method is used for global illumination simulation in diffuse scenes, or as an intermediate step in other methods. Radiosity computations using Higher-Order wavelets achieve a compact representation of the illumination on many parts of the scene, but are more expensive near discontinuities, such as shadow boundaries. Other methods use a mesh, based on the set of discontinuities of the illumination function. The complexity of this set of discontinuities has so far proven prohibitive for large scenes, mostly because of the difficulty to robustly manage a geometrically complex set of triangles. In this paper, we present a method for computing radiosity that uses higher-order wavelet functions as a basis, and introduces discontinuities only when they simplify the resulting mesh. The result is displayed directly, without post-processing

Using Graphics Hardware to Speed-up Visibility Queries

International audienceWe present a visibility method that takes advantage of the graphics hardware to give fast answers to visibility queries. Our visibility method is designed to solve two types of visibility queries: point-based visibility queries, where several visibility queries share the same origin, and plane- based visibility queries, where several visibility queries have their origins on the same plane. Both occur frequently in global illumination algorithms. Combining the speed given by graphics hardware with a software heuristic to avoid reliability problems, our visibility method is signicantly faster than ray-casting, and still gives the same results

Silicon subwavelength modal Bragg grating filters with narrow bandwidth and high optical rejection

[EN] Waveguide Bragg grating filters with narrow bandwidths and high optical rejections are key functions for several advanced silicon photonics circuits. Here, we propose and demonstrate a new, to the best of our knowledge, Bragg grating geometry that provides a narrowband and high rejection response. It combines the advantages of subwavelength and modal engineering. As a proof-of-concept demonstration, we implement the proposed Bragg filters in 220-nm-thick Si technology with a single etch step. We experimentally show flexible control of the filter selectivity, with measured null-to-null bandwidths below 2 nm, and strength of 60 dB rejection with a null-to-null bandwidth of 1.8 nm.Agence Nationale de la Recherche (ANR-MIRSPEC-17-CE09-0041, ANR-SITQOM-15-CE24-0005); European Research Council (ERC POPSTAR 647342).Oser, D.; Pérez-Galacho, D.; Le Roux, X.; Tanzilli, S.; Vivien, L.; Labonte, L.; Cassan, E.... (2020). Silicon subwavelength modal Bragg grating filters with narrow bandwidth and high optical rejection. Optics Letters. 45(20):5784-5787. https://doi.org/10.1364/OL.394455S578457874520Azzini, S., Grassani, D., Strain, M. J., Sorel, M., Helt, L. G., Sipe, J. E., … Bajoni, D. (2012). Ultra-low power generation of twin photons in a compact silicon ring resonator. Optics Express, 20(21), 23100. doi:10.1364/oe.20.023100Jiang, W. C., Lu, X., Zhang, J., Painter, O., & Lin, Q. (2015). Silicon-chip source of bright photon pairs. Optics Express, 23(16), 20884. doi:10.1364/oe.23.020884Mazeas, F., Traetta, M., Bentivegna, M., Kaiser, F., Aktas, D., Zhang, W., … Tanzilli, S. (2016). High-quality photonic entanglement for wavelength-multiplexed quantum communication based on a silicon chip. Optics Express, 24(25), 28731. doi:10.1364/oe.24.028731Gisin, N., Ribordy, G., Tittel, W., & Zbinden, H. (2002). Quantum cryptography. Reviews of Modern Physics, 74(1), 145-195. doi:10.1103/revmodphys.74.145Knill, E., Laflamme, R., & Milburn, G. J. (2001). A scheme for efficient quantum computation with linear optics. Nature, 409(6816), 46-52. doi:10.1038/35051009Piekarek, M., Bonneau, D., Miki, S., Yamashita, T., Fujiwara, M., Sasaki, M., … Thompson, M. G. (2017). High-extinction ratio integrated photonic filters for silicon quantum photonics. Optics Letters, 42(4), 815. doi:10.1364/ol.42.000815Oser, D., Tanzilli, S., Mazeas, F., Alonso-Ramos, C., Le Roux, X., Sauder, G., … Labonté, L. (2020). High-quality photonic entanglement out of a stand-alone silicon chip. npj Quantum Information, 6(1). doi:10.1038/s41534-020-0263-7Pérez-Galacho, D., Alonso-Ramos, C., Mazeas, F., Le Roux, X., Oser, D., Zhang, W., … Vivien, L. (2017). Optical pump-rejection filter based on silicon sub-wavelength engineered photonic structures. Optics Letters, 42(8), 1468. doi:10.1364/ol.42.001468Klitis, C., Cantarella, G., Strain, M. J., & Sorel, M. (2017). High-extinction-ratio TE/TM selective Bragg grating filters on silicon-on-insulator. Optics Letters, 42(15), 3040. doi:10.1364/ol.42.003040Xia, F., Rooks, M., Sekaric, L., & Vlasov, Y. (2007). Ultra-compact high order ring resonator filters using submicron silicon photonic wires for on-chip optical interconnects. Optics Express, 15(19), 11934. doi:10.1364/oe.15.011934Dong, P., Feng, N.-N., Feng, D., Qian, W., Liang, H., Lee, D. C., … Asghari, M. (2010). GHz-bandwidth optical filters based on high-order silicon ring resonators. Optics Express, 18(23), 23784. doi:10.1364/oe.18.023784Ding, Y., Pu, M., Liu, L., Xu, J., Peucheret, C., Zhang, X., … Ou, H. (2011). Bandwidth and wavelength-tunable optical bandpass filter based on silicon microring-MZI structure. Optics Express, 19(7), 6462. doi:10.1364/oe.19.006462Horst, F., Green, W. M. J., Assefa, S., Shank, S. M., Vlasov, Y. A., & Offrein, B. J. (2013). Cascaded Mach-Zehnder wavelength filters in silicon photonics for low loss and flat pass-band WDM (de-)multiplexing. Optics Express, 21(10), 11652. doi:10.1364/oe.21.011652Wang, J., Glesk, I., & Chen, L. R. (2015). Subwavelength grating Bragg grating filters in silicon‐on‐insulator. Electronics Letters, 51(9), 712-714. doi:10.1049/el.2015.0546Zou, Z., Zhou, L., Wang, M., Wu, K., & Chen, J. (2016). Tunable spiral Bragg gratings in 60-nm-thick silicon-on-insulator strip waveguides. Optics Express, 24(12), 12831. doi:10.1364/oe.24.012831Cheben, P., Čtyroký, J., Schmid, J. H., Wang, S., Lapointe, J., Wangüemert-Pérez, J. G., … Dado, M. (2019). Bragg filter bandwidth engineering in subwavelength grating metamaterial waveguides. Optics Letters, 44(4), 1043. doi:10.1364/ol.44.001043Oser, D., Mazeas, F., Le Roux, X., Pérez‐Galacho, D., Alibart, O., Tanzilli, S., … Alonso‐Ramos, C. (2019). Coherency‐Broken Bragg Filters: Overcoming On‐Chip Rejection Limitations. Laser & Photonics Reviews, 13(8), 1800226. doi:10.1002/lpor.201800226Nie, X., Turk, N., Li, Y., Liu, Z., & Baets, R. (2019). High extinction ratio on-chip pump-rejection filter based on cascaded grating-assisted contra-directional couplers in silicon nitride rib waveguides. Optics Letters, 44(9), 2310. doi:10.1364/ol.44.002310Hammood, M., Mistry, A., Ma, M., Yun, H., Chrostowski, L., & Jaeger, N. A. F. (2019). Compact, silicon-on-insulator, series-cascaded, contradirectional-coupling-based filters with >50  dB adjacent channel isolation. Optics Letters, 44(2), 439. doi:10.1364/ol.44.000439Shi, W., Wang, X., Zhang, W., Chrostowski, L., & Jaeger, N. A. F. (2011). Contradirectional couplers in silicon-on-insulator rib waveguides. Optics Letters, 36(20), 3999. doi:10.1364/ol.36.003999Qiu, H., Jiang, J., Yu, P., Dai, T., Yang, J., Yu, H., & Jiang, X. (2016). Silicon band-rejection and band-pass filter based on asymmetric Bragg sidewall gratings in a multimode waveguide. Optics Letters, 41(11), 2450. doi:10.1364/ol.41.002450Yariv, A. (1973). Coupled-mode theory for guided-wave optics. IEEE Journal of Quantum Electronics, 9(9), 919-933. doi:10.1109/jqe.1973.1077767Halir, R., Cheben, P., Janz, S., Xu, D.-X., Molina-Fernández, Í., & Wangüemert-Pérez, J. G. (2009). Waveguide grating coupler with subwavelength microstructures. Optics Letters, 34(9), 1408. doi:10.1364/ol.34.001408Benedikovic, D., Cheben, P., Schmid, J. H., Xu, D.-X., Lamontagne, B., Wang, S., … Dado, M. (2015). Subwavelength index engineered surface grating coupler with sub-decibel efficiency for 220-nm silicon-on-insulator waveguides. Optics Express, 23(17), 22628. doi:10.1364/oe.23.022628Wang, J., Xuan, Y., Qi, M., Huang, H., Li, Y., Li, M., … Gan, F. (2015). Broadband and fabrication-tolerant on-chip scalable mode-division multiplexing based on mode-evolution counter-tapered couplers. Optics Letters, 40(9), 1956. doi:10.1364/ol.40.00195