Bond orbital description of the strain induced second order optical susceptibility in silicon

We develop a theoretical model, relying on the well established sp3 bond-orbital theory, to describe the strain-induced $\chi^{(2)}$ in tetrahedrally coordinated centrosymmetric covalent crystals, like silicon. With this approach we are able to describe every component of the $\chi^{(2)}$ tensor in terms of a linear combination of strain gradients and only two parameters $\alpha$ and $\beta$ which can be estimated theoretically. The resulting formula can be applied to the simulation of the strain distribution of a practical strained silicon device, providing an extraordinary tool for optimization of its optical nonlinear effects. By doing that, we were able not only to confirm the main valid claims known about $\chi^{(2)}$ in strained silicon, but also estimate the order of magnitude of the $\chi^{(2)}$ generated in that device

Optical Gain in Carbon Nanotubes

Semiconducting single-wall carbon nanotubes (s-SWNTs) have proved to be promising material for nanophotonics and optoelectronics. Due to the possibility of tuning their direct band gap and controlling excitonic recombinations in the near-infrared wavelength range, s-SWNT can be used as efficient light emitters. We report the first experimental demonstration of room temperature intrinsic optical gain as high as 190 cm-1 at a wavelength of 1.3 {\mu}m in a thin film doped with s-SWNT. These results constitute a significant milestone toward the development of laser sources based on carbon nanotubes for future high performance integrated circuits.Comment: 4 figure

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

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

Polarization and wavelength agnostic nanophotonic beam splitter

High-performance optical beam splitters are of fundamental importance for the development of advanced silicon photonics integrated circuits. However, due to the high refractive index contrast of the silicon-on-insulator platform, state of the art Si splitters are hampered by trade-offs in bandwidth, polarization dependence and sensitivity to fabrication errors. Here, we present a new strategy that exploits modal engineering in slotted waveguides to overcome these limitations, enabling ultra-wideband polarization-insensitive optical power splitters, with relaxed fabrication tolerances. The proposed splitter relies on a single-mode slot waveguide which is transformed into two strip waveguides by a symmetric taper, yielding equal power splitting. Based on this concept, we experimentally demonstrate -3$\pm$0.5 dB polarization-independent transmission in an unprecedented 390 nm bandwidth (1260 - 1650 nm), even in the presence of waveguide width deviations as large as $\pm$25 nm

Optical microcavity with semiconducting single-wall carbon nanotubes

We report studies of optical Fabry-Perot microcavities based on semiconducting single-wall carbon nanotubes with a quality factor of 160. We experimentally demonstrate a huge photoluminescence signal enhancement by a factor of 30 in comparison with the identical film and by a factor of 180 if compared with a thin film containing non-purified (8,7) nanotubes. Futhermore, the spectral full-width at half-maximum of the photo-induced emission is reduced down to 8 nm with very good directivity at a wavelength of about 1.3 $\mu$m. Such results prove the great potential of carbon nanotubes for photonic applications