Frequency-tuning dual-comb spectroscopy using silicon Mach-Zehnder modulators

[EN] Dual-comb spectroscopy using a silicon Mach-Zehnder modulator is reported for the first time. First, the properties of frequency combs generated by silicon modulators are assessed in terms of tunability, coherence, and number of lines. Then, taking advantage of the frequency agility of electro-optical frequency combs, a new technique for fine resolution absorption spectroscopy is proposed, named frequency-tuning dual-comb spectroscopy, which combines dual-comb spectroscopy and frequency spacing tunability to measure optical spectra with detection at a unique RF frequency. As a proof of concept, a 24 GHz optical bandwidth is scanned with a 1 GHz resolution.Agence Nationale de la Recherche (ANR-17-CE09-0041, ANR-18-CE39-0009).Deniel, L.; Weckenmann, E.; Pérez-Galacho, D.; Alonso-Ramos, C.; Boeuf, F.; Vivien, L.; Marris-Morini, D. (2020). Frequency-tuning dual-comb spectroscopy using silicon Mach-Zehnder modulators. Optics Express. 28(8):10888-10898. https://doi.org/10.1364/OE.390041S108881089828

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

QPSK Modulation in the O-Band Using a Single Dual-Drive Mach Zehnder Silicon Modulator

[EN] Keeping up with bandwidth requirements in next generation short- and long-reach optical communication systems will require migrating from simple modulation formats such as on-off keying to more advanced formats such as quaternary phase-shift keying (QPSK). In this paper, we report the first demonstration of QPSK signal generation in the O-band using a silicon dual-drive Mach-Zehnder modulator (DD-MZM). The performance of the silicon DD-MZM is assessed at 20 Gb/s and compared against a similar DD-MZM based on LiNbO3, showing a limited implementation power penalty of only 1.5 dB.This work was supported in part by the European project Plat4m (FP7-2012-318178); European project Cosmicc (H2020-ICT-27-2015- 688516); French Industry Ministry Nano2017 program.Pérez-Galacho, D.; Bramerie, L.; Baudot, C.; Chaibi, M.; Messaoudène, S.; Vulliet, N.; Vivien, L.... (2018). QPSK Modulation in the O-Band Using a Single Dual-Drive Mach Zehnder Silicon Modulator. Journal of Lightwave Technology. 36(18):3935-3940. https://doi.org/10.1109/JLT.2018.2851370S39353940361

DAC-less PAM-4 generation in the O-band using a silicon Mach-Zehnder modulator

International audienceWe demonstrate 20-Gb/s 4-level pulse amplitude modulation (PAM-4) signal generation using a silicon Mach-Zehnder modulator (MZM) in the O-band. The modulator is driven by two independent binary streams, and the PAM-4 signal is thus generated directly on the chip, avoiding the use of power-hungry digital-to-analog converters (DACs). With optimized amplitude levels of the binary signals applied to the two arms of the MZM, a pre-forward error correction (FEC) bit-error rate (BER) as low as 7.6 × 10 −7 is obtained. In comparison with a commercially available LiNbO 3 modulator, the penalty is only 2 dB at the KP4 FEC threshold of 2.2 × 10 −4

Engineering the optical properties of silicon using sub-wavelength structures

In most integrated optics platforms, including silicon-on-insulator, only minor modifications in refractive index are possible. The geometry of the waveguiding structure is thus the only degree of freedom for the design of devices. The use of sub-wavelength gratings (SWGs), i.e. structures that are small enough to suppress diffraction effects, enables local engineering of both refractive index and dispersion, thereby opening new possibilities for device design. Here we present some of the recent advances in refractive index and dispersion engineering using silicon SWGs, focussing on ultra-broadband and compact multimode interference couplers and directional couplersThis work was supported by the Spanish Ministerio de Ciencia (project TEC2009-10152), the European Mirthe project (FP7-2010-257980), and the Universidad de Málaga - Campus de Excelencia Internacional Andalucìa Tech

Generation of electro-optic frequency combs with optimized flatness in a silicon ring resonator modulator

The flatness of electro-optic frequency combs (EOFCs) generated in a single silicon ring resonator modulator (RRM) is optimized by employing harmonic superposition of the radio-frequency driving signal. A differential evolution algorithm is employed in conjunction with a simplified model of the RRM for offline optimization of the amplitudes and phases of harmonic driving signals and the operating point of the RRM. The optimized driving signals are then applied to a silicon RRM. EOFCs containing 7 and 9 lines are synthesized with a power imbalance between the lines of 2.9 dB and 5.4 dB, respectively, compared to 9.4 dB for an optimized 5-line comb generated from a single sinusoidal driving signal.Comment: 4 pages, 5 figures, submitted to Optics Letter

L-shaped fiber-chip grating couplers with high- directionality and low reflectivity fabricated with deep-UV lithography

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Low-loss grating-coupled optical interfaces for large-volume fabrication with deep-ultraviolet optical lithography

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