Design of asymmetrical directional couplers on ridge and strip SOI technology with high-dimensional variation tolerance

[EN] The supermode analysis of asymmetrical directional couplers (ADC) based on SOI technology for strip and ridge structures at 1550 nm is herein reported, targeting to reduce ADC device fabrication requirements. The reported analysis based on supermodes permits us to assess the sensitivity of the ADC coupling efficiency by calculating the index difference between even and odd supermodes. Optimum designs have been found for 100 and 400 nm gaps, respectively, capable of converting and (de) multiplexing both TE0 and TE1 modes taking into account the width, gap, height, and slab thickness variations produced with respect to the nominal design. (C) 2018 Optical Society of AmericaMinisterio de Economia y Competitividad (MINECO) (TEC2015-70858-C2-1-R, RTC-2014-2232-3).García-Rodríguez, D.; Corral, JL.; Llorente, R. (2018). Design of asymmetrical directional couplers on ridge and strip SOI technology with high-dimensional variation tolerance. Optics Letters. 43(11):2491-2494. https://doi.org/10.1364/OL.43.002491S249124944311Essiambre, R.-J., Kramer, G., Winzer, P. J., Foschini, G. J., & Goebel, B. (2010). Capacity Limits of Optical Fiber Networks. Journal of Lightwave Technology, 28(4), 662-701. doi:10.1109/jlt.2009.2039464Richardson, D. J. (2016). New optical fibres for high-capacity optical communications. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 374(2062), 20140441. doi:10.1098/rsta.2014.0441Mizuno, T., Takara, H., Sano, A., & Miyamoto, Y. (2016). Dense Space-Division Multiplexed Transmission Systems Using Multi-Core and Multi-Mode Fiber. Journal of Lightwave Technology, 34(2), 582-592. doi:10.1109/jlt.2015.2482901Winzer, P. J. (2014). Making spatial multiplexing a reality. Nature Photonics, 8(5), 345-348. doi:10.1038/nphoton.2014.58Melati, D., Alippi, A., Annoni, A., Peserico, N., & Melloni, A. (2017). Integrated all-optical MIMO demultiplexer for mode- and wavelength-division-multiplexed transmission. Optics Letters, 42(2), 342. doi:10.1364/ol.42.000342Garcia-Rodriguez, D., Corral, J. L., & Llorente, R. (2017). Mode Conversion for Mode Division Multiplexing at 850 nm in Standard SMF. IEEE Photonics Technology Letters, 29(11), 929-932. doi:10.1109/lpt.2017.2694605Garcia-Rodriguez, D., Corral, J. L., Griol, A., & Llorente, R. (2017). Dimensional variation tolerant mode converter/multiplexer fabricated in SOI technology for two-mode transmission at 1550  nm. Optics Letters, 42(7), 1221. doi:10.1364/ol.42.001221Le, Y.-S., Wang, Z., Li, Z.-Y., Li, Y., Li, Q., Cui, C., & Wu, C.-Q. (2018). Three-mode all-optical (de)multiplexing on a SOI chip. Optics Communications, 406, 173-176. doi:10.1016/j.optcom.2017.04.059Sun, C., Yu, Y., Ye, M., Chen, G., & Zhang, X. (2016). An ultra-low crosstalk and broadband two-mode (de)multiplexer based on adiabatic couplers. Scientific Reports, 6(1). doi:10.1038/srep38494Hanzawa, N., Saitoh, K., Sakamoto, T., Matsui, T., Tsujikawa, K., Uematsu, T., & Yamamoto, F. (2015). PLC-Based Four-Mode Multi/Demultiplexer With LP11 Mode Rotator on One Chip. Journal of Lightwave Technology, 33(6), 1161-1165. doi:10.1109/jlt.2014.2378281Yamashita, Y., Fujisawa, T., Makino, S., Hanzasa, N., Sakamoto, T., Matsui, T., … Saitoh, K. (2017). Design and Fabrication of Broadband PLC-Based Two-Mode Multi/Demultiplexer Using a Wavefront Matching Method. Journal of Lightwave Technology, 35(11), 2252-2258. doi:10.1109/jlt.2016.2641461Zanzi, A., Brimont, A., Griol, A., Sanchis, P., & Marti, J. (2016). Compact and low-loss asymmetrical multimode interference splitter for power monitoring applications. Optics Letters, 41(2), 227. doi:10.1364/ol.41.000227Hanzawa, N., Saitoh, K., Sakamoto, T., Matsui, T., Tsujikawa, K., Koshiba, M., & Yamamoto, F. (2014). Mode multi/demultiplexing with parallel waveguide for mode division multiplexed transmission. Optics Express, 22(24), 29321. doi:10.1364/oe.22.029321Wang, J., He, S., & Dai, D. (2014). On-chip silicon 8-channel hybrid (de)multiplexer enabling simultaneous mode- and polarization-division-multiplexing. Laser & Photonics Reviews, 8(2), L18-L22. doi:10.1002/lpor.201300157Pan, C., & Rahman, B. M. A. (2016). Accurate Analysis of the Mode (de)multiplexer Using Asymmetric Directional Coupler. Journal of Lightwave Technology, 34(9), 2288-2296. doi:10.1109/jlt.2016.2530852Mikkelsen, J. C., Sacher, W. D., & Poon, J. K. S. (2014). Dimensional variation tolerant silicon-on-insulator directional couplers. Optics Express, 22(3), 3145. doi:10.1364/oe.22.003145Xu, K. (2014). Corrections to «On the Design and Optimization of Three-Terminal Light-Emitting Device in Silicon CMOS Technology» [Jul/Aug 14 8201208]. IEEE Journal of Selected Topics in Quantum Electronics, 20(4), 422-422. doi:10.1109/jstqe.2014.2318271Corral, J. L., Garcia-Rodriguez, D., & Llorente, R. (2016). Mode-Selective Couplers for Two-Mode Transmission at 850 nm in Standard SMF. IEEE Photonics Technology Letters, 28(4), 425-428. doi:10.1109/lpt.2015.249708

Mode-selective couplers for two-mode transmission at 850 nm in standard SMF

© 2016 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.The optimal design of a low-loss fused fiber mode-selective coupler for two-mode fiber transmission in the 850-nm band is presented. The coupler is based on precise phase matching of the propagation constants in each arm of a weakly fused fiber coupler. The designed component permits both mode converter and mode multiplexer/demultiplexer operation, thus enabling modal multiplexing transmission in this band with no additional component. The presented design is evaluated by simulation considering two types of structures, leading to asymmetric and symmetric coupler configurations. Mode converter and mode multiplexer operation is achieved with 93.5% efficiency in the band of 845 855 nm. Mode demultiplexer operation is achieved with an extinction ratio better than 20.4 dB in the same band.This work was supported by the Spanish Ministerio de Economia y Competitividad under Project RTC-2014-2232-3 HIDRASENSE and Project TEC2012-38558-C02-01.Corral, JL.; García Rodríguez, D.; Llorente Sáez, R. (2016). Mode-selective couplers for two-mode transmission at 850 nm in standard SMF. IEEE Photonics Technology Letters. 28(4):425-428. https://doi.org/10.1109/LPT.2015.2497080S42542828

Combined data detection scheme for zero-padded OFDM signals in MMF links

© © 2015 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.In this letter, we propose a receiver scheme for zero-padded orthogonal frequency division multiplexing (OFDM) that combines low complexity from overlap-and-add equalizer and low error rate provided by successive interference cancellation data detection from optimal ordering vertical Bell Laboratories layered space-time (V-BLAST) architecture. Results of numerical simulations on multimode optical fiber links show that the proposed scheme improves the error rate performance of zero forcing (ZF) equalization receiver, reaching results similar to V-BLAST. For example, the proposed scheme can reach 33.9 Gb/s in a 600-m link, whereas the ZF receiver would reach 29.06 Gb/s and cyclic prefix OFDM only 19.37 Gb/s. These results are obtained with a reduction in computational complexity (measured in number of real products) of 86% in detection and 66% in preprocessing with respect to the ZF receiver, and 75% and 97% with respect to the V-BLAST receiver.Manuscript received May 6, 2015; accepted May 24, 2015. Date of publication June 1, 2015; date of current version July 10, 2015. This work was supported by the Spanish Ministerio de Economia y Competitividad under Project TEC2012-38558-C02-02 and Project TEC2012-38558-C02-01, both with FEDER funds. The work of P. Medina was supported by the Formacion de Personal Investigador Grant Program of the Universitat Politecnica de Valencia.Medina Sevila, P.; Almenar Terré, V.; Corral, JL. (2015). Combined data detection scheme for zero-padded OFDM signals in MMF links. IEEE Photonics Technology Letters. 27(16):1753-1756. https://doi.org/10.1109/LPT.2015.2439158S17531756271

Transmission Over SSMF at 850 nm: Bimodal Propagation and Equalization

[EN] The combination of 850 nm vertical-cavity surfaceemitting laser (VCSEL) with standard single-mode fiber (SSMF) presents an effective and low-cost interface to increase the reach provided by multi-mode fiber links. At 850 nm, SSMF propagates two modes, and in this study, it has been experimentally shown that the different commercially available SSMF¿s present dissimilar values of differential mode delay. To cope with this unequal behavior of modal dispersion, we propose a scheme based on bidirectional decision feedback equalization (BiDFE) to overcome limited performance of other solutions as mode filtering or classical equalizers. A single span SSMF cabling model, including a measurement-derived statistical characterization of optical connectors, is simulated to evaluate the reach provided by the equalizer attending to both the conditions of the fiber excitation and the characteristics of the VCSEL. A minimum 1.45 km link length at 10 Gb/s is achieved if a linear combining BiDFE (LC-BiDFE) equalizer is included in the receiver, whatever laser launching condition and employing a single-transverse mode VCSEL. If a multitransverse mode VCSEL is used, the reach provided by LC-BiDFE is slightly reduced but assuring a minimum coverage of 1.15 km.This work was supported by the Spanish Ministerio de Economia y Competitividad under Projects TEC2015-70858-C2-2-R and TEC2015-70858-C2-1-R, both with FEDER funds. The work of P. Medina Sevila was supported by the Formacion de Personal Investigador grant program of the Universitat Politecnica de Valencia.Medina-Sevila, P.; Almenar Terré, V.; Corral, JL. (2017). Transmission Over SSMF at 850 nm: Bimodal Propagation and Equalization. Journal of Lightwave Technology. 35(19):4125-4136. https://doi.org/10.1109/JLT.2017.2726585S41254136351

Modal Selectivity at 850 nm employing Standard Single-Mode Couplers: Theory and Experimental Demonstration

[EN] In this paper, we evaluate experimentally and analyze theoretically and by simulation the demultiplexing of LP01 and LP11 modes in a 850 nm few mode optical link when a standard single-mode coupler theoretically designed for 1550 nm operation is used. The simulation analysis indicates a feasible conversion efficiency higher than 98% for the LP01 mode and 100% efficiency for LP11 mode. These results are experimentally validated considering different off-the-shelf optical couplers configured in 99:1, 90:10, 80:20 and 60:40 coupling ratios. Experimental analysis of the optical couplers demonstrate adequate functionality in correspondence with the theoretical analysis, exhibiting a good near-field pattern and modal profile for the LP01 and LP11 modes. The mode purity observed was 98.4% for the LP01 mode, and higher than 90% for the LP11 mode. The 90:10 optical coupler configuration shows best mode purity with the minimal insertion losses.This work was supported by the Ministerio de Economia y Competitividad (MINECO/FEDER), Spain (grant numbers TEC2015-70858-C2-1-R and RTC-2014-2232-3).García-Rodríguez, D.; Morant, M.; Corral, JL.; Llorente, R. (2019). Modal Selectivity at 850 nm employing Standard Single-Mode Couplers: Theory and Experimental Demonstration. Optics Communications. 436:248-252. https://doi.org/10.1016/j.optcom.2018.12.003S24825243

Low-Complexity Time Synchronization Algorithm for Optical OFDM PON System Using a Directly Modulated DFB Laser

© 2015 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.In this paper a low-complexity time synchronization algorithm for optical orthogonal frequency division multiplexing (OFDM) is proposed. The algorithm is based on a repetitive preamble that allows the use of a short cross correlator with an exponential average filter for postprocessing before a threshold detection. The signals in the correlation have been quantized with 1 bit, and the correlations have been implemented as a hard-wired tree adder to reduce the hardware cost. This solution has been verified in a passive optical network (PON) system using a directly modulated distributed feedback (DFB) laser achieving excellent performance with low computing processing complexity even in low signal-to-noise ratio scenarios. Finally, a parallel hardware architecture has been proposed for this time synchronization algorithm, and it has been implemented in a field programmable gate array device reaching a sample rate throughput up to 7.4 Gs/s.This work was supported by the Spanish Ministerio de Economia y Competitividad under projects TEC2012-38558-C02-02 and TEC2012-38558-C02-01 and with FEDER funds.Bruno, JS.; Almenar Terre, V.; Valls Coquillat, J.; Corral, JL. (2015). Low-Complexity Time Synchronization Algorithm for Optical OFDM PON System Using a Directly Modulated DFB Laser. IEEE/OSA Journal of Optical Communications and Networking. 7(11):1025-1033. doi:10.1364/JOCN.7.001025S1025103371

On the Performance and Power Consumption of Bias-T Based Drivers for High Speed VLC

[EN] LED lamps have become the predominant technology for lighting thanks to their low power consumption. Recently, the joint use of these devices for lighting and data transmission has aroused interest in the research community as a future green communication technology. During this time, many of the advances developed in this area have been demonstrated with experimental setups using LED drivers based on bias-T, thanks to their ease to combine signal modulation and LED bias. This article discusses the impact of the output impedance of the bias-T driver and the driver-LED connection parasitics on the performance and energy efficiency of the VLC system. It is concluded that the output impedance of the driver not only affects energy efficiency but also modifies the frequency response and, therefore, the LED's capacity to be modulated. A low output impedance driver is shown to offer a substantial improvement in the energy efficiency of the VLC driver.Thisworkwas supported in part by MCIN/AEI/10.13039/501100011033, in part by European Union (ERDF A way of making Europe) under Grants RTI2018101658-B100 and RTI2018-101296-B-I00, and in part byMinisterio de Ciencia, Innovacion y Universidades para la Formacion de Profesorado Universitario under Grant FPU19/04648.Salvador-Llàcer, P.; Valls Coquillat, J.; Canet Subiela, MJ.; Almenar Terre, V.; Corral, JL. (2022). On the Performance and Power Consumption of Bias-T Based Drivers for High Speed VLC. Journal of Lightwave Technology. 40(18):6078-6086. https://doi.org/10.1109/JLT.2022.319093660786086401

Linear Response Modeling of High Luminous Flux Phosphor-Coated White LEDs for VLC

[EN] The widespread deployment of LEDs for illumination purposes has open the door to the use of these devices for visible light communications (VLC). Most lighting fixtures are mounted with phosphor-based white LEDs, and a driver connected to the LED is also required for VLC. This paper shows that the parasitic effects introduced by this setup change the frequency response of the intrinsic LED. A linear model to characterize the whole setup is proposed, as well as a methodology to extract its parameters. This methodology allows the designer to characterize the frequency response of LEDs without the additional difficulty of knowing the specific parasitic components introduced by the setup. The proposed model offers an accurate estimation of the slope of the LED frequency response in order to broaden the frequency range in which the model is useful to characterize and simulate VLC links. This was corroborated with the characterization of three commercial white LEDs whose measured and modeled frequency responses matched perfectly.Salvador-Llàcer, P.; Valls Coquillat, J.; Corral, JL.; Almenar Terre, V.; Canet Subiela, MJ. (2022). Linear Response Modeling of High Luminous Flux Phosphor-Coated White LEDs for VLC. Journal of Lightwave Technology. 40(12):3761-3767. https://doi.org/10.1109/JLT.2022.315090737613767401

Model and Methodology to Characterize Phosphor-Based White LED Visible Light Communication Links

[EN] LED lighting has become the standard solution for illumination purposes thanks to its energy efficiency. Nowadays, there is growing interest in the use of LEDs for data transmission to develop future-generation communication systems. The low cost and widespread deployment of phosphor-based white LEDs make them the best candidate for visible light communications (VLC), although they have a limited modulation bandwidth. This paper presents a simulation model of a VLC link based on phosphor-based white LEDs and a method to characterize the VLC setup used to perform the data transmission experiments. Specifically, the simulation model incorporates the frequency response of the LED, the noise levels coming from the lighting source and the acquisition electronics, and the attenuation due to both the propagation channel and the angular misalignment between the lighting source and the photoreceiver. In order to validate the suitability of the model for VLC, carrierless amplitude phase (CAP) and orthogonal frequency division multiplexing (OFDM) modulation signals were employed for data transmission, and simulations with the proposed model and measurements over the equivalent scenario show high agreement.This research was funded by MCIN/AEI/10.13039/501100011033; by the European Union's "ERDF A way of making Europe" grant numbers PID2021-126514OB-I00 and RTI2018-101296-B-I00; and by the Ministerio de Ciencia, Innovacion y Universidades para la Formacion de Profesorado Universitario, grant number FPU19/04648.Salvador-Llàcer, P.; Almenar Terre, V.; Corral, JL.; Valls Coquillat, J.; Canet Subiela, MJ. (2023). Model and Methodology to Characterize Phosphor-Based White LED Visible Light Communication Links. Sensors. 23(10). https://doi.org/10.3390/s23104637231

Bimodal grating coupler design on SOI technology for mode division multiplexing at 1550 nm

© 2018 Optical Society of America. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modifications of the content of this paper are prohibited[EN] In this paper, we evaluate by means of simulation and experimentally the simultaneous coupling of the LP01x-LP11ax fiber modes and the TE0-TE1 nanophotonic SOI waveguide modes using a grating coupler for a two-mode fiber at 1550 nm. Both the grating width (ranging from 10 mu m to 15 mu m) and the grating vertical profile have been considered in the design procedure. The optimum design (14 mu m width and 609 nm grating period) has been selected in terms of coupling efficiency (both LP01x-TE0 and LP11ax-TE1), compactness and tolerance to lateral misalignments between fiber and coupler. The LP01x-TE0 and LP11ax-TE1 modes achieved coupling efficiencies of 49% and 45%, respectively. (C) 2017 Optical Society of America under the terms of the OSA Open Access Publishing AgreementMinisterio de Economia y Competitividad (MINECO/FEDER) (TEC2015-70858-C2-1-R, RTC-2014-2232-3)García-Rodríguez, D.; Corral, JL.; Griol Barres, A.; Llorente, R. (2018). Bimodal grating coupler design on SOI technology for mode division multiplexing at 1550 nm. Optics Express. 26(15):19445-19455. https://doi.org/10.1364/OE.26.019445S19445194552615Richardson, D. J. (2016). New optical fibres for high-capacity optical communications. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 374(2062), 20140441. doi:10.1098/rsta.2014.0441Kasahara, M., Saitoh, K., Sakamoto, T., Hanzawa, N., Matsui, T., Tsujikawa, K., … Koshiba, M. (2013). Design of Few-Mode Fibers for Mode-Division Multiplexing Transmission. IEEE Photonics Journal, 5(6), 7201207-7201207. doi:10.1109/jphot.2013.2292365Chen, H., Sleiffer, V., Snyder, B., Kuschnerov, M., van Uden, R., Jung, Y., … Koonen, T. (2013). Demonstration of a Photonic Integrated Mode Coupler With MDM and WDM Transmission. IEEE Photonics Technology Letters, 25(21), 2039-2042. doi:10.1109/lpt.2013.2280669Sun, C., Yu, Y., Ye, M., Chen, G., & Zhang, X. (2016). An ultra-low crosstalk and broadband two-mode (de)multiplexer based on adiabatic couplers. Scientific Reports, 6(1). doi:10.1038/srep38494Xing, J., Li, Z., Xiao, X., Yu, J., & Yu, Y. (2013). Two-mode multiplexer and demultiplexer based on adiabatic couplers. Optics Letters, 38(17), 3468. doi:10.1364/ol.38.003468Garcia-Rodriguez, D., Corral, J. L., Griol, A., & Llorente, R. (2017). Dimensional variation tolerant mode converter/multiplexer fabricated in SOI technology for two-mode transmission at 1550  nm. Optics Letters, 42(7), 1221. doi:10.1364/ol.42.001221Garcia-Rodriguez, D., Corral, J. L., & Llorente, R. (2017). Mode Conversion for Mode Division Multiplexing at 850 nm in Standard SMF. IEEE Photonics Technology Letters, 29(11), 929-932. doi:10.1109/lpt.2017.2694605Zhang, Z., Hu, X., & Wang, J. (2015). On-chip optical mode exchange using tapered directional coupler. Scientific Reports, 5(1). doi:10.1038/srep16072Ding, Y., Xu, J., Da Ros, F., Huang, B., Ou, H., & Peucheret, C. (2013). On-chip two-mode division multiplexing using tapered directional coupler-based mode multiplexer and demultiplexer. Optics Express, 21(8), 10376. doi:10.1364/oe.21.010376Zanzi, A., Brimont, A., Griol, A., Sanchis, P., & Marti, J. (2016). Compact and low-loss asymmetrical multimode interference splitter for power monitoring applications. Optics Letters, 41(2), 227. doi:10.1364/ol.41.000227Hanzawa, N., Saitoh, K., Sakamoto, T., Matsui, T., Tsujikawa, K., Koshiba, M., & Yamamoto, F. (2013). Two-mode PLC-based mode multi/demultiplexer for mode and wavelength division multiplexed transmission. Optics Express, 21(22), 25752. doi:10.1364/oe.21.025752Lai, Y., Yu, Y., Fu, S., Xu, J., Shum, P. P., & Zhang, X. (2017). Efficient spot size converter for higher-order mode fiber-chip coupling. Optics Letters, 42(18), 3702. doi:10.1364/ol.42.003702Hatori, N., Shimizu, T., Okano, M., Ishizaka, M., Yamamoto, T., Urino, Y., … Arakawa, Y. (2014). A Hybrid Integrated Light Source on a Silicon Platform Using a Trident Spot-Size Converter. Journal of Lightwave Technology, 32(7), 1329-1336. doi:10.1109/jlt.2014.2304305Hanzawa, N., Saitoh, K., Sakamoto, T., Matsui, T., Tsujikawa, K., Koshiba, M., & Yamamoto, F. (2014). Mode multi/demultiplexing with parallel waveguide for mode division multiplexed transmission. Optics Express, 22(24), 29321. doi:10.1364/oe.22.029321Dai, D., & Mao, M. (2015). Mode converter based on an inverse taper for multimode silicon nanophotonic integrated circuits. Optics Express, 23(22), 28376. doi:10.1364/oe.23.028376Taillaert, D., Van Laere, F., Ayre, M., Bogaerts, W., Van Thourhout, D., Bienstman, P., & Baets, R. (2006). Grating Couplers for Coupling between Optical Fibers and Nanophotonic Waveguides. Japanese Journal of Applied Physics, 45(8A), 6071-6077. doi:10.1143/jjap.45.6071Lardenois, S., Pascal, D., Vivien, L., Cassan, E., Laval, S., Orobtchouk, R., … Mollard, L. (2003). Low-loss submicrometer silicon-on-insulator rib waveguides and corner mirrors. Optics Letters, 28(13), 1150. doi:10.1364/ol.28.001150Orobtchouk, R., Layadi, A., Gualous, H., Pascal, D., Koster, A., & Laval, S. (2000). High-efficiency light coupling in a submicrometric silicon-on-insulator waveguide. Applied Optics, 39(31), 5773. doi:10.1364/ao.39.005773Wohlfeil, B., Rademacher, G., Stamatiadis, C., Voigt, K., Zimmermann, L., & Petermann, K. (2016). A Two-Dimensional Fiber Grating Coupler on SOI for Mode Division Multiplexing. IEEE Photonics Technology Letters, 28(11), 1241-1244. doi:10.1109/lpt.2016.2514712Koonen, A. M. J., Haoshuo Chen, van den Boom, H. P. A., & Raz, O. (2012). Silicon Photonic Integrated Mode Multiplexer and Demultiplexer. IEEE Photonics Technology Letters, 24(21), 1961-1964. doi:10.1109/lpt.2012.2219304Ding, Y., Ou, H., Xu, J., & Peucheret, C. (2013). Silicon Photonic Integrated Circuit Mode Multiplexer. IEEE Photonics Technology Letters, 25(7), 648-651. doi:10.1109/lpt.2013.2247394Galan, J. V., Sanchis, P., Blasco, J., & Marti, J. (2008). Study of High Efficiency Grating Couplers for Silicon-Based Horizontal Slot Waveguides. IEEE Photonics Technology Letters, 20(12), 985-987. doi:10.1109/lpt.2008.923546Roelkens, G., Van Thourhout, D., & Baets, R. (2006). High efficiency Silicon-on-Insulator grating coupler based on a poly-Silicon overlay. Optics Express, 14(24), 11622. doi:10.1364/oe.14.01162