2nd Kyoto University-Inamori Foundation Joint Kyoto Prize Symposium
July 11-12, 2015
Theme “Technology / Genetic Science / Arts” - Tracing the Path of Evolution, in Holistic Contemplation of Present and Future Civilization - (Finished)

Roel Baets

Roel Baets

Professor, Ghent University
Professor, imec(Interuniversity Microelectronics Centre)
・Silicon Photonics
・Photonic Integration
・Optical Communications
・Optical Sensing
・Laser Technology

Title of Presentation

“Photonic integrated circuits: enablers for the internet and for the life sciences”

Photonic integrated circuits (PIC’s) have gained considerable importance in the past 15 years and have made the transition from the research lab to the manufacturing fab. Traditionally PIC’s were fabricated in a variety of materials including glass, III-V semiconductors such as Indium Phosphide and a whole range of other materials. In the past 15 years a “new” material system has emerged for photonic IC’s: silicon, the dominant material used in electronic IC’s. Historically silicon was not considered a very interesting material for photonics, but this has changed dramatically and today silicon-based PIC’s are rapidly developing into the most versatile technology platform for a wide range of applications.

From a physical point of view the key asset of silicon photonics relates to the usage of optical waveguide devices with high refractive index contrast (silicon: 3.5 versus silica: 1.45). This high index contrast allows to confine light down to a wavelength (in silicon), to make ultra-compact devices (bends, filters, splitters, polarization converters), to make microcavities with record level Q/V, to make use of substantial Purcell enhancement, to implement photonic crystal structures and slow-wave structures, to engineer the dispersion properties of waveguides by tailoring their geometry at the nm-level, to make metamaterials based on sub-wavelength structures, to exploit the strong Kerr-effect in silicon e.g. for frequency comb generation, etc. Because of this there has been a “wealth” of achievements in the research community in which a wide variety of physical phenomena have been demonstrated by means of a silicon optical chip, in some cases in a way that is not possible in any other technology.

None of this would have been possible without the mature technological environment of CMOS-fabs. The patterning capabilities in such fabs, relying on 193 nm deep-UV lithography on 200 or 300 mm wafers, allow to fabricate structures with smallest features well below 100 nm, smallest pitches in periodic structures of the order of 100 nm and geometrical precision of the order of a few nm. That is exactly what is needed to implement high-index-contrast nanophotonic devices with good quality and reproducibility, operating at “telecom wavelengths” (1.3 and 1.55 μm) where silicon is transparent.

But the main driver for silicon photonics has been the need from the application side. The rapid growth of the internet has created a large need for high bandwidth optical transceivers with low cost and low footprint for use in short-reach interconnect in data-dense infrastructure. This is where silicon photonics excels, since it is possible to implement optical modulators and detectors for data rates up to 25 and even 40Gb/s and do so with the standard toolbox of processes in an advanced CMOS-fab. It is true to say that up to today it is still not possible to integrate lasers in the transceiver PIC’s by means of wafer-scale fabrication processes, but there is a rich variety of hybrid and even partly wafer-scale approaches to integrate III-V semiconductor based laser diodes onto silicon PIC’s. Furthermore there is promising scientific progress on truly monolithic approaches for such integration.

A system consists of more than just a photonic chip. The chip needs to be packaged and integrated with other functions, in particular electronic functions. Furthermore with the growing complexity of silicon photonic IC’s the need for hierarchical design tools has grown. Over the past years the chain of capabilities and tools for these “auxiliary” methods has gained considerable industrial momentum.
With the technology of silicon photonics gaining maturity there is a tendency to start considering it as a generic technology that can serve a diverse range of markets, not only in datacom and telecom, but also in sensors, biosensors and biomedical instruments. The driver is always the same: create compact and low-cost integrated circuits with a functionality and performance at par with otherwise bulky and costly implementations. Examples of this trend include PIC’s for sensing bioparticles such as proteins and DNA, PIC’s for spectroscopic detection of various small molecules (glucose, ammonia, markers for food spoilage etc), PIC’s for optical coherence tomography or for laser doppler vibrometry, PIC’s for readout of fiber Bragg gratings etc.

In those new applications the “traditional” wavelengths of silicon photonics (1.3 and 1.55 μm) are not necessarily optimal from the application’s point of view. This has led to the recent trend to “translate” silicon photonics to other wavelength domains, as much as possible without shying away from its major asset which is to fabricate the chip in a CMOS fab. Many groups are pushing the frontiers of silicon photonics towards longer wavelengths (mid-infrared), mainly driven by the promise of using the technology for vibrational spectroscopy. In parallel other groups are pushing towards shorter wavelengths, so as to be more compatible with biological media, fluorescent markers and Raman spectroscopy. In this case the silicon core needs to be replaced by a material that is transparent in the visible, silicon nitride being a good candidate.

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A brief Biography

Roel Baets is full professor at Ghent University (UGent). He is also associated with IMEC. He has management responsibilities within the Photonics Research Group of UGent, the Center for Nano- and Biophotonics (NB Photonics) of UGent, the international Erasmus Mundus MSc program in Photonics and the joint UGent-IMEC research program on silicon photonics.

Roel Baets received an MSc degree in Electrical Engineering from Ghent University in 1980 and a second MSc degree from Stanford University in 1981. He received a PhD degree from Ghent University in 1984. From 1984 till 1989 he held a postdoctoral position at IMEC (with detachment to Ghent University). Since 1989 he has been a professor in the Engineering Faculty of UGent where he founded the Photonics Research Group. From 1990 till 1994 he has also been a part-time professor at the Technical University of Delft and from 2004 till 2008 at the Technical University of Eindhoven.

Roel Baets has mainly worked in the field of integrated photonic components. He has made contributions to research on semiconductor laser diodes, guided wave and grating devices and to the design and fabrication of photonic ICs, both in III-V semiconductors and in silicon. As part of a team of 7 professors he leads the Photonics Research Group at Ghent University. With about 80 researchers this group is involved in numerous national and international research programs. The silicon photonics activities of the group are part of a joint research initiative with IMEC. Roel Baets is also director of the multidisciplinary Center for Nano- and Biophotonics (NB Photonics) at UGent, founded in 2010.

Roel Baets was co-founder of the interuniversity UGent-VUB MSc programme in Photonics and of the international Erasmus Mundus MSc programme in Photonics.

Roel Baets is a grant holder of the Methusalem programme of the Flemish government and of the European Research Council (ERC advanced grant). He is a Fellow of the IEEE.

From the research team of Roel Baets three spin-off companies have been founded: Trinean, Caliopa and Luceda Photonics.

Details of selected Awards and Honors
A list of selected Publications

・W. Bogaerts, R. Baets, P. Dumon, V. Wiaux, S. Beckx, D. Taillaert, B. Luyssaert, J. Van Campenhout, P. Bienstman, D. Van Thourhout, Nanophotonic Waveguides in Silicon‐on‐Insulator Fabricated with CMOS Technology, Journal of Lightwave Technology (invited), 23(1), p.401‐412 (2005)

・D. Taillaert, F. Van Laere, M. Ayre, W. Bogaerts, D. Van Thourhout, P. Bienstman, R. Baets, Grating Couplers for Coupling between Optical Fibers and Nanophotonic Waveguides, Japanese Journal of Applied Physics (invited), 45(8A), p.6071‐6077 (2006)

・K. De Vos, I. Bartolozzi, E. Schacht, P. Bienstman, R. Baets, Silicon‐on‐Insulator microring resonator for sensitive and label‐free biosensing, Optics Express, 15(12), p.7610‐7615 (2007)

・C. Koos, P. Vorreau, T. Vallaitis, P. Dumon, W. Bogaerts, R. Baets, B. Esembeson, I. Biaggio, T. Michinobu, F. Diederich, W. Freude, J. Leuthold, All‐optical high‐speed signal processing with silicon‐organic hybrid slot waveguides, Nature Photonics, 3(4), p.216‐219 (2009)

・J. Roels, I. De Vlaminck, L. Lagae, B. Maes, D. Van Thourhout, R. Baets, Tunable optical forces between nanophotonic waveguides, Nature Nanotechnology, 4, p.510‐513 (2009)

・L. Liu, R. Kumar, K. Huybrechts, T. Spuesens, G. Roelkens, E.‐J. Geluk, T. de Vries, P. Regreny, D. Van Thourhout, R. Baets, G. Morthier, An ultra‐small, low‐power, all‐optical flip‐flop memory on a silicon chip, Nature Photonics, 4(3), p.182‐187 (2010)

・W. Bogaerts, P. De Heyn, T. Van Vaerenbergh, K. De Vos, S. Selvaraja, T. Claes, P. Dumon, P. Bienstman, D. Van Thourhout, R. Baets, Silicon microring resonators, Lasers & Photonics Reviews, 6(1), p.47‐73 (2012)

・X. Liu, B. Kuyken, G. Roelkens, R. Baets, R. M. Osgood Jr., W. M. J. Green, Bridging the Mid‐Infrared‐to‐Telecom Gap with Silicon Nanophotonic Spectral Translation, Nature Photonics, p.667‐671 (2012)

・D. Jalas, A. Petrov, M. Eich, W. Freude, S. Fan, Z. Yu, R. Baets, M. Popovic, A. Melloni, J. Joannopoulos, M. Vanwolleghem, C. Doerr, H. Renner, What is ‐ and what is not ‐ an optical isolator, Nature Photonics (invited), 7, p.579‐582 (2013)

・G. Roelkens, U.D. Dave, A. Gassenq, N. Hattasan, C. Hu, B. Kuyken, F. Leo, A. Malik, M. Muneeb, E.M.P. Ryckeboer, S. Uvin, Z. Hens, R. Baets, Silicon‐based heterogeneous photonic integrated circuits for the mid‐infrared, Optical Materials Express (invited), 3(9), p.1523‐1536 (2013)

・S. Ghosh, S. Keyvaninia, W. Van Roy, T. Mizumoto , G. Roelkens, R. Baets, Adhesively bonded Ce:YIG/SOI integrated optical circulator, Optics Letters, 38(6), p.965-967 (2013)

・A. Dhakal, A. Subramanian, P.C. Wuytens, F. Peyskens, N. Le Thomas, R. Baets, Evanescent excitation and collection of spontaneous Raman spectra using silicon nitride nanophotonic waveguides, Optics Letters, 39(13), p.4025‐4028 (2014)

・F. Peyskens, A. Subramanian, P. Neutens, A. Dhakal, P. Van Dorpe, N. Le Thomas, R. Baets, Bright and dark plasmon resonances of nanoplasmonic antennas evanescently coupled with a silicon nitride waveguide, Optics Express, 23(3), p.3088-3101 (2015)

・B. Kuyken, T. Ideguchi, S. Holzner, M. Yan, T. W. Hänsch, J. Van Campenhout, P. Verheyen, S. Coen, F. Leo, R. Baets, G. Roelkens, N. Picque, An octave spanning mid-infrared frequency comb generated in a silicon nanophotonic wire waveguide, Nature Communications, 6(6310), (2015)

・R. Van Laer, B. Kuyken, D. Van Thourhout, R. Baets, Interaction between light and highly confined hypersound in a silicon photonic nanowire, Nature Photonics, 9(3), p.199-203 (2015)