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High efficiency fiber-to-waveguide grating coupler structures

Research Area: Photonics packaging

Main Researcher: Gunther Roelkens

The use of a grating coupler has the advantage of resulting in a very compact coupling structure and not requiring a polished facet for coupling, paving the way to wafer-scale testing of integrated optical components. The coupling efficiencies of fabricated devices presented in literature is limited however (typically 20 to 30 percent fiber coupling efficiency is experimentally obtained), which can be sufficient for testing but is not sufficient in practical applications. This low coupling efficiency is intrinsic to the grating structure used in these cases, as an important fraction of the optical power is diffracted towards the silicon substrate and is therefore lost. Here we propose a different grating layout based on the deposition of a silicon layer prior to etching of the grating coupler, as shown below. The fiber is slightly tilted off vertical to avoid a strong second order reflection.

Proposed grating structure layout
Proposed grating structure layout

This approach allows to obtain much higher grating directionality than in a conventional grating coupler design.Simulations show that an efficiency in the range of 60-80% is feasible, using standard CMOS technology for fabrication. A prototype of the optimized fiber coupling structure was fabricated, by local deposition of a 150nm thick amorphous silicon layer on an SOI waveguide substrate with a silicon waveguide layer thickness of 220nm. After deposition of the silicon layer, the grating structure was defined using focused ion beam etching (FIB), etching 220nm deep into the layer stack. An improvement of 2dB in fiber coupling efficiency was observed compared to the standard grating structures,although the efficiency is still substantially lower than the theoretical predictions. This discrepancy is probably related to the large optical absorption of the amorphous silicon, the damage induced into the material by the focused ion beam etching and the incorporation of gallium ions in the silicon host, substantially increasing the optical loss and can be avoided by using standard CMOS technology for the fabrication of the structures.

SEM view of a fabricated prototype structure and measured coupling spectrum
SEM view of a fabricated prototype structure and measured coupling spectrum

An addtional advantage of the fiber-to-waveguide grating coupler structure is that the diffractive nature of the coupling mechanism allows to integrate even more functionality in the coupling structure: the concept of using the diffractive grating coupler (which occupies an area of only 100m2) as a structure to duplex two (sufficiently spaced) wavelength channels, can find important applications, i.e. in the fabrication of SOI based integrated transceivers for the Fiber-to-the-Home market.

Diffractive grating structure as wavelength duplexer
Diffractive grating structure as wavelength duplexer

Other people involved:

Related Research Projects

PhD thesises

Publications

    International Journals

  1. T. Spuesens, S. Pathak, M. Vanslembrouck, P. Dumon, W. Bogaerts, Grating Coupler with Integrated Power Splitter for High-Intensity Optical Power Distribution, Photonics Technology Letters, 28(11), p.1173-1176 (2016)  Download this Publication (1.1MB).
  2. A. Subramanian, S. Selvaraja, P. Verheyen, A. Dhakal, K. Komorowska, R. Baets, Near infrared grating couplers for silicon nitride photonic wires, IEEE Photonics Technology Letters, 24(19), p.1700-1703 (2012)  Download this Publication (411KB).
  3. D. Vermeulen, Y. De Koninck, Y. Li, W. Bogaerts, R. Baets, G. Roelkens, Reflectionless grating couplers for SOI photonic integrated circuits , Optics Express, p.22278-22283 (2012)  Download this Publication (1.1MB).
  4. D. Vermeulen, S. Selvaraja, P. Verheyen, G. Lepage, W. Bogaerts, P. Absil, D. Van Thourhout, G. Roelkens, high-efficiency fiber-to-chip grating couplers realized using an advanced CMOS-compatible silicon-on-insulator platform, Optics Express, 18(17), p.18278-18283 (2010)  Download this Publication (744KB).
  5. G. Roelkens, D. Vermeulen, F. Van Laere, S. Selvaraja, S. Scheerlinck, D. Taillaert, W. Bogaerts, P. Dumon, D. Van Thourhout, R. Baets, Bridging the Gap Between Nanophotonic Waveguide Circuits and Single Mode Optical Fibers Using Diffractive Grating Structures , Journal of Nanoscience and Nanotechnology (invited), 10, p.1551-1562  (2010)  Download this Publication (3MB).
  6. L. Zimmermann, T. Tekin, H. Schroeder, P. Dumon, W. Bogaerts, How to bring nanophotonics to application silicon photonics packaging, IEEE LEOS Newsletter (invited), p.4-14 (2008)  Download this Publication (1.5MB).
  7. S. Scheerlinck, J. Schrauwen, G. Roelkens, D. Van Thourhout, R. Baets, Vertical fiber-to-waveguide coupling using adapted fibers with angled facet fabricated by a simple molding technique, Applied Optics, 47(18), p.3241-3245 (2008)  Download this Publication (2.8MB).
  8. G. Roelkens, D. Vermeulen, D. Van Thourhout, R. Baets, S. Brision, P. Lyan, P. Gautier, J.-M. Fedeli, High efficiency diffractive grating couplers for interfacing a single mode optical fiber with a nanophotonic silicon-on-insulator waveguide circuit, Applied Physics Letters, 92(13), p.131101 (2008)  Download this Publication (150KB).
  9. G. Roelkens, D. Van Thourhout, R. Baets, silicon-on-insulator ultacompact duplexer based on a diffractive grating structure, Optics Express, 15(16), p.10091 (2007)  Download this Publication (1.8MB).
  10. G. Roelkens, D. Van Thourhout, R. Baets, High efficiency grating couplers between silicon-on-insulator waveguides and perfectly vertical optical fibers, Optics Letters, 32(11), p.1495-1497 (2007)  Download this Publication (240KB).
  11. F. Van Laere, G. Roelkens, M. Ayre, J. Schrauwen, D. Taillaert, D. Van Thourhout, T. F. Krauss, R. Baets, Compact and highly efficient grating couplers between optical fiber and nanophotonic waveguides, Journal of Lightwave Technology, 25(1), p.151-156 (2007)  Download this Publication (486KB).
    Book / Book Chapter

  1. W. Bogaerts, D. Vermeulen, Off-chip coupling, Handbook of Silicon Photonics (invited), p.97-138 (2013)  Download this Publication (1.4MB).
    International Conferences

  1. T. Spuesens, S. Pathak, M. Vanslembrouck, P. Dumon, W. Bogaerts, Integrated Grating Coupler/Power Splitter for On-chip Optical Power Distribution, Group IV Photonics, France, p.141-142 (2014)  Download this Publication (1.2MB).
  2. W. Bogaerts, S. Selvaraja, H. Yu, T. Spuesens, P. Mechet, S. Stankovic, S. Keyvaninia, J. Van Campenhout, P. Absil, G. Roelkens, D. Van Thourhout, R. Baets, A Silicon Photonics Platform with Heterogeneous III-V Integration, Integrated Photonics Research, Silicon and Nano-Photonics (IPR) (invited), Canada, p.IWC2 (2011)  Download this Publication (283KB).
  3. D. Vermeulen, S. Selvaraja, R. Halir, W. Bogaerts, D. Van Thourhout, G. Roelkens, Photonic Integrated Circuits on SOI for Optical Fiber Communication Applications, 15th Annual Symposium of the IEEE Photonics Benelux Chapter, Netherlands, (2010)  Download this Publication (229KB).
  4. D. Vermeulen, S. Selvaraja, P. Verheyen, G. Lepage, W. Bogaerts, G. Roelkens, High-efficiency Silicon-On-Insulator Fiber-to-Chip Grating Couplers Using a Silicon Overlay, Group IV photonics, United States, p.FPd1 (2009)  Download this Publication (220KB).
  5. G. Roelkens, D. Taillaert, F. Van Laere, D. Vermeulen, J. Schrauwen, S. Scheerlinck, T. Claes, W. Bogaerts, P. Dumon, S. Selvaraja, D. Van Thourhout, R. Baets, Interfacing optical fibers and high refractive indx contrast waveguide circuits using diffractive grating couplers, Photonics West (invited), United States, (2009)  Download this Publication (1.8MB).
  6. D. Vermeulen, G. Roelkens, J. Brouckaert, D. Van Thourhout, R. Baets, R. Duijn, E. Pluk, G. Van den Hoven, Silicon-on-insulator nanophotonic waveguide circuit for fiber-to-the home transceivers, ECOC, Belgium, p.Tu.3.C.6 (2008)  Download this Publication (721KB).
  7. G. Roelkens, D. Vermeulen, D. Van Thourhout, R. Baets, S. Brision, P. Lyan, P. Gautier, J.M. Fedeli, High efficiency SOI fiber-to-waveguide grating couplers fabricated using CMOS technology, IPNRA, United States, (2008)  Download this Publication (232KB).
  8. G. Roelkens, D. Van Thourhout, R. Baets, Silicon-on-insulator grating duplexer for fiber-to-the-home transceivers, Proceedings of the 4th International Conference in Group IV Photonics, Japan, p.22-24 (2007)  Download this Publication (537KB).
  9. G. Roelkens, J. Schrauwen, D. Van Thourhout, R. Baets, High efficiency fiber-to-waveguide grating couplers in silicon-on-insulator waveguide structures, Proceedings of OSA Topical Meetings : Integrated Photonics and Nanophotonics and Applications (IPNRA 2007), United States, p.paper IMC2 (2007)  Download this Publication (699KB).
  10. G. Roelkens, D. Van Thourhout, R. Baets, SOI grating structure for perfectly vertical fiber coupling, European conference on integrated optics (ECIO) , Denmark, p.FC4 (2007)  Download this Publication (1.7MB).

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