Grating-based based vertical fibre coupler

Research Area: III-V Semiconductor Photonic ICs

Main Researcher: Dirk Taillaert

The small dimensions of photonic crystal or photonic wire waveguides in SOI create some challenging problems. Coupling light efficiently between a single-mode fiber, used in telecommunications, and these waveguides is not a trivial task. The use of tapered fibers can increase the coupling efficiency, but requires very critical alignment.

At the photonics research group, we are working on a photonic crystal or grating based fiber coupler which couples light from a vertical butt-coupled fiber to a planar waveguide. Compared to traditional grating couplers, which use a weak diffraction grating, our structure has a much larger bandwidth and is more compact. The out-of-plane fiber approach doesn't require cleaving or polishing of devices and allows wafer scale testing. Moreover, standard fibers or fiber arrays can be used, no lenses are needed.

coupler concept

We have demonstrated a coupling efficiency of -4.8dB (33% efficiency) and a 1dB bandwidth of 35nm (3dB bandwidth is 65nm) using standard single-mode fiber and SOI waveguides. In our experiments, we measure the fiber to waveguide to fiber insertion loss on a waveguide with a coupler on both ends. From this transmission measurement we can easily determine the efficiency of one coupler.
Compared to edge coupling (with tapered lensed fibers) the coupling efficiency is only slightly higher, but the alignment tolerances are much better. A deviation of 2um in the x or y direction results in only 1dB additional coupling loss. The efficiency can be further improved by using a more optimized grating design and a bottom reflector.

measurement result

We have optimized the coupler using numerical simulations. The optimized design has a coupling efficiency > 90% together with a 1-dB bandwidth > 40nm. The structure is shown in the picture below and more details can be found in D. Taillaert, P. Bienstman, R. Baets, "Compact efficient broadband grating coupler for silicon-on-insulator waveguides ", Optics Letters, vol. 29(23), pp. 2749-2751, Dec. 2004

When using a 1D-grating, the coupler is strongly polarization dependent, it works only for TE-polarization. The solve the polarization problem, we are also working on a 2d grating fibre coupler used as a polarization splitter.
To connect the wide fiber-matched waveguide to a narrow photonic wire, we can use a simple adiabatic taper, but this structure is relatively long. Therefore more compact solutions for this lateral spot-size conversion problem are also being investigated.

Optimized grating coupler design. The waveguide mode is incident from the left and light is coupled out upwards towards the fiber. The fiber itself is not shown in this picture.

Other people involved:

• Bert Luyssaert
• Frederik Van Laere
• Dirk Taillaert

Related Research Projects

• IST: PICCO (Photonic Integrated Circuits using photonic Crystal Optics)
• IST: ePIXnet (European Network of Excellence on Photonic Integrated Components and Circuits)
• IST: FUNFOX (Functional Photonic Crystal Devices for Metropolitan Optical Networks)

Downloads

(Nano)photonics in Silicon(-on-Insulator)

PhD thesises

• Wim Bogaerts, Nanofotonische Golfgeleiders en Fotonische Kristallen in Silicium-op-Isolator, Nanophotonic Waveguides and Photonic Crystals in Silicon-on-Insulator, (4/2004)  
• Dirk Taillaert, Roosterkoppelaars voor koppeling tussen optische vezels en nanofotonische golfgeleiders, Grating Couplers as Interface between Optical Fibres and Nanophotonic Waveguides, (11/2004)  
• Frederik Van Laere, Fotonische geïntegreerde circuits en vezelkoppelaars gebaseerd op InP gebonde membranen, Photonic Integrated Circuits and Fibre Couplers Based on InP Bonded Membranes, (1/2009)  

Patents

• D. Taillaert, R. Baets, Fiber to waveguide coupler   

Publications

International Journals


1. 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 doi:10.1364/OE.20.022278 (2012)  .
2. F. Van Laere, T. Claes, J. Schrauwen, S. Scheerlinck, W. Bogaerts, D. Taillaert, L. O'Faolain, D. Van Thourhout, R. Baets, Compact Focusing Grating Couplers for Silicon-on-Insulator Integrated Circuits, IEEE Photonics Technology Letters, 19(23), p.1919-1921 doi:10.1109/lpt.2007.908762 (2007)  .
3. S. Scheerlinck, J. Schrauwen, F. Van Laere, D. Taillaert, D. Van Thourhout, R. Baets, Efficient, broadband and compact metal grating couplers for silicon-on-insulator waveguides, Optics Express, 15, p.9639-9644 doi:10.1109/cleo.2007.4452981 (2007)  .
4. W. Bogaerts, P. Dumon, D. Van Thourhout, D. Taillaert, P. Jaenen, J. Wouters, S. Beckx, R. Baets, Compact Wavelength-Selective Functions in Silicon-on-Insulator Photonic Wires, J. Selected Topics in Quantum Electronics, 12(6), p.1394-1401 doi:10.1109/jstqe.2006.884088 (2006)  .
5. 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 doi:10.1143/jjap.45.6071 (2006)  .
6. D. Taillaert, P. Bienstman, R. Baets, Compact efficient broadband grating coupler for silicon-on-insulator waveguides , Optics Letters, 29(23), p.2749-2751 doi:10.1364/ol.29.002749 (2004)  .
7. W. Bogaerts, P. Dumon, D. Taillaert, V. Wiaux, S. Beckx, B. Luyssaert, J. Van Campenhout, D. Van Thourhout, R. Baets, SOI Nanophotonic Waveguide Structures Fabricated with Deep UV Lithography , Photonics and Nanostructures: Fundamentals and Applications (invited), 2(2), p.81-86 doi:10.1016/j.photonics.2004.07.002 (2004)  .
8. V.S. Volkov, S.L. Bozhevolnyi, D. Taillaert, Near-field imaging of light diffraction out of slab waveguides, Laser Physics Letters, 1(6), p.311-316 doi:10.1002/lapl.200410072 (2004).
9. W. Bogaerts, D. Taillaert, B. Luyssaert, P. Dumon, J. Van Campenhout, P. Bienstman, D. Van Thourhout, R. Baets, V. Wiaux, S. Beckx, Basic structures for photonic integrated circuits in Silicon-on-insulator, Optics Express (invited), 12(8), p.1583-1591 doi:10.1364/OPEX.12.001583 (2004)  .

Book / Book Chapter


1. W. Bogaerts, D. Vermeulen, Off-chip coupling, Handbook of Silicon Photonics (invited), p.97-138 doi:10.1201/b14668-4 (2013)  .

International Conferences


1. R. Baets, W. Bogaerts, D. Taillaert, P. Dumon, D. Van Thourhout, SOI Photonic Wire Based Components with Compact and Efficient Fiber Couplers , Optical Fiber Communications (invited), United States, p.OWG3 doi:10.1109/ofc.2007.4348871 (2007)  .
2. F. Van Laere, W. Bogaerts, D. Taillaert, P. Dumon, D. Van Thourhout, R. Baets, Compact Focusing Grating Couplers Between Optical Fibers and Silicon-on-Insulator Photonic Wire Waveguides , Optical Fiber Communications, United States, p.OWG1 doi:10.1109/ofc.2007.4348869 (2007)  .
3. W. Bogaerts, P. Dumon, J. Wouters, P. Jaenen, S. Beckx, V. Wiaux, D. Van Thourhout, D. Taillaert, B. Luyssaert, R. Baets, Silicon-on-Insulator Nanophotonics, SPIE Optics and Optoelectronics (invited), 5956, Poland, p.5956R-1-15 (2005)  .
4. R. Baets, D. Van Thourhout, G. Morthier, W. Bogaerts, L. Vanholme, Silicon-on-insulator based high index contrast waveguide devices: research in europe, 11th Microoptics Conference (MOC) (invited), Japan, p.E2, Session C ( 4 pages) (2005)  .
5. F. Van Laere, D. Taillaert, D. Van Thourhout, R. Baets, M.V. Kotlyar, T.F. Krauss, A Compact Fibre-to-Waveguide Coupler Based on Angled Slots, European Conference on Optical Communication (ECOC) 2005, United Kingdom, p.Tu3.6.5 doi:10.1049/cp:20050465 (2005)  .
6. R. Baets, Photonic Crystal Research in IST, European Conference on Optical Communication (ECOC) 2004 (invited), 5(Symposia), Sweden, p.80-82 (2004)  .
7. R. Baets, W. Bogaerts, Nanophotonic waveguides in SOI by means of deep UV lithography, Photonic and Electromagnetic Crystal Structures (PECS-V) (invited), Japan, p.160 (2004)  .
8. D. Taillaert, W. Bogaerts, R. Baets, Efficient coupling between submicron SOI-waveguides and single-mode fibers, IEEE/Leos Benelux Annual Symposium 2003, Netherlands, p.289-292 (2003).
9. W. Bogaerts, V. Wiaux, P. Dumon, D. Taillaert, J. Wouters, S. Beckx, J. Van Campenhout, B. Luyssaert, D. Van Thourhout, R. Baets, Large-scale production techniques for photonic nanostructures, Proc. SPIE (invited), 5225, United States, p.101-112 doi:10.1117/12.503665 (2003)  .
10. R. Baets, P. Bienstman, W. Bogaerts, D. Taillaert, B. Luyssaert, Coupling issues in strongly confined nanophotonic waveguides, ICTON 2003 (invited), Poland, p.191-192 doi:10.1109/icton.2003.1264613 (2003)  .
11. D. Taillaert, Out-of-plane fiber coupler for coupling to high-index-contrast waveguides, Workshop 2D photonic crystals, Switzerland, p.I-17 (2002).

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