Whitepaper v1.0October 2012

Towards fabless photonic integrationby Pascual Muñoz, CEO of VLC Photonics

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Brief historical perspective

Photonic integration allows to combine multiple optical functionalities into a single monolithic chip. Making this process generic allows a vertical specialisation through the value chain, by involving several spesialised partners at different stages of an optical system development. This compares to the traditional vertical aggregation model from a single device manufacturer. Such evolution mimics the case for the US semiconductor industry [1], where large corporations as AT&T and IBM, initially designed and produced their own components, and developed the fabs and processes required to manufacture them in house. In time, specialisation in two parts of the food chain: design and fabrication, lead to the appearance of fabless design houses and pure-play foundries. Considering photonics, the seed for generic integration appeared in Europe by 2007 [2], although some early work by HHI in 2000 already contains the spirit of generic photonic circuits [3].

Current state of the art

An overview example of relevant photonic foundries offering generic integration manufacturing services has been summarised in Table I. Operationally, these foundries can be described as follows: some foundries are publicly funded research institutions (like IMEC [4], CEA-LETI [4], IME [5], HHI [6], TU/e COBRA [6] or IMB-CNM [7]), whereas other are privately held companies (AMO [8], Luxtera [9], Oclaro [6], or LioniX [10]). Most of them are located in Europe, although USA and Asia are quickly catching up. A significant difference exists on the current state of access to these foundries. Silicon is well settled and public access is already available, while access to generic Indium Phosphide (InP) technology is still being developed through brokered research projects, with a roadmap for making it more openly available [11]. While some foundries only perform dedicated fabrication runs, in most cases, they offer Multi-Project Wafer (MPW) runs, sharing the wafer space

amongst different designers by dividing it into reticules. Formalisation of such access into a MWP run is done either directly with the foundry or through a brokering organisation as ePIXfab, JePPIX or OpSIS. The track record on MPW runs is currently hold by IMEC/CEA-LETI through ePIXfab, counting at the end of 2012 with nearly 30 runs in Silicon-on-Insulator (SOI) since 2007. On the InP side, TU/e COBRA has issued one MPW run per year since 2007, hence at the fall of 2012 a total of seven will have been completed. LioniX finished its first TripleX MPW on Si3N4 in 2012, and is already planning the second one.

The current photonic integration technologies can be considered stable, mature and well developed in terms of optical performance. Table I also shows the available photonic building blocks within each platform. For SOI, the trend during 2011 was the inclusion of ring modulators and photodetectors. This is currently being offered, or planned to be in the very short term, by all SOI platforms. The combination with CMOS electronics is a feature offered exclusively up to now through OpSIS using Luxtera’s technology. For InP, the adaptation of Oclaro's industrial fab (traditionally a component manufacturer using a vertical integration model) to produce generic PICs was certainly a milestone, whereas HHI is the sole generic InP foundry offering a high speed (balanced) photo-detector that can be combined with other passives. Silicon Nitride technology is mature but still relatively unexplored, owing to its very recent jump into the generic foundry arena.

For interfacing with external designers, foundries usually offer tools like the Photonic Design Kits (PDK), usually available in most of the platforms. PDK's allow to perform in a seamlessly integrated software environment both the photonic simulation and the mask layout, incorporating specific process information from each foundry. Whereas PhoeniX Software [12] is becoming the de facto standard in Europe, some foundries have proprietary libraries embedded into EDA software as Cadence. The foundries not

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having PDK's limit designers to communicate only at a basic GDS level. Back-end processes, as packaging, are an important open issue already identified and being addressed by most of the foundry players. The development of generic packages that can be reused amongst different PIC designs, minimising non-recursive engineering costs, is already in place for InP through Oclaro and HHI, whereas it will be developed for SOI by IMEC in the midterm.

As an example of these generic integration platforms, Figure 1 shows some optical chips developed in the past at several foundries and MPW runs by members of VLC Photonics, a design-house spinning-off from the Technical University of Valencia (Spain): (a) shows a frecuency discriminator receiver manufactured in InP, (b) shows an OCDMA decoder in Si3N4 (TripleX), (c) represents some microwave phase-shifters in InP, and (d) pictures a narrow-band photonic beam-former chip in SOI.

1 2 3 4 5 6 7 8 9 10FoundryTechnology

Access modeOpen access

Cost per

Shallow WaveguideDeeply Etched WaveguideWaveguide crossingY-BranchDirectional CouplerMultimode Interference CouplerSingle Polarization Grating CouplerPolarization Splitting Grating CouplerSpot-Size ConverterElectro-Optical ModulatorThermo-Optic ModulatorCarrier-Injection ModulatorRing ResonatorArrayed Waveguide GratingDistributed Bragg ReflectorSemiconductor Optical AmplifierPhotodiodeBalanced Photodiode

PackagingPhotonic Design Kit (PDK)Electronics

SOI SOI SOI SOI SOI InP InP InP Si3N4 Si3N4

MPW MPW Dedicated MPW MPW MPW MPW MPW MPW Dedicated

Area Area Project Project Area Area Area Area Area Project

BUILDING BLOCKS

Generic buldingblock availableTable I. Photonic foundry examples

Fig. 1. Examples of manufactured Photonic Integrated Circuits using four different generic platforms.

(b) (c)

(d)

(a)

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What's next?

Europe was certainly the cradle of generic photonic integration, both for Silicon and InP photonics, but as of 2011, US is quickly catching up with initiatives like OpSIS for SOI. While most of the electronic semiconductor industry already offshored its production to Asia [13], it is still unclear whether the EU and US photonic industry will do it as well in the near future. As an example, OpSIS first MPW run was already transferred to IME in Singapore.

According to current roadmaps, EU InP generic foundries will be established commercially as soon as 2016 [11]. Currently there is no known initiative to establish an InP generic foundry in the US, although we might see a step forward in the short term by some InP US fabs, as it happened for Silicon.

The fabless photonic design and prototyping ecosystem, fostered by these generic integration platforms, started to develop in Europe by 2009. Nowadays, it is made up of half a dozen SMEs, this number might keep growing in the short term. Conversely, in the US, start-ups have a strong linkage to a foundry/technology, but fabless PIC companies based upon generic integration might soon appear if developments go on.

References

[1] J.T. Macher and D.C. Mowery, "Vertical specialization and industry structure in high technology industries," Advances in Strategic Management, vol. 21, pp. 317–355, 2004.[2] "Towards a foundry model in micro- and nanophotonics: A vision for Europe," Tech. rep., EC FP6 NoE ePIXnet Steering Committee, March 2007.[3] M. Hamacher et Al., "Monolithic integration of lasers, photodiodes, waveguides and spot size converters on GaInAsP/InP for photonic IC applications," in Indium Phosphide and Related Materials, Proc. of the IEEE International Conference on, pp. 21–24, 2000.[4] "ePIXfab, the Silicon photonics platform." http://www.epixfab.eu.[5] "Institute of Microelectronics, Singapore." http://www.ime.a-star.edu.sg.[6] "Joint European Platform for InP-based Photonic Integrated Components and Circuits (JePPIX)." http://www.jeppix.eu.[7] "Instituto de Microelectrónica de Barcelona, Centro Nacional de Microelectrónica (IMB-CNM)." http://www.imb-cnm.csic.es.[8] "Gesellschaft für Angewandte Mikro- und Optoelektronik." http://www.amo.de.[9] "Optoelectronic System Integration in Silicon.” http://depts.washington.edu/uwopsis/.[10] "LioniX, microfluidics and integrated optics." http://www.lionixbv.nl.[11] M. Smit, M. Wale, D. Robbins, and H. Ambrosius, "The road to a multi-billion Euro market in InP-based Integrated Photonics: JePPIX ROADMAP 2012," Tech. rep., JePPIX, 2012.[12] “Phoenix Software” http://www.phoenixbv.com.[13] C. Brown, G. Linden, and J.T. Macher, "Offshoring in the Semiconductor Industry: A Historical Perspective," Brookings Trade

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© 2012, VLC Photonics S.L. This adapted paper was originally published in April 2012 at the 16th European Conference on Integrated Optics in Sitges, Spain. The brand names of third party companies remain trademarks of their corresponding right holder. VLC Photonics S.L. is not responsible for any consequences or damages that may arrive from the use of any of the information contained within this document or its references. The conditions for the partial reproduction of elements in this white paper are: � That VLC Photonics S.L. is cited specifically as the source of the information or material. � That the information and content is cited solely on the basis that it is used for information purposes only and not for commercial gain or any other distinct use that is not private or individual. � That no content contained in this white paper is modified in whatever form. � That no image available on this white paper shall be used, copied or distributed separately from the accompanying text or other content that accompanies it. � That it is communicated in writing and in an irrefutable manner to VLC Photonics S.L. and, that certified authorization is obtained from the company for the stated reproduction.