Can a CMOS photonics switch transform networks and data centers?

We have fabricated a silicon photonic switch with the highest scale of integration (more than thousand circuits) and the highest number of different functions ever implemented before on a single chip. We are also realizing the most advanced 3D electrical interconnect between a photonic chip and its control electronic chip. This was done as part of IRIS, a 7th Framework Program for Research and Technological Development (FP7). In this post we'll share details about the progress we have made recently in the project.

Microscope

The main aim of IRIS is to demonstrate that silicon photonics is ready to realize a complete optical processing system on a miniaturized chip to switch very-high-capacity optical data flows. The new types of photonic chips are produced with the same well-developed production infrastructure used for complementary metal–oxide–semiconductor (CMOS) electronic chips. This ensures low cost, high yield and extremely small sizes to unleash a range of new optical devices in applications spanning from 5G networks and data centers to optical transport networks.

IRIS addresses the specific field of Transport Networks where operators are crying out for new high-capacity DWDM systems able to support, at lower capital and operational costs, fully flexible, dynamic and integrated services. The same approach of ‘ring resonator based’ optical switching device may find other important applications, both from technical and commercial points of view, namely in the data center, 5G networks and high-performance computing areas.

The ‘IRIS switch’ comprises many integrated optical functions like optical multiplexer/de-multiplexer, inter-leavers, power monitors, fiber couplers, waveguide crossing and a big cross-point matrix of optical switching elements.

The key circuits for optical switching are double micro-ring resonators that allow to switch high-capacity optical flows with small chip areas (10x10 micron) and low power consumption (just a few mW are needed). Switching in micro-ring resonators is performed by injecting a small current in micro heaters placed on top of the micro-rings in order to change the index of refraction by thermo-optic effect.

 

The device also integrates the highest number of different functions ever implemented before on a single chip.

The figure below shows simultaneous switching of many wavelength-division multiplexing (WDM) signals.

Another essential block is the wavelength multiplexer (MUX) that separates the wavelength channels from the input comb received by the optical fiber. We have implemented it using two star couplers interconnected by many optical waveguides.

The 3D photonic-electronic integration has been realized by flip chip bonding the control electronic integrated chip (EIC) on top of the photonic integrated chip (PIC) and the very high density electrical interconnection between PIC and EIC is implemented by the use of many hundreds of micro pillars.

The scheme of the package is shown below. The first element to be soldered is the thermoelectric cooler (TEC) used to dissipate the heat power generated by the chip. To guarantee a good thermal dissipation the TEC’s top and bottom ceramic surfaces are gold plated. The employed TEC, which allows to dissipate up to 8.2W within a temperature span of 25°C, is soldered inside the package. Then, the chip is glued on the TEC with a thermosetting resin. Both the TEC and the chips are pick-and-placed by means of a die-attach machine.

IRIS is a European-wide project being led by Ericsson along with partners CEA-Leti: Laboratoire d'electronique des technologies de l'information (France), Scuola Superiore S. Anna-CNIT (Italy), University of Vienna (Austria), STMicroelectronics (Italy), University of Valencia (Spain), ETRI: Electronics and Telecommunications Research Institute (South Korea) and University of Trento (Italy).

I hope you found this interesting and want to learn more about the IRIS project. Why not continue reading and follow us on our journey? Visit the IRIS project website.


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