Photonic integration becomes a reality

Silicon photonics uses silicon as a miniaturized optical medium for transmitting and switching data at very high speeds. In the recently concluded IRIS project, we demonstrated the full potential of silicon photonics technology, integrating in a silicon chip only a few millimeters large thousands of complex nanoscale optical circuits that are able to process Terabit/s of data, as well as the relevant control electronic circuits.

photonic chip

Principal Researcher, photonics

Principal Researcher, photonics

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This is a world record – never before have so many optical circuits been integrated together with their electrical control circuits on the same 3D chip.

What is more, they can be mass produced at low cost and with high miniaturization, unleashing a range of new optical devices for 5G networks, data centers and optical transport networks. The project results exceeded expectations and the integrated switch device performed better than the specifications defined in the early phase of the project. Learn more here!

In a previous blog post ‘Can a CMOS photonics switch transform networks and data centers?’, we presented the architecture and design of the large scale integration optical switch with Terabit/s capacity that was developed in the IRIS project. In the final phases of the project, we were able to verify and successfully demonstrate the fabrication process and to experimentally evaluate the functionalities of the switch, reaching the highest level of photo-electronic integration ever achieved.

The result is a real breakthrough in the development of optical devices. Taking the same road as electronic integrated circuits, with increasing integration scale over time, this can enable the development of new low-cost telecom and datacom equipment that can keep pace with the exponential increase in bandwidth demands. Ericsson, together with partners, implemented a key technology enabling large scale integration: the world’s most advanced 3D electrical interconnect between a photonic chip and its control electronic chip.

A photograph of the highly integrated photonic integrated chip (PIC) is shown in Fig. 1 with the different optical functions indicated by different colors.

Fig.1: Photograph of the photonic integrated chip (PIC)

All the individual optical circuits must be controlled by an electronic integrated chip (EIC), shown in Fig. 2, which has a similar integration scale as the optical chip, including both digital control circuits and analog control and monitoring circuits (low noise amplifiers and drivers).

Fig. 2: Photograph of the electronic integrated chip (EIC)

The PIC and EIC were interconnected by a high-density 3D electrical interconnect made from more than 2000 micro-bumps. The PIC was also optically connected to a ribbon fiber, as shown in Fig. 3.

Fig. 3: 3D high density photo-electronic interconnect and ribbon fiber attachment

The PIC+EIC sub-assembly was packaged in a metallic cage, so it could be used for both evaluating the system performance and in a demonstrator, see Fig. 4.

Fig. 4: Optical switch in the package

Switching and transmission characteristics were tested, specifically the crosstalk, which isthe most critical source of performance degradation in this switch. The eye diagrams are presented in Fig. 5 showing the transmission, a) with worst case crosstalk (three interferers at the same wavelength of the wanted signal) and b) without crosstalk. The performance was very good even in the worst transmission conditions

Fig. 5: Eye diagram comparison: a) with worst case crosstalk, b) without crosstalk

Final considerations
In the IRIS project, we demonstrated that silicon photonics technology is suitable for large-scale integrated optical switches. We also proved that a large scale 3D integration of electronic and photonic chips with thousands of interconnections is feasible.

IRIS was a European Union funded FP7 Project led by Ericsson with partners: CEA-LETI, CNIT, University of Wien, ST Microelectronics, University of Valencia, ETRI and University of Trento. The results achieved are an example of how fruitful collaboration between industry and academia can lead to significant steps forward in technology. Here is the link to the IRIS EU Project web site, (2015).

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