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Design And Integration Of Photonic And Electronic Integrated Circuits For High-speed Wireline Transceivers

With the exploding data-rate needs of current and future digital applications, ever higher requirements are being set on the wireline transceivers for inter and intra data center traffic. The focus is on increasing the capacity of these optical transceivers, while simultaneously increasing the integration density and energy efficiency with each new generation. By Peter Ossieur, Program manager high-speed transceivers, imec.

Researchers at imec are taking on this double challenge by developing high-speed electronic and photonic integrated circuits for 100 to 130Gbaud transceivers, both for intensity-modulated direct-detect (IMDD) and for coherent optical transceivers. For a coherent transceiver, the specifications and functionality for the optics and electronics are much more demanding. The receiver DSP is also significantly more complex (compared to IMDD).

Scheme of an optoelectronic transceiver
For the optics, 100 to 130Gbaud operation requires at least 50 to 60GHz opto-electronic frontend bandwidth, both at the transmitter (modulator) and receiver (photodetector) side. Such bandwidths have been demonstrated with Indium Phosphate (InP)-based integrated optics, as well as with silicon photonics. Imec develops several silicon photonics platforms that include all the devices that are necessary for modulating and detecting optical signals. The same platform can also be used to realize passive devices such as silicon WDM filters and complex waveguide circuits. One component that until now was missing were electro-absorption modulators for the O-band. These are very compact modulators that don't need any additional heater power unlike ring resonators. Relying on the quantum-confined stark effect, imec demonstrated such components, that could be modulated all the way up to 60Gb/s. Further work is ongoing to integrate these devices in the full platform.

Scheme of an optoelectronic transceiver

To scale the bandwidth even higher e.g. towards 200G baud operation, compound semiconductors such as Indium phosphate can be integrated onto silicon photonic or silicon nitride wafers. Another alternative is Barium Titanate (BTO). This is a very promising electro-optic material that can push the performance of modulators even further. Imec is looking at integrating BTO-based modulators into its 200 mm platform. An important focus is to adapt the BTO deposition techniques to volume scaling. Unlike other material systems such as LiNbO3, BTO can be brought into CMOS foundries, a critical advantage for manufacturing at scale.