10Gbit/s transceiver on silicon

Abstract

We discuss our approach to monolithic integration of Germanium photodectors with CMOS electronics for high speed optical transceivers. Integration into the CMOS process and optimization of optical coupling into the devices is described, followed by a discussion on how the devices are deployed in 4×10 Gbs receiver and transmitter subsystems. We demonstrate -19 dBm optical sensitivity for a bit error rate of 1e-12. An improvement of several dB resulted from optimizing the transimpedance amplifier relative to a design that was targeted for hybrid integration with flip-chip photodetectors, in order to take advantage of the drastically reduced capacitance of the integrated photodetectors (below 20 fF). As an example of how the versatility of on-chip waveguides and integrated photodiodes can be used, we further describe how the Germanium photodetectors are deployed to obtain a fully autonomous Mach-Zehnder interferometer subsystem with built-in monitoring and control, that can be instantiated as a single cell in an IC design. A fully differential layout is implemented for optical, electro-optic and electrical components yielding very small mismatch between components and enabling control of the interferometer with a minimum penalty.

Silicon photonics WDM transmitter with single section semiconductor mode-locked laser

“…Based on the analysis done above, a minimum average power of -7.2 dBm is required at the Rx (before internal fiber coupling losses) for SOA-based 14 Gbps operation. Integrating germanium waveguide photodetectors [66] in the same SiP chip as the RR-OADMs would remove two optical interfaces in the WDM Rx; however, the link budget would still need to accommodate an interface between the SOA and the Tx SiP chip, a single polarization grating coupler between the Tx chip and the fiber, a polarization splitting grating coupler between the fiber and the Rx, the insertion losses of the RR-OADMs, and excess losses due to on-chip waveguides, the total of which is estimated to be on the order of 13 dB losses after the SOA. The additional OMA required for compensating the increased noise resulting from increasing the data rate from 14 to 25 Gbps (approximately 1.3 dB assuming dethrottling the receiver to a 20-GHz bandwidth) can be provided by transitioning to an integrated germanium photodetector without the internal optical coupling losses of the fiber-coupled commercial receiver.…”

Advances in silicon photonics segmented electrode Mach-Zehnder modulators and peaking enhanced resonant devices

“…With serial 25 Gbps Infiniband EDR systems already in production, optical interconnects have become an essential technology enabling the scaling of data centers. Maturing Silicon Photonics (SiP) technology allowing mass production of planar integrated photonics at a competitive cost due to the utilization of existing CMOS infrastructure [3] and enabling high integration of optical devices such as modulators [4] and photodetectors [5] at the waferscale is expected to be particularly competitive to service an emerging need for extended reach single-mode high-speed data center interconnects in the 500 m-2 km range [6].…”

Germanium photodetectors enable scalable silicon photonics

“…Significant financial benefits may be achieved through the use of embedded photodetectors. 4 Embedding the photodetectors directly on the wafer will eliminate the costs associated with the assembly and testing of multiple components. This technology will allow a very large number of photodetectors to be grown directly on a die during wafer manufacturing thus reducing the billof-materials cost.…”