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Data centers and high-performance computing markets are growing at a fast pace, mandating power-efficient and cost-effective high-speed interconnects [1], tackling the large attenuation and crosstalk problems of metal interconnects and allowing higher miniaturization than hybrid photonics. The emerging silicon photonics technology lends itself to low cost short-and medium-reach optical communications. Externally modulated lasers allow transmitted optical signals with higher spectral purity than directly modulated lasers [2]. Discarding electro-absorption modulators (EAMs), which imply difficult hybrid integration of III-V materials on silicon, external modulation can be realized in silicon photonics by adopting Mach-Zehnder modulators (MZMs). A dual-drive push-pull configuration allows achieving optimal chirp performance [2], reducing dispersion in the fiber. Compared to ring resonator modulators, MZMs can operate over a much wider optical bandwidth without requiring device tuning. In particular, MZMs are almost insensitive to temperature variation and thus do not require power-hungry thermal controllers [3], which can significantly increase the overall power consumption of electro-optical transmitters.In this scenario, this work presents a complete 25Gb/s silicon photonics electro-optical transmitter front-end comprising an MZM, using carrier depletion P-N junctions and operating at 1310nm wavelength, and a power-efficient CMOS driver. The transmitter optical path is integrated on STMicroelectronics 3Dcompatible silicon-photonics platform (PIC25G), which implements only optical devices in the front-end of line (FEOL) [4]. The electronic IC, realized in 65nm bulk CMOS technology, is 3D-assembled on top of the photonic IC by means of 20μm-diameter copper pillars, minimizing the interconnection parasitic capacitance. This 1310nm 25Gb/s silicon photonics electro-optical transmitter reports error-free operation with wide open optical eye diagrams at a competitive dynamic extinction ratio (ER) of up to 6dB using a depletion-mode MZM.A modular multi-stage architecture has been preferred to the classical travelling wave one to ensure the desired large ER values. For given VπLπ of the highspeed phase modulator (HSPM), which is basically set by the technology, the transmitter ER increases with modulator length and driving voltage swing. For a given ER, adopting a dual-drive push-pull configuration ( Fig. 22.9.1) allows halving either the modulator length or the driving swing compared to single-drive. In this work, we adopt dual driving together with a modular multi-stage driver architecture capable of higher ER than integrated travelling-wave modulators. Due to electrical losses along integrated travelling-wave electrodes (Fig. 22.9.1), the HSPM sections farther from the driver contribute less to phase modulation, while increasing optical attenuation and consume area. On the other hand, multi-stage drivers ensure the desired voltage amplitude along the entire electrode length. Modulator electrodes are split into several s...

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Silicon photonics platforms are emerging as attractive solutions for low power and cost effective short/medium-reach optical interconnects. To overcome the intrinsic limitations of monolithically integrated photonics with electronics, STMicroelectronics has developed a 3D-compatible silicon photonics platform that implements in the FEOL only optical devices. Photonics Integrated Circuits are made compatible with 3D assembly of Electronic Integrated Circuits through the use of copper pillars. In this paper we present a 25Gbps Opto-Electronic receiver operating at 1310nm wavelength, consisting of an integrated waveguide Germanium photodiode interfaced by means of copper pillars to a 65nm CMOS amplification chain. The receiver demonstrates an Average Optical Power sensitivity at photodiode input, at a BER of 10 -12 , of -11.9dBm with a PRBS7 input signal, corresponding to a 97μApp TIA input current. The achieved sensitivity is ~6dB better than state-of-the-art monolithically integrated silicon photonics receivers, at comparable TIA and LA power consumption.

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