High-speed optical interconnects are crucial for both high performance computing and data centers. High power consumption and limited device bandwidth have hindered the move to higher optical transmission speeds. Integrated optical transceivers in silicon photonics using pulse-amplitude modulation (PAM) are a promising solution to increase data rates. In this paper, we review recent progress in silicon photonics for PAM transmissions.
On-chip frequency comb generation is a promising solution for seeding a chip-scale optical transmitter for both Nyquist wavelength-division multiplexing (WDM) and orthogonal frequency-division multiplexing. We demonstrate flexible frequency comb generation using a silicon photonic dual-drive Mach-Zehnder modulator fabricated on a CMOS-compatible process. Our on-chip comb has five lines spaced at 20 GHz, with a high tone-to-noise ratio of about 40 dB after one stage optical amplification. Our back-to-back transmission achieves bit error rates (BERs) well below 2e-2, the threshold for 20% overhead forward error correction (FEC), for 800 Gb/s using 16 Gbaud 32QAM on five WDM channels. We also test a seamless 800 Gb/s super-channel using 5×20 Gbaud 16QAM, with BER below the 7% overhead FEC threshold of 3.8e-3. To the best of our knowledge, this is the first demonstration of high-spectralefficiency data carried by an all-silicon optical frequency comb. This establishes that a silicon optical frequency comb has sufficient optical signal to noise ratio for high order QAM, as well as excellent stability for super-channels without guard bands, paving the way to an integrated high-spectral-efficiency multi-carrier optical transmitter.
Abstract-Silicon photonic modulators have strong nonlinear behavior in phase modulation and frequency response, which needs to be carefully addressed when they are used in high-capacity transmission systems. We demonstrate a comprehensive model for depletion-mode Mach-Zehnder modulators (MZMs) on silicon-on-insulator, which provides a bridge between device design and system performance optimization. Our methodology involves physical models of p-n-junction phase-shifters and traveling-wave electrodes, as well as circuit models for the dynamic microwave-light interactions and time-domain analysis. Critical aspects in the transmission line design for high-frequency operation are numerically studied for a case of p-n-junction loaded coplanar-strip electrode. The dynamic interaction between light and microwave is simulated using a distributed circuit model solved by the finite-difference time-domain method, allowing for accurate prediction of both small-signal and large-signal responses. The validity of the model is confirmed by the comparison with experimental results for a series push-pull MZM with a 6 mm phase shifter. The simulation shows excellent agreement with experiment for high-speed operation up to 46 Gbps. We show that this time-domain model can well predict the impact of the nonlinear behavior on the large-signal response, in contrast to the poor prediction from linear models in the frequency domain.
When designing an analog front-end for neural interfacing, it is hard to evaluate the interplay of priority features that one must upkeep. Given the competing nature of design requirements for such systems a good understanding of these trade-offs is necessary. Low power, chip size, noise control, gain, temporal resolution and safety are the salient ones. There is a need to expose theses critical features for high performance neural amplifiers as the density and performance needs of these systems increases. This review revisits the basic science behind the engineering problem of extracting neural signal from living tissue. A summary of architectures and topologies is then presented and illustrated through a rich set of examples based on the literature. A survey of existing systems is presented for comparison based on prevailing performance metrics.
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