Abstract
An optical digital-to-analog converter (DAC) is a promising solution for the efficient generation of multilevel modulation signals without a high-speed electrical DAC and a large swing linear driver. We report the design and characterization of an all-Si segmented Mach–Zehnder modulator for an optical DAC transmitter. The modulator comprises a forward-biased positive intrinsic negative (PIN) phase shifter integrated with a passive resistance and capacitance (RC) equalizer (PIN-RC) to optimize a tradeoff between modulation efficiency and analog bandwidth. We successfully confirmed an eye diagram of 90-Gbaud NRZ signal owing to a wide 3-dB bandwidth of 43.9 GHz. Additionally, a 70-Gbaud four-level pulse amplitude modulation (PAM4) waveform can be obtained via the optical DAC operation using a lumped segmented modulator because of its broad electro–optic bandwidth and uniform characteristics. A two-segmented modulator has a compact footprint of 300 μm × 600 μm. Error-free performances based on the patterns of the PRBS11 of NRZ signals were obtained at 50–70 Gbaud. The bit-error-rates of 60-Gbaud PAM4 and 70-Gbaud PAM4 were less than the 7% hard and 25.5% soft decision forward error correction limits, respectively. The optical DAC transmitter using an all-Si segmented PIN-RC modulator is suitable for next-generation high-speed multilevel transmitters.
Highlights
T HE strong demand for large transmission capacities of optical network applications has resulted in an interest in lowcost and low-power integrated transceivers
The bit-error-rates (BER)s of 60-Gbaud PAM4 and 70-Gbaud PAM4 were less than the 7% hard decision (HD) and 25.5% soft decision forward error correction (SD FEC) limits, respectively
We demonstrated the broadband operations of an all-Si segmented positive intrinsic negative (PIN)–resistance and capacitance (RC) modulator fabricated via standard foundry processes
Summary
T HE strong demand for large transmission capacities of optical network applications has resulted in an interest in lowcost and low-power integrated transceivers. Si/LiNbO3 hybrid, Si-organic hybrid, and plasmonic-organic hybrid modulators are promising candidates for next-generation optical modulators that offer high-speed operation and low power consumption in Si photonics platforms [2]–[4] They have not exhibited their compatibility with the photonics foundry processes. Si-organic hybrid and plasmonic-organic hybrid modulators have not been demonstrated with long-term reliability Another trend is the demonstration of highspeed operation of all-Si-based optical modulators, which are compatible with photonics foundry processes, highly reliable, and assembled densely with an electrical driver. A PAM-8 intensity modulation has been demonstrated using a hybrid configuration comprising an optical and an electrical DAC [14] This architecture combined with a segmented modulator and a binary driver array demonstrated extremely low power consumption, i.e., 1.59–4 mW/Gbps in multilevel operations [15]–[17].
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