High-Speed-Operation of All-Silicon Lumped-Electrode Modulator Integrated with Passive Equalizer

Yohei SOBU  Shinsuke TANAKA  Yu TANAKA  

IEICE TRANSACTIONS on Electronics   Vol.E103-C   No.11   pp.619-626
Publication Date: 2020/11/01
Publicized: 2020/05/15
Online ISSN: 1745-1353
DOI: 10.1587/transele.2019OCP0006
Type of Manuscript: INVITED PAPER (Special Section on Opto-electronics and Communications for Future Optical Network)
photonic integrated circuit,  silicon photonics,  optical modulator,  passive equalizer,  

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Silicon photonics technology is a promising candidate for small form factor transceivers that can be used in data-center applications. This technology has a small footprint, a low fabrication cost, and good temperature immunity. However, its main challenge is due to the high baud rate operation for optical modulators with a low power consumption. This paper investigates an all-Silicon Mach-Zehnder modulator based on the lumped-electrode optical phase shifters. These phase shifters are driven by a complementary metal oxide semiconductor (CMOS) inverter driver to achieve a low power optical transmitter. This architecture improves the power efficiency because an electrical digital-to-analog converter (DAC) and a linear driver are not required. In addition, the current only flows at the time of data transition. For this purpose, we use a PIN-diode phase shifter. These phase shifters have a large capacitance so the driving voltage can be reduced while maintaining an optical phase shift. On the other hand, this study integrates a passive resistance-capacitance (RC) equalizer with a PIN-phase shifter to expand the electro-optic (EO) bandwidth of a modulator. Therefore, the modulation efficiency and the EO bandwidth can be optimized by designing the capacitor of the RC equalizer. This paper reviews the recent progress for the high-speed operation of an all-Si PIN-RC modulator. This study introduces a metal-insulator-metal (MIM) structure for a capacitor with a passive RC equalizer to obtain a wider EO bandwidth. As a result, this investigation achieves an EO bandwidth of 35.7-37 GHz and a 70 Gbaud NRZ operation is confirmed.