25-Gb/s broadband silicon modulator with 0.31-V·cm VπL based on forward-biased PIN diodes embedded with passive equalizer

We investigated the broadband operations of a silicon Mach-Zehnder modulator (MZM) based on a forward-biased-PIN diode. The phase shifter was integrated with a passive-circuit equalizer to compensate for the narrowband characteristics of the diodes, which consists of a simple resistance of doped silicon and a parallel-plate metal capacitance. The device structure was simple and fabricated using standard CMOS processes. The measured results for a 50-Omega driver indicated there was a small V pi L of 0.31 V.cm and a flat frequency response for a 3-dB bandwidth (f(3dB)) of 17 GHz, which agree well with the designed values. A 25-Gb/s large-signal operation was obtained using binary signals without pre-emphasis. The modulator showed a linear modulation property to the applied voltage, due to the metal capacitance of the equalizer. (C) 2015 Optical Society of America