  This study presents an effective optical equalization technique for
generating ultrahigh baud rate signals. The equalization technique was
demonstrated using a dual-drive Mach-Zehnder modulator (DDMZM) with two-phase
shifters having different bandwidths, which can be achieved by adjusting the
structural design of the modulator or by incorporating varying bias voltages.
When the two phase shifters are driven by appropriately sized driving signals,
their partially offsetting response significantly reduces the rise and fall
times of the output signal. The experiments were conducted using silicon DDMZMs
without digital signal processing (DSP). In an experiment utilizing a low-speed
silicon modulator, the on-off keying (OOK) modulating speed was improved from
30 to 90 Gbaud. In an experiment utilizing a high-speed silicon modulator, the
OOK modulating speed was improved from 100 to 128 Gbaud, which approached the
limit of our testing system. This remains the highest baud rate achieved by an
all-silicon modulator without DSP. This technique breaks the baud rate ceiling
of the modulator and has the potential to enable silicon modulators to operate
at 200 Gbaud and beyond. The versatility of this method extends to a wide range
of optoelectronic platforms, encompassing thin-film lithium niobate and indium
phosphide modulators.
