Researchers in Japan have demonstrated a silicon optical modulator capable of transmitting data at up to 200 gigabits per second, offering a potential route to denser, energy-efficient connections in AI data centers. The device, which converts electrical signals into optical signals, measures 320 micrometers in length, including its equalizer section. Conventional silicon Mach-Zehnder modulators typically measure 2–4 millimeters. The study was published in Nature Communications.
The design combines a photonic crystal waveguide with an integrated electro-optic equalizer. Carefully arranged holes slow light as it travels through the silicon, strengthening its interaction with the device and improving modulation efficiency. Although electrical resistance ordinarily restricts the high-frequency response of slow-light modulators, the equalizer adjusts how parts of the optical signal combine to counter this limitation. It extended the usable frequency range from 35 to 80 gigahertz in one design and from 23 to 55 gigahertz in another. Using four-level pulse-amplitude modulation, the team achieved 180 gigabits per second without digital signal processing. Adding an 11-tap receiver equalizer increased transmission to 200 gigabits per second, with modulator energy consumption of 63 femtojoules per bit.
Despite its compact footprint and compatibility with established semiconductor manufacturing processes, the device has substantial optical insertion loss: light intensity falls by 11.7–15.5 decibels during transmission through it. An optical amplifier compensated for this loss in the experiments. Practical deployment would benefit from design improvements that reduce attenuation. The researchers also plan to broaden the supported wavelength range, potentially allowing multiple optical channels to operate together.
