Researchers in Japan have demonstrated a compact silicon optical modulator operating at up to 200 gigabits per second (Gb/s). Such devices convert electrical signals into optical signals, supporting data transfer between chips. Published in Nature Communications, the work addresses the challenge of increasing connection speeds in AI data centres while limiting energy consumption.
The modulator incorporates a photonic crystal waveguide: a structure whose patterned holes slow the propagation of light. This strengthens light–device interaction, improving modulation efficiency within a smaller footprint. Although electrical resistance normally restricts the high-frequency response of slow-light modulators, an integrated electro-optic equaliser compensates by adjusting how components of the optical signal combine. In one design, the supported frequency range increased from 35 to 80 gigahertz. The complete device is 320 micrometres long, compared with 2–4 millimetres for conventional silicon Mach–Zehnder modulators. Using four-level pulse-amplitude modulation, it achieved 180 Gb/s without digital signal processing; an 11-tap receiver equaliser raised this to 200 Gb/s, with modulator energy consumption of 63 femtojoules per bit.
The architecture could support denser optical connections with limited energy use, but optical insertion loss remains substantial at 11.7–15.5 decibels. An optical amplifier compensated during testing, while practical deployment would benefit from reduced losses. The researchers also intend to broaden the supported wavelength range so that multiple channels can operate together. They project that 16–32 channels could provide an aggregate capacity of 3.2–6.4 terabits per second, although this has not been demonstrated. The approach is compatible with conventional chip-manufacturing processes.
