Institute of Science Tokyo built a 320-µm silicon modulator reaching 200 Gb/s

Researchers from the Institute of Science Tokyo, Yokohama National University, and the National Institute of Advanced Industrial Science and Technology demonstrated a compact silicon slow-light modulator with an integrated equalizer, according to nature.com nature.comnature.comnature.comOpen source ↗. The prototype features an active device length of 320 µm and is engineered to enhance data transmission bandwidth while minimizing energy consumption in optical interconnects.

Built-in electro-optic equalization

Standard silicon Mach-Zehnder modulators often rely on millimeter-scale phase shifters, which exhibit bandwidth constraints below 50 GHz and require power-hungry digital signal processing to exceed 100 Gb/s per lane. In contrast, the demonstrated architecture integrates a photonic crystal waveguide slow-light modulator with a built-in electro-optic equalizer. By monolithically combining optical delay lines and optical crossings within segmented slow-light phase shifters, the team formed an on-chip feedforward response. This structure produces a high-pass frequency response that directly compensates for the device's intrinsic roll-off, expanding the 3-dB electro-optic bandwidth beyond the Nyquist bandwidth required for high-speed operation.

High-speed testing and low power consumption

Experimental testing of the fabricated 320-µm device showed that it can operate using low drive voltages compatible with fin field-effect transistor complementary metal-oxide-semiconductor technology. Under on-off keying modulation, the modulator achieved a data rate of 140 Gb/s with an energy consumption of 26 fJ/bit. Operating under four-level pulse amplitude modulation, the device achieved a transmission speed of 180 Gb/s without requiring any digital signal processing. When tested with a low-complexity 11-tap digital equalizer, the data transmission rate reached 200 Gb/s. The integrated feedforward design provides an approach for optical transceivers without relying on complex, nearly 100-tap digital equalizers or high-voltage standalone electrical drivers.