Key Findings
The developed silicon photonic crystal waveguide (PCW) modulator achieves a data rate of 200 Gb/s per wavelength using a low-complexity 11-tap digital equalizer. Without any DSP, the device maintains a performance of 180 Gb/s using four-level pulse amplitude modulation (PAM4). Additionally, the modulator demonstrated 140-Gb/s on-off keying (OOK) operation with an energy consumption of 26 fJ/bit, utilizing drive voltages compatible with FinFET-based complementary metal-oxide-semiconductor (CMOS) technology.
Technical Details
The device overcomes the traditional bandwidth-efficiency trade-off by integrating a built-in EO equalizer. Key technical specifications include:
- Device Dimensions: A small footprint with a device length of 320 µm.
- Architecture: Monolithically integrated optical delay lines and crossings within segmented slow-light phase shifters to synthesize an on-chip feedforward response.
- Mechanism: The EO equalizer provides a high-pass response to compensate for intrinsic roll-off, extending the 3-dB bandwidth.
- Efficiency: By utilizing a high group index (n g > 20), the modulator reduces the V π L to approximately 0.1 V·cm.
Background and Context
Conventional silicon Mach-Zehnder modulators are limited by low modulation efficiency (V π L of 2–5 V·cm), requiring millimeter-scale electrodes and high-swing drivers. These factors lead to RF propagation loss and RC time constant bottlenecks, often limiting bandwidth to under 50 GHz. To compensate, current transceivers rely on complex DSPs with nearly 100-tap equalizers that consume Watt-level power. While previous slow-light modulators reduced size, they remained limited by RC time constants (f 3dB < 40 GHz) or required high-power standalone drivers and neural-network-based DSPs to reach high speeds.
Significance and Outlook
By integrating the EO equalizer directly into the slow-light modulator, this approach eliminates the need for large footprints and high drive voltages typically associated with EO equalization. This strategy reduces dependence on power-dissipating electronics, offering a potential route for dense multi-Tb/s co-packaged optics in energy-constrained switching systems for AI data centers.
Source: https://doi.org/10.1038/s41467-026-78128-1
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