Wavelength-scale optical modulators are essential building blocks for future on-chip optical interconnects. Any modulator design is a trade-off between bandwidth, size and fabrication complexity, size being particularly important as it determines capacitance and actuation energy. Here, we demonstrate an interesting alternative that is only 3 μm long, only uses silicon on insulator (SOI) material and accommodates several nanometres of optical bandwidth at 1550 nm. The device is based on a photonic crystal waveguide: by combining the refractive index shift with slow-light enhanced absorption induced by free-carrier injection, we achieve an operation bandwidth that significantly exceeds the shift of the bandedge. We compare a 3 μm and an 80 mm long modulator and surprisingly, the shorter device outperforms the longer one. Despite its small size, the device achieves an optical bandwidth as broad as 7 nm for an extinction ratio of 10 dB, and modulation times ranging between 500 ps and 100 ps.

Sci. Rep.

Opheij, A., Rotenberg, N., Beggs, D. M., Rey, I. H., Krauss, T. F., & Kuipers, K. (2013). Ultracompact (3μm) silicon slow-light optical modulator. Sci. Rep., 3(Article number: 3546), 1–5. doi:10.1038/srep03546