100 GHz silicon–organic hybrid modulator

Electro-optic modulation at frequencies of 100 GHz and beyond is important for photonic-electronic signal processing at the highest speeds. To date, however, only a small number of devices exist that can operate up to this frequency. In this study, we demonstrate that this frequency range can be addressed by nanophotonic, silicon-based modulators. We exploit the ultrafast Pockels effect by using the silicon–organic hybrid (SOH) platform, which combines highly nonlinear organic molecules with silicon waveguides. Until now, the bandwidth of these devices was limited by the losses of the radiofrequency (RF) signal and the RC (resistor-capacitor) time constant of the silicon structure. The RF losses are overcome by using a device as short as 500 µm, and the RC time constant is decreased by using a highly conductive electron accumulation layer and an improved gate insulator. Using this method, we demonstrate for the first time an integrated silicon modulator with a 3dB bandwidth at an operating frequency beyond 100 GHz. Our results clearly indicate that the RC time constant is not a fundamental speed limitation of SOH devices at these frequencies. Our device has a voltage–length product of only VπL=11 V mm, which compares favorably with the best silicon-photonic modulators available today. Using cladding materials with stronger nonlinearities, the voltage–length product is expected to improve by more than an order of magnitude. Researchers have developed an integrated silicon–organic device capable of modulating light at frequencies of up to 100 GHz. The ultrafast modulator, fabricated by Luca Alloatti and co-workers, relies on the electro-optic Pockels effect that occurs in a polymer cladding covering a silicon slot waveguide. Application of an electric field to the polymer causes its refractive index to change, which in turn modifies the phase of light passing through it. The 500-µm-long device has a half-wave voltage of 22 V, meaning that this voltage is required in order to achieve a π phase shift for the output light. However, the researchers are confident that using a cladding material with a stronger nonlinearity could improve this figure of merit by a factor of ten.