High speed silicon photonic crystal waveguide modulator for low voltage operation

A high speed compact silicon modulator is experimentally demonstrated to work at a low driving voltage desirable for on-chip applications. As carrier injection is the only practical option for optical modulation in silicon, a lower limit of current density $(\sim {10}^4\mathrm{A}∕{\mathrm{cm}}^2)$ exists for achieving gigahertz modulation in the $p\text{-}i\text{-}n$ diode configuration. Exploiting the slow group velocity of light in photonic crystal waveguides, the interaction length of this Mach-Zehnder interferometer-type silicon modulator is reduced significantly compared to conventional modulators. The required high current density is achieved with a low voltage $\left(2\mathrm{V}\right)$ by scaling down the interaction length to $80\mu \mathrm{m}$ .