We provide detailed analysis of a four terminal p + pnn + optical modulator integrated into a silicon-on-insulator (SOI) rib waveguide. The proposed depletion device has been designed to approach birefringence free operation. The modulation mechanism is the carrier depletion effect in a pn junction; carrier losses induced are minimised in our design and because we use a depletion device, the device is insensitive to carrier lifetime. The rise time and fall time of the proposed device have both been calculated to be 7 ps for a reverse bias of only 5 volts. A maximum excess loss of 2 dB is predicted for TE and TM due to the presence of p type and n type carriers in the waveguide.
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