High-modulation efficiency silicon Mach-Zehnder optical modulator based on carrier depletion in a PN Diode

We present a high phase-shift efficienct Mach-Zehnder silicon optical modulator based on the carrier-depletion effect in a highly-doped PN diode with a small waveguide cross-sectional area. The fabricated modulator show a V pi L pi of 1.8V.cm and phase shifter loss of 4.4dB/mm. A device using a 750 mu m-long phase-shifter exhibits an eye opening at 12.5Gbps with an extinction ratio of 3 dB. Also, an extinction ratio of 7 dB is achieved at 4 Gbps for a device with a 2 mm-long phase shifter. Further enhancement of the extinction ratio at higher operating speed can be achieved using a travelling-wave electrode design and the optimal doping. (C) 2009 Optical Society of America