High Extinction Ratio Dual-Racetrack Modulator for DAC-less PAM4 Modulation

A parallel-coupled dual racetrack modulator is experimentally demonstrated. At 50 Gb/s, the extinction ratio (ER) is over 9 dB; and 40~50% modulation depth enhancement is obtained compared to a single resonator modulator with a peak-to-peak driving voltage of 2.3 V. A procedure for configuring four-level pulse-amplitude modulation (PAM-4) states is theoretically developed to tackle the complex multi-variable transfer function of this modulator. We demonstrate 100 Gb/s PAM-4 modulation without an external digital-to-analog converter (DAC), with electro-optic modulation power consumption < 40 fJ/bit for this device.