Silicon mode-loop Mach-Zehnder modulator with L-shaped PN junction for 0.37 V·cm VπL high-efficiency modulation

Optical signaling without a high voltage driver for electric-optic modulation is in high demand to reduce power consumption, packaging complexity, and cost. In this work, we propose and experimentally demonstrate a silicon mode-loop Mach–Zehnder modulator (ML-MZM) with record-high modulation efficiency. We used a mode-loop structure to recycle light twice in the phase shifter. With an L-shaped PN junction, a comparably large overlap between the PN junction and optical modes of both TE 0 and TE 1 was achieved to lower the driving voltage or decrease the photonic device size. Proof-of-concept high-efficiency modulation with low V π L of 0.37 V · cm was obtained. Subvoltage V π can be realized with a millimeter’s length phase shifter by this scheme, which makes the realization of CMOS-compatible driverless modulation highly possible. 40 Gb/s signaling with a bit error rate below the 7% forward-error-correction threshold was then demonstrated with the fabricated ML-MZM, indicating great potential for high-speed optical communication.