Transparent conductive oxides have emerged as a new type of plasmonic material and demonstrated unique electro-optic (E-O) modulation capabilities for next-generation photonic devices. In this paper, we report an ultra-compact, broadband electro-absorption (EA) modulator using an epsilon-near-zero (ENZ) indium-tin oxide (ITO). The device is fabricated on a standard silicon-on-insulator platform through the integration with a 3 μm long, 300 nm wide gold plasmonic slot waveguide. The active E-O modulation region consists of a metal–HfO2–ITO capacitor that can electrically switch the ITO into ENZ with ultra-high modulation strengths of 2.62 and 1.5 dB/μm in simulation and experiment, respectively. The EA modulator also demonstrated a uniform E-O modulation with 70 nm optical bandwidth from 1530 to 1600 nm wavelength.

We demonstrate an integrated Si optical single-sideband (OSSB) modulator composed of a parallel dual-ring modulator (PDRM) and a quadrature hybrid coupler (QHC). Both the PDRM and the QHC are carefully designed for 30 GHz opearation, and their operations are verified by measurement. The Si OSSB modulator successfully generates a single sideband with larger than 15 dB suppression of the undesired sideband.

In this paper, a substrate removing technique in a silicon Mach–Zehnder modulator (MZM) is proposed and demonstrated to improve modulation bandwidth. Based on the novel and optimized traveling wave electrodes, the electrode transmission loss is reduced, and the electro-optical group index and 50 Ω impedance matching are improved, simultaneously. A 2 mm long substrate removed silicon MZM with the measured and extrapolated 3 dB electro-optical bandwidth of >50 GHz and 60 GHz at the 8 V bias voltage is designed and fabricated. Open optical eye diagrams of up to 90 GBaud/s NRZ and 56 GBaud/s four-level pulse amplitude modulation (PAM-4) are experimentally obtained without additional optical or digital compensations. Based on this silicon MZM, the performance in a short-reach transmission system is further investigated. Single-lane 112 Gb/s and 128 Gb/s transmissions over different distances of 1 km, 2 km, and 10 km are experimentally achieved based on this high-speed silicon MZM.

We demonstrate a high-speed silicon carrier-depletion Michelson interferometric (MI) modulator with a low on-chip insertion loss of 3 dB. The modulator features a compact size of <1 mm2 and a static high extinction ratio of >30 dB. The Vπ·Lπ of the MI modulator is 0.95–1.26 V·cm under a reverse bias of 1 to 8 V, indicating a high modulation efficiency. Experimental results show that a 4-level pulse amplitude modulation up to 20 Gbaud is achieved with a bit error rate of 6×10 3, and a 30 Gb/s binary phase-shift-keying modulation is realized with an error vector magnitude of 25.8%.

Parallel-coupled dual-racetrack silicon microresonators can potentially be used for quadrature amplitude modulation. We analyze the evolution of the coverage of coherent output states of devices with varying device parameters. As the coupling constant increases, the coverage of coherent states initially improves then degrades, which is unexpected based on a prior preference for overcoupling. Increasing the quality factor generally improves the coverage. The influence of the refractive index modulation is found to saturate after reaching a certain level. Analytic formulas are developed to provide insight into the coverage evolution. These results are fairly robust against a small asymmetry of device parameters.

We propose a novel silicon optical phase shifter structure based on heterogeneous strip-loaded waveguides on a photonic silicon on insulator (SOI) platform. The features of an etchless SOI layer and loaded strip would enhance the performance and uniformity of silicon optical modulators on a large-scale wafer. We implemented the phase shifter by loading an amorphous silicon strip onto an SOI layer with a vertical PN diode structure. Compared to the conventional lateral PN phase shifter based on half-etched rib waveguides, this phase shifter shows a >1.5 times enhancement of modulation efficiency and provides >20 GHz high-speed operation.

We demonstrate binary phase shift keying (BPSK) modulation using a silicon Mach–Zehnder modulator with a π-phase-shift voltage (Vπ) of 4.5 V. The single-drive push–pull traveling wave electrode has been optimized using numerical simulations with a 3 dB electro-optic bandwidth of 35 GHz. The 32 Gb/s BPSK constellation diagram is measured with an error vector magnitude of 18.9%.