We present the design and numerical simulation results for a silicon waveguide modulator based on carrier depletion in a linear array of periodically interleaved PN junctions that are oriented perpendicular to the light propagation direction. In this geometry the overlap of the optical waveguide mode with the depletion region is much larger than in designs using a single PN junction aligned parallel to the waveguide propagation direction. Simulations predict that an optimized modulator will have a high modulation efficiency of 0.56 V·cm for a 3V bias, with a 3 dB frequency bandwidth of over 40 GHz. This device has a length of 1.86 mm with a maximum intrinsic loss of 4.3 dB at 0V bias, due to free carrier absorption.

Graphene resting on a silicon-on-insulator platform offers great potential for optoelectronic devices. In the paper, we demonstrate all-optical modulation on the graphene–silicon hybrid waveguides (GSHWs) with tens of micrometers in length. Owing to strong interaction between graphene and silicon strip waveguides with compact light confinement, the modulation depth reaches 22.7% with a saturation threshold down to 1.38 pJ per pulse and a 30-μm-long graphene pad. A response time of 1.65 ps is verified by a pump–probe measurement with an energy consumption of 2.1 pJ. The complementary metal-oxide semiconductor compatible GSHWs with the strip configuration exhibit great potential for ultrafast and broadband all-optical modulation, indicating that employing two-dimensional materials has become a complementary technology to promote the silicon photonic platform.

The polarization dependence of a directional coupler (DC) based on asymmetric cross-slot waveguides is investigated. Due to structural birefringence, the coupling behaviors of the quasi-TE and quasi-TM modes in the DC vary with the waveguide geometry. A polarization-independent directional coupler (PIDC) and polarization beam splitter (PBS) are proposed by tailoring the ratio of the coupling length for quasi-TE and quasi-TM modes. The simulated results show that the coupling lengths of the designed PIDC and PBS are 8 and 28.25 μm, respectively. Both the PIDC and PBS show an insertion loss (IL) $<0.7\mathrm{dB}$ on a bandwidth over 100 nm. The extinction ratios are $\sim 20\mathrm{dB}$ for PIDC and $\sim 14\mathrm{dB}$ for PBS. The fabrication-error tolerance of the practical devices is also discussed. In this study, we employ a commercial software tool for finite difference eigenmode and three-dimensional finite difference time domain methods to perform the numerical simulations.

A four-mode (de-)multiplexer with transverse electric field light ( T E 0 − T E 3 ) is experimentally demonstrated on a thin film lithium niobate–silicon rich nitride hybrid platform. Enabled by cascaded asymmetrical directional couplers, a (de-)multiplexer with low insertion loss (0.38 dB to 1.6 dB) and low cross talk ( − 18.46 d B to − 20.43 d B ) is obtained at 1550 nm. All channels have cross talk < − 16 d B from 1480 nm to 1580 nm. The transmission of 4 × 50 Gbps on–off keying signals is experimentally achieved on the proposed (de-)multiplexer. Experimental results show that the proposed (de-)multiplexer is a promising approach to enhance the transmission capacity in thin film lithium niobate based photonics integrated circuits.

We propose and demonstrate a Michelson interferometer modulator with integrated Bragg reflectors on a silicon-rich nitride–thin-film lithium niobate hybrid platform. High-reflectivity Bragg reflectors are placed at the ends of both arms, which double the electro-optic (E-O) interaction length and reduce the velocity mismatch between the microwave and optical wave. The presented Michelson interferometer modulator achieves a measured half-wave voltage length product as low as 1.06 V cm and high-speed modulation up to 70 Gbps. A 3-dB E-O bandwidth beyond 40 GHz is also achieved, which is, to the best of our knowledge, the highest modulation bandwidth of Michelson interferometer modulators.

We experimentally demonstrate the first all-silicon microring photodetector with 40-Gb/s operation speed based on the defect-assisted subbandgap avalanche mechanism in reverse p-n junction. A novel zigzag p-n junction providing a high responsivity of 48 mA/W upon 8 V in avalanche mode is demonstrated with a low doping concentration of 2 × 10 ¹⁷ cm ^-3 . With the optimized operation wavelength, a 3-dB optical to electrical response of ~20 GHz and high-speed photodetections of 20-40 Gb/s are achieved experimentally, showing great potential in the application of all-silicon ultrahigh-capacity optical interconnects.