On-chip integrated mode-division multiplexing (MDM) is an emerging technique for large-capacity data communications. In the past few years, while several configurations have been developed to realize on-chip MDM circuits, their practical applications are significantly hindered by the large footprint and inter-mode cross talk. Most importantly, the high-speed MDM signal transmission in an arbitrarily routed circuit is still absent. Herein, we demonstrate the MDM circuits based on digitized meta-structures which have extremely compact footprints. 112 Gbit/s signals encoded on each mode are arbitrarily routed through the circuits consisting of many sharp bends and compact crossings with a bit error rate under forward error correction limit. This will significantly improve the integration density and benefit various on-chip multimode optical systems.

Recently, 2-μm wave band has gained increasing interest due to its potential application for next-generation optical communication. But the development of 2-μm optical communications is substantially hampered by the modulation speed due to the device bandwidth constraints. Thus, a high-speed modulator is highly demanded at 2 μm. Motivated by this prospect, we demonstrate a high-speed silicon Mach–Zehnder modulator for a 2-μm wave band. The device is configured as a single-ended push–pull structure with waveguide electrorefraction via the free carrier plasma effect. The modulator was fabricated via a multiproject wafer shuttle run at a commercial silicon photonic foundry. The modulation efficiency of a single arm is measured to be 1.6 V · cm . The high-speed characterization is also performed, and the modulation speed can reach 80 Gbit/s with 4-level pulse amplitude modulation (PAM-4) formats.

Hollow-core fiber (HCF) has been attracting broad interests in recent decades, and has extended the communication window to longer wavelength, 2 micron. In this paper, we present a demonstration of low-latency HCF short-reach optical interconnection at 2 micron, achieving a high single-lane speed of 100 Gbps. High physical speed (near vacuum-light-speed) and high information speed (100-Gbps) optical interconnection with 100-m transmission distance is experimentally achieved with error-free performance. Probabilistically shaped discrete multi-tone (PS-DMT) modulation with entropy loading is employed to accommodate the deteriorated frequency response caused by the mode dispersion in HCF. Compared with conventional solid-core fiber (SCF), HCF contributes 30.95% (1.5-'s per kilometer) latency reduction for the physical link. The system level latency reduction is 28% for 1-km interconnection distance (11% for 100-m), with respect to a microsecond-scale switching network for typical datacenter applications. This work substantially leaps over the 100G milestone of 2-micron HCF optical interconnection, and shows the potentiality with lower latency and further higher capacity.

Recently, significantly raised interests have emerged for the 2 µm waveband as an extended new window for fiber optic communication. Much research progress has been made on the photonic integrated circuits for the 2 µm waveband, especially on the CMOS-compatible silicon-on-insulator wafer. In this work, a silicon integrated microring modulator (MRM) with record high-speed performances at the 2 µm waveband was demonstrated. An L-shaped PN junction was specially designed for 2 µm to achieve a high modulation efficiency with V π L of 0.85 V · cm . The measured 3 dB bandwidth is 18 GHz, supporting up to 50 Gbps signaling at 2 µm. Additionally, optical bistability induced by the thermo-optical effect and nonlinear effects was analyzed theoretically and observed experimentally in the 2 µm MRM for the first time to our knowledge. Nonlinear coupled mode theory and the Runge–Kutta method were used to simulate the behaviors of bistability in the 2 µm MRM. The simulation and experimental results indicate that, when the MRM is launched by a high optical power, the distorted resonant spectrum under an optical bistable state deteriorates the modulation efficiency and signal performances. This work breaks the record of high-speed silicon MRM at 2 µm, drawing a promising prospect for the silicon photonic integration and high-speed interconnection at the 2 µm waveband, and it provides the referenceable analysis of optical bistability, which guides the design and experimental investigation of 2 µm MRM.

Few-mode fiber (FMF) supporting many modes with weak-coupling is highly desired in mode division multiplexing (MDM) systems. The multi-parameter design of FMF becomes comparably difficult, inaccurate and time-consuming when it comes for complex fiber structures and many high order modes. In this work, we demonstrate a machine learning method using neural network to inversely design the desired FMF based on multiple-ring structure. By using the minimum index difference between adjacent modes as the weak-coupling optimization aim, we realize the inverse design of 4-ring step-index FMFs for supporting 4, 6 and 10 -mode operation, and 6-ring step-index FMF for supporting 20-mode operation. This method provides high-accuracy, high-efficiency and low-complexity for fast and reusable design of optical fibers, including particularly weak-coupling FMF in this work. It can be widely extended to a lot of fibers and has great potential for instantaneous applications in the optical fiber industry.

In this work, a silicon-integrated edge coupler supporting dual-mode fiber-to-chip coupling was designed and fabricated on 220-nm-thick SOI wafer with standard CMOS-compatible fabrication process. The proposed low-complexity structure consists of a multimode interference and triple-tip inverse taper. Both LP₀₁ and LP₁₁ modes in the few mode fiber (FMF) can be stimulated simultaneously by the edge coupler from TE₀ and TE₁ modes in silicon waveguide. Such a design is compatible with broadband wavelength division multiplexing and can be scaled up to 4-polarization-mode coupling as well. Using the proposed edge coupler, 2×100-Gbps/lambda PAM4 multimode interface through dual-mode fiber was demonstrated successfully.