Silicon photonics beyond the singlemode regime is applied for enabling ultralow-loss waveguide propagation for the fundamental mode even without any special fabrication process. Here a micro-racetrack resonator is fabricated with a standard 220-nm-SOI (silicon-on-insulator) multiproject-wafer foundry and shows a record high intrinsic quality factor of 1.02×10 7 , corresponding to an ultralow propagation loss of only 0.065 dB cm −1 , which is about 20 times less than that of regular 450-nm-wide waveguides on the same chip. A state-of-the-art microwave photonic filter on silicon is then realized with an ultranarrow 3-dB bandwidth of 20.6 MHz and a tuning range of ≈20 GHz for the first time. A 100-cm-long delayline employed the broadened waveguides is also demonstrated with compact 90°Euler-curve bends, and the measured average propagation loss is about 0.14 dB cm −1 . The concept of silicon photonics beyond the singlemode regime helps solve the issue of high propagation loss significantly. In particular, it enables silicon photonic devices with enhanced performances, which paves the way for realizing large-scale silicon photonic integration. This concept can be extended further to any other material platforms, such as silicon nitride and lithium niobate. This also brings numerous new opportunities for various applications such as nonlinear photonics, large-scale photonic integration, quantum photonics, microwave photonics, etc.

Motivated by applications in mobile optical sensing, ultracompact high‐resolution integrated spectrometers have attracted much interest. Here, a high‐resolution integrated speckle spectrometer, comprising a linear coherent network formed by mutually coupled Mach–Zehnder interferometers and nonidentical microring resonators, is proposed and demonstrated. Deep‐etched grating lines used as mirrors on the edges of the coherent network increase the effective optical path lengths. The speckle spectrometer is realized on a silicon nitride platform, operating at 776 nm central wavelength. The eight‐in−eight‐out linear coherent network provides 64 physical channels. Fine spectral lines separated by 20 pm are experimentally resolved within a device footprint of 520 µm × 220 µm. Compressive sensing is achieved for sparse spectra over a wide optical bandwidth. Up to 600 distinctive wavelength channels can be reconstructed from the 64 physical channels, giving 12 nm operating bandwidth. Both sparse spectra and continuous spectra are well reconstructed experimentally. The integrated speckle spectrometer has great potential for use in future biosensing and bioimaging applications where high spectral resolution is desired.

Reconfigurable silicon photonic devices are widely used in numerous emerging fields such as optical interconnects, photonic neural networks, quantum computing, and microwave photonics. Currently, phase change materials (PCMs) have been extensively investigated as promising candidates for building switching units due to their strong refractive index modulation. Here, nonvolatile multilevel switching of silicon photonic devices with Ge2Sb2Te5 (GST) is demonstrated with In2O3 transparent microheaters that are compatible with diverse material platforms. With GST integrated on the silicon photonic waveguides and Mach‐Zehnder interferometers (MZIs), repeatable and reversible multilevel modulation of GST is achieved by electro‐thermally induced phase transitions. Particularly, the segmented switching unit of In2O3 and GST is proposed and demonstrated to be capable of producing about one order of magnitude larger temperature gradient than that of the nonsegmented unit, resulting in up to 64 distinguishable switching levels of 6‐bit precision, and fine‐tuning of the switching voltage pulses is promising to push the precision even further, to 7‐bit, or 128 distinguishable switching levels. The capability of precise multilevel phase‐change modulation is crucial to further facilitate the development of nonvolatile reconfigurable switches and variable attenuation devices as building blocks in large‐scale programmable optoelectronic systems.

Fast electro-optic modulators with an ultracompact footprint and low power consumption are always highly desired for optical interconnects. Here we propose and demonstrate a high-performance lithium niobate electro-optic modulator based on a new 2 × 2 Fabry–Perot cavity. In this structure, the input and reflected beams are separated by introducing asymmetric multimode-waveguide gratings, enabling TE 0 − TE 1 mode conversion. The measured results indicate that the fabricated modulator features a low excess loss of ∼ 0.9    dB , a high extinction ratio of ∼ 21    dB , a compact footprint of ∼ 2120    μm 2 , and high modulation speeds of 40 Gbps OOK and 80 Gbps PAM4 signals. The demonstrated modulator is promising for high-speed data transmission and signal processing.