A multimode bend for TE0, TE1, TE2 and TE3 modes with a radius of 3.9 μm is demonstrated. The insertion loss is measured to be < 1.8 dB, and the crosstalk is below −17 dB.

In-plane diffractive optical networks based on metasurfaces are promising for on-chip application. The design constraints of regular antenna unit place ultimate limits on the functionalities of the meta-systems. This fundamental limitation has been reflected by the large footprints of cascaded metasurfaces. Here, we propose a digital meta-lens with a large degree of design freedom, enabling significantly improved beam focusing, collimation, and deflection capabilities. A highly dispersive and compact diffractive optical system is constructed for spectrometer via five layers of meta-lenses in a folded configuration. The device only occupies a 100 μm × 100 μm chip area on a silicon photonic platform. Sparse and continuous spectra reconstruction is achieved over a 35 nm bandwidth. Fine spectral lines separated by 0.14 nm are resolved. In addition to such a compact and high-resolution on-chip spectrometer, it is also expected to be promising for imaging, optical computing, and other applications due to the great versatility of the digital lens design.

Growing research interests have been directed to the emerging optical communication band at 2-µm wavelengths. The silicon photonic components are highly desired to operate over a broad bandwidth covering both C-band and the emerging 2-µm wave band. However, the dispersions of the silicon waveguides eventually limit the optical bandwidth of the silicon photonic devices. Here, we introduce a topology-optimized Y-junction with a shallow-etched trench and its utility to reverse the detrimental dispersion effect. The shallow trench enables the Y-junction to have an adaptive splitting capability over a broad spectral range. The 0.2-dB bandwidth of the power splitter exceeds 800 nm from 1400 nm to 2200 nm. The device has a compact footprint of 3 µm × 1.64 µm. The device is characterized at the C-band and 2-µm band with a measured excess loss below 0.4 dB for a proof-of-concept demonstration.