Compact waveguide bend implemented by a subwavelength Mikaelian lens

Improving the integration density of photonic integrated circuits is essential for reducing chip cost, and waveguide bends are a critical component that governs routing density and device compactness. However, achieving compact waveguide bends is particularly challenging in the short-wave mid-infrared band, where longer wavelengths weaken optical confinement and increase radiation loss, imposing strict limits on the minimum bending radius. Here, we propose and experimentally demonstrate a compact waveguide bend for the short-wave mid-infrared wavelength band by implementing a Mikaelian lens using subwavelength engineering. The aberration-free property of the Mikaelian lens enables efficient optical connection between parallel ports with flexible longitudinal separation within a device footprint of 19 × 16 μm². The fabricated device achieves a bending loss of 0.5 dB and crosstalk of -17 dB. This work demonstrates a promising approach to achieving flexible, dense routing in photonic integrated circuits for short-wave mid-infrared or even longer-wavelength applications.