Long-distance transmission of broadband near-infrared light guided by a semi-disordered 2D array of metal nanoparticles

Near-infrared (NIR) waveguides are a key component of planar photonic devices such as optical communication couplers, image sensors, and spectroscopes for chemical or biological molecules. Conventional NIR waveguides used for signal transmission include silicon-on-insulator (SOI) waveguides and channel/ridge-type metal micro-strips. However, these waveguides usually have limitations of either signal delay or signal loss in optically integrated devices. In this study, a novel NIR waveguide composed of a semi-disordered array of metal nanoparticles (sDAMNPs) on Si substrate was proposed, fabricated, and tested. The disordered metallic nanoparticles array is geometrically localized in the form of 1D metal strips, thus replacing sDAMNPs with less lossy micro strip channel waveguides. From the measurements supported by various computational models, the fabricated waveguides operate effectively in the broadband NIR region (1100 to 1700 nm). The waveguide does not support signal transmission in the ultra violet-visible spectrum due to strong signal absorption, scattering, and localization effects inside the metal nanoparticles. Instead, it is capable of transmitting NIR over a distance longer than 100 μm (signal loss ∼3.85 dB per 100 μm for NIR from 1200 to 1600 nm), which is also sufficiently longer than the conventional surface plasmon polariton propagation distance at the metal-Si interface. Compared to a waveguide-free reference, the waveguide exhibited greatly improved signal transmission efficiency up to a factor of 7.42 × 10⁴ at 1367 nm. It also exhibits a high deflection angle sensitivity of 1.89 dB per 0.01 rad, thus efficiently and straightly guiding the broadband NIR signal over a long distance.