Metasurfaces are artificial electromagnetic surfaces that consist of subwavelength scatterers in an array configuration, exhibiting exceptional abilities to manipulate electromagnetic waves. Based on the metasurface concept, a novel beam splitter for a single-frequency same-polarization light is proposed in the visible spectrum. Using metal–dielectric–metal (MDM) scattering unit cells, an array of the circular gold nanocylinders with two different diameters is designed and fabricated on the surface which introduces phase discontinuity on the scattering wavefronts. At 240 nm thick, the flat beam splitter can efficiently reflect an incident wave toward two predesigned directions. More importantly, the split angle and power distribution between these two beams can be readily controlled by setting a proper incident angle. Compared to conventional bulky optical components, the ability of this metasurface-based beam splitter would be very desirable in integrated optical systems.

Miniaturization of functional devices and systems demands new design and fabrication approaches for lab-on-a-chip application and optical integrative systems. By using a direct laser writing (DLW) technique based on two-photon polymerization (TPP), a highly integrative optofluidic refractometer is fabricated and demonstrated based on tubular optical microcavities coupled with waveguides. Such tubular devices can support high quality factor (Q-factor) up to 3600 via fiber taper coupling. Microtubes with various diameters and wall thicknesses are constructed with optimized writing direction and conditions. Under a liquid-in-tube sensing configuration, a maximal sensitivity of 390 nm per refractive index unit (RIU) is achieved with subwavelength wall thickness (0.5 μm), which offers a detection limit of the devices in the order of 10 RIU. Such tubular microcavities with coupled waveguides underneath present excellent optofluidic sensing performance, which proves that TPP technology can integrate more functions or devices on a chip in one-step formation.

Enhancing the nonlinear frequency conversion efficiency at the nanoscale is important for on-chip communication, information processing and sensing. Plasmonic nanostructures can significantly enhance the nonlinear signal due to localized surface plasmon (LSP) resonances, i.e., localized electric field enhancements. Ideally, a double resonance occurs, in which both the excitation and the harmonic wavelengths are enhanced, but this is restricted by the available modes. It has been recently shown that thin films of epsilon-near-zero (ENZ) materials can also enhance optical nonlinear effects if excited at the ENZ wavelength. Here, we report the first demonstration of a new mechanism to enhance the second harmonic generation (SHG), combining a structural LSP resonance at the fundamental frequency, and the material ENZ resonance at the second harmonic frequency. We show that when both resonances are present, the SHG is substantially enhanced. With its refractory nature and CMOS compatibility, our results show considerable promise for TiN micro and nanostructures in integrated on-chip nonlinear optical devices.