Free-space-to-waveguide demultiplexer featuring zero-contrast gratings

We present here a method to achieve an optical demultiplexer working in the visible range to achieve either a polarization beamsplitter (PBS) or the wavelength-division multiplexer (WDM), which is based on the integration of different periodic gratings using the suspended zero contrast grating (ZCG) structure. The proposed demultiplexer comprises two independent ZCG HfO2 filters, which are very close to each other so that they can be illuminated and measured at the same time. By combining two independent HfO2 ZCG filters with selectable functionalities in parallel and extending the waveguides on both sides, a PBS device or WDM device can be achieved. The finite difference time-domain (FDTD) method is used to simulate the coupling properties of the ZCG filters. The simulation results show that the proposed PBS device can effectively direct different polarized light with a wavelength of 650 nm into separate waveguides. The WDM device can also separate incoming 550 nm and 650 nm light beams into separate waveguides. The fabricated devices are characterized by the optical microscope and the atomic force microscope (AFM).