Figure 1. Classical characterization of the HW-based CNOT gate.

(a) A schematic of the simplified CNOT gate composed of three PDBSs as proposed in refs ⁷ and ⁸. The photons enter the gate from the input couplers C_in (control) and T_in (target) and get out from the output couplers C_out and T_out. (b) The sketch of the CNOT gate realized by the HW-based PDBS. (c) The scanning electron microscopy image of the PDBS on a metal film. The input coupler consists of two kinds of gratings: the working gratings having five grooves with depth d=30 nm, length l=5 μm, width w=200 nm and period P=540 nm, and the reflecting gratings with different specifics, w=100 nm and P=270 nm for high conversion efficiency. This approach aims to obtaining the high conversion efficiency from p-polarized light to SPP, in a direction-dependent way. The SPP reflecting grating comprises of three grooves with d=50 nm, w=100 nm and P=380 nm. The slits of the output coupler have l=5 μm, w=600 nm and P=830 nm. The scale bar denotes 4 μm. (d,e) The CCD images of the output setup with p-polarized light input from the left coupler (d) p-Polarized light input from the right coupler (e) and s-polarized light input from the left coupler (f) where the blue arrows mark the positions of input lights and their polarizations.