Dual-function plasmonic structure for logic operations and circular polarization detection

Many integrated photonic devices have a high potential for dual applications, making them more versatile components in photonic integrated circuits. In this study, we show that a plasmonic XOR gate structure, originally designed to perform logic operations, can also be used as a circular polarization detector. This multi-purpose capability stems from the phase-encoded input mechanism that controls the output response of the structure. We adapted this mechanism to select the output based on the polarization state of light. The design of this structure, utilizing the subwavelength field confinement of plasmonic waveguides, enables the integration of logic and detection functions into a compact form factor. To achieve the desired polarization–dependent output behavior, a practical phase adjuster structure is incorporated into the device to introduce an approximately 90° relative phase difference, enabling selective transmission based on the input polarization state. After designing two plasmonic XOR gates optimized for operation at 1310 nm, we fabricated them using standard nanofabrication techniques. These structures were experimentally tested using circularly polarized light, including left-handed circular polarization and right-handed circular polarization. The output responses were recorded by an infrared camera, and the resulting images were analyzed using digital image processing to quantify the light intensity at each output port. Although these structures were initially designed as logic gates, the results demonstrate that they can also be used as circular polarization detectors or splitters, as they have a good ability to discriminate between right-handed and left-handed circular polarization, with a maximum extinction ratio of 6.86 dB.