Nanoscale all-optical logic gate devices are very important mesoscopic photonic devices, having great potential applications in the fields of optical computing and ultrahigh speed information processing. The basic idea is to form linear constructive/destructive interference between two light signals to obtain output logic states ‘1’ and ‘0’, where the logic operation depends on the relative optical phase difference of two input signals. Owing to the difficulty in precisely controlling the optical phase difference, this method suffers from an inherent instability and low intensity contrast ratio between output logic states ‘1’ and ‘0’.

Gong’s group proposed a new surface plasmon polariton (SPP) waveguide, to construct all-optical logic gates. The proposed SPP waveguide, also called plasmonic slot waveguide, exhibits both ultra-long range propagation of over several tens microns and strong spatial confinement of light into a subwavelength scale region. They adopted miniature device featuring lateral dimensions of less than 5 μm, precisely controlled optical phase differences obtained through exact patterning of logic gates using focused ion-beam (FIB) etching technology, and quasi-monochromatic SPP modes excited by an 830-nm continuous-wave (CW) laser beam to overcome the shortcoming of the linear interference method. They successfully realized four low-power, ultracompact, integrated all-optical logic XNOR, XOR, NOT, and OR gates with high intensity contrast ratio between output logic states ‘1’ and ‘0’. High intensity contrast ratio of 24 dB between output logic states ‘1’ and ‘0’ was reached. Moreover, the operation of the logic function does not have any high power requirement.

This work not only improve the process of practical applications of mesoscopic photonic devices including all-optical logic gates, but also provide a new approach for the study of nanophotonic processors.

The work was supported by the Creative Research Group Project of the National Natural Science Foundation of China, and the National Basic Research Program of China.