Professor Qihuang Gong’s group has made new progress in the field of surface plasmon polariton (SPP) waveguides. The research was reported as a cover article in the journal of Applied Optics. (Yusheng Bian and Qihuang Gong*, Low-loss hybrid plasmonic modes guided by metal-coated dielectric wedges for subwavelength light confinement, Applied Optics, 52, 5733-5741 (2013)).

Micro/nano structures based on SPPs are capable of breaking the fundamental diffraction limit and achieving light transport at the truly sub-wavelength scale. Along with many other advantages such as enabling simultaneous transport of photonic and electric signals, they have been regarded as one of the key solutions to realize highly-integrated photonic chips. However, most of the existing metallic micro/nano waveguides that could realize deep-subwavelength optical confinement have huge propagation losses, which greatly hinders their further applications in integrated photonic devices. Therefore, how to reconcile the conflict between subwavelength field confinement and low propagation loss becomes one of the major issues to be solved in current SPP technology.

Prof. Gong and his group presented a subwavelength metal-coated silicon hybrid plasmonic waveguide, which is capable of supporting two types of low-loss plasmonic modes. Comprehensive numerical investigations show that the guided quasi-transverse-electric (quasi-TE) hybrid plasmonic mode enables tight field confinement down to the subwavelength scale, and also exhibits low modal loss, with propagation distances ranging from tens to hundreds of microns at telecommunication wavelengths. In addition, light can be strongly confined within the low-index, nanometer dielectric gap layer between the metal cladding and the silicon structure, along with significant local field enhancement achievable simultaneously. Investigations on the directional coupling between adjacent identical waveguides reveal that the coupling length of the studied metal-coated hybrid structures can be more than one order of magnitude larger than that achieved by their conventional hybrid counterparts, which greatly reduces the crosstalk between adjoining waveguiding structures and significantly improves the packing densities of optically integrated circuits. The presented metal-coated silicon hybrid waveguide can be employed as important building blocks for a number of ultra-compact integrated nanophotonic components, and also facilitates numerous applications at the subwavelength scale.

This work was supported by the National Key Basic Research Program of China, the Innovative Research Group of the National Natural Science Foundation of China, State Key Laboratory of Mesoscopic Physics and the Postdoctoral Science Foundation of China.