Ultra-high Purcell factor using long-range modes in asymmetric plasmonic waveguides

TL;DR

This paper introduces asymmetric hybrid plasmonic waveguides that enable long-range, low-loss, subwavelength optical modes with high Purcell factors, overcoming symmetry constraints and enhancing device performance.

Contribution

The work presents a novel asymmetric hybrid plasmonic waveguide design that achieves record low loss, small mode area, and high Purcell factor without requiring structural symmetry.

Findings

Propagation loss of 0.03 dB/μm

Mode area of 0.002 μm^2

Purcell factor of 1.5×10^4

Abstract

For integrated optical devices, realistic utilization of the superior wave-matter interaction offered by plasmonics is typically impeded by optical losses, which increase rapidly with mode volume reduction. Although coupled-mode plasmonic structures has demonstrated effective alleviation of the loss-confinement trade-off, stringent symmetry requirements must be enforced for such reduction to prevail. In this work, we report an asymmetric plasmonic waveguide that is not only capable of guiding subwavelength optical mode with long-range propagation, but is also unrestricted by structural, material, or modal symmetry. In these composite hybrid plasmonic waveguides (CHPWs), the versatility afforded by coupling dissimilar plasmonic structures, within the same waveguide, allow better fabrication tolerance and provide more degrees of design freedom to simultaneously optimize various device attributes. The CHPWs used to demonstrated the concept in this work, exhibit propagation loss and mode area of only 0.03 dB/{\mu}m and 0.002 {\mu}m^2 respectively, corresponding to the smallest combination amongst experimentally demonstrated long-range plasmonic structures to-date. Moreover, CHPW micro-rings were realized with record in/out coupling excitation efficiency (71%), extinction ratio (29 dB), as well as Purcell factor (1.5\times10^4).