Plasmonically Enhanced Kerr Frequency Combs

Abstract

Optical\nfrequency combs are high repetition rate, broad spectral bandwidth\ncoherent light sources. These devices have numerous applications in\nmany fields, ranging from fundamental science to defense. Recently,\nlow-threshold and small-footprint frequency combs have been demonstrated\nusing ultrahigh quality factor (<i>Q</i>) whispering gallery\nmode resonant cavities. The majority of research in cavity-based combs\nhas focused on optimizing the <i>Q</i>. An alternative strategy\nis to engineer the cavity material to enhance the underlying nonlinear\nprocess for comb generation. In this work, we demonstrate that gold\nnanorods coated with a nonlinear material reduce the comb generation\nthreshold when decorated on the surface of the resonant cavities.\nThe enhancement mechanism is explored with finite element method modeling\nand can be explained in terms of photonic–plasmonic mode hybridization.\nA comb span of ∼300 nm in the near-IR range is observed with\nincident intensity <2 GW cm<sup>–2</sup>. The required threshold\nfor parametric oscillation directly scales with nanorod concentration\nand ranges from 148 μW to 1.5 mW, which is 15 times lower than\nuncoated silica devices with similar optical performance.