Fig. 4

Experimental validation of tunable, narrow-band guiding by NW GSLs. a (Top) False-colored SEM image of a NW GSL (red) with d = 334 ± 1 nm and p = 781 ± 9 nm prepared by the doping-inverted ENGRAVE process followed by a 50 μm-long NW WG (blue); scale bar: 5 μm. (Bottom) Magnified views of dotted regions in the top image; scale bars: 500 nm. b–e False-colored optical images of the NW from a without an excitation beam (b) and under excitation at wavelengths of 1400 nm (c), 1455 nm (d), and 1550 nm (e). Yellow arrow and circles denote locations of the excitation beam and the NW tip, respectively. f–h SEM images of GSLs with geometrical parameters of d = 334 ± 1 nm, p = 781 ± 9 nm (f), d = 284 ± 3 nm, p = 882 ± 6 nm (g), d = 266 ± 1 nm, p = 772 ± 6 nm (h); scale bars, 1 μm. i–q Spectra of GSL extinction (i–k), NW WG extinction (l–n), and WG emission (o–q). Experimental measurements (right-hand axes) are shown as circles (and blue shaded area for guided spectra), and simulated spectra (left-hand axes) are shown as black lines. r–s Fabry-Perot patterns in guided power spectra for NW WGs with length of 21 μm (r, WG₁) and 53 μm (s, WG₂)