A major challenge in optics is how to deliver and concentrate light from the micron-scale into the nano-scale. As the wavelength of light is on the micro-scale, it can not be guided, by conventional mechanisms, with optical beam sizes significantly smaller than this wavelength due to the diffraction limit of light.1 On the other hand, focusing of light into very small volumes beyond the diffraction limit can be achieved by exploiting the wavelength scalability of surface plasmon polaritons. By slowing down an optical wave and shrinking its wavelength during its propagation, optical energy can be concentrated down to nanometer scale, namely, nanofocusing. Nanofocusing of plasmons was first proposed by Nerkararyan in a metallic wedge2 and then on a metallic cone.3 The growing interest in nano-optics and the advances in nano-fabrication, have led to further theoretical investigations of nanofocusing on the wedge1 and cone as well as in several different plasmonic systems. A recent experimental study of plasmons propagating on a rectangular metallic strip of tapered width showed increased photoluminescence in some regions.4 Here, we present an experimental evidence for nanofocusing of SPPs in tapered metallic V-grooves down to deep sub-wavelength scale (~λ/40 at wavelength of 1.5 micron). We measure the power emerging from V-grooves with different output widths and find the output intensity is increased with decreased output width.

© 2008 Optical Society of America

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