Dielectric waveguide with deep subwavelength mode confinement based on coupled semiconductor nanowires is proposed. Through the coupling between two adjacent nanowires with high refractive indexes, light can be efficiently confined in the nano-gap between the nanowires with a low refractive index. Numerical simulations indicate that the effective mode area of such a waveguide can be as small as lambda(2)(0)/200, which is one order of magnitude smaller than that of a single nanowire, and such a mode confinement is comparable to that of hybrid plasmonic waveguide. It is also shown that from the view of real applications, possible existing low refractive index oxidization layers of nanowires, low refractive index substrate and small deviation of nanowire dimensions do not have significant influence on the property of the waveguide. As the propagation length is theoretically infinite for dielectric waveguides, such a coupled nanowire waveguide with deep subwavelength mode confinement may have important applications in future integrated photonic circuits.
A dielectric-film-coated asymmetric single nanoslit is proposed to realize broadband unidirectional generation of surface plasmon polaritons (SPPs). Due to the tight field confinements by the dielectric film and the deep groove in the asymmetric single slit, the transmittance of the SPPs in the groove to the left side considerably decreases. This greatly suppresses the left-propagating SPP generation efficiency for a broad bandwidth. Meanwhile, the right-propagating SPP generation efficiency has a flat spectra range because of the low transmittance, too. So the unidirectional SPP generation with bandwidth of > 100 nm around lambda = 750 nm is experimentally achieved for the device lateral dimension of only 865 nm. (C) 2011 Optical Society of America
Using strong couplings of different Fabry-Perot (FP) resonators in metal-insulator-metal waveguides, a compact plasmonic wavelength demultiplexer is numerically demonstrated with high wavelength resolution. In the demultiplexer, it is found that new right-angle resonators emerge with bandwidth narrower than that of the isolated FP resonators. These narrowband right-angle resonators interfere with the broadband FP resonators, resulting in Fano-line shapes in the transmission spectra. Consequently, these sharp and asymmetric Fano-line shapes considerably increase the resolution of wavelength demultiplexing, which is significantly narrower than the full width of the isolated FP resonator. (C) 2011 Optical Society of America
By engaging a compact asymmetric single slit coated with a photorefractive polymer, surface-plasmon-polariton (SPP) generation was efficiently controlled by a pump beam. In the structure, the nonlinear light-matter interaction is enhanced because of the cavity effect, which increases the sensitivity of SPPs to the surrounding dielectric. By variation of the real part of the refractive index together with an interferometric configuration, high on/off switching ratios are achieved. Moreover, the SPP generation and modulation processes are integrated in the same asymmetric single slit, which makes the device ultracompact. Experimentally, a high on/off switching ratio of > 20 dB and phase variation of >pi were observed with the device lateral dimension of only about 2 mu m.
By exciting a plasmonic lens with femtosecond laser and utilizing the optical nonlinearity of the gold, an ultrasmall and ultrafast all-optical modulation spot was achieved inside a thin gold film. Near-field pump-probe measurements indicated a modulation spot size of about 600 nm, and a response time of about 1.5 ps. Even smaller spot size of about 300 nm was inferred from numerical simulations, beyond the diffraction limit given an incident wavelength of 1000 nm. Moreover, the optical nonlinearity and the modulation depth were increased by one order of magnitude at the focus compared to that at positions without structures. (C) 2011 American Institute of Physics. [doi:10.1063/1.3581895]
By coating a metal with a finite-thickness dielectric film, evident differences in the wave-vector magnitude between surface plasmon polaritons (SPPs) and quasicylindrical waves (quasi-CWs) emerge. This brings modulation patterns to the total field on the metal surface near the electromagnetic source. Based on such an effect, an ultracompact SPP splitter with a lateral dimension of only 800 nm is experimentally demonstrated at wavelengths of 740 nm and 832 nm in a dielectric-film-coated asymmetric single nanoslit. These results imply that the additional modulation of quasi-CWs to the total field provide new possibilities for the design of ultracompact plasmonic devices. (C) 2011 American Institute of Physics. [doi:10.1063/1.3564935]