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In this study, we proposed morphology-modulated Si nanowires (NWs) with a hexagonal cross-section and numerically investigated their resonant optical absorption and scattering properties. The calculated absorption and scattering efficiency spectra of the NWs exhibited optical resonances that could be controlled by tuning the aspect ratio (AR) of the NW cross-sectional shapes. The spectra also revealed interesting spectral behaviors including resonant peak shifts in the absorption spectrum and asymmetric line shapes in the scattering spectrum. To achieve spatially confined and wavelength-selective light absorption, we periodically modulated the geometry of the diameter in a single NW by combining two different ARs; we call these “diameter-modulated NWs.” We designed various diameter-modulated NWs with short and long pitch sizes, and we observed unique and interesting features in the optical resonance and corresponding light absorption spectra such as grating modes and three-dimensional cavity modes. The proposed diameter-modulated NWs can be promising building blocks for the nanoscale localized light absorption and detection in compact nanophotonic integrated circuits.

High-index semiconductor photonic crystal (PhC) cavities in a flexible substrate support strong and tunable optical resonances that can be used for highly sensitive and spatially localized detection of mechanical deformations in physical systems. Here, we report theoretical studies and fundamental understandings of resonant behavior of an optical mode excited in strain-sensitive rod- type PhC cavities consisting of high-index dielectric nanorods embedded in a low-index flexible polymer substrate. Using the three-dimensional finite-difference time-domain simulation method, we calculated two-dimensional transverse-electric-like photonic band diagrams and the three-dimensional dispersion surfaces near the first Gamma-point band edge of unidirectionally strained PhCs. A broken rotational symmetry in the PhCs modifies the photonic band structures and results in the asymmetric distributions and different levels of changes in normalized frequencies near the first Gamma-point band edge in the reciprocal space, which consequently reveals strain-dependent directional optical losses and selected emission patterns. The calculated electric fields, resonant wavelengths, and quality factors of the band-edge modes in the strained PhCs show an excellent agreement with the results of qualitative analysis of modified dispersion surfaces. Furthermore, polarization-resolved time-averaged Poynting vectors exhibit characteristic dipole-like emission patterns with preferentially selected linear polarizations, originating from the asymmetric band structures in the strained PhCs. (C) 2016 Optical Society of America

We demonstrate new types of dielectric-band photonic crystal lasers in a two-dimensional modified single-cell cavity with enlarged air holes. Finite-difference time-domain simulations performed in real and Fourier spaces show that the dielectric-band cavity modes originating from the first band edge point in the dielectric band have mode patterns that are distinguishable from conventional air-band cavity modes. In our experiment, the observed multimode lasing peaks are identified as the hexapole and the monopole dielectric-band cavity modes through the spectral positions and mode images. The thresholds of these lasers are measured as approximately 340 microW and approximately 450 microW, respectively, at room temperature. In addition, using the simulation based on the actual fabricated structures, quality factors and mode volumes are computed as 4900 and 1.09 (lambda/n)3 for the hexapole mode, and 4300 and 2.27 (lambda/n)3 for the monopole mode, respectively.