The study shows that comet moth cocoon fibers exhibit radiative cooing properties with enhanced solar reflectivity and thermal emissivity. Nanostructured voids inside the cocoon fiber enables the cocoons to exhibit strong scattering in the visible and near-infrared. These structures also allow the fibers to exhibit strong shape birefringence and directional reflectivity. Optical waveguiding due to transverse Anderson localization is observed in these natural fibers, where the invariance and large concentration of the voids in the longitudinal direction allow the fiber to confine light in the transverse direction. To mimic the optical effects generated by these natural silk fibers, nanostructured voids are introduced into regenerated silk fibers through wet spinning to enhance reflectivity in the solar spectrum.
Butterfly wings are live organs embedded with multiple sensory neurons and, in some species, with pheromoneproducing cells. The proper function of butterfly wings demands a suitable temperature range, but the wings can overheat quickly in the sun due to their small thermal capacity. We developed an infrared technique to map butterfly wing temperatures and discovered that despite the wings’ diverse visible colors, regions of wings that contain live cells are the coolest, resulting from the thickness of the wings and scale nanostructures. We also demonstrated that butterflies use behavioral traits to prevent overheating of their wings.
A three-dimensional extension of the recently demonstrated generalization of the laws of refraction and reflection was investigated for both flat and curved metasurfaces. We found that out-of-plane refraction occurs for a metasurface that imparts a wavevector out of the plane of incidence onto the incident light beam. Metasurfaces provide arbitrary control over the direction of refraction, and yield new critical angles for both reflection and refraction. A spherical metasurface with phase discontinuities leads to unconventional light bending compared to standard refractive lenses.
Micro-cavity lasers with directional emission are getting more and more attention in the optoelectronic device and application field. In this paper, we presented two kinds of micro-cavity with the limason and triangle shape cavity for the directional emission application. By using quantum cascade material, the two kinds of micro cavity lasers are compared about output emission characteristics such as the far-field patterns, light output and the threshold current. The two kinds of micro-cavity lasers show good directional emission, and the limason cavity laser can reach about 30° on the main lobe of the far-field pattern with about 4.3mW peak power and the triangle can show a large one lobe with about 110° on the one side emission pattern. From the measurement result of the threshold current of the two lasers, the cavity quality factor Q finally has been obtained.
We explore guided modes in metallic "spoof-insulator-spoof" (SIS) waveguides: parallel plate
structures with subwavelength corrugation on the surfaces of both conductors. A dispersion relation for
SIS waveguides is analytically obtained. The modes in the structure arise from the coupling of
conventional parallel plate waveguide modes with the localized modes of the grooves. SIS waveguides
can be engineered to guide modes with low group velocities and SIS tapers can be used to convert light
between photonic modes and plasmonic ones.
We study the multimode operation regimes of midinfrared quantum cascade lasers (QCLs), taking into account nonlinear phase-sensitive interactions between transverse modes. We show the possibility of the coherent coupling of several transverse modes, which results in a number of interesting effects including frequency and phase locking between transverse modes, bistability, and beam steering. We present an analytical model for the modal dynamics and its numerical analysis. Effects of amplitude and phase fluctuations on the modal stability are explored. The theoretical results are in agreement with our experimental measurements of buried heterostructure QCLs.
We report a surface-emitting THz source based on intracavity difference-frequency generation in dual-wavelength midinfrared
quantum cascade lasers with integrated giant second-order nonlinear susceptibility. The THz light is coupled out
of the waveguide by a second-order grating etched into the laser ridges. In contrast to sources where the difference-frequency
radiation is emitted from the facet, this approach enables extraction of the THz emission from the whole
length of the device even when the coherence length is small. We also studied the properties of the mid-infrared pump
beams and found that due to gain competition, mid-infrared modes tend to start lasing in higher order lateral modes. The
mid-infrared mode with the lower threshold current reduces population inversion for the second laser with the higher
threshold current due to stimulated emission. We developed a rate equation model to quantitatively describe mode
interactions due to mutual gain depletion.