Tunable optical materials can enable more functionality while maintaining flexibility in a single aperture, which is relevant to making visible and infrared image sensing more context aware. DARPA’s Accelerating discovery of Tunable Optical Materials (ATOM) program is exploring fundamental insights into the physics of tunable optical materials with the goal of developing new materials for optic and photonic applications. The specific characteristics of interest are a large change in refractive index (Δn) to delay light, low loss for high transmissivity (k), and fast switching speeds. Rare earth nickelates and phase change materials, integrated with machine learning to accelerate insights into new materials, show initial promise toward the ATOM program goals.
Metasurfaces—structured planarized optical devices with a thickness thinner than or comparable to the wavelength of light—typically support a “local” response, i.e., they tailor the optical wavefront through the independent response of each meta-unit. In contrast, “nonlocal” metasurfaces are characterized by an optical response dominated by collective modes over many meta-units. In this talk, I will illustrate a rational design paradigm using quasi-bound states in the continuum to realize nonlocal metasurfaces. I will report experimental demonstration of a few device functionalities: (a) devices that produce narrowband spatially tailored wavefronts at multiple selected wavelengths and yet are otherwise transparent, (b) nonlocal metasurfaces based on CMOS-compatible dielectric materials with thermo-optically reconfigurable wavefronts, and (c) nonlinear resonant GaN metasurfaces growth by templated molecular beam epitaxy for efficient sum frequency generation.
Optical phase modulators are essential to large-scale integrated photonic systems at visible wavelengths, promising for many emerging applications. However, current technologies require large device footprints and either high power consumption or high drive voltage, limiting the number of active elements in a visible integrated photonic circuit. Here, we demonstrate visible silicon-nitride thermo-optical phase modulators based on adiabatic micro-ring resonators that offer at least a one-order-of-magnitude reduction in both device footprint and power consumption compared to waveguide phase modulators. Designed to operate in the strongly over-coupled regime, the micro-resonators provide 2 pi phase modulation with minimal amplitude variations, corresponding to less than 1 dB device insertion losses. By delocalizing the resonant mode, the adiabatic micro-rings also exhibit substantially improved robustness against fabrication variations.
This Conference Presentation, “Programmable hyperbolic polaritons in van der Waals semiconductors,” was recorded for the Photonics West 2021 Digital Forum.
Diffractive photonic devices manipulate light via local and nonlocal optical modes. Local devices, such as metasurfaces, can shape a wavefront at multiple selected wavelengths, but inevitably modify light across the spectrum; nonlocal devices, such as grating filters, offer great frequency selectivity but limited spatial control. In this talk, I will introduce a rational design paradigm using quasi-bound states in the continuum to realize multifunctional nonlocal devices: metasurfaces that produce narrowband spatially tailored wavefronts at multiple selected wavelengths and yet are otherwise transparent.
KEYWORDS: Temperature metrology, Thermography, Mid-IR, Temperature sensors, Neurons, Solar radiation, Head, Abdomen, Nanostructures, Infrared radiation
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.
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.
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.
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