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1. Giant terahertz polarization rotation in ultrathin films of aligned carbon nanotubes

   https://doi.org/10.1364/OPTICA.422826  

   Baydin, Andrey ; Komatsu, Natsumi ; Tay, Fuyang ; Ghosh, Saunab ; Makihara, Takuma ; Noe, G_Timothy ; Kono, Junichiro ( May 2021 , Optica)

   For easy manipulation of polarization states of light for applications in communications, imaging, and information processing, an efficient mechanism is desired for rotating light polarization with a minimum interaction length. Here, we report giant polarization rotations for terahertz (THz) electromagnetic waves in ultrathin ($\sim <\#comment/>45\mathrm{n}\mathrm{m}$), high-density films of aligned carbon nanotubes. We observed polarization rotations of up to$\sim <\#comment/>{20}^{\circ <\#comment/>}$and$\sim <\#comment/>{110}^{\circ <\#comment/>}$for transmitted and reflected THz pulses, respectively. The amount of polarization rotation was a sensitive function of the angle between the incident THz polarization and the nanotube alignment direction, exhibiting a “magic” angle at which the total rotation through transmission and reflection becomes exactly 90°. Our model quantitatively explains these giant rotations as a result of extremely anisotropic optical constants, demonstrating that aligned carbon nanotubes promise ultrathin, broadband, and tunable THz polarization devices.

    

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2. Resonance tuning for dynamic Huygens metasurfaces

   https://doi.org/10.1364/JOSAB.427848  

   Ollanik, Adam_J ; Oguntoye, Isaac ; Ji, Yaping ; Escarra, Matthew_D ( July 2021 , Journal of the Optical Society of America B)

   Metasurfaces with dynamic optical performance have the potential to enable a broad range of applications. We computationally investigate the potential of dielectric Huygens metasurfaces, supporting both electric and magnetic dipole resonances, as a candidate platform for dynamic tuning. The asymmetric response of the two dipole resonances to changes in geometric and material parameters, and the potential for separate control of amplitude and phase, is analyzed. A review of dynamic materials, and their promise and limitations for use in dynamic Huygens metasurfaces, is discussed. Vanadium dioxide (${\mathrm{V}\mathrm{O}}_2$) is recognized as a singularly interesting material, due to its variable refractive index and optical absorption in response to several stimuli. Transmitted phase modulation of$\pm <\#comment/>\mathrm{\pi <\#comment/>}$is computationally demonstrated as a function of decaying resonance utilizing only the first 5% of the insulator-metal transition, corresponding to a temperature change of$<<\#comment/>{10}^{\circ <\#comment/>}\mathrm{C}$. As another case study utilizing asymmetric resonance tuning in response to changing incidence angle, phase modulation ($2\mathrm{\pi <\#comment/>}$range for reflected light and$><\#comment/>1.5\mathrm{\pi <\#comment/>}$for transmitted light) and amplitude modulation (from$\mathrm{R}=1$to$\mathrm{T}=1$) are demonstrated using a simple silicon metasurface with varying incident angle within a range of$\sim <\#comment/>{15}^{\circ <\#comment/>}$on two axes. A promising implementation within a micro-electromechanical system (MEMS)-based spatial light modulator, similar to conventional digital micromirror devices, is discussed.

    

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3. Determination of size and complex index of refraction of single particles with elastic light scattering

   https://doi.org/10.1364/AO.413675  

   Waez, Mir_Seliman ; Eckels, Steven_J ; Sorensen, Christopher_M ( January 2021 , Applied Optics)

   We show that for spherical particles greater than ca. 5 µm, the differential scattering cross section is only weakly dependent on the real and imaginary parts of the refractive index ($m=n+i\mathrm{\kappa <\#comment/>}$) when integrated over angle ranges near$37\pm <\#comment/>5^{\circ <\#comment/>}$and$115\pm <\#comment/>5^{\circ <\#comment/>}$, respectively. With this knowledge, we set up an arrangement that collects scattered light in the ranges$37\pm <\#comment/>5^{\circ <\#comment/>}$,$115\pm <\#comment/>5^{\circ <\#comment/>}$, and$80\pm <\#comment/>5^{\circ <\#comment/>}$. The weak functionality on refractive index for the first two angle ranges simplifies the inversion of scattering to the particle properties of diameter and the real and imaginary refractive indices. Our setup also uses a diamond-shaped incident beam profile that allows us to determine when a particle went through the exact center of the beam. Application of our setup to droplets of an absorbing liquid successfully determined the diameter and complex refractive index to accuracies ranging from a few to ten percent. Comparisons to simulated data derived from the Mie equations yielded similar results.

    

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4. High-performance electron-blocking-layer-free deep ultraviolet light-emitting diodes implementing a strip-in-a-barrier structure

   https://doi.org/10.1364/OL.400917  

   Velpula, Ravi_Teja ; Jain, Barsha ; Velpula, Swetha ; Nguyen, Hoang-Duy ; Nguyen, Hieu_Pham_Trung ( September 2020 , Optics Letters)

   In this Letter, the electron-blocking-layer (EBL)-free AlGaN ultraviolet (UV) light-emitting diodes (LEDs) using a strip-in-a-barrier structure have been proposed. The quantum barrier (QB) structures are systematically engineered by integrating a 1 nm intrinsic${\mathrm{A}\mathrm{l}}_x{\mathrm{G}\mathrm{a}}_{(1-<\#comment/>x)}\mathrm{N}$strip into the middle of QBs. The resulted structures exhibit significantly reduced electron leakage and improved hole injection into the active region, thus generating higher carrier radiative recombination. Our study shows that the proposed structure improves radiative recombination by$\sim <\#comment/>220\mathrm{\%<\#comment/>}$, reduces electron leakage by$\sim <\#comment/>11$times, and enhances optical power by$\sim <\#comment/>225\mathrm{\%<\#comment/>}$at 60 mA current injection compared to a conventional AlGaN EBL LED structure. Moreover, the EBL-free strip-in-a-barrier UV LED records the maximum internal quantum efficiency (IQE) of$\sim <\#comment/>61.5\mathrm{\%<\#comment/>}$which is$\sim <\#comment/>72\mathrm{\%<\#comment/>}$higher, and IQE droop is$\sim <\#comment/>12.4\mathrm{\%<\#comment/>}$, which is$\sim <\#comment/>333\mathrm{\%<\#comment/>}$less compared to the conventional AlGaN EBL LED structure at$\sim <\#comment/>284.5\mathrm{n}\mathrm{m}$wavelength. Hence, the proposed EBL-free AlGaN LED is the potential solution to enhance the optical power and produce highly efficient UV emitters.

    

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5. High energy yield bifacial spectrum-splitting photovoltaic system

   https://doi.org/10.1364/AO.391821  

   Chrysler, Benjamin_D ; Kostuk, Raymond_K ( April 2020 , Applied Optics)

   In this paper a photovoltaic system is proposed that achieves high energy yield by integrating bifacial silicon cells into a spectrum-splitting module. Spectrum splitting is accomplished using volume holographic optical elements to spectrally divide sunlight onto an array of photovoltaic cells with different bandgap energies. Light that is reflected from the ground surface onto the rear side of the module is converted by the bifacial silicon cells. The energy yield of the system is optimized by tuning the volume holographic element parameters, such as film thickness, index modulation, and construction point source positions. An example is presented for utility-scale illumination parameters in Tucson, Arizona, that attains an energy yield of$1010\frac{kw\cdot <\#comment/>hr}{yr\cdot <\#comment/>m^2}$, which is 32.8% of the incident solar insolation.

    

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