More Like this

1. 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. 

   more » « less
2. Electroelastic metasurface with resonant piezoelectric shunts for tunable wavefront control

   https://doi.org/10.1088/1361-6463/acbd5f  

   Lin, Z.; Tol, S. (March 2023, Journal of Physics D: Applied Physics)

   Abstract In this paper, we design a tunable phase-modulated metasurface composed of periodically distributed piezoelectric patches with resonant-type shunt circuits. The electroelastic metasurface can control the wavefront of the lowest antisymmetric mode Lamb wave (A₀mode) in a small footprint due to its subwavelength features. The fully coupled electromechanical model is established to study the transmission characteristics of the metasurface unit and validated through numerical and experimental studies. Based on the analysis of the metasurface unit, we first explore the performance of electroelastic metasurface with single-resonant shunts and then extend its capability with multi-resonant shunts. By only tuning the electric loads in the shunt circuits, we utilize the proposed metasurface to accomplish wave deflection and wave focusing ofA₀mode Lamb waves at different angles and focal points, respectively. Numerical simulations show that the metasurface with single-resonant shunts can deflect the wavefront of 5 kHz and 6 kHz flexural waves by desired angles with less than $2\mathrm{\%}$deviation. In addition, it can be tuned to achieve nearly three times displacement amplification at the designed focal point for a wide range of angles from $-{75}^{\circ }$to 75^∘. Furthermore, with multi-resonant shunts, the piezoelectric-based metasurface can accomplish anomalous wave control over flexural waves at multiple frequencies (i.e. simultaneously at 5 kHz and 10 kHz), developing new potentials toward a broad range of engineering applications such as demultiplexing various frequency components or guiding and focusing them at different positions. 

   more » « less
3. Unified k-space theory of optical coherence tomography

   https://doi.org/10.1364/AOP.417102  

   Zhou, Kevin_C; Qian, Ruobing; Dhalla, Al-Hafeez; Farsiu, Sina; Izatt, Joseph_A (June 2021, Advances in Optics and Photonics)

   We present a general theory of optical coherence tomography (OCT), which synthesizes the fundamental concepts and implementations of OCT under a common 3D $k$-space framework. At the heart of this analysis is the Fourier diffraction theorem, which relates the coherent interaction between a sample and plane wave to the Ewald sphere in the 3D $k$-space representation of the sample. While only the axial dimension of OCT is typically analyzed in $k$-space, we show that embracing a fully 3D $k$-space formalism allows explanation of nearly every fundamental physical phenomenon or property of OCT, including contrast mechanism, resolution, dispersion, aberration, limited depth of focus, and speckle. The theory also unifies diffraction tomography, confocal microscopy, point-scanning OCT, line-field OCT, full-field OCT, Bessel beam OCT, transillumination OCT, interferometric synthetic aperture microscopy (ISAM), and optical coherence refraction tomography (OCRT), among others. Our unified theory not only enables clear understanding of existing techniques but also suggests new research directions to continue advancing the field of OCT. 

   more » « less
4. Self-adaptive amplified spontaneous emission suppression with a photorefractive two-beam coupling filter

   https://doi.org/10.1364/OL.410695  

   Pettine, Jacob; Zhu, Miao; Anderson, Dana_Z (November 2020, Optics Letters)

   Optical bandpass filters can be utilized to suppress parasitic broadband spectral power prior to laser amplification but are typically designed around specific frequencies or require manual adjustment, thus limiting their compatibility with highly tunable or integrated laser systems. In this Letter, we introduce a self-adaptive volume holographic filter using the dynamic two-beam coupling interaction in photorefractive ${\mathrm{B}\mathrm{a}\mathrm{T}\mathrm{i}\mathrm{O}}_3$, demonstrating $-<\#comment/>10\mathrm{d}\mathrm{B}$suppression of amplified spontaneous emission noise surrounding a tunable 780 nm diode laser peak, with $<<\#comment/>2\mathrm{n}\mathrm{m}$filter bandwidth and 50% power throughput. The spectral filtering is automatically centered on the lasing mode, with an estimated auto-tuning rate of 100 GHz/s under typical conditions. Furthermore, the filter suppression and bandwidth can be optimized via the two-beam coupling intensity ratio and angle, respectively, for versatile control over the self-adaptive filter characteristics. 

   more » « less
5. Beam displacement tolerances on a segmented mirror for higher-order Hermite–Gauss modes

   https://doi.org/10.1088/2040-8986/ad1120  

   Tao, Liu; Brown, Nina; Fulda, Paul (December 2023, Journal of Optics)

   Abstract Odd-indexed higher-order Hermite–Gauss (HG) modes are compatible with four-quadrant segmented mirrors due to their intensity nulls along the principal axes, which guarantees minimum beam intensity illuminating the bond lines between the segments thus leading to low power loss. However, a misplaced HG beam can cause extra power loss due to the bright intensity spots probing the bond lines. This paper analytically and numerically studies the beam displacement tolerances on a segmented mirror for the $\mathrm{H}{\mathrm{G}}_{3,3}$mode. We conclude that for ‘effective’ bond lines with 6 µm width, and the $\mathrm{H}{\mathrm{G}}_{3,3}$beam size chosen to guarantee 1 ppm clipping loss when centered, the beam can be rotated by roughly 1^∘or laterally displaced by 4% of its beam size while keeping the total power on the bond lines under 1 ppm. We also demonstrate that the constrained beam displacement parameter region that guarantees a given power loss limit, or the beam displacement tolerance, is inversely proportional to the bond line thickness. 

   more » « less