arXiv subjects

I-Lin Ho

Publications and source records attributed to I-Lin Ho.

8 recordsLinked to original sources

arXiv2019

K-series approximation of vectorial optical fields for designing diffractive optical elements with subwavelength feature sizes

Diffractive optical elements (DOEs) are widely applied as compact solutions for desired light manipulations via wavefront shaping. Recent advanced chip applications further require their feature sizes to move down to the subwavelength, which inevitably brings forth vectorial effects of optical fields and makes the typical scalar-based theory invalid. However, simulating and optimizing their vectorial fields, which are associated with billions of adjustable parameters in the optical element, are difficult to do, because of the issues of numerical stability and the highly-demanding computational cost. To address this problem, this research proposes an applicable algorithm by means of a wave-vector (k) series approximation of vectorial optical fields. On the basis of the semi-analytical rigorous coupled wave analysis (RCWA), an adequate selection scheme on k-series enables computationally efficient yet still predictive calculations for DOEs. The performance estimations for exemplary designs by the finite difference time domain (FDTD) method show that the predicted intensity profiles by the proposed algorithm agree with the target by just a fractional error. Together with optimizing the geometrical degrees of freedom (e.g., DOE depth h) as compensation for errors from the truncation of k-series, the algorithm demonstrates its outperformance by one or two orders of magnitude in accuracy versus the scalar-based model, and demands only a reasonable computational resource.

physics.optics↗

arXiv2019

Excitation transport in quantum devices: analytical time-dependent non-equilibrium green function algorithm

This research demonstrates analytical time-dependent non-equilibrium green function (TD-NEGF) algorithms to investigate dynamical functionalities of quantum devices, especially for photon-assisted transports. Together with the lumped element model, we also study the effects of transiently-transferring charges to reflect the non-conservation of charges in open quantum systems, and implement numerical calculations in hetero-junction systems composed of functional quantum devices and electrode-contacts (to the environment). The results show that (i) the current calculation by the analytical algorithms, versus those by conventional numerical integrals, presents superior numerical stability on a large-time scale, (ii) the correction of charge transfer effects can better clarify non-physical transport issues, e.g. the blocking of AC signaling under the assumption of constant device charges, (iii) the current in the long-time limit validly converges to the steady value obtained by standard time-independent density functional calculations, and (iv) the occurrence of the photon-assisted transport is well-identified.

cond-mat.mes-hall↗

arXiv2018

A fast model based on muffin-tin approximation to study charge transfer effects in time-dependent quantum transport simulations: doped Si-SiO2 quantum-dot systems

In order to quickly study quantum devices in transient problems, this work demonstrates an analytical algorithm to solve the Hartree potential associated with charge fluctuations in the time-dependent non-equilibrium green function (TDNEGF) method. We implement the calculations in the heterojunction system of gold metals and silicon quantum dots for applications of photoelectric semiconductors in the future. Numerical results for the transient solutions are shown to be valid by comparing with the steady solutions calculated by the standard time-independent density functional method.

physics.pop-ph↗

arXiv2018

Study of wide-spectrum and high-resolution diffraction optical elements by stacks of binary phase gratings

This work theoretically investigates wide-spectrum and high-resolution diffraction optical elements (DOE) that are made of stacks of low-resolution binary phase gratings, whereby the two-dimensional grids in different grating layers are arranged with specified displacements. We remodel the common Kinoform algorithm for this multi-scale architecture. Numerical computations show that, by increasing the number of stacking layers, the resolution of diffraction fields can be improved and that the stability of optical elements within broad spectrums is significantly enhanced. Practical concern on largely increasing the number of grating layers are efficiency of the optical designs in theory and the manufacture of stacks of ultra-thin grating films.

physics.optics↗

arXiv2014

Multiscale Talbot effects in Fibonacci geometry

This article investigates the Talbot effects in Fibonacci geometry by introducing the cut-and-project construction, which allows for capturing the entire infinite Fibonacci structure into a single computational cell. Theoretical and numerical calculations demonstrate the Talbot foci of Fibonacci geometry at distances that are multiples $(\tau+2)(F_{\mu}+\tau F_{\mu+1} )^{-1}p/(2q)$ or $(\tau+2)(L_{\mu}+\tau L_{\mu+1} )^{-1}p/(2q)$ of the Talbot distance. Here, ($p$, $q$) are coprime integers, $\mu$ is an integer, $\tau$ is the golden mean, and $F_{\mu}$ and $L_{\mu}$ are Fibonacci and Lucas numbers, respectively. The image of a single Talbot focus exhibits a multiscale pattern due to the self-similarity of the scaling Fourier spectrum.

physics.pop-ph↗

arXiv2004

Axial-vector Form Factors for $K_{\ell 2γ}$ and $π_{\ell 2γ}$ at $O(p^6)$ in Chiral Perturbation Theory

We present two-loop calculations on the axial-vector form factors $F_A$ of semileptonic radiative kaon and pion decays in chiral perturbation theory. The relevant dimension-6 terms of the lagrangian are evaluated from the resonance contribution and the results of the irreducible two-loop graphs of the sunset topology are given in detail. We also explicitly show that the divergent parts in $F_A$ are cancelled exactly as required.

hep-ph↗

arXiv2003

Forward-backward Asymmetry in $K^+\toπ^+ \ell^+\ell^-$

We study the forward-backward asymmetries in the decays of $K^+\toπ^+\ell^+ \ell^-$ ($\ell=e$ and $μ$) in the presence of scalar or tensor terms. We find that with the scalar (tensor) type interaction the asymmetry can be up to ${\cal O}(10^{-3})$ (${\cal O}(10^{-1}))$ and arbitrary large for the electron and muon modes, respectively, without conflict with the experimental data. We also discuss the cases in the minimal supersymmetric standard model where the scalar terms can be induced. In particular we show that the asymmetry in $K^+\toπ^+μ^+μ^-$ can be as large as ${\cal O}(10^{-3})$ in the large $\tanβ$ limit, which can be tested in future experiments such as CKM at Fermilab.

hep-ph↗

arXiv2002

Lepton Universality, Rare Decays and Split Fermions

We investigate the constraint on the split fermions in extra dimensions by considering the universality of $W$ leptonic decays $W\to l_i ν_i$, the charged lepton decays $l_i \ra l_jν_i\barν_j$, and the lepton flavor violating process $l_i\ra \bar{l}_j l_k l_h$ where $l_i= e,μ$ or $τ$. For the Standard Model (SM) background of $W\ra l_i ν_i$, we extended the one loop quantum correction to include effects of order $m_l^2/M_W^2$ and the Higgs mass dependence. We find that in general the split fermion scenarios give rise to a 4D effective Yukawa matrix of the Kaluza-Klein Higgs bosons is misaligned with respect to the fermion mass matrix. This holds true also for gauge bosons as well. This leads to decays of $l_i\ra \bar{l_j}l_k l_h$ at tree level and muonium antimuonium conversion. Interestingly the leptonic universality of $W$ boson decays are not affected at this level.

hep-ph↗