Professional Education

  • Doctor of Philosophy, University of Texas Austin (2017)
  • Master of Science in Engr, University of Texas Austin (2014)
  • Bachelor of Science, University of Texas Austin (2010)

Lab Affiliations

All Publications

  • Reprogrammable Electro-Optic Nonlinear Activation Functions for Optical Neural Networks IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS Williamson, I. D., Hughes, T. W., Minkov, M., Bartlett, B., Pai, S., Fan, S. 2020; 26 (1)
  • Wave physics as an analog recurrent neural network. Science advances Hughes, T. W., Williamson, I. A., Minkov, M., Fan, S. 2019; 5 (12): eaay6946


    Analog machine learning hardware platforms promise to be faster and more energy efficient than their digital counterparts. Wave physics, as found in acoustics and optics, is a natural candidate for building analog processors for time-varying signals. Here, we identify a mapping between the dynamics of wave physics and the computation in recurrent neural networks. This mapping indicates that physical wave systems can be trained to learn complex features in temporal data, using standard training techniques for neural networks. As a demonstration, we show that an inverse-designed inhomogeneous medium can perform vowel classification on raw audio signals as their waveforms scatter and propagate through it, achieving performance comparable to a standard digital implementation of a recurrent neural network. These findings pave the way for a new class of analog machine learning platforms, capable of fast and efficient processing of information in its native domain.

    View details for DOI 10.1126/sciadv.aay6946

    View details for PubMedID 31903420

  • Forward-Mode Differentiation of Maxwell's Equations ACS PHOTONICS Hughes, T. W., Williamson, I. D., Minkov, M., Fan, S. 2019; 6 (11): 3010–16
  • Penetration Depth Reduction with Plasmonic Metafilms ACS PHOTONICS Zhao, N. Z., Williamson, I. D., Zhao, Z., Boutami, S., Fan, S. 2019; 6 (8): 2049–55
  • Broadband Optical Switch based on an Achromatic Photonic Gauge Potential in Dynamically Modulated Waveguides PHYSICAL REVIEW APPLIED Williamson, I. D., Fan, S. 2019; 11 (5)
  • High Reflection from a One-Dimensional Array of Graphene Nanoribbons ACS PHOTONICS Zhao, N., Zhao, Z., Williamson, I. D., Boutami, S., Zhao, B., Fan, S. 2019; 6 (2): 339–44
  • Broadband Switches Using Photonic Aharonov-Bohm Interferometers and Dynamic Modulation Williamson, I. D., Fan, S., IEEE IEEE. 2019
  • High Reflection from a One-Dimensional Array of Graphene Nanoribbons Zhao, N., Zhao, Z., Williamson, I. D., Boutami, S., Zhao, B., Fan, S., IEEE IEEE. 2019
  • Absence of frequency ranges of undirectional propagation in nonreciprocal plasmonics Buddhiraju, S., Shi, Y., Song, A., Wojcik, C., Minkov, M., Williamson, I. D., Dutt, A., Fan, S., IEEE IEEE. 2019
  • Training of Photonic Neural Networks through In Situ Backpropagation Hughes, T. W., Minkov, M., Williamson, I. D., Shi, Y., Fan, S., IEEE IEEE. 2019
  • Adjoint-based inverse design of nonlinear nanophotonic devices Hughes, T. W., Minkov, M., Williamson, I. D., Fan, S., IEEE IEEE. 2019
  • Lossless Zero-Index Guided Modes via Bound States in the Continuum Minkov, M., Williamson, I. D., Xiao, M., Fan, S., IEEE IEEE. 2019
  • Zero-Index Bound States in the Continuum PHYSICAL REVIEW LETTERS Minkov, M., Williamson, I. D., Xiao, M., Fan, S. 2018; 121 (26)
  • Adjoint Method and Inverse Design for Nonlinear Nanophotonic Devices ACS PHOTONICS Hughes, T. W., Minkov, M., Williamson, I. D., Fan, S. 2018; 5 (12): 4781–87
  • Dual-Carrier Floquet Circulator with Time-Modulated Optical Resonators ACS PHOTONICS Williamson, I. D., Mousavi, S., Wang, Z. 2018; 5 (9): 3649–57
  • Zero-Index Bound States in the Continuum. Physical review letters Minkov, M., Williamson, I. A., Xiao, M., Fan, S. 2018; 121 (26): 263901


    Metamaterials with an effective zero refractive index associated with their electromagnetic response are sought for a number of applications in communications and nonlinear optics. A promising way that this can be achieved in all-dielectric photonic crystals is through the design of a Dirac cone at zero Bloch wave vector in the photonic band structure. In the optical frequency range, the natural way to implement this design is through the use of a photonic crystal slab. In the existing implementation, however, the zero-index photonic modes also radiate strongly into the environment due to intrinsic symmetry properties. This has resulted in large losses in recent experimental realizations of this zero-index paradigm. Here, we propose a photonic crystal slab with zero-index modes which are also symmetry-protected bound states in the continuum. Our approach thus eliminates the associated radiation loss. This could enable, for the first time, large-scale integration of zero-index materials in photonic devices.

    View details for PubMedID 30636117

  • Large Cavity-Optomechanical Coupling with Graphene at Infrared and Terahertz Frequencies ACS PHOTONICS Williamson, I. D., Mousavi, S., Wang, Z. 2016; 3 (12): 2353–61
  • Extraordinary wavelength reduction in terahertz graphene-cladded photonic crystal slabs SCIENTIFIC REPORTS Williamson, I. D., Mousavi, S., Wang, Z. 2016; 6: 25301


    Photonic crystal slabs have been widely used in nanophotonics for light confinement, dispersion engineering, nonlinearity enhancement, and other unusual effects arising from their structural periodicity. Sub-micron device sizes and mode volumes are routine for silicon-based photonic crystal slabs, however spectrally they are limited to operate in the near infrared. Here, we show that two single-layer graphene sheets allow silicon photonic crystal slabs with submicron periodicity to operate in the terahertz regime, with an extreme 100× wavelength reduction from graphene's large kinetic inductance. The atomically thin graphene further leads to excellent out-of-plane confinement, and consequently photonic-crystal-slab band structures that closely resemble those of ideal two-dimensional photonic crystals, with broad band gaps even when the slab thickness approaches zero. The overall photonic band structure not only scales with the graphene Fermi level, but more importantly scales to lower frequencies with reduced slab thickness. Just like ideal 2D photonic crystals, graphene-cladded photonic crystal slabs confine light along line defects, forming waveguides with the propagation lengths on the order of tens of lattice constants. The proposed structure opens up the possibility to dramatically reduce the size of terahertz photonic systems by orders of magnitude.

    View details for PubMedID 27143314

  • Kinetic inductance driven nanoscale 2D and 3D THz transmission lines SCIENTIFIC REPORTS Mousavi, S., Williamson, I. D., Wang, Z. 2016; 6: 25303


    We examine the unusual dispersion and attenuation of transverse electromagnetic waves in the few-THz regime on nanoscale graphene and copper transmission lines. Conventionally, such propagation has been considered to be highly dispersive, due to the RC time constant-driven voltage diffusion below 1 THz and plasmonic effects at higher optical frequencies. Our numerical modeling across the microwave, THz, and optical frequency ranges reveals that the conductor kinetic inductance creates an ultra-broadband linear-dispersion and constant-attenuation region in the THz regime. This so-called LC region is an ideal characteristic that is known to be absent in macro-scale transmission lines. The kinetic-LC frequency range is dictated by the structural dimensionality and the free-carrier scattering rate of the conductor material. Moreover, up to 40x wavelength reduction is observed in graphene transmission lines.

    View details for PubMedID 27137628

  • Suppression of the skin effect in radio frequency transmission lines via gridded conductor fibers APPLIED PHYSICS LETTERS Williamson, I. D., Nguyen, T. N., Wang, Z. 2016; 108 (8)

    View details for DOI 10.1063/1.4942649

    View details for Web of Science ID 000373057000053