Volume: 3 Issue 5
4 Article(s)

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Color centers in wide-bandgap semiconductors for subdiffraction imaging: a review
Stefania Castelletto, and Alberto Boretti
Solid-state atomic-sized color centers in wide-band-gap semiconductors, such as diamond, silicon carbide, and hexagonal boron nitride, are important platforms for quantum technologies, specifically for single-photon sources and quantum sensing. One of the emerging applications of these quantum emitters is subdiffraction imaging. This capability is provided by the specific photophysical properties of color centers, such as high dipole moments, photostability, and a variety of spectral ranges of the emitters with associated optical and microwave control of their quantum states. We review applications of color centers in traditional super-resolution microscopy and quantum imaging methods, and compare relative performance. The current state and perspectives of their applications in biomedical, chemistry, and material science imaging are outlined.
Advanced Photonics
  • Publication Date: Sep. 18, 2021
  • Vol.3 Issue, 5 054001 (2021)
Enhanced generation of nondegenerate photon pairs in nonlinear metasurfaces
Matthew Parry, Andrea Mazzanti, Alexander Poddubny, Giuseppe Della Valle, Dragomir N. Neshev, and Andrey A. Sukhorukov
Advanced Photonics
  • Publication Date: Sep. 07, 2021
  • Vol.3 Issue, 5 055001 (2021)
Research Articles
Nonlinear topological valley Hall edge states arising from type-II Dirac cones
Hua Zhong, Shiqi Xia, Yiqi Zhang, Yongdong Li, Daohong Song, Chunliang Liu, and Zhigang Chen
A Dirac point is a linear band crossing point originally used to describe unusual transport properties of materials like graphene. In recent years, there has been a surge of exploration of type-II Dirac/Weyl points using various engineered platforms including photonic crystals, waveguide arrays, metasurfaces, magnetized plasma and polariton micropillars, aiming toward relativistic quantum emulation and understanding of exotic topological phenomena. Such endeavors, however, have focused mainly on linear topological states in real or synthetic Dirac/Weyl materials. We propose and demonstrate nonlinear valley Hall edge (VHE) states in laser-written anisotropic photonic lattices hosting innately the type-II Dirac points. These self-trapped VHE states, manifested as topological gap quasi-solitons that can move along a domain wall unidirectionally without changing their profiles, are independent of external magnetic fields or complex longitudinal modulations, and thus are superior in comparison with previously reported topological edge solitons. Our finding may provide a route for understanding nonlinear phenomena in systems with type-II Dirac points that violate the Lorentz invariance and may bring about possibilities for subsequent technological development in light field manipulation and photonic devices.
Advanced Photonics
  • Publication Date: Oct. 26, 2021
  • Vol.3 Issue, 5 056001 (2021)
Active spintronic-metasurface terahertz emitters with tunable chirality
Changqin Liu, Shunjia Wang, Sheng Zhang, Qingnan Cai, Peng Wang, Chuanshan Tian, Lei Zhou, Yizheng Wu, and Zhensheng Tao
The ability to generate and manipulate broadband chiral terahertz waves is essential for applications in material imaging, terahertz sensing, and diagnosis. It can also open up new possibilities for nonlinear terahertz spectroscopy and coherent control of chiral molecules and magnetic materials. The existing methods, however, often suffer from low efficiency, narrow bandwidth, or poor flexibility. Here, we propose a novel type of laser-driven terahertz emitters, consisting of metasurface-patterned magnetic multilayer heterostructures, that can overcome the shortcomings of the conventional approaches. Such hybrid terahertz emitters combine the advantages of spintronic emitters for being ultrabroadband, efficient, and highly flexible, as well as those of metasurfaces for the powerful control capabilities over the polarization state of emitted terahertz waves on an ultracompact platform. Taking a stripe-patterned metasurface as an example, we demonstrate the efficient generation and manipulation of broadband chiral terahertz waves. The ellipticity can reach >0.75 over a broad terahertz bandwidth (1 to 5 THz), representing a high-quality and efficient source for few-cycle circularly polarized terahertz pulses with stable carrier waveforms. Flexible control of ellipticity and helicity is also demonstrated with our systematic experiments and numerical simulations. We show that the terahertz polarization state is dictated by the interplay between laser-induced spintronic-origin currents and the screening charges/currents in the metasurfaces, which exhibits tailored anisotropic properties due to the predesigned geometric confinement effects. Our work opens a new pathway to metasurface-tailored spintronic emitters for efficient vector-control of electromagnetic waves in the terahertz regime.
Advanced Photonics
  • Publication Date: Oct. 26, 2021
  • Vol.3 Issue, 5 056002 (2021)