We present coherent perfect absorbers based on topological guided-mode resonances at a topological junction of two thin-film waveguide lattices. The proposed structure provides a fully confined resonance state in both vertical and lateral dimensions, creating a compact coherent absorber possibly operating at the critical coupling condition for the complete annihilation of certain optimized coherent incoming waves. We provide a promising Si-photonic design, incoming wave configuration, and theoretical performance for its operation as a compact coherent absorber in the integrated optics platform.
KEYWORDS: Waveguides, Systems modeling, Telecommunications, Energy transfer, Design and modelling, Tunable filters, Solid state physics, Silicon, Photonics systems, Optical filters
A basic model of topological insulators, the Su-Schrieffer-Heeger (SSH) model, has been applied in various photonic systems for novel optical effects and related applications. Here, we show that odd-numbered SSH chains may enable extremely broadband waveguide couplers. A special feature of odd-numbered SSH chain is that there is always a zero-energy localized state regardless of its bulk topological invariant value. We utilize this unique feature in adiabatic photonic waveguide systems for spectrally robust optical power dividers or combiners as opposed to the conventional interferometric components such as directional couplers and multimode interference couplers. We demonstrate broadband edge-to-edge and 1N couplers with their power balance persisting over the entire optical telecommunications bands. We provide detailed theory, experimental results, and remaining challenges.
The transportation of in-plane photonic topological states, achieved by mimicking electronic systems, has gained a lot of attention. However, there has not been much exploration of their out-of-plane radiation effects. By treating leakage radiation, the concept of the band topology can be extended to resonant metasurfaces, providing new opportunities to directly measure them and to create new features for free-space applications. In this talk, we examine the basic mechanisms of far-field radiation and resonant excitation in topological junction metasurfaces made of thin film dielectric subwavelength gratings. These structures have distinctive topological characteristics such as complex Dirac masses, Berry phases, and band structures shown through Fano spectral responses. Considering the correlation between the topological quantities and structural parameters, we discuss new optical functionalities discovered in the topological metasurfaces such as Dirac-mass engineered beam shaping.
Optical nonreciprocity is required in many optical systems for signal stabilization, laser protection, non-destructive probing. Here, we experimentally demonstrate a nonreciprocal fiber-optic amplifier enabled by encircling-an-exceptional-point emulation and gain-saturation nonlinearity. We realize the proposed system by combining optical attenuators, Erbium-doped fiber amplifiers (EDFA), and 2x2 couplers. We obtain remarkably high nonreciprocal transmission ratio > 20 dB persisting over the entire gain band from 1,530 to 1,560 nm at moderate input power conditions from 0.1 to 1 mW.
We theoretically suggest ultra-sparse 1D and 2D arrays of high-index dielectric wires as broadband, omnidirectional reflectors and polarizers. Using diffraction potential arguments and numerical simulations, we show the proposed device for 1D array supports a high-extinction polarizing function. For an optimized 1D SrTiO3-wire array, a TE reflection resonance has a remarkably wide bandwidth while the TM wave almost freely passes through the array in the entire zero-order spectral domain. Based on the theoretically observed performance of the 1D array, we design fully conical omnidirectionality in the reflection for the 2D extension at the center wavelength of the fundamental-mode resonance condition. We briefly discuss possibility of the proposed 1D and 2D wire grid architectures for space-variant beam transforming optics and vector beam generations. Applications to THz photonic components and other long-wave devices such as radio-wave telescopes and satellite antenna are envisioned.
We experimentally demonstrate a robust Si-photonic waveguide architecture that realizes dynamically encircling an exceptional point (EP) in the optical domain and broadband asymmetric modal transmission as an essential consequence. The structure consists of a pair of coupled channel waveguides and an adjacent slab-waveguide patch that enable precise lithographic controls on the phase velocities and radiation rates of the guided photonic modes. Complex modal index and inter-mode coupling constant profiles required for the encircling-an-EP parametric control are precisely coded in the geometry of those elements. The device created on this basis induces the symmetry-exchanging adiabatic state flip for one transmission direction and symmetry-preserving anti-adiabatic state-jump for the transmission in the opposite direction. In fabrication, we use a state-of-the-art electron-beam lithography for creating mm-long devices with nm-scale transversal precision. A comprehensive spectral measurement for the intensity and phase distributions of the transmitted optical states is obtained with a specially designed phase-sensitive infrared microscopy integrated with a tunable diode-laser system and spectrum analyzer. On this basis, we confirm in the experiment the highly asymmetric modal transmission persisting over a broad spectral band exceeding 100 nm in the telecommunications window around 1,550 nm. Hence, we establish a substantive experimental step toward broadband non-reciprocal photonic devices based on the unique non-Hermitian dynamics.
The guided-mode resonance (GMR) concept refers to lateral quasi-guided waveguide modes induced in periodic layers. Whereas these effects have been known for a long time, new attributes and innovations continue to appear. Here, we review some recent progress in this field with emphasis on sparse, or minimal, device embodiments. We discuss properties of wideband resonant reflectors designed with gratings in which the grating ridges are matched to an identical material to eliminate local reflections and phase changes. This critical interface therefore possesses zero refractive-index contrast; hence we call them “zero-contrast gratings.” Applying this architecture, we present single-layer, wideband reflectors that are robust under experimentally realistic parametric variations. We introduce a new class of reflectors and polarizers fashioned with dielectric nanowire grids that are mostly empty space. Computed results predict high reflection and attendant polarization extinction for these sparse lattices. Experimental verification with Si nanowire grids yields ~200-nm-wide band of high reflection for one polarization state and free transmission of the orthogonal state. Finally, we present bandpass filters using all-dielectric resonant gratings. We design, fabricate, and test nanostructured single layer filters exhibiting high efficiency and sub-nanometer-wide passbands surrounded by 100-nm-wide stopbands.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.