Volume: 6 Issue 8
12 Article(s)

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Engineering the emission of laser arrays to nullify the jamming from passive obstacles
Constantinos Valagiannopoulos, and Vassilios Kovanis
Non-Hermitian characteristics accompany any photonic device incorporating spatial domains of gain and loss. In this work, a one-dimensional beam-forming array playing the role of the active part is disturbed from the scattering losses produced by an obstacle in its vicinity. It is found that the placement of the radiating elements leading to perfect beam shaping is practically not affected by the presence of that jammer. A trial-and-error inverse technique of identifying the features of the obstacle is presented based on the difference between the beam target pattern and the actual one. Such a difference is an analytic function of the position, size, and texture of the object, empowering the designer to find the feeding fields for the lasers giving a perfect beam forming. In this way, an optimal beam-shaping equilibrium is re-established by effectively cloaking the object and nullifying its jamming effect.
Photonics Research
  • Publication Date: Jul. 10, 2018
  • Vol. 6, Issue 8, A43 (2018)
Passive parity-time-symmetry-breaking transitions without exceptional points in dissipative photonic systems [Invited]
Yogesh N. Joglekar, and Andrew K. Harter
Over the past decade, parity-time (PT)-symmetric Hamiltonians have been experimentally realized in classical, optical settings with balanced gain and loss, or in quantum systems with localized loss. In both realizations, the PT-symmetry-breaking transition occurs at the exceptional point of the non-Hermitian Hamiltonian, where its eigenvalues and the corresponding eigenvectors both coincide. Here, we show that in lossy systems, the PT transition is a phenomenon that broadly occurs without an attendant exceptional point, and is driven by the potential asymmetry between the neutral and the lossy regions. With experimentally realizable quantum models in mind, we investigate dimer and trimer waveguide configurations with one lossy waveguide. We validate the tight-binding model results by using the beam-propagation-method analysis. Our results pave a robust way toward studying the interplay between passive PT transitions and quantum effects in dissipative photonic configurations.
Photonics Research
  • Publication Date: Jul. 24, 2018
  • Vol. 6, Issue 8, A51 (2018)
Research Articles
Lasers and Laser Optics
Bismuth nanosheets as a Q-switcher for a mid-infrared erbium-doped SrF2 laser
Jingjing Liu, Hao Huang, Feng Zhang, Zhen Zhang, Jie Liu, Han Zhang, and Liangbi Su
Photonics Research
  • Publication Date: Jul. 05, 2018
  • Vol. 6, Issue 8, 762 (2018)
High-efficiency broadband polarization-independent superscatterer using conformal metasurfaces
He-Xiu Xu, Shiwei Tang, Chen Sun, Lianlin Li, Haiwen Liu, Xinmi Yang, Fang Yuan, and Yunming Sun
Safe detection of an arbitrarily shaped platform is critical for survivability, rescue, or navigation safety in a remote region. Metasurfaces afford great potential due to their strong electromagnetic (EM) wave control. However, studies have mainly focused on the physics and design of metasurfaces on planar plates, which does not satisfy the current requirements of aerodynamics and aesthetics. Herein, we propose a sophisticated strategy to design a metasurface that can wrap over arbitrarily shaped objects with moderate curvature on which optical aberrations are commonly introduced. By designing each meta-atom on the basis of the required position and phase compensation, exact EM wavefronts are restored. For verification, several conformal metasurfaces were designed and numerically studied on metallic cylinders at the microwave spectrum. A proof-of-concept device is fabricated and is experimentally characterized. The results demonstrate the availability of the desirable dual-beam superscatterer with strong backscattering enhancement toward two directions, thus indicating that the distortions induced by an arbitrary platform can be efficiently corrected. Our method affords an efficient alternative for designing high-performance multifunctional optoelectronic devices equipped on a moderately curved platform.
Photonics Research
  • Publication Date: Jul. 09, 2018
  • Vol. 6, Issue 8, 782 (2018)
Nonlinear Optics
Intermodal four-wave mixing in silicon waveguides
Stefano Signorini, Mattia Mancinelli, Massimo Borghi, Martino Bernard, Mher Ghulinyan, Georg Pucker, and Lorenzo Pavesi
In this work, we report the modeling and the experimental demonstration of intermodal spontaneous as well as stimulated four-wave mixing (FWM) in silicon waveguides. In intermodal FWM, the phase-matching condition is achieved by exploiting the different dispersion profiles of the optical modes in a multimode waveguide. Since both the energy and the wave vectors have to be conserved in the FWM process, this leads to a wide tunability of the generated photon wavelength, allowing us to achieve a large spectral conversion. We measured several waveguides that differ by their widths and demonstrate large signal generation spanning from the pump wavelength (1550 nm) down to 1202 nm. A suited setup evidences that the different waves propagated indeed on different order modes, which supports the modeling. Despite observing a reduced efficiency with respect to intramodal FWM due to the decreased modal overlap, we were able to show a maximum spectral distance between the signal and idler of 979.6 nm with a 1550 nm pump. Our measurements suggest the intermodal FWM is a viable means for large wavelength conversion and heralded photon sources.
Photonics Research
  • Publication Date: Jul. 20, 2018
  • Vol. 6, Issue 8, 805 (2018)
Quantum Optics
Directly modulated quantum dot lasers on silicon with a milliampere threshold and high temperature stability | On the Cover
Yating Wan, Daisuke Inoue, Daehwan Jung, Justin C. Norman, Chen Shang, Arthur C. Gossard, and John E. Bowers
Microring lasers feature ultralow thresholds and inherent wavelength-division multiplexing functionalities, offering an attractive approach to miniaturizing photonics in a compact area. Here, we present static and dynamic properties of microring quantum dot lasers grown directly on exact (001) GaP/Si. Effectively, a single-mode operation was observed at 1.3 μm with modes at spectrally distant locations. High temperature stability with T0~103 K has been achieved with a low threshold of 3 mA for microrings with an outer ring radius of 15 μm and a ring waveguide width of 4 μm. Small signal modulation responses were measured for the first time for the microrings directly grown on silicon, and a 3 dB bandwidth of 6.5 GHz was achieved for a larger ring with an outer ring radius of 50 μm and a ring waveguide width of 4 μm. The directly modulated microring laser, monolithically integrated on a silicon substrate, can incur minimal real estate cost while offering full photonic functionality.
Photonics Research
  • Publication Date: Jul. 10, 2018
  • Vol. 6, Issue 8, 776 (2018)
Chirped coupled ridge waveguide quantum cascade laser arrays with stable single-lobe far-field patterns
Yue Zhao, Jin-Chuan Zhang, Chuan-Wei Liu, Ning Zhuo, Shen-Qiang Zhai, Li-Jun Wang, Jun-Qi Liu, Shu-Man Liu, Feng-Qi Liu, and Zhan-Guo Wang
Power scaling in a broad area quantum cascade laser (QCL) tends to deteriorate beam quality with the emission of a multiple-lobe far-field pattern. In this paper, we demonstrate a coupled ridge waveguide QCL array consisting of five elements with chirped geometry. In-phase mode operation is secured by managing supermode loss with properly designed geometries of ridges. A single-lobe lateral far-field with a near diffraction limited beam pattern was obtained in the whole current dynamic range. The devices were fabricated with the wet and dry etching method. The regrowth technique of the InP:Fe insulation layer and InP:Si waveguide layer was employed. Such a structure has the potential to optimize the beam quality of the recently reported high-power broad-area QCL with a reduced cascade number.
Photonics Research
  • Publication Date: Jul. 20, 2018
  • Vol. 6, Issue 8, 821 (2018)
Robust and accurate terahertz time-domain spectroscopic ellipsometry
Xuequan Chen, Edward P. J. Parrott, Zhe Huang, Hau-Ping Chan, and Emma Pickwell-MacPherson
Photonics Research
  • Publication Date: Jul. 05, 2018
  • Vol. 6, Issue 8, 768 (2018)
Ultrafast Optics
Femtosecond laser-induced periodic surface structures on lithium niobate crystal benefiting from sample heating
Qiang Li, Qiang Wu, Yanan Li, Chunling Zhang, Zixi Jia, Jianghong Yao, Jun Sun, and Jingjun Xu
Periodic surface structures were fabricated by irradiating lithium niobate (LN) crystals with femtosecond laser pulses at sample temperatures ranging from 28°C to 800°C. Carrier density and conductivity of the samples were increased via heating LN, which inhibited coulomb explosion to obtain a uniform periodic surface structure. The periodic surface structures cover an area of 8 mm×8 mm and have an average spacing of 174±5 nm. Meanwhile, the absorption of the processed sample is about 70% in the spectral range of 400–1000 nm, which is one order of magnitude higher than that of pure LN. Fabrication of periodic surface structures on heating LN with femtosecond laser pulses provides a possibility to generate nanogratings or nanostructures on wide-bandgap transparent crystals.
Photonics Research
  • Publication Date: Jul. 10, 2018
  • Vol. 6, Issue 8, 789 (2018)
Decaying evolution dynamics of double-pulse mode-locking
Guomei Wang, Guangwei Chen, Wenlei Li, Chao Zeng, and Huiran Yang
Photonics Research
  • Publication Date: Jul. 20, 2018
  • Vol. 6, Issue 8, 825 (2018)