Longitudinally uniform transmission lines with frequency-enabled mode conversion

ABSTRACT: A class of longitudinally uniform transmission lines with low loss, low dispersion, and high-field confinement, called mode-selective transmission lines (MSTLs), has been proposed for ultra-broadband and ultra-fast electromagnetic signal guidance and processing. Their operation is mainly based on the concept of frequency-enabled mode selectivity. This paper presents our latest research results on this emerging MSTL, including its operating mechanism, propagation characteristics, higher-order modes, and transition design. Throughout the detailed discussion, two MSTL structures operating in distinct frequency ranges (DC to 60 GHz and DC to 500 GHz as showcased here) are considered. First of all, a comparative study among MSTLs and several conventional transmission lines is made, illustrating significant differences in structural features, wave guidance, field distributions, and frequency characteristics. Second, the phenomenon of mode selectivity occurred in MSTLs is examined by means of identified physical evidence (i.e., field distributions in connection with modal behavior) and theoretical foundation. It is verified that, with increasing frequency, the dominant modes of MSTLs are converted from a quasi-TEM microstrip mode to a quasi-TE 10 waveguide mode over a certain frequency range. Following this thread, a more rigorous analysis is carried out by defining and formulating three characteristic frequencies based on the observed inherent physical dispersions, and the operating frequency ranges of MSTLs are thus divided into several distinct frequency regions associated with the frequency-related variable dominant mode. In addition, a general analysis of the attenuation characteristics of MSTLs and higher order modes in MSTLs is conducted. To facilitate practical measurements and to expedite the integrated applications of MSTLs, we propose a low-loss and ultra-broadband transition between MSTL and microstrip line, through which undesired higher order modes are effectively suppressed. The numerical and theoretical analyses of MSTLs are carried out with experimental verifications. At the end of this paper, different fabrication and measurement techniques for the two MSTLs of interest are briefly described

Nano-film functionalized exposed core fibers enabling resonance-driven dispersive wave tailoring

Light sources with specific optical properties are the backbone of optical technologies such as spectroscopy or hyperspectral imaging. Yet, the creation of broadband, stable, and spectrally flat light sources, especially at low pump energies, remains a particular challenge. Supercontinuum generation (SCG) is a well-established method for broadband light generation in optical fibers. For tailorable SCG spectra, it is essential to accurately design and precisely control the dispersion of fibers with new methods. This thesis aims to explore nonlinear frequency conversion in resonance-enhanced fibers to create tunable broadband light sources with tailored properties at low pump energies. By depositing high refractive index nano-films with different thicknesses on the surface of the exposed fiber core, the dispersion of the fibers and thus the output spectrum of SCG can be tuned. Different nano-film geometries are investigated, featuring TiO2 nano-films with a uniform thickness, Ta2O5 nano-films with a gradually increasing thickness along the fiber length, and periodically structured Ta2O5 nano-films. Experiments and simulations reveal the advantages of a longitudinally varying dispersion over uniformly coated fibers concerning an enhanced spectral flatness and an enlarged bandwidth. Furthermore, periodically structured nano-films lead to multi-color tailorable higher-order dispersive waves via quasi phase-matching, which are outside of the wavelength range of classical soliton-based SCG. Resonance-based modifications of the fiber dispersion by using nano-films are a powerful new tool to efficiently shape nonlinear frequency conversion in SCG even at low pump energies. It has high technological potential for the realization of novel, ultrafast, broadband, and stable nonlinear light sources for biophotonics, environmental, life sciences, medical diagnostics, and metrology

Toward Chiral Sensing and Spectroscopy Enabled by All-Dielectric Integrated Photonic Waveguides

This is the peer reviewed version of the following article: Vázquez-Lozano, J. E., Martínez, A., Toward Chiral Sensing and Spectroscopy Enabled by All-Dielectric Integrated Photonic Waveguides. Laser & Photonics Reviews 2020, 14, 1900422, which has been published in final form at https://doi.org/10.1002/lpor.201900422. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.[EN] Chiral spectroscopy is a powerful technique enabling to identify optically the chirality of matter. So far, most experiments to check the chirality of matter or nanostructures have been performed through arrangements wherein both the optical excitation and detection are realized via circularly polarized light propagating in free space. However, for the sake of miniaturization, it would be desirable to perform chiral spectroscopy in photonic integrated platforms, with the additional benefit of massive parallel detection, low¿cost production, repeatability, and portability. Here it is shown that all¿dielectric photonic waveguides can support chiral modes under proper combination of fundamental eigenmodes. Two mainstream configurations are investigated: a dielectric wire with square cross section and a slotted waveguide. Three different scenarios in which such waveguides could be used for chiral detection are numerically analyzed: waveguides as near¿field probes, evanescent¿induced chiral fields, and chiroptical interaction in void slots. In all the cases, a metallic nanohelix is considered as a chiral probe, though all the approaches can be extended to other kinds of chiral nanostructures as well as matter. These results establish that chiral applications such as sensing and spectroscopy could be realized in standard integrated optics, in particular, with silicon-based technology.The authors thank S. Lechago for valuable comments and technical support with the numerical simulations. This work was partially supported by funding from the European Commission Project THOR H2020-EU-829067. A.M. also acknowledges funding from Generalitat Valenciana (Grant No. PROMETEO/2019/123) and Spanish Ministry of Science, Innovation and Universities (Grant No. PRX18/00126).Vázquez-Lozano, JE.; Martínez Abietar, AJ. (2020). Toward Chiral Sensing and Spectroscopy Enabled by All-Dielectric Integrated Photonic Waveguides. Laser & Photonics Review. 14(9):1-12. https://doi.org/10.1002/lpor.201900422S112149FDA’S policy statement for the development of new stereoisomeric drugs. (1992). Chirality, 4(5), 338-340. doi:10.1002/chir.530040513Hutt, A. J., & Tan, S. C. (1996). 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emiT: an apparatus to test time reversal invariance in polarized neutron decay

We describe an apparatus used to measure the triple-correlation term (\D \hat{\sigma}_n\cdot p_e\times p_\nu) in the beta-decay of polarized neutrons. The \D-coefficient is sensitive to possible violations of time reversal invariance. The detector has an octagonal symmetry that optimizes electron-proton coincidence rates and reduces systematic effects. A beam of longitudinally polarized cold neutrons passes through the detector chamber, where a small fraction beta-decay. The final-state protons are accelerated and focused onto arrays of cooled semiconductor diodes, while the coincident electrons are detected using panels of plastic scintillator. Details regarding the design and performance of the proton detectors, beta detectors and the electronics used in the data collection system are presented. The neutron beam characteristics, the spin-transport magnetic fields, and polarization measurements are also described.Comment: 15 pages, 13 figure

Guided-wave properties of mode-selective transmission line

The so-called mode-selective transmission line or simply ‘‘MSTL’’ is studied theoretically and experimentally. This low-loss and low-dispersion transmission line operates with a frequency-dependent mode-switching behavior. This self-adaptive mode-selective guided-wave structure begins with the propagation of electromagnetic waves over the lower frequency range in the form of a quasi-TEM fundamental mode similar to the microstrip line case, then followed by a fundamental quasi-TE10 mode with reference to rectangular waveguide over the higher frequency region. To gain insight into the physical mechanism and fundamental features of this mode-selective transmission line, a detailed semi-analytical hybrid-mode analysis is developed through the application of a method of lines. This method allows accurate and effective modeling of MSTL guided-wave properties. Propagation characteristics of this proposed mode-agile structure in terms of dispersion, modal, and loss properties are examined, which leads to the establishment of some basic MSTL design guidelines. Numerical results confirm the expected mode conversion and low-loss behavior through the observation of field evolutions along the structure. For experimental verification, a set of MSTL prototypes are fabricated on two different substrates through dissimilar fabrication processes. Measurements are carried out from dc-to-500 GHz using a vector network analyzer. Excellent agreement between theoretical and experimental results is observed. It is confirmed that the low-dispersion and lowloss behavior of MSTL makes it an outstanding integrated waveguide in support of high-performance superbroadband signal transmission and/or ultra-fast pulse propagation in a fully-integrated platform

Nanoscale magnetophotonics

This Perspective surveys the state-of-the-art and future prospects of science and technology employing the nanoconfined light (nanophotonics and nanoplasmonics) in combination with magnetism. We denote this field broadly as nanoscale magnetophotonics. We include a general introduction to the field and describe the emerging magneto-optical effects in magnetoplasmonic and magnetophotonic nanostructures supporting localized and propagating plasmons. Special attention is given to magnetoplasmonic crystals with transverse magnetization and the associated nanophotonic non-reciprocal effects, and to magneto-optical effects in periodic arrays of nanostructures. We give also an overview of the applications of these systems in biological and chemical sensing, as well as in light polarization and phase control. We further review the area of nonlinear magnetophotonics, the semiconductor spin-plasmonics, and the general principles and applications of opto-magnetism and nano-optical ultrafast control of magnetism and spintronics

Moth wings are acoustic metamaterials

Metamaterials assemble multiple subwavelength elements to create structures with extraordinary physical properties (1–4). Optical metamaterials are rare in nature and no natural acoustic metamaterials are known. Here, we reveal that the intricate scale layer on moth wings forms a metamaterial ultrasound absorber (peak absorption = 72% of sound intensity at 78 kHz) that is 111 times thinner than the longest absorbed wavelength. Individual scales act as resonant (5) unit cells that are linked via a shared wing membrane to form this metamaterial, and collectively they generate hard-to-attain broadband deep-subwavelength absorption. Their collective absorption exceeds the sum of their individual contributions. This sound absorber provides moth wings with acoustic camouflage (6) against echolocating bats. It combines broadband absorption of all frequencies used by bats with light and ultrathin structures that meet aerodynamic constraints on wing weight and thickness. The morphological implementation seen in this evolved acoustic metamaterial reveals enticing ways to design high-performance noise mitigation devices

Tunable Wire Metamaterials for an Axion Haloscope

Metamaterials based on regular two-dimensional arrays of thin wires have attracted renewed attention in light of a recently proposed strategy to search for dark matter axions. When placed in the external magnetic field, such metamaterials facilitate resonant conversion of axions into plasmons near their plasma frequency. Since the axion mass is not known a priori, a practical way to tune the plasma frequency of metamaterial is required. In this work, we have studied a system of two interpenetrating rectangular wire lattices where their relative position is varied. The plasma frequency as a function of their relative position in two dimensions has been mapped out experimentally, and compared with both a semi-analytic theory of wire-array metamaterials and numerical simulations. Theory and simulation yield essentially identical results, which in turn are in excellent agreement with experimental data. Over the range of translations studied, the plasma frequency can be tuned over a range of 16%