The quest to understand, design, and synthesize new forms of quantum matter guides much of contemporary research in condensed matter physics. One-dimensional (1D) electronic systems form the basis for some of the most...
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The quest to understand, design, and synthesize new forms of quantum matter guides much of contemporary research in condensed matter physics. One-dimensional (1D) electronic systems form the basis for some of the most interesting and exotic phases of quantum matter. Here, we describe a family of quasi-1D nanostructures, based on LaAlO3/SrTiO3 electron waveguides, in which a sinusoidal transverse spatial modulation is imposed. These devices display unique dispersive features in the subband spectra, namely, a sizeable shift (similar to 7 T) in the spin-dependent subband minima, and fractional conductance plateaus. The first property can be understood as an engineered spin-orbit interaction associated with the periodic acceleration of electrons as they undulate through the nanowire (ballistically), while the second property signifies the presence of enhanced electron-electron scattering in this system. The ability to engineer these interactions in quantum wires contributes to the tool set of a 1D solid-state quantum simulation platform.
We investigate a time-harmonic wave problem in a waveguide. We work at low frequency so that only one mode can propagate. It is known that the scattering matrix exhibits a rapid variation for real frequencies in a vic...
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We investigate a time-harmonic wave problem in a waveguide. We work at low frequency so that only one mode can propagate. It is known that the scattering matrix exhibits a rapid variation for real frequencies in a vicinity of a complex resonance located close to the real axis. This is the so-called Fano resonance phenomenon. And when the geometry presents certain properties of symmetry, there are two different real frequencies such that we have either R = 0 or T = 0, where R and T denote the reflection and transmission coefficients. In this work, we prove that without the assumption of symmetry of the geometry, quite surprisingly, there is always one real frequency for which we have T = 0. In this situation, all the energy sent in the waveguide is backscattered. However in general, we do not have R = 0 in the process. We provide numerical results to illustrate our theorems.
EBG waveguides in an electromagnetic crystal are studied in the form of a two-dimensionally periodic array of metal cylinders located between conducting screens. The dispersion characteristics of waveguides formed by ...
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EBG waveguides in an electromagnetic crystal are studied in the form of a two-dimensionally periodic array of metal cylinders located between conducting screens. The dispersion characteristics of waveguides formed by removing one, two, and three rows of cylinders along the diagonal of a square crystal lattice are obtained. As a result of analyzing the frequency dispersion of the fundamental waveguide modes and eigenmodes of a homogeneous crystal, the factors limiting the operating frequency bands of the waveguides are determined and the lattice parameters optimal from the aspect of the band properties are obtained. The characteristics of waveguides oriented along the diagonal of the crystal lattice are compared with similar characteristics of waveguides formed along the principal axes in crystals with a square lattice.
Ultra-low-loss waveguide fabrication typically requires high-temperature annealing beyond 1000ffiC to reduce the hydrogen content in deposited dielectric films. However, realizing the full potential of an ultra-low lo...
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Ultra-low-loss waveguide fabrication typically requires high-temperature annealing beyond 1000ffiC to reduce the hydrogen content in deposited dielectric films. However, realizing the full potential of an ultra-low loss will require the integration of active materials that cannot tolerate high temperature. Uniting ultra-low-loss waveguides with on-chip sources, modulators, and detectors will require a low-temperature, low-loss dielectric to serve as a passivation and spacer layers for complex fabrication processes. We report a 250 degrees C deuterated silicon dioxide film for top cladding in ultra-low-loss waveguides. Using multiple techniques, we measure propagation loss below 12 dB/m for the entire 1200-1650 nm range and top-cladding material absorption below 1 dB/m in the S, C, and L bands. (C) 2020 Optical Society of America
We propose a novel scheme to investigate the Brillouin properties of waveguides with high loss and severe reflection through comparison experiments with a single-mode fiber (SMF). An optical filter is adopted to filte...
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We propose a novel scheme to investigate the Brillouin properties of waveguides with high loss and severe reflection through comparison experiments with a single-mode fiber (SMF). An optical filter is adopted to filter the reflected pump light. Brillouin scattering is detected with a lock-in amplifier (LIA). To obtain a large Brillouin gain in a short medium, a modulation signal with a time width of 2 ms is applied. With application of the mathematical relationship between the output power and measurement range of the LIA, the measured Brillouin gains of the waveguides and the SMF are normalized to derive the relationship among the Brillouin gain coefficients. This scheme is verified on two doped silica waveguides. The Brillouin scattering properties of the doped silica waveguides are further described and the Brillouin gain coefficients are derived.
Valley photonic crystals (VPhCs) are an attractive platform for the implementation of topologically protected optical waveguides in photonic integrated circuits (PICs). The realization of slowlight modes in the topolo...
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Valley photonic crystals (VPhCs) are an attractive platform for the implementation of topologically protected optical waveguides in photonic integrated circuits (PICs). The realization of slowlight modes in the topological waveguides may lead to further miniaturization and functionalization of the PICs. In this Letter, we report an approach to realize topological slow light waveguides in semiconductor slab-based VPhCs. We show that a bearded interface of two topologically distinct VPhCs can support topological kink modes with large group indices over 100 within the topological bandgap. We numerically demonstrate robust light propagation in the topological slow light waveguide with large group indices of similar to 60, even under the presence of sharp bends. Our work opens a novel route to implement topological slow light waveguides in a way compatible with current PIC technology. (C) 2020 Optical Society of America
We propose a strategy of temperature gradient assisted femtosecond laser writing for elaboration of low loss waveguides (WGs) over a large depth in glass. The matter flow driven by the temperature distribution is resp...
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We propose a strategy of temperature gradient assisted femtosecond laser writing for elaboration of low loss waveguides (WGs) over a large depth in glass. The matter flow driven by the temperature distribution is responsible for forming a highly densified WG core with tunable size. Importantly, the unique position of the guiding core outside the focus allows for abating the influence of laser energy redistribution and inscribing low loss deep WGs. A low insertion loss (L-i) of 0.6 dB at 1550 nm is achieved for WGs at the depth from 300 mu m to 900 mu m. Establishing strong dependence of L-i on the WG size offers a unique route to improve WG performance. These findings highlight that the present method would provide new opportunities for creating low loss WG lattices at large depth. (C) 2020 Optical Society of America
We report on waveguides laser writing inside porous glass. Depending on applied laser regimes, two types of waveguides are fabricated in the same glass sample. A gradient waveguide type is achieved under the lowest pu...
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We report on waveguides laser writing inside porous glass. Depending on applied laser regimes, two types of waveguides are fabricated in the same glass sample. A gradient waveguide type is achieved under the lowest pulse energy regime, which results in gradual densification of a nanoporous framework forming a core with an increased refractive index. The surrounding unirradiated material acts as a cladding. The highest pulse energy applied enables formation of the densified core surrounded by rarefaction regions in the nanoporous framework - a core-cladding waveguide type. Laser light guiding is also accomplished for both types to estimate the refractive index contrast. In addition, we determine the temperature distribution based on the thermal conduction model to reveal the difference of temperature gradients for the regimes applied.
The availability of nonlinear parametric processes, such as frequency conversion in photonic integrated circuits is essential. In this contribution, we demonstrate a highly tunable second-harmonic generation in a full...
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The availability of nonlinear parametric processes, such as frequency conversion in photonic integrated circuits is essential. In this contribution, we demonstrate a highly tunable second-harmonic generation in a fully complementary metal-oxide-semiconductor (CMOS)-fabrication-compatible silicon nitride integrated photonic platform. We induce the second-order nonlinearity using an all-optical poling technique with the second-harmonic light generated in the fundamental mode, and a narrow quasiphase matching (QPM) spectrum by avoiding higher-order mode mixing. We are then able to broadly tune the phasematched pump wavelength over the entire C-band (1540 nm to 1560 nm) by varying the poling conditions. Fine-tuning of QPM is enabled by thermo-optic effect with the tuning slope Delta lambda/Delta T in our device being 113.8 pm/degrees C. In addition, we exploit the measurable variation of the 3 dB QPM bandwidth to confirm how the length of the all-optically inscribed grating varies with exposure time. (C) 2020 Optical Society of America
The nonlinear coefficient gamma is central to the study of cubically nonlinear optical guided-wave structures. It is well understood for lossless waveguides, but less so for lossy systems. A number of methods for calc...
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The nonlinear coefficient gamma is central to the study of cubically nonlinear optical guided-wave structures. It is well understood for lossless waveguides, but less so for lossy systems. A number of methods for calculating gamma in lossy systems have been proposed, each resulting in different expressions. Here we identify the most accurate and practical expression for gamma. We do so by applying the different expressions gamma to air-gold surface plasmon polariton modes in the interband region of gold and compare with a fully numerical iterative method. We thus resolve the outstanding issue of which expression for the nonlinear coefficient to use for lossy waveguides, enabling new insights into the nonlinear response of such systems. (C) 2020 Optical Society of America
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