Recent advances towards the loss reduction in silicon nitride (SiN) has increased its interest as a material platform compatible with complementary metal-oxide-semiconductor (CMOS) processing [1]. SiN offers a large t...
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ISBN:
(纸本)9798350345995
Recent advances towards the loss reduction in silicon nitride (SiN) has increased its interest as a material platform compatible with complementary metal-oxide-semiconductor (CMOS) processing [1]. SiN offers a large transparency range reducing multiphoton absorption processes, yet its nonlinear Kerr coefficient remains about 10 times lower than that of Silicon. Now, the new coming challenges in the development of optical integrated devices rise the need for highly nonlinear CMOS-compatible optical platforms based on hybrid waveguide structures. Hereafter we report on the properties of nonlinear hybrid SiN waveguides with a Ge 23 Sb 7 S 70 (GSS) chalcogenide glass cladding of layer thickness comprised between 100 and 200 nm. Using a bi-directional spectral broadening based method, we demonstrate that hybrid SiN waveguides with a 200 nm thick GSS cladding reach an effective nonlinear refractive index $n_{2} = 0.8\pm 0.2 \cdot 10^{-18} \mathrm{m}^{2}/\mathrm{W}$ close to that of Silicon ( $n^{2} = 2 \cdot 10^{-18} \mathrm{m}^{2}/\mathrm{W}$ ), but without noticeable TPA.
We study the robustness of a photonic Chern insulator (in both linear and nonlinear regimes) supporting multiple-winding slow light modes over a broad range of frequencies against fabrication disorder and nonlinearity...
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ISBN:
(纸本)9781957171258
We study the robustness of a photonic Chern insulator (in both linear and nonlinear regimes) supporting multiple-winding slow light modes over a broad range of frequencies against fabrication disorder and nonlinearity by numerics and analytics.
The transport behaviors of topological guiding modes for classical waves in heterostructures with width degree of freedom have attracted much attention recently. With the width degree of freedom, topological waveguide...
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The transport behaviors of topological guiding modes for classical waves in heterostructures with width degree of freedom have attracted much attention recently. With the width degree of freedom, topological waveguides are endowed with increased capacity in energy transport and improved flexibility in interfacing existing devices. However, to date, such topological waveguides are only realized in hexagonal lattices, by virtue of the known valleys existing at the Brillouin zone corners. Here, we report on the implementation of topological waveguides in heterostructures of a square lattice, consisting of three domains of acoustic crystals: the middle domain has Dirac points and the two side domains have valleys of opposite valley Chern numbers. A pair of counterpropagating topological waveguide modes, with amplitudes that are uniform in the central domain and attenuated sidewards in the two side domains, are supported in the heterostructure. We experimentally verify that the topological waveguide modes are valley locked and backscattering immune, and they have a high capacity for energy transport. We also demonstrate experimentally the conversion between the valley waveguide states and the usual valley edge states. More interestingly, when the central domain of the Dirac points is applied with a transverse structural gradient mirror symmetrically, a different kind of topological waveguide mode emerges. We verify that the waveguide modes possess the same topological properties.
We present the fabrication, characterisation and modelling of an in-house fabricated source of decorrelated, indistinguishable photon pairs at 1550 nm based on a periodically poled Rb:KTP waveguide.
ISBN:
(纸本)9781957171258
We present the fabrication, characterisation and modelling of an in-house fabricated source of decorrelated, indistinguishable photon pairs at 1550 nm based on a periodically poled Rb:KTP waveguide.
Enhancement of elastic wave energy harvesting by utilizing a phononic crystal (PnC) is a hot topic in electroelastic systems. Piezoelectric energy harvesting (PEH) is implemented herein due to attaching a piezoelectri...
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Enhancement of elastic wave energy harvesting by utilizing a phononic crystal (PnC) is a hot topic in electroelastic systems. Piezoelectric energy harvesting (PEH) is implemented herein due to attaching a piezoelectric transducer (PZT) disk on a 2D starlike hole-type PnC with a line-defect. Waveguide and energy localization will lead to the amplification of harvestable mechanical energy using the opened complete bandgaps of the PnC. For a given line-defect PnC structure, two geometric parameters (diameter and thickness of the PZT disk) of the PEH device are found to be key factors to influence the energy harvesting performance. Therefore, the finite element method is used to obtain the optimal diameter and thickness of the PZT disk through the design of numerical experiments. Using the two optimal geometric parameters, the electric power amplification ratio of the present PEH device will be 26.7 times over that of the PEH device using a thin plate with the same outer dimensions.
We report unprecedentedly low second harmonic band propagation losses in highly nonlinear AlGaAs-on-insulator waveguides pumped in the telecom L-band. These findings pave the way towards para metric nonlinearities at ...
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ISBN:
(纸本)9781957171258
We report unprecedentedly low second harmonic band propagation losses in highly nonlinear AlGaAs-on-insulator waveguides pumped in the telecom L-band. These findings pave the way towards para metric nonlinearities at single photon-level.
In this paper, we demonstrate how conventional finite element modal analysis of a slice of an infinite homogeneous or periodic waveguide provides essential information on its properties. The novelty aspects are the ri...
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In this paper, we demonstrate how conventional finite element modal analysis of a slice of an infinite homogeneous or periodic waveguide provides essential information on its properties. The novelty aspects are the rigorous derivation of requested boundary conditions from the analytical bi-orthogonality relation for free waves in a waveguide and conversion of these 'class consistent' conditions to the finite element format. Eigen-frequencies and mode shapes obtained from the modal analysis are used to reconstruct dispersion diagram for propagating waves in a homogeneous waveguide. A novel method is proposed to assess their decay rates in the presence of material losses. For a periodic waveguide, the modal analysis of a symmetric unit periodicity cell with the 'class consistent' boundary conditions is innovatively used to identify partial (modal) and full stop-bands. Computational efficiency of the proposed modal analysis-based methodology as compared with standard Wave (and) Finite Element method is discussed.
Photonic-crystal waveguides formed at the interface between photonic topological insulators have recently received much attention as they promise robust forward propagation under a variety of disorder classes [1]. An ...
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ISBN:
(纸本)9798350345995
Photonic-crystal waveguides formed at the interface between photonic topological insulators have recently received much attention as they promise robust forward propagation under a variety of disorder classes [1]. An example is time-reversal-symmetric valley-Hall (VH) topological waveguides, which can be implemented in dielectric slabs and free of intrinsic radiative losses. This makes them attractive as contenders for integrated optical waveguides to slow down light without suffering from backscattering at unavoidable fabrication defects [2]. While numerical simulations find VH interface waveguides to outperform conventional waveguides at the same group index for very small disorder levels [3], the failure of modelling real fabrication imperfections, i.e., surface roughness, due to the steep computational cost limits the scope of such results, warranting experimental investigation. We report here on the experimental characterization of the scattering properties of VH waveguides etched into a 220 nm-thick silicon membrane, an example of which is shown in Fig. 1 a. Due to the glide symmetry of the waveguide and the degeneracy it enforces, the structure supports not only the topological mode ensured by the bulk-edge correspondence, but also a topologically trivial mode [4]. To characterize the propagation losses of the two modes we employ the cutback method: we measure the transmittance of a series of photonic circuits containing VH waveguide segments of varying length and fit the transmittance drop with an exponential decay. We observe no significant difference in propagation loss of trivial and topological modes at high group indices (Fig. 1 b) and, by fitting to a simple model, we find backscattering to dominate in both cases [5]. Such backscattering is strong enough to dictate the modal properties of the field, as evidenced by the formation of high-Q spatially localized optical modes observed by far-field imaging techniques. We observe backscattering-induced local
The field for potential sensing applications in the terahertz (THz) domain (0.3-10 THz) has seen increased attention in the last years, due to the progress in the development of THz sources and detectors, and due to t...
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ISBN:
(纸本)9798350345995
The field for potential sensing applications in the terahertz (THz) domain (0.3-10 THz) has seen increased attention in the last years, due to the progress in the development of THz sources and detectors, and due to the manifold of large THz absorption cross-sections of molecules relevant for environmental screening and medical analysis [1]. Practical applications rely on the development of compact, fast and low-cost gas sensing systems. As an alternate solution to standard gas cells, substrate-integrated hollow waveguides (iHWGs) have been introduced in the mid-infrared range, recently [2]. iHWGs offer an excellent volume-to-optical path length ratio increasing the sensitivity of the system, while maintaining a robust device with small footprint.
While optical waveguides for visible and infrared radiation are widely used for many applications, including photonic integrated circuits, optical communications and resonators for lasers, guiding extreme ultraviolet ...
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ISBN:
(纸本)9798350345995
While optical waveguides for visible and infrared radiation are widely used for many applications, including photonic integrated circuits, optical communications and resonators for lasers, guiding extreme ultraviolet (XUV) radiation below 100 nm is challenging. Since virtually no solid material is transparent at XUV wavelengths, vacuum is the only option for the core. A suitable choice of cladding material can confine the XUV radiation and allow it to propagate with low losses [1], [2]. In this study, we demonstrate multimode hollow-core waveguides formed in a solid substrate that can transport vacuum-ultraviolet radiation from 20 to 200 nm. Figure 1(a, b) shows an example structure of straight hollow-core waveguide and the numerical evaluation results of the fundamental TE mode at a wavelength of 120 nm. To fabricate this waveguide, a NiP plated stainless steel base plate was mechanically machined to form triangular-shaped micro grooves. An ultra-high precision five-axis machining center developed by Canon Inc was used for this process [3]. Another NiP plated substrate was bonded to the top to complete the hollow-core waveguides. The inner surfaces of the waveguides were coated with gold, which acted as a cladding for the waveguides. The longitudinal length of each waveguide was 20 mm and the side length of the triangular cross-section ranged from 4 to $35\ \upmu\mathrm{m}$ . The rms roughness of the waveguide surface was less than 1 nm, which is not expected to affect the waveguide performance.
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