We experimentally demonstrate free space excitation of coupled Anderson-localized modes in photonic crystal (PhC) line-defect waveguides (W1) with polarization tailored beams. The corresponding light beam is tightly f...
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We experimentally demonstrate free space excitation of coupled Anderson-localized modes in photonic crystal (PhC) line-defect waveguides (W1) with polarization tailored beams. The corresponding light beam is tightly focused on a pristine W1, and out-of-plane scattering is imaged. By integrating the scattering spectra along the guide, at the W1 modal cut-off, Anderson-localized cavities are observed due to residual W1 fabrication-disorder. Their spectral lines exhibit high quality Q factors up to 2 x 10(5). The incident beam polarization and scattering intensities of the localized modes characterize the efficiency of free-space coupling. The coupling is studied for linearly and radially polarized input beams and for different input coupling locations along the W1 guide. The proposed coupling scheme is particularly attractive for excitation of PhC waveguide modes and Anderson-localized cavities by beam steering and scanning microscopy for sensing applications. Published by AIP Publishing.
Aluminum nitride (AlN) is an emerging platform for a wide range of on-chip applications. One promising feature is that both the second-and third-order nonlinearities are available in crystalline AlN waveguides. We des...
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Aluminum nitride (AlN) is an emerging platform for a wide range of on-chip applications. One promising feature is that both the second-and third-order nonlinearities are available in crystalline AlN waveguides. We design an AlN slot waveguide with a flat and low dispersion over an ultrawide spectral range from near-infrared to mid-infrared. A dual-slot structure is designed and the flattened group velocity dispersion within -13 and +11 ps/(***) over 2000-nm-wide bandwidth with three zero dispersion wavelengths is achieved. The impacts of the structural parameters are analyzed in detail and the phase-matching condition in four-wave mixing process is investigated as well. A 3-dB conversion bandwidth of 1200 nm and -28-dB conversion efficiency are predicted in a 1-cm-long horizontal dual-slot AlN waveguide with the pump power of 2 W.
High-speed Silicon Photonics calls for solutions providing a small footprint, high density, and minimum crosstalk, as exemplified by the recent development of integrated optical modulators. Yet, the performances of su...
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High-speed Silicon Photonics calls for solutions providing a small footprint, high density, and minimum crosstalk, as exemplified by the recent development of integrated optical modulators. Yet, the performances of such modulators are hindered by intrinsic material losses, which results in low energy efficiency. Using the concept of Adiabatic Elimination, here, we introduce a scheme allowing for the low-loss modulation in densely packed waveguides. Our system is composed of two waveguides, whose coupling is mediated by an intermediate third waveguide. The signal is carried by the two outer modes, while the active control of their coupling is achieved via the intermediate dark mode. The modulation is performed by the manipulation of the central-waveguide mode index, leaving the signal-carrying waveguides unaffected by the loss. We discuss how Adiabatic Elimination provides a solution for mitigating signal losses and designing relatively compact, broadband, and energy-efficient integrated optical modulators. Published by AIP Publishing.
We measured and analyzed reflection spectra of directly coupled systems of waveguides and cavities. The observed Fano lines offer insight on the reflection and coupling processes. Very different from side-coupled syst...
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We measured and analyzed reflection spectra of directly coupled systems of waveguides and cavities. The observed Fano lines offer insight on the reflection and coupling processes. Very different from side-coupled systems, the observed Fano line shape is not caused by the termini of the waveguide but by the coupling process between the measurement device fiber and the waveguide. Our experimental results and analytical model show that the Fano parameter that describes the Fano line shape is very sensitive to the coupling condition. A movement of the fiber well below the Rayleigh range can lead to a drastic change of the Fano line shape.
A rigorous approach for precise and efficient calculation of light propagation along nonuniform waveguides is presented. Resonant states of a uniform waveguide, which satisfy outgoing-wave boundary conditions, form a ...
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A rigorous approach for precise and efficient calculation of light propagation along nonuniform waveguides is presented. Resonant states of a uniform waveguide, which satisfy outgoing-wave boundary conditions, form a natural basis for expansion of the local electromagnetic field. Using such an expansion at fixed frequency, we convert the wave equation for light propagation in a nonuniform waveguide into an ordinary second-order matrix differential equation for the expansion coefficients depending on the coordinate along the waveguide. We illustrate the method on several examples of nonuniform planar waveguides and evaluate its efficiency compared to the aperiodic Fourier modal method and the finite element method, showing improvements of one to four orders of magnitude. A similar improvement can be expected also for applications in other fields of physics showing wave phenomena, such as acoustics and quantum mechanics.
We propose a robust scheme to achieve optical pulling force using the guiding modes supported in a hollow core double-mode photonic crystal waveguide instead of the structured optical beams in free space investigated ...
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We propose a robust scheme to achieve optical pulling force using the guiding modes supported in a hollow core double-mode photonic crystal waveguide instead of the structured optical beams in free space investigated earlier. The waveguide under consideration supports both the 0th order mode with a larger forward momentum and the 1st order mode with a smaller forward momentum. When the 1st order mode is launched, the scattering by the object inside the waveguide results in the conversion from the 1st order mode to the 0th order mode, thus creating the optical pulling force according to the conservation of linear momentum. We present the quantitative agreement between the results derived from the mode conversion analysis and those from rigorous simulation using the finite-difference in the time-domain numerical method. Importantly, the optical pulling scheme presented here is robust and broadband with naturally occurred lateral equilibriums and has a long manipulation range. Flexibilities of the current configuration make it valuable for the optical force tailoring and optical manipulation operation, especially in microfluidic channel systems. Published by AIP Publishing.
In this paper, transitions between substrate integrated waveguides (SIW) within a multi-layered printed circuit board (PCB) are studied. Particularly, horizontal (within the same layer) and vertical (between different...
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In this paper, transitions between substrate integrated waveguides (SIW) within a multi-layered printed circuit board (PCB) are studied. Particularly, horizontal (within the same layer) and vertical (between different layers) transitions are investigated. Horizontal transitions are studied by implementing SIW arcs with various radii having their side wall ground vias located on a curve. Vertical transitions are implemented between SIWs in different layers by placing a narrow rectangular opening in the PCB ground plane between the waveguides. The size of this opening is varied to provide an effective layer-to-layer transition between the SIWs. Insertion losses and field distributions of both types of transitions are examined. Both are shown to have relatively low-loss, with approximately 3.8 dB/inch loss for the straight and curved SIW structures at 100GHz and only an additional 0.2 dB of loss over a straight SIW's when a vertical transition is incorporated.
Microwave engineering of high average-power (hundreds of kilowatts) devices often involves a transition from a waveguide to a device, typically a resonant cavity. This is a basic operation, which nds use in various ap...
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Microwave engineering of high average-power (hundreds of kilowatts) devices often involves a transition from a waveguide to a device, typically a resonant cavity. This is a basic operation, which nds use in various application areas of signicance to science and industry. At relatively low frequencies, L-band and below, it is convenient, sometimes essential, to couple the power between the waveguide and the cavity through a coaxial antenna, forming a power coupler. Power ow to the cavity in the fundamental mode leads to a Fundamental Power Coupler (FPC). High-order mode power generated in the cavity by a particle beam leads to a high-order mode power damper. Coupling a cryogenic device, such as a superconducting cavity to a room temperature power source (or damp) leads to additional constraints and challenges. We propose a new approach to this problem, wherein the coax line element is operated in a TE11 mode rather than the conventional TEM mode. We will show that this method leads to a signicant increase in the power handling capability of the coupler as well as a few other advantages. We describe the mode converter from the waveguide to the TE11 coax line, outline the characteristics and performance limits of the coupler and provide a detailed worked out example in the challenging area of coupling to a superconducting accelerator cavity.
The cross-section method is extended to the case of waveguides containing sharp metal edges. Such structures comprise strip lines, microstrip lines, and slot transmission lines. Relationships for eigenmode coupling co...
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The cross-section method is extended to the case of waveguides containing sharp metal edges. Such structures comprise strip lines, microstrip lines, and slot transmission lines. Relationships for eigenmode coupling coefficients in a section with parameters varying in the longitudinal direction are derived by passing to the limit: from a waveguide with smooth contour of the cross section to a waveguide with sharp edges. These relationships are applied to a single-mode strip line with conductor having variable width. It is shown that the obtained results agree with the results of the theory of microwave transmission lines.
Nanophotonic waveguides are a promising platform to trap cold atoms using red-and blue-detuned evanescent-field optical dipole forces. The asymmetric structure of integrated waveguides leads to a large birefringence t...
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Nanophotonic waveguides are a promising platform to trap cold atoms using red-and blue-detuned evanescent-field optical dipole forces. The asymmetric structure of integrated waveguides leads to a large birefringence that is not encountered in cylindrically symmetric optical nanofibers. We have studied both theoretically and experimentally the modal properties and suitability of silicon nitride rib waveguides for cold-atom trapping. The dependence of the modal effective index on the rib width is explored experimentally by measuring beat lengths between propagating modes. These measurements are made using a novel spatial Fourier analysis technique based on conventional far-field imaging of elastic scattering from the waveguide. We find that the beat length between the lowest order TE00 and TM00 modes is approximately 5 mu m, in excellent agreement with numerical calculations. We propose to take advantage of this birefringence and mode structure to create novel, one-dimensional periodic trapping potentials for atoms within the evanescent field of the waveguide. (C) 2016 Optical Society of America
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