Search results for "Guide"
showing 10 items of 1478 documents
Dielectric versus topographic contrast in near-field microscopy
1996
Using a fully vectorial three-dimensional numerical approach (generalized field propagator, based on Green's tensor technique), we investigate the near-field images produced by subwavelength objects buried in a dielectric surface. We study the influence of the object index, size, and depth on the near field. We emphasize the similarity between the near field spawned by an object buried in the surface (dielectric contrast) and that spawned by a protrusion on the surface (topographic contrast). We show that a buried object with a negative dielectric contrast (i.e., with a smaller index than its surrounding medium) produces a near-field image that is reversed from that of an object with a posi…
Supercontinuum generation in silicon waveguides relying on wave-breaking
2015
Four-wave-mixing processes enabled during optical wave-breaking (OWB) are exploited in this paper for supercontinuum generation. Unlike conventional approaches based on OWB, phase-matching is achieved here for these nonlinear interactions, and, consequently, new frequency production becomes more efficient. We take advantage of this kind of pulse propagation to obtain numerically a coherent octave-spanning mid-infrared supercontinuum generation in a silicon waveguide pumping at telecom wavelengths in the normal dispersion regime. This scheme shows a feasible path to overcome limits imposed by two-photon absorption on spectral broadening in silicon waveguides.
Photonic transfer through subwavelength optical waveguides
1998
Optical tunneling effect through dielectric junctions with subwavelength transverse sizes has been demonstrated some years ago. In this letter, we demonstrate how similar effects can be exploited to perform photonic transfer through a subwavelength optical wave guide (SOW) by structuring its optical index along the direction of propagation. The optical transmittance of the SOW is computed self-consistently in direct space through the numerical solution of a Dyson equation. We apply this scheme to investigate the optical properties of different SOW architectures. Even under total internal reflection, in which the light is coupled to the SOW by an evanescent mode, an efficient optical transfe…
Inverse dispersion engineering in silicon waveguides
2014
We present a numerical tool that searches an optimal cross section geometry of silicon-on-insulator waveguides given a target dispersion profile. The approach is a gradient-based multidimensional method whose efficiency resides on the simultaneous calculation of the propagation constant derivatives with respect to all geometrical parameters of the structure by using the waveguide mode distribution. The algorithm is compatible with regular mode solvers. As an illustrative example, using a silicon slot hybrid waveguide with 4 independent degrees of freedom, our approach finds ultra-flattened (either normal or anomalous) dispersion over 350 nm bandwidth in less than 10 iterations.
Time-Domain Integration of Terahertz pulses
2021
We report on the time-domain integration of terahertz pulses obtained via the tight confinement of the radiation in a tapered two-wire waveguide. Both simulation and experimental results prove the time integration capability of this structure.
Accurate consideration of metal losses at waveguide junctions using admittance and impedance integral equation formulations
2005
[1] At higher frequencies, metal loss effects in passive waveguide components become more pronounced and hazardous. In this paper, we propose two integral equation techniques, based on the generalized admittance and impedance matrices, for the accurate consideration of losses in the metal walls of waveguide junctions. Both techniques have been evaluated in terms of accuracy and numerical efficiency, and conclusions are drawn regarding the best properties of the admittance parameter formulation. Finally, combining such technique with a classical perturbative method for considering propagation losses, we have successfully predicted all loss effects in two real waveguide filters used for comme…
Analysis of Inhomogeneously Dielectric Filled Cavities Coupled to Dielectric-Loaded Waveguides: Application to the Study of NRD-Guide Components
2004
In this paper, we present two contributions. First, we develop a computationally efficient technique for the full-wave characterization of inhomogeneously dielectric-filled cavities connected to inhomogeneously dielectric-loaded waveguides. This method is based on the expansion of the electromagnetic field within the cavity in terms of their solenoidal and irrotational modes. The presented formulation allows the treatment of hybrid modes in the waveguide ports, where the definition of a characteristic modal impedance or admittance is not possible. The multimode scattering matrix of the structure is computed throughout an efficient implementation of the orthonormal-basis method for the calcu…
Experimental demonstration of Bloch mode parity change in photonic crystal waveguide
2004
We experimentally show coupling between two photonic crystal waveguide Bloch modes having a different parity. A monomode ridge waveguide etched in a silicon-on-insulator substrate and connecting to the photonic crystal waveguide allows us to excite the even Bloch mode. Transmission measurements, performed on a broad spectral range, show the even mode propagation along the defect line. Then, spectrally resolved near-field patterns obtained by using a scanning near-field optical microscope in collection mode for wavelengths, inside and outside the multimode region of the photonic crystal waveguide, clearly demonstrate coupling phenomenon between even and odd modes.
Sodium vapor cell laser guide star experiments for continuous wave model validation
2016
Recent numerical simulations and experiments on sodium Laser Guide Star (LGS) have shown that a continuous wave (CW) laser with circular polarization and re-pumping should maximize the fluorescent photon return flux to the wavefront sensor for adaptive optics applications. The orientation and strength of the geomagnetic field in the sodium layer also play an important role affecting the LGS return ux. Field measurements of the LGS return flux show agreement with the CW LGS model, however, fluctuations in the sodium column abundance and geomagnetic field intensity, as well as atmospheric turbulence, induce experimental uncertainties. We describe a laboratory experiment to measure the photon …
Wavelength-flattened directional couplers for mirror-symmetric interferometers
2005
In the context of guided optics, we derive, analytically and geometrically, a rigorous general criterion to design wavelength insensitive interferometers with mirror symmetry, which are needed for wavelength multiplexing/demultiplexing. The criterion is applied to a practical case, resulting in an interferometer that works on a band wider than 70 nm.