1,270 research outputs found
PSTM / NSOM modeling by 2-D quadridirectional eigenmode expansion
A two-dimensional (2-D) model for photon-scanning tunneling microscopy (PSTM) of integrated optical devices is evaluated. The simulations refer to a setup where the optical field in the vicinity of the sample is probed by detecting the optical power that is transferred via evanescent or radiative coupling to the tapered tip of an optical fiber close to the sample surface. Scanning the tip across the surface leads to a map of the local optical field in the sample. As a step beyond the mere analysis of the sample device, simulations are considered that include the sample as well as the probe tip. An efficient semianalytical simulation technique based on quadridirectional eigenmode expansions is applied. Results for a series of configurations, where slab waveguides with different types of corrugations serve as samples, allow assessment of the relation between the PSTM signal and the local field distribution in the sample. A reasonable qualitative agreement was observed between these computations and a previous experimental PSTM investigation of a waveguide Bragg grating
Defect Grating Simulations: Perturbations with AFM-like Tips
A defect grating in a silicon on insulator waveguide is simulated. We consider spectral changes in the optical transmission when a thin silicon nitride or silicon tip is scanned across the defect. The tip perturbs the resonance field, moving its peak wavelength andpossibly changing its shape and quality factor. For the nitride tip, the influence is mostly a spectral shift; for silicon, the change of the resonance shape is pronounced. In particular for the nitride tip we observe a close correspondence between the wavelength shift as a function of tip position, and the local intensity in the unperturbed structure
Widely wavelength-selective Al2O3:Er3+ ring laser
Integrated Al2O3:Er3+ channel waveguide ring lasers were realized on thermally oxidized silicon substrates. High pump power coupling into- and low output power coupling from the ring is achieved in a straightforward design. Wavelength\ud
selection in the range 1532 to 1557 nm was demonstrated by\ud
varying the length of the output coupler from the ring
Optical bistability in a nonlinear photonic crystal waveguide notch filter
Optical bistability occurs when the effects of nonlinear behaviour of materials cause hysteresis in the transmission and reflection of a device. A possible mechanism for this is a strong dependence of the optical intensity on the index of refraction, e.g. in a cavity near resonance. In a 2- dimensional photonic crystal composed of rods of high-index material in air, a waveguide can be created by removing a line of rods. When a cavity is made by taking away several rods perpendicular to the waveguide, a notch filter characteristic in the transmission occurs. Due to the high intensity in the cavity in resonance, nonlinear effects are enhanced. This paper shows numerical simulations of bistability in the transmission and in the field inside the cavity both when a material inside the cavity has third-order (Kerr-type) nonlinear effects, and when the high-index rods themselves are nonlinear
Modeling of Multimodal Effects in Two-port Ring-Resonator Circuits for Sensing Applications
Multimodal effects in two-port ring-resonator circuits for sensing applications were modeled using a transfer matrix method and previously published rigorous 3-D modeling tools. Device parameters which are relevant for evaluating sensing performance are numerically deduced from the model. Some examples will be given.\u
A perturbed lepton-specific two-Higgs-doublet model facing experimental hints for physics beyond the Standard Model
The BaBar, Belle, and LHCb collaborations have reported evidence for new
physics in and of approximately .
There is also the long lasting discrepancy of about in the anomalous
magnetic moment of the muon, and the branching ratio for is
() above the Standard Model expectation using the HFAG
(PDG) values. Furthermore, CMS found hints for a non-zero decay rate of
. Interestingly, all these observations can be explained by
introducing new scalars. In this article we consider these processes within a
lepton-specific two-Higgs doublet model (i.e. of type X) with additional
non-standard Yukawa couplings. It is found that one can accommodate
with modified Higgs-- couplings. The anomalous
magnetic moment of the muon can be explained if the additional neutral CP-even
Higgs is light (below 100 GeV). Also and can be easily
explained by additional ----Higgs couplings. Combining these --
couplings with a light the decay rate for can be in a testable
range for the LHC. Effects in are also possible, but in this case
a simultaneous explanation of the anomalous magnetic moment of the muon is
difficult due to the unavoidable decay.Comment: 14 pages, 10 figure
A Dispersive Treatment of Decays
decays offer several reasons of interest: they allow an accurate
measurement of -scattering lengths; they provide the best source for
the determination of some low-energy constants of ChPT; one form factor is
directly related to the chiral anomaly, which can be measured here. We present
a dispersive treatment of decays that provides a resummation of
- and -rescattering effects. The free parameters of the
dispersion relation are fitted to the data of the high-statistics experiments
E865 and NA48/2. The matching to ChPT at NLO and NNLO enables us to determine
the LECs , and . With recently published data from
NA48/2, the LEC can be determined as well. In contrast to a pure chiral
treatment, the dispersion relation describes the observed curvature of one of
the form factors, which we understand as a rescattering effect beyond NNLO.Comment: 86 pages, 21 figures. Draws on and extends arXiv:1412.5171 [hep-ph]
and arXiv:1209.0755 [hep-ph
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