Propagating beam analysis of fiber wavelength filters with a depressed-index section

A wavelength filter consisting of single-mode and few-mode fibers is investigated numerically. A simple finite-difference beam-propagation method, in which a transparent boundary condition can be imposed, is developed for circularly symmetric waveguides. After confirming the validity of the numerical method by the mode-mismatch loss, we calculate the propagating field in the fiber wavelength filter, in which interference between LP₀₁, and LP₀₂ modes occurs. To improve the filtering operation, a depressed-index fiber is employed for the few-mode fiber. The effects of the radius and refractive index of the depressed section on the transmission power are revealed and discussed. Power is suppressed to less than 0.1% at 1.3 μm, while maintaining power transmission of more than 85% at 1.55 μm. It is also found that the filtering operation shifts to higher wavelengths as the input power is increased when we choose a self-focusing nonlinear material in the depressed section.     

Mid-infrared emissions from Ho3+ in Ga2S3-GeS2-Sb2S3 glass

Emission properties were investigated in the infrared region for Ga₂S₃-GeS₂-Sb₂S₃ glasses doped with Ho³⁺. We performed Judd–Ofelt analysis and lifetime measurements of the ⁵I₄, ⁵I₅, and ⁵I₆ levels, which are the initial levels of the mid-infrared emissions between 3 to 5 μm of Ho³⁺. The quantum efficiencies reached approximately 18%, 64%, and ～100% for the ⁵I₄, ⁵I₅, and ⁵I₆, respectively. Population analyses were carried out from the relative intensities of the emissions in the near-infrared region. We investigated the dependences on the Ho³⁺ ion concentration of the population ratio of the initial levels to the final levels, [initial]/[final], of the mid-infrared emissions. The population ratio of [⁵I₅]/[⁵I₆] decreased with increase of the Ho³⁺ concentration while those of [⁵I₄]/[⁵I₅] and [⁵I₆]/[⁵I₇] increased. Particularly, the former, [⁵I₄]/[⁵I₅], rapidly increased because of the strong concentration quenching of the ⁵I₅ level through cross relaxation. It was found that the population inversion for the 4.8 μm emission due to the transition, ⁵I₄→⁵I₅, was achieved at high Ho³⁺ concentration in the present experiments.     

Intra-abdominal fat area is a predictor for new onset of individual components of metabolic syndrome: MEtabolic syndRome and abdominaL ObesiTy (MERLOT study)

Objective: To investigate the significance of intra-abdominal fat area (IAFA) on new onset of individual components of the metabolic syndrome: high blood pressure, dyslipidemia, or hyperglycemia. Methods: We conducted a longitudinal study using checkup data of a hospital from 1994 to 2010. Of 25,255 subjects, we examined 1,380 Japanese, who underwent computed tomography to measure IAFA and had no metabolic syndrome components at baseline. Results: During 3.6 years of the mean follow-up period, one of metabolic syndrome components occurred in 752 subjects. Of three components, high blood pressure was more prevalent. The multiple Cox regression analysis disclosed that IAFA is significantly associated with onset of metabolic syndrome components (HR: 1.05 per 10 cm², 95%CI: 1.03–1.07). This finding was independent of BMI, and significant even in non-obese individuals with body mass index <25 kg/m². Conclusions: MERLOT study demonstrates that IAFA is an independent predictor for new onset of individual components of the metabolic syndrome, even in non-obese healthy Japanese.     

Uniqueness of preduals of certain Banach spaces

In [1], the authors have shown the existence of non-quasireflexive Banach spaces having unique isomorphic preduals. In fact, certain James-Lindenstrauss’ spaces have this property. In this paper it is shown that there are many such separable spaces. More precisely, there exist infinitely many different isomorphic types of James-Lindenstrauss’ spaces which are non-quasireflexive and have unique isomorphic preduals. The research of both authors was partially supported by N.S.F. Grant No. MPS75-07115     

Phase diagrams of noisy traffic states in the presence of a bottleneck

The traffic states are investigated for the noisy traffic flow in the presence of a bottleneck under the open boundary condition. The phase diagrams of the different kinds of congested traffic are presented for different values of sensitivity (the inverse of delay time). It is shown that the five different types of traffic states appear below the critical point: the free traffic with a pinned localized cluster, the weak standing shock, the moving localized cluster, the oscillatory congested traffic, and the strong standing shock. Above the critical point, the moving localized cluster and oscillatory congested traffic do not occur. Also, in the traffic flow without noise, the moving localized cluster and oscillatory congested traffic do not appear.     

Spontaneous Ga incorporation in ZnO nanowires epitaxially grown on GaN substrate

Surface‐diffusion‐induced spontaneous Ga incorporation process is demonstrated in ZnO nanowires grown on GaN substrate. Crucially, contrasting distributions of Ga atoms in axial and radial directions are experimentally observed. Ga atoms uniformly distribute along the ～10 μm long ZnO nanowire and show a rapidly gradient distribution in the radial direction, which is attributed substantially to the difference between surface and volume diffusion. The understanding on the incorporation process can potentially modulate doping and properties in semiconductor nanomaterials.

     

Correction for Shift-variant Characteristics of Single Photon Emission Computed Tomography Acquisition System Using Sensitivity Functions

The single photon emission computed tomography (SPECT) imaging system has shift-variant characteristics due to non-uniform attenuation of gamma-ray, collimator design, scattered photons, etc. In order to provide quantitatively accurate SPECT images, these characteristics should be compensated in the reconstruction. This paper presents a new method to correct the shift-variant characteristics, which is based on a continuous-discrete mapping model and filtered backprojection (FBP) method, in which the projection data are assumed to be acquired by narrow ray sum beams in the FBP method and the assumed data set is expressed as a linear combination of the actual projection data. Narrow ray sum beams are approximated by a weighted sum of the original sensitivity functions. Thus, at the reconstruction the projection data are first modified using an approximation and the FBP method is then applied to the corrected projection data and a SPECT image is reconstructed. We further propose a technique that requires the inversion of smaller matrices than the conventional algebraic method; the amount of calculation and memory space become smaller and the stability of the calculation is greatly improved as well. The results of the numerical simulations are also demonstrated.     

High Efficiency Electrically-Addressable Phase-Only Spatial Light Modulator

To realize a high efficiency electrically addressable phase-only modulator, we have coupled a liquid crystal display (LCD) to an optically addressed parallel-aligned nematic liquid crystal spatial light modulator (PAL-SLM) with a set of lenses. Phase modulation exceeding 3ϖ at 532 nm wavelength was obtained. We obtained linear transfer characteristics for phase modulation at various desired phase levels after calibration and adjustment of the transfer characteristics of the PAL-SLM and the LCD. Diffraction efficiency of 40% for binary phase grating and of 90% for 8-level blazed phase grating, which were very close to the simulation values, were observed. The power loss of the readout light was caused when passed through a half mirror, therefore, we examined a setup using an oblique readout light at the modulator. Very high diffraction efficiency was obtained from the setup by optimizing the polarization direction and optical path for this light, and the orientation of liquid crystals. Since the modulator can perform at better than 90% diffraction efficiency and at nearly 100% reflectivity, various high efficiency systems utilizing such modulators are expected.     

Nonlinear effects of electrolyte diodes and transistors in a polymer gel medium

The polarization curve of an acid-base interface in a hydrogel medium has a diode characteristic. Two of each such electrolyte diodes can be combined to give an electrolyte transistor. When a salt is added to the alkaline or to the acidic part of a reverse biased electrolyte diode, the current response is highly nonlinear. If the salt is added to the acidic side, even bistability can be observed. This bistability can generate complex oscillations in a base-acid-base electrolyte transistor. These nonlinear effects are studied experimentally and theoretically. While the nonlinear salt effect can be explained with the Nernst-Planck equations, to understand the bistable behavior further investigations are necessary. (c) 1999 American Institute of Physics.