In this paper, the ionospheric models for GNSS (Global Navigation Satellite System) positioningin the local area like as Japan are investigated and the prediction models are discussed. The ...ionosphericdelay is modeled by applying SCHA (Spherical Cap Harmonic Analysis). It is well knownthat the ionosphere varies according to solar activity. Therefore, ionospheric effect on GNSS positioningvaries with not only the position but also the local time, and it has a periodicity. The periodiccharacteristics of the ionosphere are investigated by SCHA ionospheric models. The purpose of thisresearch is to predict the ionospheric delay model for the real time positioning. Based on our investigation,the ionospheric delays are predicted with AR (Auto-Regression) model. Furthermore thecapability for ionospheric model prediction is discussed. In the experiments, the proposed predictionmodels are compared with Klobuchar model.
We experimentally and theoretically investigate the effect of an air hole between cores in a multi-core fiber (MCF) on the suppression of crosstalk (XT). We clarify that XT decreases in proportion to ...the air hole diameter and that XT of about 20 dB in an MCF can be suppressed by employing just one air hole between cores. We confirm that the calculated XT suppression value is in good agreement with the measured value. We also clarify numerically that the minimum distance between cores satisfies the required XT without reducing the effective area by using an air hole. Next, we consider the influence of air holes on macro-bending loss and cutoff wavelength. We confirm that none are related to the arrangement of the air holes. Moreover, we discuss the relationship between the effective area and the core multiplicity factor (CMF) against several core arrangements. As a result, we show that the CMF in MCF with air holes can increase by 1 or more compared with that without air holes.
An optimized two-mode optical fiber (TMF) with the graded index (GI) profile is designed and fabricated. We clarify an appropriate region of GI-TMF satisfying DMD = 0 ps/km, the large effective area ...A(eff), and the low bending loss for LP(11) at 1550 nm. According to our fiber design, GI-TMF is successfully fabricated to have the large effective area A(eff) of 150 μm(2) for LP(01) mode, and low DMD below 36 ps/km including zero in the C-band. We expect that our design GI-TMF is suitable for MDM and can reduce MIMO-DSP complexity.
The polarization dependence of the resonance wavelength of long period fiber gratings (LPFGs) that employ the photoelastic effect is investigated based on a simple model. The proposed model for ...estimating the birefringence of these LPFGs provides a good explanation of the experimental results.
•A high-frequency excitation is necessary to detect nonmagnetic metals using SQUID.•It is possible to detect a high-frequency magnetic field using the open loop technique.•Open loop operation leads ...to a change in the conversion factor.•Conversion between voltage and magnetic field for open loop operation are examined.
Measurement methods with SQUID can accurately detect small magnetic metal contaminants based on their magnetic remanence. But, a high-frequency excitation is necessary to detect nonmagnetic metals, on the base of contrasts in electric conductivity. In this work, an open loop technique is introduced to facilitate this. The SQUID is negative feedback controlled (flux locked loop (FLL) operation) for the low frequency range, which includes significant noise due to the movement of the magnetic body or the change of the ambient magnetic field composed of the geomagnetic field and technical signals, and it operates in an open loop configuration for the high frequency range. When using the open loop technique, negative feedback is not applied to the high frequency range. Consequently, the V–Φ characteristic changes due to various causes, which leads to variations in the conversion factor between the SQUID output voltage and the magnetic field. In this study, conversion techniques for the magnetic field for open loop operation of SQUID in the high frequency range are examined.
We propose a two-mode optical fiber (TMF) with a low sensitivity of differential modal group delay (DMD) to change of the core radius and the refractive index of the core in the index profile which ...are major factors for DMD deviation. This was done to achieve high reproducibility of fiber fabrication. The proposed TMF has a graded index (GI) core and a depressed inner cladding, and we optimize structural parameters. We fabricated different kinds of TMFs to confirm the low DMD sensitivity of our proposed fiber. The fabricated TMF showed that the DMD sensitivity to changes in core radius of the TMF was approximately 8 ps/km/μm which is 98% smaller than that of a GI-TMF without a depressed inner cladding.
The design of multi-branch optical waveguides having 3 or more output ports is not so easy as that of 2-output branches because some innovative geometry is required to realize equal power splitting. ...All previous studies take the same approach in which they first introduce innovative geometries and then adjust the structural parameters for equal splitting. On the other hand, we propose quite a different method where distribution of refractive index is calculated from an ideal field distribution which is synthesized artificially. The method is extended to design 3-D 4-branch waveguides. It is exemplified that 4-branch waveguides with low-loss and equal splitting can be realized by the proposed method.
We propose a variable mode excitation ratio method for measuring the attenuation coefficients of individual transmission modes in few-mode fiber (FMF). The experimental results we obtained with 2LP ...mode fiber agree well with those measured by the conventional mode-selective launching method and the optical time domain reflectometer (OTDR) method. We also show that the proposed method can be applied to an FMF with more than two mode groups by measuring the transmitted power property under various mode excitation ratios with a multiple mode group combination. Finally, we reveal that our method can provide an accurate modal attenuation coefficient even if we cannot use a mode multiplexer with a sufficient mode extinction ratio.
We present a theoretical model and propose a technique based on this model for measuring the mode field diameter, relative-index difference, and chromatic dispersion along a randomly-coupled ...multi-core fiber using an optical time domain reflectometer. Experimental investigations demonstrate the feasibility of the technique.
Abstract
A tractor-based robot with the capability of real-time assessing and visualizing the radioactive material density and fertility distribution of farmlands has been developed to accelerate the ...recovery process of the farmlands suffered by the accident of the Fukushima Daiichi Nuclear Power Plant (FDNPP). In a field test at a decontaminated farmland near FDNPP, within-field heterogeneities of soil contamination and fertility are clarified almost in real-time. Results obtained by this robot are consistent with the map by the conventional soil sampling or the history of decontamination activities.
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