GNSS Multipath Detection Using Continuous Time-Series C/N0.

The reduction of multipath errors is a significant challenge in the Global Navigation Satellite System (GNSS), especially when receiving non-line-of-sight (NLOS) signals. However, selecting line-of-sight (LOS) satellites correctly is still a difficult task in dense urban areas, even with the latest GNSS receivers. This study demonstrates a new method of utilization of C/N0 of the GNSS to detect NLOS signals. The elevation-dependent threshold of the C/N0 setting may be effective in mitigating multipath errors. However, the C/N0 fluctuation affected by NLOS signals is quite large. If the C/N0 is over the threshold, the satellite is used for positioning even if it is still affected by the NLOS signal, which causes the positioning error to jump easily. To overcome this issue, we focused on the value of continuous time-series C/N0 for a certain period. If the C/N0 of the satellite was less than the determined threshold, the satellite was not used for positioning for a certain period, even if the C/N0 recovered over the threshold. Three static tests were conducted at challenging locations near high-rise buildings in Tokyo. The results proved that our method could substantially mitigate multipath errors in differential GNSS by appropriately removing the NLOS signals. Therefore, the performance of real-time kinematic GNSS was significantly improved.

Efficient hydrogen production using photosystem I enhanced by artificial light harvesting dye.

In this study, we improved the hydrogen production efficiency by combining photosystem I with an artificial light harvesting dye, Lumogen Red. In the reaction system, Lumogen Red allows light absorption and energy transfer to photosystem I by Förster resonance energy transfer; therefore, the Pt nanoparticles act as active sites for hydrogen generation.

Reflection noise reduction effect of graded-index plastic optical fiber in multimode fiber link.

We experimentally demonstrate that a graded-index plastic optical fiber (GI POF) can significantly reduce reflection noise in a multimode fiber link with a vertical-cavity surface-emitting laser (VCSEL). By directly observing beams backreflected to the VCSEL, we show that the noise reduction effect is closely related to random mode coupling because of light scattering by microscopic heterogeneities in the GI POF core material. This suggests that intrinsic mode coupling can lower the self-coupling efficiency of the light backreflected to the VCSEL cavity through beam quality degradation. Using GI POFs, low-cost radio-over-fiber systems for indoor networks can be realized without optical isolators or fiber end-face polishing.

Evaluation of modal noise in graded-index silica and plastic optical fiber links for radio over multimode fiber systems.

We have evaluated and compared modal noise induced in a graded-index silica multimode fiber (GI-MMF) link and a graded-index plastic optical fiber (GI-POF) link with the misaligned fiber connections. In radio over fiber (RoF) systems using these optical fibers, modal noise appears as unwanted amplitude modulation in the received signal, and results in degradation of the RoF transmission performance. In this work, we have evaluated the modal noise induced in GI-MMFs and GI-POFs with its same core diameter of 50 µm. Our results show that GI-POFs have an inherently higher tolerance to misaligned connection and less modal noise than GI-MMFs in terms of both the error-vector magnitude and the speckle pattern of the transmitted signals.

Efficient group delay averaging in graded-index plastic optical fiber with microscopic heterogeneous core.

Intrinsic mode coupling in a graded-index plastic optical fiber (GI POF) is investigated using the developed coupled power theory for a GI POF with a microscopic heterogeneous core. The results showed that the intrinsic material properties can induce random power transitions between all the guided modes, whereas the structural deformation of microbending results in nearest-neighbor coupling. It was numerically demonstrated that efficient group-delay averaging due to intrinsic mode coupling brings the pronounced bandwidth enhancement in fibers with much shorter length than the case of glass multimode fibers.

Pressure measurement based on a multimode phase retarder plastic optical fiber.

This paper demonstrates a polarimetric pressure measurement using a multimode phase retarder plastic optical fiber fabricated from a birefringence-controllable copolymer. An optimal composition that gives the most pronounced response to pressure was studied by comparing the extinction ratio of fibers fabricated with different copolymer compositions. A simple sensor design with a single-fiber structure was proposed that has detection capabilities similar to those of the conventional dual-path structure of a Mach-Zehnder interferometer. A linear relationship between the fiber birefringence and the applied pressure was observed in a range from 0 to 0.06 MPa. A polarimetric sensitivity of 1.56 x 10(-5) MPa(-1) was obtained experimentally from the relationship between the birefringence and pressure.