This work demonstrates the fabrication of poly-(dimethylsiloxane) (PDMS)-based volume Bragg gratings (VBGs) by stitching of femtosecond laser filament. The refractive index change induced by femtosecond laser pulses is low (orders of 10−4 to 10−3) in PDMS. Therefore, the VBG thickness is the key parameter to fabricate high-efficiency VBGs in PDMS. With the intention of increasing diffraction efficiency, this paper presents fabrication of multi-layered PDMS-based VBGs. We produce VBGs with 10 μm line pitch using a femtosecond pulse laser (100 fs pulse width, 1 kHz repetition frequency). The modified zone thickness can be controlled by arranging the relative displacement of filament at different depths and the distances between layers. High-efficiency VBGs were created by depth multiplexing of 350 μm long filamentary modification in PDMS. Diffraction efficiency of 87.2% was realized by forming 0.63 mm grating thickness.

This study develops a heuristic for the weighted Steiner tree problem, which is the minimization problem for the total edge cost of the graph interconnecting each terminal on a plane. This heuristic discretizes a plane by using a random Delaunay network and searches terminals' spanning trees in a terminals' Voronoi dual graph. Each edge on a tree is given by the weighted shortest path on a random Delaunay network. We show that this heuristic can get a closer result to the exact solution from the perspective of the tree shape and total cost than previous methods, and understand discontinuous changes in the tree shape due to weight changes. For the practicality verification of this heuristic, we apply it to the airway network of large-scale drones, which are poised to become a new passenger and logistics industry.

Abstract:The jack-knife shrimp, Haliporoides sibogae, is an unutilized fisheries resources with a population widely distributed on the continental slope in the East China Sea, southwest of Nagasaki. The growth and longevity of this shrimp were investigated based on 3,733 specimens collected by monthly beam-trawl sampling between May 2006 and March 2009. The spawning season of the H. sibogae population southwest of Nagasaki was from November to March, and the main spawning season was in January and February. The longevity of H. sibogae was estimated to be about 38 months and the growth coefficient of this shrimp population was found to be less than half that of another two populations in Japanese waters. The secondary sexual characters of H. sibogae females were also confirmed.