For astronomy, the search of exo-planets and spectral analysis of galaxies and stars with ground based telescopes is an ongoing topic especially with the future planned telescopes with even larger mirror diameters. But for the ground based observation the atmosphere is a limiting factor. Besides of air fluctuations also spectral noise is influencing the observation. A forest of emission lines by OH relaxations that are orders of magnitudes stronger than the stars and galaxies appear in the night sky. These lines vary in intensity but are fixed in wavelength. Therefore, fiber Bragg gratings (FBG) are a perfect tool for the suppression of these emission lines. FBGs provide a high filter quality by filtering out magnitudes of intensity in a narrow wavelength window of below 0.5nm bandwidth. Because fibers are already widely used in telescopes to deliver light into spectrographs, the FBGs could be inscribed directly into the fibers. But for astronomy mostly multimode fibers are used where FBGs do not work as needed because of the different propagation constants of higher modes. The solution is the transition to single mode fibers. In terms of compactness and robustness a multicore fiber would be the optimal solution. But the homogeneous modification of a multicore fiber is a challenging task. We report on the ultrashort pulse laser inscription of FBGs into a multicore fiber consisting of 7 cores. Furthermore, investigations on the homogeneity of the inscribed modifications as well as the spectral properties are presented.
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Thorsten A. Goebel, Ria G. Krämer, Maximilian Heck, Daniel Richter, and Stefan Nolte, "Fs-written fiber Bragg gratings in multicore fibers for astrophotonic applications (Conference Presentation)," Proc. SPIE 10522, Frontiers in Ultrafast Optics: Biomedical, Scientific, and Industrial Applications XVIII, 105220P (Presented at SPIE LASE: January 29, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2289553.5751469675001.
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Study of self-shadowing effect as a simple means to realize nanostructured thin films and layers with special attentions to birefringent obliquely deposited thin films and photo-luminescent porous silicon