Iuzzolino, M.M.IuzzolinoSANNA, NicolettaNicolettaSANNATOZZI, AndreaAndreaTOZZIOLIVA, ErnestoErnestoOLIVA2020-04-062020-04-0620150037-8720http://hdl.handle.net/20.500.12386/23853Many scientific instruments are nowadays coupled to the telescope through optical fibers. This is also the case of the current configuration of GIANO, the high resolution near infrared echelle spectrograph installed at the TNG telescope. As experienced and frequent users of the IR optical fiber, the GIANO building team decided to go deep in the characterization of the optical fiber in the IR band, and in particular to understand and analyze the fiber modal noise. This work is also a preparatory study for the future HIRES@E-ELT instrument design. This paper consists in the description of the fiber laboratory tests, and in the explanation of the results. The whole job defines a wider comprehension of the modal noise, and demonstrates the existence of two aspects influencing this noise. The first one, well known in literature, refers to the interferences between the fiber modes at the exit endface of the fiber, and it can be mitigated by mechanical scrambling techniques. The second one, unknown before, is entirely dependent on the way in which light is injected at the entrance of the fiber, and no mitigation have been observed with any classical scrambling technique (e.g. double-scramblers). These considerations apply to both ZBLAN or fused silica optical fiber, and to both circular and octagonal core shape.ELETTRONICOenArticlehttp://sait.oat.ts.astro.it/MSAIt860315/index.html2015MmSAI..86..490IFIS/05 - ASTRONOMIA E ASTROFISICA