Zeh, C.C.ZehSpittel, R.R.SpittelUnger, S.S.UngerOpitz, J.J.OpitzKöhler, B.B.KöhlerKirchhof, J.J.KirchhofBartelt, H.H.BarteltEng, L.M.L.M.Eng2022-03-042022-03-042010https://publica.fraunhofer.de/handle/publica/22285010.1063/1.34841462-s2.0-77956565650We report on the development of elliptical, index tailored optical fibers for higher-order mode preservation for fiber-based, apertureless, internally illuminated scanning near-field optical microscopy (ai-SNOM). The fiber structure is simulated by the finite element method, showing large spreads of the effective indices for neighboring first higher-order modes. We demonstrate experimentally that due to this spread, the first higher-order modes do not couple, hence, the polarization is maintained, when the fiber is bent down to 1 cm radius. Further, we discuss the implications for ai-SNOM applications.en620621journal article