The invention relates to a method and device for transmitting light over a fat fiber (1) between optical components (B1; B2) of an optical measuring device, which are provided at a launching end (C) and at an extraction end (R; K; O) of the fat fiber (1). Said measuring device comprises a guiding means for the curved rigid guidance of a first partial section (PQ; FGHI; IJ; FL; LM; MN) of the fat fiber (1). If the radius of curvature of the curved guidance falls below a first limit, the light beam profile of the fat fiber (1) is homogenized by a mode mixing. In order to diminish the effect on the transmitted light caused by a permitted change in position of the fat fiber (1), a stiffening means, which is rigidly connected to the guiding means, is provided for rigidly guiding a second partial section (QR; JK; NO) of the fat fiber (1). Said second partial section connects to the first partial section (PQ; FGH; IJ; FL; LM; MN) and extends essentially up to the optical component (B2) located at the extraction end (R; K; O), whereby the entire length of the first and second partial section is at least provided with a length that renders the extraction end (R; K; O) of the fat fiber (1) mechanically stable.