Abstract: A catheter system including a catheter having a proximal end and a distal end and a device for determining the position of the distal end of the catheter relative to the position of the proximal end of the catheter, the device for determining the position including a glass fiber within a lumen of the catheter, the lumen being defined by a wall, a first polarization filter near the proximal end of the catheter, and a second polarization filter near the distal end of the catheter, wherein the first and second polarization filters are fixed with respect to the wall, and wherein the glass fiber is suitable for transporting polarized light while maintaining the direction of the polarization of the light substantially unchanged during torsional stress of the catheter.