Abstract: A fiber optic sensor for magnetic bearings includes a stator 12, a rotor 14, and an optical transmit/receive fiber 50 which propagates transmit light 112 which is launched across a gap 15 between the stator and the rotor and which receives reflected light 114 that is reflected off of the rotor 14 and travels along the fiber 50 as the light 116. The gap 15 distance is determined by the change in intensity of the return light 114. The transmit/receive fiber 50 may be located radially through or longitudinally along the stator 12. The receive light 116 is detected by a photodetector 120 which provides an electrical signal to a control circuit 124 which controls electromagnetic coils 31-34 of the magnetic bearing. Alternatively, two separate fibers may be used for the transmit and receive light. Also, time or wavelength multiplexing may be employed to allow for remote optical source and detection/control of the gap 15 distance. Further, a plurality of such sensors may be used around the gap 15.