A multimode optical fiber (302), and means (308) for averaging the signal level variation induced by an in-mode noise signal level variation of the light propagating through the multimode optical fiber (302) within, optical mode noise averaging device (300). The device may be cyclically changing the refractive index of the multimode optical fiber over a selected time period (302), to scrambling the light distribution of the multimode optical fiber (302) within, or its both may average the signal level variation induced by mode noise. The refractive index of the multimode optical fiber may be cyclically varied by circulating varying the temperature of the multimode optical fiber (302). Alternatively, by operating cyclically multimode optical fiber (302), or the refractive index may be changed, or the light distribution within the multi-mode optical fiber may be scrambled.