Sub-milliwatt sub-millisecond recording of population gratings in ytterbium-doped optical fibers at 976Â nm

► First demonstration of effective two-wave mixing in ytterbium doped fiber at 976 nm. ► Sub-millisecond dynamic fiber grating recording at sub-milliwatt cw laser power. ► Up to 40% transient TWM response in 10 cm long fiber pieces. ► Comparable contributions of the amplitude and phase grating components. ► Significantly slower response of the phase grating.