  High-resolution magnetostriction measurement of $\Delta L/L\sim10^{-6}$ at a
speed of 5 MHz is performed, using optical filter method as the detection
scheme for the fiber Bragg grating (FBG) based strain monitor is performed
under 35-millisecond pulsed high magnetic fields up to 45 T at 2.2 K. The
resolution of magnetostriction is about the same order as the conventionally
reported value from FBG based magnetostriction measurement systems for
millisecond pulsed magnetic fields. The measurement speed is $\sim$100 times
the conventional ones. Present system can be a faster alternative for the
conventional FBG based magnetostriction measurement system for millisecond
pulsed high magnetic fields.
