Fiber Bragg grating based spatially resolved characterization of flux-pinning induced strain of rectangular-shaped bulk YBCO samples

► Fiber Bragg gratings (FBG) act as strain sensors, also at cryogenic temperatures. ► FBGs are not sensitive to magnetic fields. ► Local, shape dependent magnetostriction was detected on rectangular samples. ► Magnetostrictive effects of the top surface and in a gap between two samples are different.