In polymeric films of bacteriorhodopsin (BR) a photoconversion product named F540-state, which is excited by 790 nm femtosecond laser pulses, is stable either for photochemical reaction or thermal pathway. The optical properties of the F540-state were studied, and Jones-matrix theory was adopted to analyze the photoinduced anisotropy of the F540-state. Based on the permanently photoinduced anisotropy, write-once-read-many (WORM) optical data storage was demonstrated by using two polarization states of femtosecond pulsed laser. Since the polarization information is also written on the storage media, it is impossible to copy it in a common way. This storage technique has a potential application in advanced optical security.