Three-dimensional optical memory with photorefractive materials is discusse
d for ultra-high density/capacity memory exceeding the classical limit of a
conventional optical recording system. Bit data are recorded as highly loc
alized refractive index variations in three-dimensional volume using a focu
sed laser beam. We show recording and reading results using a multilayered
recording medium with a photoisomerization polymer and transparent films. T
wo-photon recording is also demonstrated. We also discuss the spherical abe
rration corrections using a volume holographic device, and compact confocal
configuration using a semiconductor laser. (C) 2001 Society of Photo-Optic
al Instrumentation Engineers.