Optical EngineeringMultilayer optical storage disk based on the frequency up-conversion effect from rare-earth ions
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We present a multilayered optical storage disk design based on the use of frequency up-conversion in rare earth. This design offers the potential of increased optical storage density. In our experiment, a three-layered sample is prepared by stacking three sections of a thin glass slide on which stripes of Ho3+/Yb3+ codoped TeO2 are deposited via a sol-gel technique. The layers are selectively illuminated by a focused 980-nm laser beam by bringing them into the focal plane. The up-converted green luminescence signals from the tracks in the three layers are clearly resolved without any observable interlayer crosstalk, thus demonstrating the successful data retrieval from our multilayered optical disk. Based on the nonlinear property associated with the up-conversion effect, we also perform a theoretical calculation on the bit resolution enhancement in relation to the number of photons involved in the up-conversion process. The use of laser heating to induce phase change from an amorphous state to a polycrystalline one in the sol-gel film for write-once-read-many optical storage is also discussed.