Three-dimensional optical storage inside transparent materials

TLDR

The authors propose a novel 3‑D optical data‑storage technique with sub‑micrometer resolution, high refractive‑index contrast, and broad applicability to transparent media. Bits are written by focusing 100‑fs laser pulses with a 0.65‑NA objective inside the material, creating sub‑micrometer refractive‑index changes in multiple planes that are later read with a short‑depth‑of‑field microscope objective. The technique yields sub‑micrometer, high‑contrast refractive‑index bits, enabling 17 Gbits cm⁻³ storage with 2‑µm in‑plane and 15‑µm interplane spacing, and SEM/AFM confirm ~200‑nm‑diameter structural changes.

Abstract

We present a novel method for three-dimensional optical data storage that has submicrometer size resolution, provides a large contrast in index of refraction, and is applicable to a wide range of transparent materials. Bits are recorded by use of a 0.65-N.A. objective to focus 100-fs laser pulses inside the material. The laser pulse produces a submicrometer-diameter structurally altered region with high contrast in index of refraction. We record binary information by writing such bits in multiple planes and read it out with a microscope objective with a short depth of field. We demonstrate data storage and retrieval with 2-microm in-plane bit spacing and 15-microm interplane spacing (17 Gbits/cm(3)). Scanning electron microscopy and atomic force microscopy show structural changes confined to an area 200 nm in diameter.