Method for three dimensional optical data storage and retrieval

A method of reading optical data stored as a refractive index inhomogeneity in a medium, comprising:

• producing a polarized laser read beam;
• producing from said read beam a pair of focused cross-polarized component beams;
• focussing said component beam pair at adjacent locations in a medium containing inhomogeneities, and
• scanning said focussed beams through said medium to produce an optical interference signal indicative of inhomogeneities in said medium.

A method of writing and subsequently reading optical data with three-dimensional resolution, comprising:

• providing a three-dimensional medium of photosensitive material capable of modification by the application of light of a predetermined intensity;
• producing a single, intense beam of light;
• focussing said beam of light at a focal point within said medium;
• scanning said focal point through said medium to produce at selected points in said medium two-photon excitation of said medium to produce a modification of a selected characteristic of the medium, each such modification representing an optical data bit in said medium;
• and
• thereafter reading optical data bits produced in said medium by scanning a focused reading beam through said medium to produce an interference pattern corresponding to said optical data bits.

A method of reading optical data stored as a refractive index inhomogeneity in a medium, comprising:

• producing a polarized laser read beam;
• producing from said read beam a pair of divergent cross-polarized component beams;
• focusing said component beam pair at adjacent locations in a medium containing index inhomogeneities;
• collecting the component beam pair transmitted through said medium;
• recombining the transmitted component beam pair to produce a recombined beam;
• and
• analyzing polarization of the recombined beam to produce a signal beam indicative of refractive index inhomogeneities in the medium.