A nonlinear light absorption material includes a compound having a nonlinear light absorption property at a wavelength of 390 nm or more and 420 nm or less and represented by the formula (1) as a main component:

##STR00001##

in the formula (1), X is an oxygen atom.

A nonlinear light absorption material includes a compound represented by the following formula (1) as a main component:

##STR00001##

in the formula (1), R.sup.1 to R.sup.6 are each independently a hydrocarbon group.

The present invention relates to an ultra-thin data carrier for long-term data conservation and to a method of reading out such a data carrier.

An information recording medium includes three or more information layers. The three or more information layers include a first information layer including a first dielectric film, a recording film, and a second dielectric film in this order. The first dielectric film contains an oxide of D1. The D1 represents at least one element selected from a first group consisting of Nb, Mo, Ta, W, Ti, Bi, and Ce. The recording film contains at least W, Cu, Mn, and oxygen and M. The M represents at least one element selected from a second group consisting of Nb, Mo, Ta, and Ti. The W, the Cu, the Mn, and the M except the oxygen in the recording film satisfy a following formula (1):

W.sub.xCu.sub.yMn.sub.zM.sub.100-x-y-z (atom %)(1) wherein x, y, and z satisfy 15x60, yz, 0<z40, and 60x+y+z98.

Long term optical memory includes a storage medium composed from an array of silicon nanoridges positioned onto the fused silica glass. The array has first and second polarization contrast corresponding to different phase of silicon. The first polarization contrast results from amorphous phase of silicon and the second polarization contrast results from crystalline phase of silicon. The first and second polarization states are spatially distributed over plurality of localized data areas of the storage medium.

Data can be transmitted and represented by signal gaps in a transmission, the gaps having various attributes. In various examples, data points are encoded and represented by the attributes of said signal gaps. Various attributes of such gaps, including duration, pattern, quantity, time, and/or coordination with a gap in another signal can represent data.

Data can be transmitted and represented by signal gaps in a transmission, the gaps having various attributes. In various examples, data points are encoded and represented by the attributes of said signal gaps. Various attributes of such gaps, including duration, pattern, quantity, time, and/or coordination with a gap in another signal can represent data.

A recording medium includes a recording layer. The recording layer includes an aliphatic polymer, and a multiphoton absorption compound containing at least one bond selected from the group consisting of a carbon-carbon double bond, a carbon-nitrogen double bond, and a carbon-carbon triple bond, and having a multiphoton absorption characteristic. When the thickness of the recording layer is 100 ?m, the transmittance of the recording layer in the thickness direction with respect to light having a wavelength of 405 nm is greater than or equal to 80%.

An optical disc device includes a first error correction coding circuit that codes the recording data according to a first error correction coding format, a second error correction coding circuit that codes the recording data according to a second error correction coding format, and a recorder that converts the recording data into a recording signal and records it on an optical disc. The second error correction coding format is different in an arrangement of the recording data from the first error correction coding format. The second error correction coding format is configured to generate a second parity code with a higher degree of redundancy. The recorder records the recording data coded by the first error correction coding circuit and only the second parity code in the recording data coded by the second error correction coding circuit.

An optical disc device includes a first error correction coding circuit that codes the recording data according to a first error correction coding format, a second error correction coding circuit that codes the recording data according to a second error correction coding format, and a recorder that converts the recording data into a recording signal and records it on an optical disc. The second error correction coding format is different in an arrangement of the recording data from the first error correction coding format. The second error correction coding format is configured to generate a second parity code with a higher degree of redundancy. The recorder records the recording data coded by the first error correction coding circuit and only the second parity code in the recording data coded by the second error correction coding circuit.