Apparatus and methods for reading multilayer storage media using short coherence length sources

An apparatus for reading data, comprising:

• a) an optical medium comprising at least two layers, each layer of said at least two layers containing data and having a spacing L;
• b) a source of light having a coherence length L.sub.c less than said spacing L;
• and
• c) an optical system focusing said light from said source of light onto a preselected layer of interest in said optical medium,
• wherein coherence of light reflecting from the preselected layer and light reflecting from each other of said at least two layers is substantially reduced.

A method of reading data, comprising:

• a) providing a source of light having a coherence length L.sub.c ;
• and
• b) focusing said light from said source of light onto a preselected layer of an optical medium comprising at least two layers, each layer of said at least two layers containing data and having a spacing L,
• wherein said coherence length Lc is less than said spacing L so that coherence of light reflecting from the preselected layer and light reflecting from each other of said at least two layers is substantially reduced.

A method for reading data, comprising:

• a) providing an optical medium comprising at least two layers, each layer of said at least two layers containing data and having a spacing L;
• b) providing a source of light having a coherence length L.sub.c less than said spacing L;
• and
• c) focusing said light from said source of light onto a preselected layer of said optical medium so that coherence of light reflecting from the preselected layer and light reflecting from each other of said at least two layers is substantially reduced.

An apparatus for reading data, comprising:

• a) a source of light having a coherence length L.sub.c ;
• and
• b) an optical system focusing said light from said source of light onto a preselected layer of an optical medium comprising at least two layers, each layer of said at least two layers containing data and having a spacing L,
• wherein said spacing L is greater than a Rayleigh range L.sub.r of the optical medium and the optical system.