According to the quality standard of CD, the thickness of (1.2 0. 1) mm is qualified. What do you mean by 1.2mm and 0. 1mm?

1.2 mm is the specification standard of optical disc, and its thickness is1.2mm..

0. 1mm is qualified, and the allowable error range is 0. 1mm, in other words, 1. 1mm or 1.3mm is unqualified.

Common disc sizes:

120 CD

Dimensions: external diameter 120mm, internal diameter 15mm.

Thickness:1.2mm.

Capacity: DVD 4.7 GB/8.6 GB；; CD 650MB/700MB/

Small compact disc

Size: 80mm outside diameter and 2 1mm inside diameter.

Thickness:1.2mm.

Capacity: 200MB.

Extended data:

Physical characteristics,

From the main structure, the structure of CD and DVD is the same, but the thickness and material are different. In the above introduction, we mentioned that the thickness of CD is1.2mm. Can this thickness be changed? The answer is no.

In practical applications, the lasers used to read and burn CDs, DVDs and Blu-ray discs are different. As we all know, the capacity of CD is only about 700MB, while DVD can reach 4.7GB and Blu-ray disc can reach 25GB. The capacity difference between them is closely related to the wavelength of the related laser beam.

Generally speaking, the recording density of an optical disc is limited by the size of the readout spot, that is, the optical diffraction limit, which includes the laser wavelength λ and the numerical aperture NA of the objective lens. Therefore, in order to improve the recording density, the traditional optical disc technology can generally use short-wavelength laser or increase the numerical aperture of the objective lens to reduce the spot.

For CD, the laser wavelength is 780nm, the numerical aperture NA of the objective lens is 0.45, and the distance that the laser beam will converge to a point needs 1.2 mm, which determines that the thickness of the CD substrate is1.2 mm. No matter whether the substrate of CD is too thick or too thin, the laser beam cannot converge to a point, which seriously affects the recording and reading of data.

The laser wavelength of DVD disc is 650nm, the numerical aperture NA of objective lens is 0.6, and the distance at which the laser beam will converge to a point is only 0.6mm, which determines that the thickness of DVD disc substrate is 0.6 mm. But if the thickness of 0.6 mm is too thin, the disc made of it will be easily broken because it is too thin.

So in the actual manufacturing process of DVD, two substrates with a thickness of 0.6mm are stacked together, and the thickness of * * * is1.2 mm. Of course, in this case, only one substrate is recording data, and the other substrate is completely protective.

The development trend of optical discs is to develop into large-capacity storage (such as DVD+R DL products produced in 20 10), and the technical research and development of the industry is also guided by this. Single-sided and double-layer DVD discs have appeared.

Single-sided dual-layer optical disc is to make two recording layers on the same surface by using different laser focusing positions. The laser power and reflectivity of the first and second single-sided dual-layer optical discs are the same (reflectivity is 18% ~ 30%). When recording, you can continuously record from the first layer to the second layer to realize uninterrupted data recording.

References:

Baidu encyclopedia-CD