0

# What is the track pitch or groove spacing on a CD DVD or Blu-ray?

Wiki User

2009-06-22 06:47:39

The groove spacing is also called the "track pitch". It is the distance between each track.

Here is a list of the track pitches of some common formats.

Type -------- Capacity ---------------Track pitch ----------Wavelength of laser light------Numerical Aperture

CD -------------- 0.7 Gb ------------------ 1.6 ∓0.1 μm ------------- 780 nm (0.780 μm) ------------------- 0.45

DVD ------------ 4.7 GB ------------------- 0.74 μm ------------------ 650 nm (0.650 μm) ------------------- 0.60

Blu-ray Disc --- 25 GB ------------------- 0.32 μm -------------------405 nm (0.405 μm) ------------------- 0.85

Because of diffraction they can't make the 'grooves' to close together. (Diffraction is the reason you see a play of colors on CDs and DVDs.)

Notice the shorter the wavelength of the laser light they use the closer they can make the grooves and the more information they can get on the disk.

Also notice however that the track pitch decreases more rapidly than the wavelength of the lasers in the above table, this is because you can also reduce the track pitch if you increase what is called the Numerical aperture of the lens you use.

In fact how much information you can store on a disk depends on how small you can get the "spot size" of the laser beam and the radius of the smallest spot that you can get equals the laser light wavelength divided by the numerical aperture. (R=λ/NA)

For more details and a microscopic picture of the tracks of a CD and DVD go to the related links below this window.

(1 μm = 1 micrometer = 1 micron = 0.000001 meters = 1 x 10^-6 meters)

(1 nm = 1 nanometer = 1 x 10^-9 meters)

Wiki User

2009-06-22 06:47:39