Say you’ve just finished work on your first multi-billion-dollar 3D Hollywood Blockbuster.
All the fancy lighting, celebrities, explosions, and romance gets distilled down into one big
movie file – or, the way a computer sees it, one long string of ones and zeros.
Now you want your movie to be on a disc, meaning all those ones and zeros need to be stored
in some kind of physical form -- like a DVD or Blu-ray.
But your movie file is really big -- it’s really long, and super high definition -- so
you’ve run out of room on a DVD, which only holds 4.7 gigabytes of data.
Well, you could always try putting it on a Blu-ray.
Since Blu-ray players use a higher-energy, blue laser, they can fit much more data -- up
to 50 gigabytes -- on one disc.
On both types of discs, all the zeros are stored by cutting little tiny pits into the
disc, and all the ones are stored by not cutting pits, in what are called lands.
When it’s time to watch your movie, the player shines a laser: a super-concentrated
beam of light emitted by electrons that absorb extra energy, then release that energy in
the form of light.
The laser goes through a lens, then focuses on the disc.
Your player detects whether the light hit a land or a pit depending on how the beam
is reflected or scattered, and interprets that as either a one or a zero.
But how much data you can put on the disc depends on the laser -- the beam needs to
be narrow enough to detect the pits and lands without accidentally reading two at the same
time.
That’s where color comes in.
Every color of light has its own wavelength, and the smaller the wavelength, the smaller
you can focus a laser beam of that color -- and the smaller the pits and lands you can read.
The colors at the top of the rainbow, like red, have longer wavelengths, while colors
at the bottom of the rainbow, like blue, have shorter wavelengths.
That’s why Blu-ray players, with blueish-violet lasers, can read smaller pits and lands than
DVD players, which use a red laser.
Since Blu-ray discs have smaller pits and lands, they can pack in much more data to
the same surface area.
Creating a blue laser wasn’t easy, however.
For one thing, scientists needed a specific form of a crystal called gallium nitride -- one
with extra holes, or lower-energy spots for higher-energy electrons to drop down into,
emitting blue light.
The physicists who figured out how to do it in the early 1990s eventually won the 2014
Nobel Prize in physics -- and in 1996, they started using the crystal to make blue lasers.
Over the next decade, blue lasers got better and better, until they were reliable enough
to be used in a new generation of players that can read discs that hold a lot more information
-- including Blu-Rays.
And that is why your huge movie file fits neatly on one little disc.
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