Why does an optical drive use laser light?
This may be a boring answer for electrical engineers, but it is all about the optics. The optical system for a CD looks something like this.



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As can be seen from the figure, the light traveling to the disc needs to go one way and the reflected light needs to be directed towards the detector. This is achieved with the polarizing prism, which forms an optical isolator together with the quarter wave plate. Here is a close up of this part of the optical system.



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Because the polarization of the reflected beam has been altered, the light undergoes total internal reflection and all the power is directed towards the detector. This has the added benefit of the reflection not interfering with the transmitted beam transmission line style.

It should be obvious that this strategy only works with light having a very narrow bandwidth. If you use a different frequency, the quarter wave plate will no longer be a quarter wave plate, due to the different wavelength. Hence using a laser is the obvious choice.

The other reason you need to use a laser is for the detection of the digital data itself. The reflected light destructively interferes near the edges.



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The distance from a pit to a land is a quarter wavelength. Hence the total extra distance travelled by the laser beam is half a wavelength. As you transition from a pit to a land or vice versa, the focused laser beam will illuminate both the pit and the land. Since the path difference is half a wavelength when the beam reflects from both a land and a pit, the reflected waves destructively interfere with each other. If the light reflects from only a land or a pit, there is no path difference.

P.S. I continue to claim that optics is electrical engineering, since light is, you know, an electromagnetic wave.