I thought I would just interject with a terminology comment. Often people will refer to the modulation of a laser as "intensity modulation". This distinguishes it from the very advanced "coherent communications" that is possible (although quite difficult) with lasers. It is possible to directly do AM, FM and PM modulation on the light carrier itself, and then all of the known radio detection techniques (heterodyne, homodyne, etc) can be used. However, it is far more common to do intensity modulation of the laser, which is often done with a brute force modulation of the current (external modulation is also possible).
There are some key differences between AM and intensity modulation. For example, intensity modulation is likely to modulate both the frequency (this is called chirp) and the amplitude of the light. But this does not matter for simple intensity modulation because of the way detection is done with a simple square-law photodiode detector. The other key difference is the detection process itself since we measure "power" with a photodiode, and not amplitude. The power is converted proportionally to current, so we sometimes forget that, from a communications-carrier point of view, we are dealing with a square-law detector.