How PDAF Works?

[Carl Fredrik Ahl]

 

Hi,

I understand the principle of how PDAF (Phase Detection Auto Focus) works. Look at the image I inserted. I don't understand how the incoming light splits into two rays of light in the two extreme sides of the lens. Why aren't lots of rays of light coming all over the lens?

Source: https://photographylife.com/how-phase-detection-autofocus-works

 

[CharonY]

There are. This is a simplified illustration to show where the lightbeams converge (or don't).