https://www.cnbc.com/2017/11/14/apple-iphone-rear-facing-3d-sensor.html

Apple is exploring a rear-facing 3-D sensor system for the iPhone to be released in 2019, Bloomberg reported on Tuesday citing people familiar with the matter.

The technology would be different than the TrueDepth sensor that's currently on the front of the iPhone X. The iPhone X's system relies on a light technique that projects thousands of laser dots on a person's face to generate an image. The new technology could bounce light of a person's face and calculate the time it takes for the laser to bounce off in order to create a 3-D image.