The normal digital zoom makes poor quality of the image as it increases zoom ratio which causes low quality of the image by S/W. However, Optical Zoom guarantees advanced image quality than digital zoom because it zooms in the subject at closest distance. 
The optical 5x zoom, which is increasing in demand, is a periscope-type H/W that places left and right lenses, and it focuses on minimizing the prominent of camera modules. This is called Folded Zoom or Prism.

The prism deflects the light that comes through the outer lens so that the image sensor can have an image, and is located in front of the inside lens in the camera module.
Prism stands out its function, applied for high-end smartphones.