Shanghai Pushen Optoelectronics Technology Co., Ltd (abbreviation as POET) Explains as following:

This question fueled the development of the fiber optic rotary joint, or FORJ. The FORJ is a precision component that utilizes a precise lens and prisms to funnel and align the light, and the data/signals the light carries.

The FORJ component can carry the data over an air gap while the component is rotating. In short, the FORJ preserves the integrity of the data so that nothing is lost in the transfer. Fiber Optic Rotary Joints are available in many configurations. The amount of data to be transferred and the distance the light needs to travel between the transmission and the receiving points will dictate which FORJ is right for your project