What is the purpose of eye diagrams?
Eye diagrams are graphics that can be used to describe the loss of transmitted light, received light, and reflected/diffracted light.
The eye diagram shows how much of the signal is lost or discarded by the optical system as a function of time. For example if you are looking at a sinusoidal wave with a maximum TRV-transit time = 0.1 ms then 1% will be lost in the first 10 µs and 90% will be lost after 100 μs (i.e., it is very fast). And this applies to all lighting conditions from dimmer lights where more energy is needed for human eyes to see 3D images (30 lux) up to outdoor bright sunlight where only 8% is lost (it is very slow).
The eye diagram also shows the actual voltage at any time (up) and the maximum expected voltage that was sent by the encoder (Vmax), both of these are important for triggering or strobe control circuits. This information can be used to design specialized lighting conditions which gives better 3D perception e.g., High Dynamic Range (HDR) and Active Stereo.
The actual voltage at any time (V(t)) is the ideal voltage that was sent by the encoder minus the loss due to optical receiver or receiver circuit; V(t)=Vmax-Loss. So if Loss=0.5% for a certain time period, the voltage at this time period will be 0.5% less than the normal strobe voltage sent by the encoder. Furthermore it is a good idea to check for fast transients and overloads, so one can see if V(t) is close to or higher than Vmax.
In summary, eye diagrams provide insight into how the optical system is performing in a given lighting condition.