Photonics is the science of generating, controlling, and detecting photons (especially in the visibile light spectrum).
Photonic engineers develop new products that use light to function, ex: holographic art. They can also create optical materials to make workhouses more efficient. The fields that benefit from photonics are the medical field (laser surgery), telecommunications field (optical fiber communications), manufacturing field ( lasers for efficiency), the construction field (laser rangefinding), etc.
I chose this field to be the most fascinating out of all the others because we can find these products in everyday life, but we don't ever give it enough credit.