in my prior post, 'field' IS better than 'wave',,,,,I meant to draw no distinction here.
"what constitutes [into] a photon??"
What 'constitutes' any particle is it's measured/observed behaviors...We create models to replicate those.
So we can observe, describe, and model other characteristics of photons as well but those descriptions depend on what models we use...different model behaviors can manifest as 'spin' for example. What's 'really' there is
anybody's guess unless we can smash something apart and look at the constituents...[which still seems like an odd approach, but it works. Like taking a car apart to see how its made by beating it!]
from the link I posted:
The quanta of an Abelian gauge field must be massless, uncharged bosons, as long as the symmetry is not broken; hence, the photon is predicted to be massless, and to have zero electric charge and integer spin.
That's a mathematical statement.
Meantime, string theory, another theory, also describes photon characteristics but I don't know enough about the math to divine exactly how [or if] AdS/CFT precisely relates string theory to gauge theory strictly enough to make direct characteristic 'spin' comparisons...
Seems that things like spin pop out of mathematical models and clever physicsts exclaim "Oh that looks just like 'spin'...and so it is...but it takes a lot of work to compare the origins of such different mathematical model outcomes...