In quantum mechanics, which concept caters for light rays?
None, analogous to the fact that there is no concept for temperature in quantum mechanics either. Light rays are emergent from quantum mechanics the way thermodynamics emerges from statistical mechanics.
The photon is an elementary point particle in the standard model of particle physics. It has zero mass, spin 1 and energy = hν , where ν is the frequency the ensemble of such photons will show building the classical electromagnetic wave, h is Planck's constant.
Photons obey the quantized Maxwell's equation of quantum mechanics, with the corresponding wave function. The comlex conjugate square of the wavefunction gives the probability of finding the given photon at (x,y,z,t).
But, does the wave function also represent the whole length and direction of the particle's trajectory (like : from the Sun to the Earth) ?
The wavefunction of elementary particles leads to the probability of finding the particle. That is all. As to be called particles they have macroscopically to have a limited probability to be found outside a classical definition of a particle's footprint , no, the probability to be anywhere except close to a particle track is so small, it is zero.
This double slit experiment one photon at a time might help you acquire an intuition.
Single-photon camera recording of photons from a double slit illuminated by very weak laser light. Left to right: single frame, superposition of 200, 1’000, and 500’000 frames.
The photon footprint at the left screen looks random, but the probability distribution accumulated at the right shows the classical interference pattern of a classical light wave of that frequency.
One could draw a direction, from the two slits to the individual photon footprint. What happens is that the individual wave function of the photon give this path as most probable, but because of the quantum mathematics, the boundary conditions, imposed by the width of the slits and the distance between them on the wavefunction (the same describes all these photons), gives the interference pattern on the right. The superposition is already in the wavefunction, induced by the boundary conditions.
You ask in a comment:
how do you get straight optical rays
It can be shown mathematically that the superposition of photons generates the classical electromagnetic field, and all its accoutrements. See here for example. The classical electromagnetic tools are so successful in describing light that not much stress is placed on the quantum mechanical wavefunction of the photon. Rays emerge from classical light analysis, are emergent.