  Two quantum states of two half-charge optical vortexes with relative
azimuthal angle {\pi} are orthogonal, by which two half-charge spiral phase
plates with intersection angle {\pi} can be used to demonstrate a parabolic
coincident fringe in the Bell inequality experiment with high-dimensional
two-photon orbital angular momentum entanglement and to thereby obtain a strong
Bell parameter of 3.2. I theoretically demonstrate various orthogonal relations
between two quantum states, each of which is a state with a rotational symmetry
superposition made up of n fractional orbital angular momentum states, where n
is N. I propose a Bell inequality experiment with two n-section spiral phase
plates that have these two quantum states, whereby various angle periods with
parabolic coincident fringes 2{\pi}/n and Bell's parameter 3.2 in each period
can be obtained.
