  The integrability nature of a nonparaxial nonlinear Schr\"odinger (NNLS)
equation, describing the propagation of ultra-broad nonparaxial beams in a
planar optical waveguide, is studied by employing the Painlev\'e singularity
structure analysis. Our study shows that the NNLS equation fails to satisfy the
Painlev\'e test. Nevertheless, we construct one bright solitary wave solution
for the NNLS equation by using the Hirota's direct method. Also, we numerically
demonstrate the stable propagation of the obtained bright solitary waves even
in the presence of an external perturbation in a form of white noise. We then
numerically investigate the coherent interaction dynamics of two and three
bright solitary waves. Our study reveals interesting energy switching among the
colliding solitary waves due to the nonparaxiality.
