LINEAR PARTS OF HYPERBOLAE. “Since the wave pattern describes hyperbolae for single or double slits, the symmetry of the light diffraction is that of an elliptic cylindrical coordinate system. In that setting, the hyperbolae describe lines parameterized by one of the coordinate variables, providing an elementary example of straight lines.”
https://link.springer.com/content/pdf/10.1007/JHEP07(2019)140.pdf