We analyze the evolution of the vortex and the asymmetrical parts of orbital angular momentum during its propagation through separable first-order optical systems. We find that the evolution of the vortex part depends on only parameters ax, ay, bx, and by of the ray transformation matrix and that isotropic systems with the same ratio b/a produce the same change of the vortex part of the orbital angular momentum. Finally, it is shown that, when light propagates through an optical fiber with a quadratic refractive-index profile, the vortex part of the orbital angular momentum cannot change its sign more than four times per period.
© 2004 Optical Society of America
(030.5630) Coherence and statistical optics : Radiometry
(070.2580) Fourier optics and signal processing : Paraxial wave optics
(070.4690) Fourier optics and signal processing : Morphological transformations
(120.4820) Instrumentation, measurement, and metrology : Optical systems
(140.3300) Lasers and laser optics : Laser beam shaping
Tatiana Alieva and Martin J. Bastiaans, "Evolution of the vortex and the asymmetrical parts of orbital angular momentum in separable first-order optical systems," Opt. Lett. 29, 1587-1589 (2004)