For simple nanosystems, it is usually sufficient to investigate the system's behavior under a single polarization excitation. However, in the case of coupled nanoparticles in three-dimensional space, it is often necessary to study different excitation polarizations in different scattering directions and matrix methods using all possible modes of excitation become important. In this note, we examine the optical response of coupled metallic nanorods. We introduce a 3D Jones matrix for arbitrarily

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... oriented nanorods in three-dimensional space and we formulate the scattering matrix of the coupled nanorod system for arbitrary excitation and scattering directions. We also study the optical activity of the nanorod system and show that, contrary to general belief, optical activity does not arise from the coupling (interaction) between nanorods. Although, optical activity for forward scattering occurs only for coupled nanorods, for other scattering directions, in general, the system can manifest strong optical activity even if there is no coupling between the particles. We conclude that the main cause of optical activity is the phase difference in the light rays scattered from different parts of the system.