Proceedings of SPIE - the International Society for Optical Engineering
A novel multiplexing technique known as Spatial Domain multiplexing (SDM) has been developed in recent years and offers many advantages over its counterparts. With multiple channel transmission of the same wavelength over a single multimode carrier fiber, SDM increases the data capacity by multiple folds. Input channels are launched at appropriate input angles to produce skew ray propagation. The output of the system when projected on a screen is observed as concentric rings. These SDM beams carry orbital angular momentum. Experiments show that two input sources with the same launch conditions, but opposite topological charge take different helical paths inside the transmission fiber. Consequently the shadow of a straight wire does not remain straight. Instead, it is displaced by a specific distance. This endeavor presents a model of such a system by analyzing the shadow distortion, using principles of geometric optics. Experimentally obtained shadow displacement results are quantified and then compared to the model. We also show that when two channels with opposite topological charges are transmitted with same launch conditions, their orbital angular momenta are equal and opposite. As a result orbital Angular momentum based multiplexing can be used to add another degree of freedom to photons.
Murshid, S. H., Muralikrishnan, H. P., & Kozaitis, S. P. (2012). Mathematical modeling and experimental analysis of multiple channel orbital angular momentum in spatial domain multiplexing. Paper presented at the Proceedings of SPIE - the International Society for Optical Engineering, 8397 doi:10.1117/12.920818