Mathematical model and experimental verification of spatially multiplexed system using ray theory and modified Laguerre Gaussian beams
Spatial/Space Division Multiplexing (SDM) is based on a channel spacing technique in optical fibers that has the potential to inspire a revolution in optical communications. This patented technique provides a method to launch, transport, and detect two or more optical channels that operate at exactly the same wavelength inside a single multimode optical fiber. In addition, the patented technique added a new dimension and a new degree of photon freedom to the existing fiber multiplexing techniques and complements Time Division Multiplexing (TDM) and Wavelength Division Multiplexing (WDM). As a result, the bandwidth of existing and new optical fiber systems maybe increased by multiple folds. Therefore, Multi-TB/s hybrid architectures are feasible. SDM is a multi-input multi-output (MIMO) system that achieves spatial multiplexing by controlling the orientation of the input launching angles. The angles of the spatially multiplexed channels leaving the fiber at the output end depend on the input angles. These MIMO channels traverse the length of the fiber without interfering with each other and the screen projection of the intensity profile at the exit end of the fiber resembles donut shaped concentric circles. Spatial filtering techniques are employed at the output end of the fiber to de-multiplex and process the individual channels. The endeavor demonstrates the feasibility of a two channel SDM system operating at 10Gbps, using standard C-band Tunable Small Form Factor Pluggable (TXFP) laser transcivers, and develops a mathematical model for SDM channels that relate the incident and output angles to topological charge and the orbital angular momentum (OAM), by combining ray theory and modified Laguerre Gaussian (LG) beam equations. Experimental results and model predictions are compared and analyzed. In addition, the relationship between Bessel Beams inside the fiber and the output Laguerre Gaussian beams in free space is explored.