Acoustooptic Generation and Characterization of the Higher Order Modes in a Four-Mode Fiber for Mode-Division Multiplexed Transmission

We demonstrate a highly efficient acoustooptic mode converter for selective excitation of the higher-order modes in a four-mode fiber which guides the LP
₀₁
, LP
₁₁
, LP
₂₁
, and LP
₀₂
modes at telecommunication wavelengths. The coupling efficiency and the mode extinction ratio are measured by analyzing the output far-field patterns. The acoustic resonance frequencies and the operating bandwidths are compared with the theoretical results, by which the modal characteristics, the core diameter, and the core-cladding index difference are estimated.