Asymmetric excitation of symmetric single-mode Y-junction: the radiation mode effects

A symmetric single-mode Y-junction under asymmetric excitation by an optical fiber is studied. The asymmetric excitation is due to fiber displacement with respect to the junction axis. The power splitting between the two outputs of the junction is found to depend strongly on the fiber position. Theoretical analysis shows a splitting ratio as high at 14 dB, which cannot be explained if the radiation mode coherent coupling is neglected. A GaAs/GaAlAs junction is tested and the experimental results confirm these theoretical predictions.<>