Optical performance of symmetrical and asymmetrical Y-branch couplers for plastic optical fibers.

The excess loss and output optical power ratio of symmetrical and asymmetrical Y-branch couplers for plastic optical fibers (POFs) are studied in this work. A ray-tracing model for the Y-branch coupler is derived to investigate the effect of coupling parameters on its optical performance. The coupling parameters, namely coupling angle, axial displacement, and refractive index of filling medium between the emitting-end and receiving-end POFs, are studied. The simulated and measured results indicate that the coupling efficiency is sensitive to all these coupling parameters. A minimum excess loss of approximately 0.83 dB is observed for the symmetrical Y-branch coupler. It is found that both the excess loss and the output power ratio are increased with the increase of the refractive index of the filling medium and the total coupling angle (α+β) for the asymmetrical Y-branch coupler. The experimental results indicate that the maximum output power ratio P1∶P2 is found to be 3.8∶1 for excess loss of less than 2.8 dB for the asymmetrical Y-branch coupler.