In-line optical isolators integrated into a fiber array without alignment

We demonstrate lens-free optical isolators integrated into an array of two thermally expanded core (TEC) fibers without optical alignment. The backward losses are more than 30 dB ranging from 1550 nm to 1575 nm and the insertion loss is 0.91 dB at 1555 nm, the excess insertion loss being successfully suppressed to 0.19 dB. This result verifies and endorses the principle and usefulness of integrating functional devices into TEC fibers.