External optical feedback (EOF), caused by the return loss of connected circuits, is well known to have a strong impact on the performance of semiconductor lasers . Feedback effects are usually prevented by placing an optical isolator at the output of the laser. A strong isolation value of approximately 60dB is typically required for tunable lasers. It has proven difficult to implement sufficiently strong optical isolators in a form suited to photonic integration . For this reason we have previously proposed a ring laser with weak intracavity isolation to enable a feedback insensitive integrated tunable laser .
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