A highly coherent multi-section semiconductor swept source OCT laser

We show theoretically that optical feedback can be used to phase lock the successive modes of multi-section frequency-swept source lasers as a means to increase the coherence length. The time-gated feedback technique can be applied to transfer the coherence between the subsequent modes to retain the coherence along the full sweep or to synchronise two independent swept sources. In analogy with CW lasers, we derive an Adler equation describing the locking conditions. When the constant feedback is applied, the laser can operate in a self-mixing, mode-locking or chaotic regime, depending on the sweeping speed. In order to verify the theoretical results, we have developed an experimental set up and performed initial measurements with optical feedback.