Cavity length effect and modal effect on coherence in a semiconductor diode laser subjected to an external optical feedback

Semiconductor diode lasers are known to be sensitive to external optical feedback. The time delay with which an optical feedback is provided is an important parameter towards deciding the laser's output characteristics. It is known that if the external cavity time delay is longer, the feedback is less coherent. Plotting of Light - Current characteristics ( L-I curve) is a standard method to understand certain properties of a diode laser. Depending upon the nature of coherence of optical feedback, the position of L-I curve varies. However, there is no explicit work known to best of author's knowledge about the dependence of L-I curve on the delay of external cavity optical feedback and this work provides the explicit proof for this dependence. Also, this work, provides evidence for the decoherence arising from multi-mode nature of a semiconductor diode laser.