Optical Communications by Martin Sibley

Author:Martin Sibley
Language: eng
Format: epub
ISBN: 9783030343590
Publisher: Springer International Publishing

A further advantage of the BH structure is that, by using a small active region, the gain profile is considerably narrowed. Thus the emission spectrum can consist of a single line – a considerable advantage in long-haul routes operating at a zero dispersion wavelength. Unfortunately the gain profile is dependent on the junction temperature, and so the wavelength of emission can change during operation so introducing dispersion. One solution is to use a Peltier cooler to stabilise operation.

A truly single-mode source results from distributing the feedback throughout the laser, the so-called distributed feedback, or DFB, laser. In these devices, a grating replaces the Fabry-Perot cavity resonator (Fig. 3.19). The effect of this grating is to select just one propagating mode. This happens because each perturbation reflects some of the light and, in order to propagate successfully, the phase of the twice reflected light must match that of the incident light. We can write this condition as

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