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DFB lasers with longitudinal variations in their grating pitch and, consequently, their Bragg wavenumber (corrugation-pitch-modulated or CPM-DFB) can achieve single-mode oscillation with good threshold gain margins and flatter longitudinal photon-density distributions than conventional quarter-wave-shift (QWS) DFB lasers. Moreover, substantial improvements of these two characteristics are provided by adequate variation of the coupling coefficient κ along the cavity In the paper, a three-section corrugation-pitch-modulated DFB laser with distributed-coupling-coefficient (DCC-CPM-DFB) is studied extensively. Threshold and above-threshold numerical simulations show that these structures can achieve very good single-mode operation by correct optimisation of the Bragg detuning and coupling strength profile at threshold and can maintain these characteristics up to high injection currents.
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T. Fessant (1997) studied this question.
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