Abstract

It has been found theoretically that gain-coupled DFB lasers give a higher single-mode yield than index-coupled DFB lasers,¹ and recent results have shown high side-mode suppression ratios² and low-chirp³ in such devices. Kudo et al. have shown analytically that an effective small-signal linewidth enhancement factor, α_eff, can be reduced by adding anti-phase index coupling.⁴ In this paper, we show numerically that the ratio of index-coupling, K_i to gain-coupling, K_g, significantly affects the maximum intrinsic 3 dB modulation bandwidth of the laser, quantified by the K-factor⁵ as $f_{-3}{}_{\text{dB}}\approx 2\sqrt{2}\pi /\text{K}$ Furthermore, careful choice of the coupling ratio, K_i<K_g, can almost triple f_-3dB.

© 1993 Optical Society of America