In this paper, we propose and analyze gain-coupled laser diodes (GC LDs) and a gain-coupled double phase-shift-controlled distributed feedback (GC-2PSC-DFB) optical filter. Our analysis is based on the transfer matrix method. It is showed that in a distributed feedback diode laser with gain coupling, we can have an enhanced peak in the Bragg wavelength. We also show that in a (GC-2PSC-DFB) optical filter the range of tuning, the Side-mode suppression ratio (SMSR) and the power of the transmittance peaks can be improved by increasing the pitch of grating.