Investigation of characteristics of GaN-based blue DFB laser diodes over a wide detuning range

GaN-based distributed feedback laser diodes (DFB-LDs) with diffraction gratings of different periods at 2 nm intervals were fabricated from a single epi-wafer. Nine DFB oscillations between 441.1 and 461.9 nm at almost 2.6 nm intervals at 25 °C were confirmed. The detuning between the DFB-oscillation wavelengths and the gain-peak wavelengths of the obtained DFB-LDs ranged from −6.4 to +13.1 nm. From their I–L characteristics and the temperature variation of the threshold current, we discussed how much the detuning can be increased on both the positive and negative sides. Additionally, the intervals between the detunings of adjacent DFB-LDs with neighboring oscillation wavelengths were uneven. This is because the amount of blue shift of the gain-peak wavelength increased with the increase in threshold current, as made clear by the measurement results of the emission spectra. Due to the same mechanism, the temperature coefficient of the gain-peak-wavelength shift also increased super-linearly with increasing detuning.