Abstract
Successful operation of long-wavelength InGaAsP low-threshold-current gain-coupled DFB lasers was demonstrated by using an InGaAsP quaternary grating that absorbs the DFB (distributed feedback) emission. The amount of gain (loss)-coupling is controlled by the composition (bandgap) and thickness of the grating quaternary and the InP-spacer layer between the grating and the active layer. With optimally designed lasers, CW (continuous-wave) threshold currents were 10-15 mA (250- mu m cavity, as-cleaved), slope efficiency was approximately 0.4 mW/mA (both facets) and SMSR (side-mode suppression ratio) was as high as 52 dB. The laser operated in the same DFB mode with SMSR staying approximately 50 dB throughout the entire current range. At 100 degrees C, the CW threshold current stayed low, approximately 50 mA, and SMSR was approximately 40 dB. Results also indicate that the presence of gain-coupling removes the degeneracy in lasing wavelength. >
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