Long wavelength InGaAsP/InP distributed feedback lasers grown by chemical beam epitaxy

Abstract

We have demonstrated successful operation of long wavelength InGaAsP low threshold-current gain-coupled DFB lasers. This is accomplished by using a InGaAsP quarternary grating or quantum well grating that absorbs the DFB emission. The use of a quantum well grating, in particular, greatly facilitates the reproducible regrowth (defect-free) over grating and the control of the coupling coefficient. CW threshold currents were in the range of 10–15 mA for 250 μm and 13–18 mA for 250 and 500 μm cavities, respectively. Slope efficiencies were high, ∼0.4 mW/mA (both facets). SMSR was as high as 52 kB and remained in the same DFB mode with SMSR staying ∼50 dB throughout the entire current range. Linewidth x power products of 1.9-4.0 were measured with minimum linewidths of 1.8-2.2 MHz. No detectable chirp was measured under 2.5 Gb/s modulation. Unlike index-coupled DFB lasers in which mode partition events decrease slowly even when biased above threshold, these lasers have mode partition events shut off sharply as bias approaches threshold (≿0.95 I th). A very small dispersion penalty of 1.0 dB was measured at 10 -11 BER in transmission experiments using these lasers as sources at 1.7 Gb/s over an amplified fiber system of 239 km. No self-pulsation was observed in these gain-coupled DFB lasers.