LONG-WAVELENGTH INGAASP INP MULTIQUANTUM-WELL DISTRIBUTED-FEEDBACK AND DISTRIBUTED-BRAGG-REFLECTOR LASERS GROWN BY CHEMICAL BEAM EPITAXY/

We demonstrated the successful operation of long-wavelength InGaAsP lo w threshold-current index-coupled and gain-coupled DFB lasers grown by chemical beam epitaxy (CBE). For index-coupled DFB lasers, buried-het erostructure six-QW DFB lasers (250 mum long and as-cleaved) operated at 1.55 mum with CW threshold currents 10-15 mA and slope efficiencies up to 0.35 mW/mA (both facets). A side-mode suppression ratio (SMSR) as high as 49 dB was obtained. The lasers operated in the same range e ven at high temperatures (70-degrees-C checked). For gain-coupled DFB lasers, gain-coupling is accomplished by using a InGaAsP quaternary gr ating or quantum-well grating that absorbs the DFB emission. The use o f a quantum-well grating, in particular, greatly facilitates the repro ducible regrowth (defect-free) over grating and the control of the cou pling coefficient. CW threshold currents were in the range of 10-15 mA for 250-mum and 13-18 mA for 250-mum and 500-mum cavities, respective ly. Slope efficiencies were high, approximately 0.4 mW/mA (both facets ). SMSR was as high as 52 dB and remained in the same DFB mode with SM SR staying approximately 50 dB throughout the entire current range. Li newidth x power products of 1.9-4.0 were measured with minimum linewid ths of 1.8-2.2 MHz. No detectable chirp was measured under 2.5 Gb/s mo dulation. Unlike index-coupled DFB lasers in which mode partition even ts decrease slowly even when biased above threshold, these lasers have mode partition events shut off sharply as bias approaches threshold ( greater than or similar to 0.95 I(th). A very small dispersion penalty of 1.0 dB was measured at 10(-11) BER in transmission experiments usi ng these lasers as sources at 1.7 Gb/s over an amplified fiber system of 230 km. No self-pulsation was observed in these gain-coupled DFB la sers. Gain-switching at 4 GHz with a 100% optical modulation depth and a FWHM pulse width of 23 ps was achieved with these gain-coupled DFB lasers. The peak power was approximately 72 mW and the FWHM bandwidth was 0.14 nm. We also fabricated InGaAs/InGaAsP multiquantum-well DBR l asers by CBE. Taking advantage of uniform thickness growth and proper design of weak and long gratings, a record high SMSR of 58.5 dB was ob tained.