We have investigated the use of uncooled and unisolated 1.3 mu m DFB l
asers in a QPSK transmission system. Our measurements include both BER
measurements and detailed analog tests on two commercial DFB lasers i
n cylindrical packages. Error-free transmission was observed even in t
he presence of back reflections as large as -8 dB. The laser relative
intensity noise (RIN) was measured as a function of temperature and ba
ck reflection. The change in RIN in the temperature range -10 degrees
C to +60 degrees C was less than that due to back reflections, suggest
ing that error-free QPSK transmission can be acheived over a large tem
perature range with these DFB lasers