TRANSMISSION OF QPSK SIGNALS USING UNISOLATED DFB LASERS

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