Transmission of QPSK signals using unisolated DFB lasers

We have investigated the use of uncooled and unisolated 1.3 μm DFB lasers in a QPSK transmission system. Our measurements include both BER measurements and detailed analog tests on two commercial DFB lasers in cylindrical packages. Error-free transmission was observed even in the presence of back reflections as large as -8 dB. The laser relative intensity noise (RIN) was measured as a function of temperature and back reflection. The change in RIN in the temperature range -10/spl deg/C to +60/spl deg/C was less than that due to back reflections, suggesting that error-free QPSK transmission can be acheived over a large temperature range with these DFB lasers.