We present a quantum key distribution system based on two polarization beam splitters, by means of which the phase modulator's polarization dependence is cancelled out. A high key generation rate has been obtained for the first time at 1310nm transmitted over a 25 km long fiber, with a fringe visibility of 99.4%. A sifted key rate of about 0.6 kbits/s and quantum bit error rate of about 0.5% are obtained.