A novel InP monolithically integrated coherent transmitter has been designed, fabricated and tested. The photonic integrated circuit consists of a distributed Bragg reflector laser and a modified nested Mach-Zehnder modulator having tunable input power splitters. Back-to-back coherent transmission for PDM-QPSK signals is reported up to 10 Gbaud (40 Gb/s) using the integrated laser and up to 32Gbaud (128 Gb/s) using an external low phase noise laser.