We report the fabrication and characterisation or a twoelectrode DFB laser. By biasing one section above threshold and using the other section as a phase modulator, a uniform FM response from 100 kHz to 300 MHz is obtained. The linewidth under this operating condition is as narrow as 10 MHz. Combining the narrow linewidth and uniform FM response, this laser is adequate to be used as a source in coherent optical fibre communication using an FSK scheme.