Fast wavelength-tunable semiconductor lasers will be the key components in future optical packet switching
networks. Especially, they are of great importance in the optical network nodes: transmitters, optical wavelength-routers,
etc. In this paper, a new scheme of a next-generation fast tunable ring laser was given. Tunable lasers in this design have
better wavelength tunability compared with others, for they are switched faster in wavelength and simpler to control with
the injecting light from an external distributed Bragg-reflector(DBR). Then some discussion of the waveguide material
system and coupler design of the ring laser were given. And we also derived the multimode rate equations corresponding
to this scheme by analyzing some characteristics of the semiconductor ring cavity, directionality, nonlinear mode
competition, optical injection locking, etc. We did MatLab simulation based on the new rate equations to research the
process of mode competition and wavelength switching in the laser, and achieved the basic functions of a tunable laser.
Finally some discussion of the impact of several key parameters was given.