The present invention is a tunable semiconductor laser for swept source optical coherence tomography, comprising a semiconductor substrate; a waveguide on top of said substrate with multiple sections of different band gap engineered multiple quantum wells (MQWs); a multiple of distributed feedback (DFB) gratings corresponding to each said band gap engineered MWQs, each DFB having a different Bragg grating period; and anti-reflection (AR) coating deposited on at least the laser emission facet of the laser to suppress the resonance of Fabry-Perot cavity modes. Each DFB MQWs section can be activated and tuned to lase across a fraction of the overall bandwidth as is achievable for a single DFB laser and all sections can be sequentially activated and tuned so as to collectively cover a broad bandwidth, or simultaneously activated and tuned to enable a tunable multi-wavelength laser. The laser hence can emit either a single lasing wavelength or a multiple of lasing wavelengths and is very suitable for swept-source OCT applications.