A monolithic integrated two-section distributed feedback (TS-DFB) semiconductor laser for high-speed direct modulation is proposed and theoretically analyzed. The grating structures of the TS-DFB laser are designed by the reconstruction-equivalent-chirp (REC) technique, which can reduce the manufacturing cost and difficulty, and achieve high wavelength controlling accuracy. The detuned loading and photon-photon resonance (PPR) effects are utilized to enhance the modulation bandwidth of the TS-DFB laser, which can exceed 37 GHz. While that of the conventional one-section DFB laser is only 16 GHz. The clear eye diagrams with large open extents can still be obtained when the bit rate of the non-return-to-zero (NRZ) signal reaches 55 Gb/s. These results show that the proposed method can enhance the modulation bandwidth of DFB laser significantly.

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The ranging distance and precision of the coherent frequency modulated continuous wave (FMCW) lidar systems are mainly limited by the modulation linearity and the intrinsic line width of the laser sources. To this issue, we design and experimentally demonstrate a monolithic integrated linear frequency modulated (LFM) dual-wavelength (DW) DFB laser with high frequency sweep linearity and without a complicated predistortion compensation system. Our results show that the nonlinearity of the LFM beat signal from the DW-DFB laser chip can reach 0.0146%. Furthermore, using the LFM DW-DFB laser, we implement an accurate measurement of a single mode fiber (SMF) with a length of 12.6 km, which is hundreds of times the intrinsic coherent length of the DW-DFB laser. Due to the high linearity of the LFM DW-DFB laser, the measurement error does not deteriorate significantly when the target distance increases from 0.43 to 24.24 m.