Theoretical and experimental demonstration on narrow-linewidth DFB laser utilizing equivalent CPM-apodized grating

Due to their various modulation formats, high receive sensitivity and spectral utilization efficiency, coherent optical communication systems are being invested to satisfy the future demands for huge traffic capacity. DFB lasers with narrow spectral linewidth are necessary for such systems, which limit the capacity of the whole system. In this paper, a low-cost narrow-linewidth DFB laser with equivalent CPM-apodized grating was demonstrated. The grating was fabricated by the reconstruction-equivalent-chirp (REC) technique based on conventional holograph exposure combined with lithograph technology. By employing the equivalent CPM-apodized grating, the spatial hole burning effect (SHB) in the DFB laser was significantly reduced. At room temperature, the linewidth of the laser is 224 kHz with injection current of 100 mA and side mode suppression ratio of 48 dB.