Modulation Bandwidth Enhancement and Frequency Chirp Suppression in Two-Section DFB Laser

We demonstrate a two-section distributed feedback (DFB) laser for direct modulation based on the reconstruction equivalent chirp (REC) technology. The two-section DFB laser exhibits a stable single-mode characteristic. Utilizing the photon-photon resonance (PPR) effect and detuned-loading effect, the 3-dB modulation bandwidth of the two-section DFB laser is improved from 8 GHz to 23 GHz. A 25 Gb/s non-return to zero (NRZ) signal is applied to the two-section DFB laser and eye diagrams with large open extent are obtained. In addition, the relative intensity noise is reduced to below −143 dB/Hz. The frequency chirp is also suppressed. The chirp parameter is reduced from 5.67 to 1.37, which is a small value in directly modulated DFB laser. We compared the eye diagrams after transmitting different distances, the results show that the two-section structure reduces the frequency chirp significantly. The modulation of the two-section DFB laser also has good linearity, with a 1-dB compression point of more than 18 dBm.