Study on Two-Section DFB Lasers and Laser Arrays Based on the Reconstruction Equivalent Chirp Technique and Their Application in Radio-Over-Fiber Systems

Abstract

Two-section distributed feedback (TS-DFB) semiconductor lasers based on the reconstruction equivalent chirp technique is proposed. A four-channel TS-DFB laser array (TS-DFB-LA) is theoretically studied and experimentally demonstrated. Compared with the conventional one-section DFB lasers, the proposed TS-DFB lasers have much higher output efficiency and higher side-mode suppression ratio (SMSR) when both the facets of the laser cavity are coated with antireflection coatings. About 39% increase in output efficiency, more than 10 mA decrease in threshold current, and about 5 dB increase in SMSR have been achieved experimentally. Furthermore, experimental results show that the wavelength spacing accuracy of the four-channel TS-DFB-LA can be improved by tuning the injection current of one of the two sections. Using the two-section structure, the dynamic characteristics including small-signal frequency response, relative intensity noise, and spurious-free dynamic range are also improved significantly. A radio-over-fiber link utilizing the TS-DFB laser as directly modulated light source was experimentally achieved. About 50 MSymbol/s 64-QAM signal with 10 GHz carrier was transmitted from the TS-DFB laser. After 40 km transmission in single-mode fiber, the average error vector magnitude of the whole link is 2.97%.