Unintentional Polarization Dependent Pulsewidth of Graphene Mode-Locked Er-Doped Fiber Lasers

• Published in: IEEE journal of selected topics in quantum electronics Vol. 23; no. 1; pp. 50 - 59
• Main Authors: Chen, Ting-Hui, Lin, Yung-Hsiang, Cheng, Chih-Hsien, Tsai, Cheng-Ting, Chi, Yu-Chieh, Lin, Gong-Ru
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.01.2017; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Absorption; Cavity resonators; Coefficients; Fiber lasers; Garphene; Graphene; mode-locking laser; Modulation; Nonlinearity; Optical fiber couplers; Optical fiber dispersion; Optical fiber polarization; Polarization; polarization dependent pulsation; Twisting
• ISSN: 1077-260X; 1558-4542
• DOI: 10.1109/JSTQE.2016.2564647

The unique polarization dependent pulsation phenomenon in a graphene mode-locked erbium-doped fiber laser (ML-EDFL) is explored by the interaction between intracavity weak nonlinear polarization rotation and strong saturable absorption. With unintentional polarization dependent loss (PDL) induced by twisting single-mode fiber (SMF) in an intracavity polarization controller (PC), the unique pulsewidth tunability in a polarizer-free graphene ML-EDFL can be observed. Numerical and experimental procedures are established to combine the hybrid effects and to realize the possible detuning range of intracavity polarization angle for polarization dependent mode-locking dynamics. Twisting SMF induced unintentional PDL in the polarizer-free EDFL contributes a tiny self-amplitude modulation (SAM) coefficient of γ NPR = 5.36 × 10 -4 sin 2θ P . The modelocking stability still relies on the graphene saturable absorption to optimize the SAM up to γ total = 1.46 × 10 -3 ands horten the EDFL pulsewidth to 330 fs. These clearly elucidate the enigma on polarization dependency of most polarizer-free ML-EDFLs with built-in PC. Even an unintentional weak polarization dependency in the EDFL without any polarizer can induce a residual PDL to introduce a polarization angle-dependent SAM coefficient, which declares the importance on controlling intracavity polarization for stabilizing and optimizing the graphene ML-EDFL with unintentional nonlinear polarization rotation induced PDL.