The Investigation of Hybrid Fiber Amplifiers in Fiber Laser Structures for Multi-Carrier Signals Generation

• Main Authors: Bing-Sheng Wu, 吳秉昇
• Other Authors: Ro-Min Weng
• Format: Others
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/42830755713928703613

博士 === 國立東華大學 === 電機工程學系 === 104 === 　In this thesis, we confirm through experimental results that hybrid fiber amplifiers with fiber laser structures demonstrate the advantages of high gains, broadband, and gain flatness, and can be deployed to generate high power multi-carrier signals. 　As a basis for comparison, the first hybrid fiber amplifier proposed in this thesis is a broadband dispersion compensating Raman/erbium-doped-fiber (Raman/EDF) hybrid amplifier, which used 11.4 km of dispersion-compensation fiber (DCF) as a gain medium. The 3dB bandwidth was increased from 20 nm to 40 nm by recycling residual pump power with the use of a 1480 nm single pump. To increase the 3dB bandwidth and gain flatness of the Raman/EDF hybrid amplifier, this study employed a multi-pump method. The optimal pump combination was 1435 nm with 1480 nm. Using the multi-pump method, the 3dB bandwidth was further increased to 58 nm, covering the primary bandwidth for fiber optic communications. In addition, gains higher than 17 dB could be obtained from the signals within this range. Because an 11.4 km DCF was used as a gain medium, the proposed amplifier can be installed as a discrete amplifier in metropolitan area networks (MANs) or wide area networks (WANs). 　As the first to combine hybrid amplifier with a fiber laser structure, this study proposed a EDF/Double Pass-Raman fiber oscillator (EDF/DP-RFO) hybrid amplifier that specifically provides high modal gains for signals within the L-band wavelength range. At a pump power of < 1 W, a maximal gain of 24.47 dB could be derived from the L-band wavelength range. That is, when the 3dB bandwidth reached 54 nm, which encompassed the entire L-band wavelength range, as well as a portion of the L+-band range. In addition, for the L-band, L+-band, and 3dB bandwidth ranges, gains of 21 dB can be derived for the signals, with the gain flatness measuring 2.93 dB. 　To compensate for the dispersion accumulated in long transmission fibers, and to provide flat modal gains for C+L broadband signals, RFO and Raman fiber amplifiers (RFA) can be integrated to form hybrid Raman amplifiers. The experimental results confirmed that the 3dB bandwidth of the hybrid Raman amplifier could reach 97 nm. Furthermore, gains higher than 13.7 dB can be provided to signals within the 3dB bandwidth, with a gain flatness measuring only 1.98 dB. The hybrid Raman amplifier can reach a similar broadband and flattened transmission effect as that of conventional RFAs, and can increase saturation input power. Because a 4.34 km DCF was used as the gain medium for the hybrid Raman amplifier, it can be deployed in LANs and MANs. 　In this study’s final application, the C+L broadband EDF/RFO hybrid amplifier, constructed by integrating RFO and EDF, provided higher modal gains and lower NF in the 3dB bandwidth of 92 nm. For signals in the 3dB bandwidth range, gains higher than 19 dB can be provided, with the gain flatness measuring only 1.88 dB. In addition, the NF measured was the lowest among all the hybrid amplifiers proposed in this thesis. Furthermore, the 980 nm pump power can be adjusted to output flat gains when the input signal power is -10 dBm. Because a 4.74 km DCF was used as the gain medium, the amplifier can be deployed in LANs or MANs. 　In summary, the hybrid fiber amplifier with a fiber laser structure can be deployed to generate high power multi-carrier signals for the following reasons: it is a simple model, capable of providing broadband and high gains, and has the ability to flexibly choose DCF length to compensate for the dispersion accumulated in transmission fibers of varying lengths.