This study presents a directly modulated 1550 nm NTSC AM-VSB 74-channel Wber optical CATV long-distance (over 100 km) transmission system. In this system, 1550 nm analog distributed feedback (DFB) laser diodes, push-pull preampliWer, half-split-band, wavelength-division-multiplexing (WDM), and in-line erbiumdoped Wber ampliWers (EDFAs) were used. Performances of carrier-to-noise ratio (CNR) of ¶ 49 dB, compositie second order (CSO) of ¶ 70 dB, and composite triple beat (CTB) of ¶ 65 dB were obtained over 100 km of standard single-mode Wber (SMF) transmission. This proposed directly modulated transmission system is simpler and more cost-eVective than conventionally externally modulated 1550 nm transmission systems.For long-distance AM video transmission in ® ber optical CATV systems, the maximum ® ber link length using cascaded in-line erbium-doped ® ber ampli® ers (EDFAs) is limited by AM-VSB video system RF parameters such as carrier-to-noise ratio (CNR), composite second-order (CSO), and composite triple beat (CTB) at the end of the ® ber link. These parameters are seriously degraded by stimulated Brillouin scattering (SBS) and ® ber chromatic dispersion eOE ect in 1550 nm AM-VSB ® ber optical CATV systems [1,2]. Several ways have been proposed to improve system performances such as using diOE erential detection at the receiver site [3] or using dispersion compensation ® ber (DCF) within the link [4]. However, for the former one, an additional set of an expensive externally modulated transmitter, a ® ber link, and an optical receiver are required, while poor CNR quality may be induced in the latter one due to high loss characteristics of the DCF. Moreover, it is di cult to obtain good CNR, CSO, and CTB performances for the full channel loading simultaneously. In this study, a directly modulated NTSC AM-VSB 74-channel system 279 Fiber and Integrated Optics, 20:279± 285, 2001
This study presented a directly modulated 1550 nm NTSC AM-VSB CATV longdistance transmission system using Fabry±Perot laser diode, optical isolator, ®ber Bragg grating,, composite second-order ( 64 dB), and composite triple-beat ( 60 dB) performances were obtained after a 100 km standard single-mode ®ber transmission. Our proposed system does not use an externally modulated 1550 nm transmitter and a sophisticated stimulated Brillouin scattering suppression technique. It reveals a prominent technique with simpler and more economical advantages than that of externally modulated 1550 nm transmission system.Since ®ber Bragg grating (FBG) exhibits a very narrowband wavelength response, it can be potentially applied as a narrowband wavelength ®lter in AM-VSB Cable Television (CATV) wavelength-division multiplexing (WDM) systems [1]. An optical ®lter based on the FBG has become a very important device in lightwave communication applications because of its compactness and potentially low cost. Multiple-mode Fabry±Perot (FP) laser diodes exhibit a wide spectrum spread. This wavelength spread will cause higher intensity noise and higher ®ber dispersion-induced nonlinear distortions. Therefore, to build a system with high linearity and low noise requirements, we should reluctantly choose laser diodes that operate in a single longitudinal mode. Many techniques, such as the use of distributed Bragg re¯ector (DBR) and distributed feedback (DFB) laser diodes, have been proposed to obtain the single 43 longitudinal mode operation. However, DBR and DFB laser diodes not only are very expensive for CATV long-distance transmission system applications, but they also make it di cult to obtain a good carrier-to-noise ratio (CNR), composite secondorder (CSO), and composite triple-beat (CTB) performances due to full channel loading (NTSC AM-VSB 80-channel). When the output of an FP laser diode was coupled into an optical isolator and BGF combination, an appropriate narrowband wavelength would be selected. Therefore, the combination of an FP laser diode, an optical isolator, and a FBG can be used to replace the conventional DFB laser diode in CATV WDM systems. In view of the con®guration, a DFB laser diode can be considered as the combination of an FP laser diode and Bragg grating structures monolithically fabricated on both sides. In this paper, we proposed and then experimentally demonstrated a directly modulated 1550 nm NTSC 80-channel erbium-doped ®ber ampli®er (EDFA) ampli®ed system using split-band and WDM techniques, as well as a combination of an FP laser diode, an optical isolator, and a FBG to replace the conventional DFB laser diode. By replacing the DFB laser diode with this combination of an FP laser diode, an optical isolator, and a FBG, good CNR, CSO, and CTB performances were obtained after a 100 km standard singlemode ®ber (SMF) transmission.
We propose and demonstrate, for the first time, a bidirectional externally modulated NTSC AM-VSB 77-channel transport system over an 80-km large effective area fiber (LEAF) which used bidirectional transport and densewavelength-division-multiplexing (DWDM) techniques. By comparing with the system link with a transmission length of 80 km single-mode fiber (SMF) and truewave fiber (TWF), not only channel capacity was doubling, but also good carrier-to-noise ratio (CNR) ≥ 50 dB, composite second order (CSO) ≥ 68 dB and composite triple beat (CTB) ≥ 64 dB performances were obtained in our proposed system after an 80-km LEAF transport.
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