Long-Distance Transmission of AM-VSB CATV Systems Using Fabry-Perot Laser Diode and Fiber Bragg Grating

Abstract

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.