Optisystem based CATV System-Performance Improvement by Using External Light-Injection Technique
S.Adithyan1, S.Srinath2
U.G. Student, Department of EEE, C. Abdul Hakeem College of Engineering & Technology, Vellore, Tamilnadu, India1
Final Year Student, B.Tech, Department of ECE, Vellore Institute of Technology, Vellore, Tamilnadu, India2
ABSTRACT: Cable Television (CATV) is designed with erbium-doped amplifier-repeated system that uses an external light – injection technique and a directly modulated wave using amplitude modulation. The external light – injection technique can greatly enhance the frequency response of the laser diode, and hence improve the overall performance of the fibre optical CATV system. It implemented using Optiwave Optisystem 10.0.
KEYWORDS: External Light–Injection Technique, Semiconductor Lasers, Optical Communication, Directly Modulated Transmitter.
I.INTRODUCTION
CATV is a shared cable system that uses a tree-and-branch topology in which multiple households within a neighborhood share the same cable. Cable television is a system of distributing television programs to subscribers via radio frequency (RF) signals transmitted through coaxial cables or light pulses through fiber-optic cables. The abbreviation CATV is often used for cable television. It originally stood for Community Access Television or Community Antenna Television, from cable television's origins in 1948, in areas where over-the-air reception was limited by distance from transmitters or mountainous terrain, large "community antennas" were constructed, and cable was run from them to individual homes.
II.RELATED WORK
Lu et al [7] developed a CATV system Based on Lower-Frequency Sidemode Injection-Locked Technique with an injection power level of 4.8 dBm.
Wen et al [8] proved that Injection-locking enhances the resonance frequency of the laser and the electrical feedback achieves strong resonance at the base-rate frequency of the injected data streams.
Our paper is based on directly modulated transport system which employs the external light-injection technique. The external light-injection technique greatly enhances the frequency response of the laser diode, and thus improves the overall performance of the fibre optical CATV system. The idea is implemented using Optisystem 10.0 and we analyse how the output power varies with and without the external light-injection technique. Using external light-injection technique we are analysing how the output power varies with 3dBm, 4dBm, 5 dBm and 8 dBm external injected power.
III.INTODUCTION TO THE EXTERNAL-LIGHT INJECTION TECHNIQUE
The recent changes in telecommunication regulations and changing market forces are making the market for broadband network services to the home an extremely lucrative and competitive area. Out of many competing technologies for such broadband services, major CATV companies are banking heavily on various methods of making the network more and more fast and efficient. Most of the interest exists in broadband network services to deliver a variety of products to consumers, such as Internet access, telephony, interactive TV, and video on demand. But due to its cost efficiency, we need to find a better way to do that. When we send any optical signal, we find there is some loss in the transmission and hence there is the loss in data. So to increase the fibre transmission distance, achieve high quality for the given system and increase the performance is the ultimate goal of the fibre optical cable television (CATV) transport systems. However, nonlinear distortions introduced by laser chirp, fibre dispersion effects can degrade the system performance as well as limit the maximum transmission distance. Till now many techniques have been devised to circumvent these problems, but many of them just increase the complexity of the system. In a recent study, external light-injection technique has been employed in a hybrid radio–fibre system to improve the bit-error-rate performance but it has not been employed as a system-performance improvement technique in an analog light wave system. We suggest that the external light injection technique can be used to meet all the goals of CATV system efficiently. The external light- injection technique can greatly enhance the frequency response of the laser diode. It is expected to have good performances in analog fibre optical CATV systems.
IV.THE CATV NETWORK
A CATV network is made up of three main parts: the trunk, the feeder, and the customer drop. The trunk is usually intended to cover large distances of tens of miles. The feeder portion of the cable is used by the consumers for tapping signal. Its maximum length is only a few miles since energy is tapped off to feed homes (subscribers) which require relatively high power levels. The drop is the flexible cable which goes to the home and it has a maximum length of approximately 600 feet and is made up of lower quality co-axial cable than the feeder or trunk. Older generation CATV systems used co-axial cables in the trunk and feeder portions of the network and therefore experienced many problems related to (a) interference from spurious radiation, (b) distortions introduced by amplifiers and (c) limited bandwidth. Long-distance transmission of fibre AM-VSB 80-channel CATV systems is used widely and is spread throughout the cable industry. Whereas, the maximum transmission distance of such systems is still limited by RF parameters and it is difficult to obtain better CNR performance due to full channel loading. In an optical CATV system, the signal is directly or externally modulated with light