تجزیه و تحلیل عملکرد از فرمت های مدولاسیون متفاوت در سیستم انتقال CATV چهار کاناله با استفاده از OADM

In this paper we have analyzed the performance of different modulation formats for a four-channel WDM CATV system using optical ad drop multiplexers and the impact of frequency and wavelength on Q-value, and eye opening is observed for added and dropped channels at different lengths.

With the recent development optical networks require a variety of new features of which are security and reliability. Since the information carried by the optical carrier is too large and requires features that ensures the signal is always up to the user even in damage whatsoever [1] and [4]. To meet up the rapid development will require further improvements in the existing optical networks by using OADM (optical add–drop multiplexer). Optical multiplexers are specially designed for WDM (wavelength division multiplexing) systems. The demultiplexers undo the operation which the multiplexers have done. It separates the multiplicity of wavelengths into fiber and directs them to many fibers. Optical multiplexers are used to couple two or more wavelengths into a single fiber. If a demultiplexer and a multiplexer are properly aligned and placed back-to-back, it is clear that in the area between them, two individual wavelengths exist [9] and [10]. This presents an opportunity for an enhanced function, one in which individual wavelengths could be removed and also inserted. Such a function would be called an optical wavelength add and drop multiplexer/demultiplexer or we can say optical add–drop multiplexer (OADM). The OADM selectively removes (drops) a wavelength from a multiplicity of wavelengths in a fiber, and thus from the traffic on the particular channel. It then adds in the same direction of data flow the same wavelength, but with different data content. Mohammad Syuhaimi Ab-Rahman [1] proposed a paper to do improvements in the function of OADM devices by combining these two devices in parallel. This increases the reliability of an optical network. Ahmed Nabih Zaki Rashed [2] discussed that the OADM based on DWDM (dense wavelength division multiplexing) technology is moving the telecommunications industry significantly closer to the development of optical networks. The OADM can be placed between two end terminals along any route and be substituted for an optical amplifier. Commercially available OADM allows carriers to drop and/or add up to multi channels between DWDM terminals. By deploying an OADM instead of optical amplifier, service providers can gain flexibility to distribute revenue-generating traffic and reduce costs associated with deploying end terminals at low traffic areas along a route. This paper has proposed OADM for high transmission bit rates at room temperature for best performance efficiency. It is observed that the decreased number of transmitted channels increased the optical transmitted power. Optical Add/drop comprised many optical passive devices such as Fiber Bragg grating, interference filters, circulators and Mach–Zehnder interferometer. Although add/drop filters including those devices have good operating performances, their cost is too expensive to apply for DWDM based optical networks [5] and [6]. Mohammad Syuhaimi Ab-Rahman [3] and [8] discussed that wavelength selective add–drop filter is required for adding and dropping a particular wavelength division multiplexing channel at each subscriber's node in the WDM based optical networks. We came to our results with the help of Simulative analysis of integrated DWDM and MIMO-OFDM system with OADM was done recently for optical-OFDM system [11] and monitoring and compensation of optical telecommunication channels [12].

Different modulation formats have been compared for 4-channels of CATV transmission system. Q-value (dB) is decreased due to fiber non-linearities. The better Q-value is provided by the RZ Rectangular modulation format in channel 2. RZ Raised Cosine have high BER rate. NRZ Rectangular gives the better performance because it has high eye opening and less eye closure. This paper concluded that with decrease in wavelength there is no change in Q-value of Inserted channel 2 in OADM. NRZ Rectangular modulation format has maximum Q-value, that is 40 dB. When this channel has dropped from OADM has 25 dB Q-value. RZ soliton has maximum eye opening. Jitter value of RZ Raised Cosine is increases with increase in wavelength. Jitter remains same for other modulation formats with increase in wavelength. Q-value decreases with increase in fiber length.