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Abstract- This paper present an investigation into the effect on the performance of an optical network based on OADM by changing different filters at the receiver side. The calculated average BER and with the help of eye diagrams analyze the response of the filter Bessel, Butterworth and chebyshev filter and compare the results of the three filters responses in OADM based environment. With the help of OADM we can used the network resources efficiently and provide protection to network and routing features for add and drop channel.
For analyzing we design a OADM based network having four nodes transmitting at 10 Gbps data rate connected with four fiber span of 10 Km long of type non linear single mode fiber with average power per channel is -9dBm.
Key Words: DWDM, OADM, OXC, SMF, Chebyshev, Butterworth and Bessel filter and DSB
As increase in bandwidth demand in the field of network due to advent of data services the use of fiber is recommended. To achieve the higher data rate to support bandwidth ravenous services network providers are moving towards a crucial milestone in the network evolution that is the optical network. Optical networks, based on the optical layer, provide propensity of higher data rate and reduced the cost of the bandwidth starving application such as the video and multimedia services and interaction etc. 
The explosive growth of new multimedia applications and services are driving the demand for bandwidth, it is growing at a rapid pace in the near future. Therefore, Dense Wavelength Division Multiplexing (DWDM) technology is developed to support tremendous bandwidth. Recently, the channel bandwidth of commercial DWDM communication systems has reached to OC-192 (10Gbps), and the total bandwidth of an optical fiber exceeds 20 Tbps. 
Optical networks like DWDM give ease to the infrastructure by providing high bandwidth without the high infrastructure cost.  Thus new implementations in the optical networks can abolish layers of equipments. For example, SDH multiplexing equipment can be avoided altogether by interfacing directly to DWDM equipment from ATM and other packet switches. 
The term "dense" WDM or DWDM, was once used to signify the use of more than eight wavelengths per fiber. Long-haul DWDM systems take standard optical signals from "clients" such as SONET/SDH network elements, IP routers, or ATM switches, and convert each signal to a distinct, precise wavelength in the 1530- to 1610 nm range. These individual wavelengths are then combined (optically multiplexed) onto a single fiber. 
In the receive direction of the system, the reverse process takes place. Individual wavelengths are filtered from the multiplexed fiber and converted back to a standard SONET/SDH optical signal to the client. The complete DWDM system typically includes modules for each client interface in addition to equipment for multistage optical combining or splitting of wavelengths, amplification, and management/control, comprising several racks of equipment.
DWDM make use of different light wavelength to transmit data. It is transparent technology which allows transmission of data, voice, video, ATM and SONET/SDH respectively over the optical channel. In today's high demanding bandwidth services can be supported by DWDM backbone through which each wavelength can operate at up to 10Gbps. 
Optical Add/Drop Multiplexer (OADM) is an important network element. In the ring architecture, OADM can be introduced to make efficient use of network capacity, network protection, wavelength routing and many more good features.  An optical add-drop multiplexer (OADM) is a device which is used in WDM systems for multiplexing and routing different channels carrying wavelength of light from a single mode fiber (SMF). This is a type of optical device or node, which is generally, used for the construction of optical networks. An OADM may be well thought-out to be a certain type of optical cross-connect.
II. SYSTEM MODEL
In the optical network, the signal riding on one of the wavelength channels may originate at one edge, in the network and leave the network at any other point. Along any particular route in the network, that wavelength may pass through several optical network elements such as OXCs and OADM  (that uses their drop function and re-inject the signal to add port to perform 'U turn' protection) .
The proposed network architecture is based on a single unidirectional fiber ring topology having data rate of 10 Gbps; it consists of four OADM nodes as shown in Fig 1 connected by fiber spans of specified length and type of the fiber (non linear single mode fiber). For simplicity we assumed that all nodes are equidistant and all four fiber spans are 10-km long. The power per channel of negative 9dBm was used at transmitters.
Each node is converting the electrical data into optical signal and transmitted to the optical link of DWDM ring. Each node is also equipped with a tunable transmitter with power normalizer and operating in multiband environment and compound receiver with capable of multiple filters; each receiver takes case of a particular data channel which owns a unique specific wavelength.
Fig. 1 Network architecture of OADM ring network
To perform full ring simulation rather than conventional point-to-point link simulation we use Time Delay block to connect signal from the last node back to the first node and then use Multiple Iterations mode of simulations. This way we can provide steady-state solution for ring simulation.
Nodes can simultaneously receive data from any wavelengths (or receivers). Channels can works independently without mutual interference to each other. In the network architecture, each node has the ability to access any wavelength of each data channel. Logically, the network can be treated as a multi-ring network as shown in Fig. 2.
Each node is consisting of transmitter and compound receiver with capability of different filter and working in multiband environment. The random data block generate the pseudo random bits which are change into electrical signals and then converted into 1550 nm optical signal to be transmitted as shown in Fig 3. The optical multiplexer combines the add signal from the current node and the data arriving from the other neighboring downstream node. In each node optical power normilizer is use for optical signal power by attenuating the input optical signal(s) to the specified average output power level.
Fig. 2 Logical OADM Ring Network
Each node is an OADM in which the switching of the signal performed between the signals arriving from the upstream node to the active node signal and then multiplexed by using and multi band multiplexer. Pre and post amplifiers are use to sustain the signal power to the required level of receiver sensitivity. The modulation is used in this research is Mach zehnder and Manchester The figure 3 shows the individual node internal architecture.
Fig. 3 Node diagram of OADM
III. SIMULATION RESULTS
The simulation is done by some parameters which are defined on transmitter and receiver as shown in the table 2 and 3 respectively. In the simulation we have compared the results of different filters (Bessel, Butterworth and Chebyshev Filters and ideal).
The eye diagram is a useful tool for the qualitative analysis of signal used in network. When screening parametric performance of any network, eye diagrams are an observant way. If done correctly, an eye should show every possible pattern combination overlaid one on top of the other. With all combinations in one place, it becomes easy to see when rise times are too slow, when overshoot is present, or when the eye is being closed due to jitter and this can be seen in the Fig. 6, 7, 8 and 9.
Fig 4 and 5 shows the baseband electrical signal generated at the transmitter and receiver respectively showing the double side band signal, power (dBm) as a function of frequency ranging from 20 dBm to -120 dBm at transmitter and ranging from 0 dBm to -180 dBm at the receiver.
Fig.4 Baseband electrical signal spectrum at transmitter
Fig. 5 Baseband electrical signal spectrum at receiver
Table 1 describes the observed value of parameter for BER test at the receiver side.
Table 1 BER TEST
The total average power at the transmitter is -22.99 dBm and all other observed parametric values are given below in table 2.
Table 2 TRANSMITTER PARAMETRIC VALUES
Source ID 1
Source ID 2
Source ID 3
Source ID 4
Peak noise density dBm/Hz
Bit rate (bps)
Start time (s)
Voltage Avg. V
Avg. noise std. dev (V)
Table 3 RECEIVER PARAMETRIC VALUES
Source ID 2
Average Power (dBm)
Peak noise density (dBm/Hz)
Bit rate (bps)
Start time (s)
Average Voltage (V)
Avg. noise std. dev. (V)
Table 3 describes the observed value at the receiver after dropping one of four wavelengths at the receiver.
Fig. 6 Eye diagram Bessel filter including noise and phase error
Fig. 7 Eye diagram Butterworth filter including jitter and distortion at the bottom
Slope indicate timing error
Amount of distortion
Signal Excursion or Wasted power
Fig. 8 Eye diagram using Chebyshev filter
Fig. 9 Eye diagram using ideal filter
At the receiver eye diagram is used to analyze the behavior and quality of the received electrical signal. An eye diagram is used to study the quality of digital signal waveforms; especially after their passage through communication channels that cause inter symbol interference (ISI). With the help of eye diagram we can measure the rise times, fall times, jitter at the middle of the crossing point of the eye as displayed in fig. 6, 7, 8 and 9 by using Bessel, Butterworth and chebyshev filter.
After analyzing the response of the three filters with the ideal filter the chebyshev filter is more accurate towards the ideal filter response. Because the slope of the eye diagram is smaller in chebyshev as compare to Butterworth and Bessel filter, the amount of distortion is also less than the other three filters response and Timing error: Misalignment of rise and fall times (jitter) is less by using chebyshev filter.
The eye diagram also describes the randomization of the binary bit pattern and from the entire eye diagram; we can say that at the transmitter the binary bit pattern is totally randomized. The horizontal band represents the amount of signal variation. This variation is directly related to the SNR of the signal. In all three filter eye diagram the smaller band is of chebyshev filter which means by using Chebyshev we can achieve large SNR.
The slope of eye diagram determines how sensitive the signal is to timing error. A smaller slope allows eye to be opened more and hence less sensitivity to timing errors which is achieve by the chebyshev filter. The width of the crossover represents the amount of the jitter present in the signal. Smaller is better as achieve by chebyshev filter.
This paper discovers few conclusion of OADM based optical network. The basic idea of the paper is to analyze the performance of an OADM based network through Mach Zehnder modulation and by using three different types of filters and compare those to ideal filter response.
So I concluded that the chebyshev filter is best among the Bessel and Butterworth filter in terms of SNR, Misalignments of rise and fall time (Jitter or width of cross over), exhausted power, timing error and quality of signal under interference and noise.
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