Wavelength Division Multiplexing summary
- 1. Four-Channel Wavelength Division Multiplexing using Optisystem CE 1.1 Introduction This Project is entitled “Four-Channel Wavelength Division Multiplexing using Optisystem”. This was an assignment project for the course of Network Design Exercise (ELE5NDE) of masters in Telecommunication and network engineering at LaTrobe University, Bundoora, Victoria, Australia. The duration of this project was 2 months which was carried from 5th of April to 30th of May 2014 and was completed exactly within the specified time. This was a simulation project done by using software called Optisystem by Optiwave in the lab environment of Beth Gleeson building at Bundoora Campus. This project was carried out by a team of two, including me and a fellow friend Abhimanyu Pandey. I contributed mostly to the research and theory section of the project. CE 1.2 Background The Optical Fiber communication technology has many advantages over electrical modes of communication where reliability for a long distance transmission with low BER(Bit Error Rate) (BER) is significant. I present the technique which incorporates single mode fiber to send data using 4 channel WDM (Wavelength division multiplexing) and De multiplexing at a distance of 120 kilometers with the speed of 10 Giga bits per second (Gbps). The Design of the 4 Channel WDM was carried out using three modules fundamentally such as Transmitter, Channel and Receiver as such of any other communication system. The optical transmitter converts electrical signals into optical signal which is then transmitted through the fiber, and eventually to the receiver that has several units to process the distorted optical signals back to electrical signals. The general outlook can be as shown below: CE 1.2.1: Major objective of this project is to obtain BER of 10-6 or less for the given specification. We also had to comment on inter-relation between the optical fiber parameters such as amplifier gain, optical power vs Bit error rate and Dispersion etc. Another objective of this project was to apply similar working principle to demonstrate 64 Channel WDM and analyze the system. CE 1.2.2: I was interested in the optical fiber channel research and optimization since the start of the project. So I basically focused on three components of channel, namely optical amplifier EDFA (Erbium Doped Fiber Amplifier), DCF (Dispersion Compensation Fiber) and properties of SMF (single mode fiber) itself. My focus area also extended to whole receiver module and some portions of transmitter module because it was the project of only two. CE 1.2.3 TRANSMITTER Optical Fiber Receiver Transmitter Optical Fiber Receiver
- 2. Four-Channel Wavelength Division Multiplexing using Optisystem Figure 1 Organizational chart There were only two members in this project but we carried out every tasks in formal basis. We conducted regular formal meetings with our tutor Mr. Karthik Kamalakannanand and shared our tasks by using decisions made in the meetings. Documentation portion were divided according to the task completed where I did the final formatting and Proof Reading. Final assessment works were project report and Individual Presentation. CE 1.2.4: My duties included channel design and receiver design. Basically Transmission line design was the most critical to the project because of 120 kms of fiber route and the challenges to design transmission parameters like amplifiers, compensation fibers and modulation techniques. Similarly, receiver module included the choice of photodetector, regenerators etc. My duties also included some simulation tasks related to channel and receiver design. CE 1.2.5: Design Selection: Dispersion for SMF = 16.75 ps/nm/km, Linear attenuation =0.2db/km, Slope for dispersion=0.075 ps/nm2 /km and reference wavelength=1550nm. DCF Dispersion=-90ps/nm/km and attenuation =0.2dB/km CE 1.3Personal Engineering Activity I completed most of the initial research activity whereas most of the preliminary simulation part was undertaken by my project partner. However, I revised and edited simulation tasks after the initial phase of the project. CE 1.3.1: I placed PRBS of order 15 and external modulated transmitter with lasers. The frequency of first laser was 193.1 THz and frequency spacing was 100GHz .I started with the transmission line design on self. The transmission line was a combination of Single Mode fiber, EDFA and Dispersion Compensation Fiber. Mr. Mohsen Goodarzi Mahesh Tripathy Abhimanyu Pandey Mr. Karthik Kamalakannanand
- 3. Four-Channel Wavelength Division Multiplexing using Optisystem Figure 2Channel configuration for the design Another portion was a receiver module design which consisted of Photo-detector PIN, a low pass Bessel Filter and a 3R generator component. I considered a Bessel filter for it’s linearity with flat group delay and better shaping which ensures the separation of channels in frequency domain and suppresses the linear cross-talk. Figure 3Receiver module I used the viewing tool of optisystem software and its eye diagram to track and rectify my immediate output results from the simulation. Another tool was WDM analyzer which I used to observe the presence of carriers and Signal to noise ratio. CE 1.3.2 I made two loops of 60 kms each as in figure 2 to design complete length of 120 kms. I needed DCF to compensate the chromatic or material dispersion caused by the use of SMF. This is due to the fact that the glass we used varies slightly with the wavelength. So for every 50 kms length of SMF, I used 10 km of DCF which I based on arithmetic calculation for dispersion calculation. Example, Dispersion caused by Fiber = 16.75*50 = 837.5 ps/nm whereas Dispersion cancellation by DCF = -90*10 = -900 ps/nm which is seemingly sufficient in the cancelation process. I used negative sign to show the dispersion being cancelled. Practically, DCF could be implemented by varying the temperature for dispersion tuning or using virtually imaged phased arrays. But for simulation, I got direct access to DCF by just changing the parameters. Another important factor was optical power amplifier for which I used EDFA with two gain values i.e. 10db and 5db. EDFA’s amplifies optical signal by using pump lasers and uses the phenomena
- 4. Four-Channel Wavelength Division Multiplexing using Optisystem of stimulated emission. I used EDFA to compensate for large distance transmission losses. As shown in the design parameter, the attenuation of SMF=0.2dB/km which makes it 0.2*50=10 dB loss for 1st 50 km segment which is why I chose EDFA with the gain of 10dB after this segment. I also used an EDFA with gain of 5 dB gain to amplify optical signal attenuated by DCF at next 10 km of length. This is a part of first-order linear dispersion cancellation whereas the second- order dispersion is not fully compensated. The second-order dispersion occurs at certain wavelengths other than the center wavelength which is not fully covered by my cancellation technique, especially while I did the 64 channel simulation. The next portion of my project was an extension to the 64 channel WDM. WDM Multiplexer that I used in my design was for the 64 input ports and center frequency kept as 196.3 THz for the internal filters which are equally spaced. The Bandwidth used was 6.4 THz which could be accounted as 64 * 100GHz (equally spaced channels). Figure 4Block diagram of 64 channel WDM Our System starting wavelength λ1 was 1552 nm and has a spacing of 0.8nm for 64 channels. At the Receiver I deployed BER analyzer to the desired WDM output ports of De-multiplexer which was my ultimate output tester for the application. This calculates the system performance giving the useful output parameters such as BER, Q-Factor, threshold and Eye aperture of a system. CE 1.3.3: This was a simulation task which is why the output BER were not consistent and were variable at all instances. The best value was obtained in the order of 10-8 and at an instance, I performed the simulation for whole length of 120 km for 4 channel WDM and got the following outputs: Channels(THz) BER 193.1 6.015*10-6 193.2 4.45*10-6 193.3 4.6*10-6 193.4 9.8*10-9
- 5. Four-Channel Wavelength Division Multiplexing using Optisystem I observed BER vs. laser power relation and did some changes in laser power level. The value of BER was equal to 6.01509*10-7 when the input laser power was equal to 15mw. Similarly the value of BER was equal to 4.814*10-7 when the laser input power was 5 mw. I noted that there is a saturation level which is reached in this case. I increased power by 10 mW but didn’t find any remarkable increase in the order of BER. CE 1.3.4: At an initial stage, I thoroughly used the simulation software to see what could be done. I gave the initial parameters for the transmitter design like optical pulse generator and optical modulator then my friend started simulation for it with other necessary startup blocks such as multiplexers and selection of precise blocks. Meanwhile I started to search necessary materials to design optical fiber channel then, we together sat for simulation whereby he was already much familiar with the simulation tool. So it started with step by step design and then I continued in a similar manner to design the receiver module. We followed up with our lecturer whenever we found our objective vague. Final results were optimized by both of us sitting for hours to get the things just right. CE 1.4 Summary I got the comprehensive idea of working mechanism of WDM and optical fiber infrastructures. This not only gave me idea about the transmission and reception process but also enriched my knowledge on optical fiber and its contribution on management of high bandwidth data which is an evolving substance of telecommunication industry today. This project met its goal on analyzing properties of WDM when used for a long distance. I contributed 50% to this project, yet I am aware on each and every aspects of it because I was enthusiastically involved throughout its time period.