- Question 2 Total Marks 25 Marks A Few Years Ago Your Company Has Supervised A Design Of A 1550nm 4 Node Network As S 1 (537.69 KiB) Viewed 46 times
Question 2 (Total Marks: 25 marks) A few years ago, your company has supervised a design of a 1550nm 4-node network as shown in Fig. 1. Each node has the ability to send, receive and route signals. Information to be sent to Node D from Node A would have to trasverse through Node B and C. The link was to operate at 2.5 Gb/s and an optical amplifier with variable gain was available between Nodes C and D to ensure acceptable performance at Node D. The receiver sensitivity at Node D was measured to be -26 dBm for 2.5 Gb/s to maintain a bit-error-rate of 10-⁹. Within Nodes B and C, there are optical routers that are capable to route signals to different node if the network expands in the future and also optical add-drop multiplexers (OADMs) to enable signals to be dropped or added within these nodes. As an evaluation of the project, you have been assigned to do the testing. While testing the designed link, you found the following parameters on file that were able to assist with the analysis: the optical router and OADM within each node have a loss of 6 dB for all optical signals that propagate through it; the optical router and OADM within each node has an accumulated dispersion of 500 ps/nm for all optical signals that propagate through it; assume no other losses in the link apart from the losses in the Nodes that the signal propagates through and losses in the fibre links; single-mode fibre with fibre loss of 0.2 dB/km and dispersion parameter (D) of 17 ps/km.nm; total accumulated dispersion (DL (ps/nm)) that the 4-node link can handle is 5000 ps/nm; and transmission power at Node A is 0 dBm. A 0 50 km B 20 km Fig. 1 C 30 km D a. For signal transmission from Node A to Node D, calculate the minimum optical amplifier gain required to meet the specifications. (4 marks) b. Based on the current node configuration, calculate the accumulated dispersion from Node A to Node D. Is this link dispersion limited? (3 marks)
c. Over the years, the network has evolved with new nodes added and the current configuration is shown in Fig. 2: A 50 km A 30 km 50 km B 30 km F B 40 km F 20 km 40 km Fig. 2 where Node E and F have been added and now there are multiple paths for transmission from Node A to Node D. Consider a transmission from Node A to Node D via ABCD, in the event of a fibre cut between Node C and Node D, the signal will not be able to reach Node D (Fig. 3). 40 km 20 km E 40 km E 60 km с 30 km 60 km D Fibre cut Ⓒ Fig. 3 To ensure seamless transmission, Node C will re-route the signal back to Node B once it senses the fibre cut between Node C and D, so that the signal can be sent to Node D now via ABCBED. If such an event occurs, calculate the minimum optical amplifier gain between Node E and Node D to ensure the specifications are met. Here you can assume that the new Nodes E and F are exactly the same as Node B and C. (5 marks) d. Calculate the total accumulated dispersion for the signal that has been routed through ABCBED. Is the link dispersion limited? (4 marks)
e. Based on your results in part d, how much dispersion compensating fibre (DCF) in kilometres that will be needed to compensate for the dispersion if an event of fibre cut occurs between Node C and D for the transmission of signal from Nodes A to D. Here assume that you have access to DCF with D = -100 ps/km.nm and DCF loss is negligible. Also assume 100% compensation. (3 marks) f. While conducting a test on the newly-evolved network in Fig. 2, you noticed that the filtering of the OADM module in the nodes is not perfect. In conducting the test, you have used wavelength ₁ from Node A to Node C via AFC. You have also re-used the same wavelength 2₁ from Node A to Node D via ABCD. Since 2₁ from AFC will be dropped at Node C, it should not interfere with the wavelength 2₁ from Node A to D that passes via ABCD. However the performance of the signal received at Node D is not good and has degraded. From a thorough investigation, you found that the filtering process in Node C was not perfect and 10% of the signal meant to be dropped at Node C, was leaking through to Node D, causing crosstalk (as shown by the dashed line in Fig. 4). A i. ii. 50 km 30 km B 40 km 20 km 40 km Fig. 4 What kind of crosstalk will this be? E 60 km 30 km Leakage from AFC (1 marks) Calculate the optical signal-to-noise ratio (OSNR = Pave/Pcrosstalk) in dB at Node D. Assuming crosstalk is the only source of noise in the link and the gain of the optical amplifier is set to 18 dB. You can also assume the optical transmission power is 0 dBm at Node A. (5 marks)