Question 6 (Total Marks: 10 marks) A group of new optical engineers is designing a 4-channel WDM network operating in th

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Question 6 Total Marks 10 Marks A Group Of New Optical Engineers Is Designing A 4 Channel Wdm Network Operating In Th 1 (214.11 KiB) Viewed 56 times

Question 6 (Total Marks: 10 marks) A group of new optical engineers is designing a 4-channel WDM network operating in the 1550 nm window as a training task during their induction. During their design, they have encountered a number of issues that puzzled them. As their line manager, they have approached you for advice and listed below are the issues they have encountered. a. When testing a DFB laser which will be used as one of the WDM transmitters (without any data modulation), they found that the optical spectrum and power of the laser was stable when it was biased above threshold. When biased at the recommended bias current, the optical power was measured at 10 dBm. However, when the DFB laser (biased at the recommended bias current) was connected to a 500 m single- mode fibre, the optical spectrum measured after the fibre was no longer stable, i.e. its wavelength fluctuates with time. What do you think has caused this scenario? How would you remove this instability? (3 marks) b. To further investigate the phenomenon seen in part a, you suggest that they use an optical circulator in conjunction with the DFB laser and fibre to observe any light being reflected back to the transmitter. Taking up your suggestion, the optical engineers measured the optical spectrum of the backreflected light as shown in Fig. 8. Explain what has caused this backreflection. How would you advise the engineers to overcome this reflection? (4 marks) C. Power (dBm) Optical spectrum 1550 11.1 GHz Fig. 8 Wavelength (nm) After solving the issues in part a and b, the optical engineers are confident to put together the 4-channel WDM network. The 4 WDM channels are located 100 GHz apart. The optical engineers have decided to lower each transmitter power to 0 dBm to minimise the impact of fibre nonlinearity. Based on their chosen parameters, do you think their 4-channel WDM network will be limited by stimulated Raman scattering (SRS)? Please explain your answer. (3 marks)