Elect. & Comm. Engineering Department ECE571: Optical Fiber Communications Sheet 5: Optical Fiber Link Design Dr.-Ing. Saleh Hussin & Dr. Mohamed Assed 1. An Optical fiber communication link has the following specified components: • Laser diode source with output power of 5.1 m watts. • Coupling loss of 6 dB. • 200 Km of single mode optical fiber cable with attenuation of 0.17 dB/km. • One intermediate EDFA amplifier with 11.5 dB gain. • Splicing and connection loss equals 0.03 dB per km in average. • The photo detector sensitivity is -30 dBm. a. Compute the system gain of the optical fiber link. b. Compute the link power margin. c. Let the used laser diode has 3dB-power life time of 5 years. Check if the link budget will stay feasible after 5 years. Give reasons for your answer. 2. Given the following optical fiber communication link specifications: • Cable attenuation: 0.17 dB/km, Link length: 500 km. • Laser diode: optical output power = 7 mw, = 1.55 𝜇m, Spectral width = 1.5 nm. • Coupling and splicing losses: 1.6 dB, Optical amplifier gain: 11 dB per unit. • Photo detector sensitivity: 1.5 𝜇w. Compute the following link parameters: a. The System gain (without amplifiers) and total link losses. b. The number of optical amplifiers required to achieve system margin of 10 dB or better. c. The optical pulse spreading due to material dispersion. d. The digital transmission information bit rate for NRZ signaling. MIU / Elect. & Comm. Dep. Sheet 5 Page 1 of 4 Elect. & Comm. Engineering Department ECE571: Optical Fiber Communications Sheet 5: Optical Fiber Link Design Dr.-Ing. Saleh Hussin & Dr. Mohamed Assed 3. An optical fiber system uses a LD with = 1.2 𝜇m, ∆ = 0.4 nm and 10 dBm to transmit 155 MBits/sec over a distance of 71 km without repeaters. The optical fiber cable with is available in maximum lengths of 1 km, with attenuation and dispersion characteristics as shown in fig. 1 (a) and (b) respectively. The connector loss is 0.8 dB, a splice loss is 0.05 dB, and repair power margin is 5 dB. While the receiver sensitivity for some types of detectors is depicted in fig. 2-a, and the dispersion penalty for different bit rate options is depicted in fig. 2-b. MIU / Elect. & Comm. Dep. Sheet 5 Page 2 of 4 Elect. & Comm. Engineering Department ECE571: Optical Fiber Communications Sheet 5: Optical Fiber Link Design Dr.-Ing. Saleh Hussin & Dr. Mohamed Assed Hint: Dispersion Penalty is the required increase in input power the receiver to eliminate the degradation caused by dispersion. Analyze the above mentioned link and advice: • Which one of the illustrated detectors can be used for this link? • If a system upgrade to operation at 622 Mbits/sec is required at a later date discuss concisely the impact of this requirement on the fiber specification. 4. An STM-4 optical transmission system is to operate at a wavelength of 1550 nm over an unrepeated distance of 51 km. The transmitter available has an output power of 2 dBm, while the receiver has a sensitivity of -28 dBm. Two types of fiber with different specifications are available as shown in Table 1 below. Two connectors are to be used in the system with a loss of 0.5 dB each, while the splice loss for both fiber types is 0.05 dB maximum. Calculate the dispersion penalty associated with the use of each fiber. Prepare a power budget for each system and decide which fiber type should be used and why? 5. After a number of years of service an existing single mode fiber is upgraded to a bit rate of 622 Mb/s at 1550 nm, using a new transmitter and receiver. The fiber span is 81 km and the fiber have a loss of 0.24 dB per km at 1550 nm and a material dispersion coefficient equal to 0.007. The fiber was originally operated at 1330 nm, where the fiber loss was 0.7 dB. The fiber was installed in lengths 700 m long and the maximum splice loss was 0.05 dB. The original repair margin was 6 dB, but no repairs have been required. Two MIU / Elect. & Comm. Dep. Sheet 5 Page 3 of 4 Elect. & Comm. Engineering Department ECE571: Optical Fiber Communications Sheet 5: Optical Fiber Link Design Dr.-Ing. Saleh Hussin & Dr. Mohamed Assed connectors were used with a loss of 0.2 dB each. Two different types of transmitter are available for the upgrade. Transmitter A has an output power of +3 dBm and a spectral width of 0.35 nm. Transmitter B has an output power of +4 dBm and a spectral width of 0.47 nm. Both transmitters are capable of operating at 622 Mb/s. The receiver available for the upgrade has a worst case sensitivity of -32 dBm. Complete a power budget for the upgraded system using each of the transmitters in turn to determine which transmitter should be chosen on the basis of the highest repair margin. State all of your assumptions clearly. MIU / Elect. & Comm. Dep. Sheet 5 Page 4 of 4