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EE 164 Problem Set 9

EE 164 Problem Set 9 - demulitiplexer with inputs at 1 ...

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EE 164 Problem Set 9 Spring 2005 Problem 1: A four-port directional coupler has a 4:1 splitting ratio and an excess loss equal to 2 dB. The coupler’s directionality is 40 dB. a) What fraction of the input power goes to each of the ports? b) Compute the throughput loss and the tap loss. c) Compute the loss (in decibels) due to radiation, scattering, and absorption in the coupler. Problem 2: A laser diode illuminates a 2.5 km length of fiber. The total link loss over the 2.5 km is 4 dB. Power is reflected back toward the laser by the end of the fiber, which is cleaved so as to have a smooth, polished surface. The fiber end radiates into air. Compute the level of the reflected light power when it returns to the LD- that is how many decibels down from the emitted signal is the reflected signal? Problem 3: An ideal tapered and fused single-mode coupler is used as a two-wavelength
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Unformatted text preview: demulitiplexer with inputs at 1 λ and 2 at port 1. At wavelength 1 , the coupling coefficient has the value 2 rad/mm. This wavelength is coupled entirely to port 3. Wavelength 2 is transmitted entirely to port 2. a) Compute the interaction length. b) Compute the value of the coupling coefficient at 2 . c) Compute the value of the coupling length C L at 2 . Problem 4: In an AWG, the crosstalk is 30dB between adjacent fibers at a channel wavelength of 1550 nm. The signal power in fiber x is 0.1 mW and the signal power in fiber y is 0.01 mW. For the 1550 nm signals, compute the amount of power coupled into each of the two fibers from the others. Compute the ratio of the power in the desired signal divided by the power in the unwanted coupled signal in each fiber. Express this ratio in dB. This ratio is a measure of the quality of the desired signal....
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