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EECE4900/5900 Fiber Optic Communications Fall 2022 Test #1

发布时间：2022-10-06

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EECE4900/5900

Fiber Optic Communications

Fall 2022

Test #1

Problem #1 (15 pts). You are designing an optical link using an optical receiver that requires a minimum received power of -30 dBm. You are provided a laser transmitter that has an output power of 2 mW.

a) What is the maximum length of the link if the laser emits at a wavelength of 850 nm?

(8 pts)

b) If you increase the length of the link from part (a) by a factor of 10, what wavelength laser would you need to use to operate the link? (7 pts)

Problem #2 (15 pts.) An isosceles glass prism has an index of refraction of 1.5 and is immersed in oil that has an index of 1.2. A ray of light enters the prism normal to one of the equal sides.

a) Calculate the angle of the ray that escapes into the oil, 9oil , with respect to the normal of the prism hypotenuse. (10 pts)

b) What is the speed of light as it travels in the oil? (5 pts)

oil

Problem #3 (15 pts)

A multimode, step index fiber has a 25 m core radius and a core index of n1=1.48 and a cladding index of n2 = 1.46.

(a) What is the normalized frequency and the number of modes if the light source has a wavelength of 900 nm? (10 pts)

(b) Using the same fiber, what is the number of modes that would propagate in the fiber if you changed the source wavelength to 1.35 m? (5 pts)

Problem #4 (20 pts). A step index fiber accepts input light at a maximum half angle of 6.95 degrees (coming from the air) and the following parameters:

core index = 1.465

core radius = 4.4 m

(a) What is the numerical aperture of this fiber?

(b) What is the index of refraction of the cladding (calculate to 3 decimal places)

(d) If light with a wavelength 1.1 m is launched into the fiber, how many modes would propagate in the fiber?

Make sure you use at least 3 decimal places in working this problem.

Problem #5 (15 pts)

You are designing a optical link using a GeO2/SiO2 fiber. Assume the dispersion properties of the fiber are dominated by material dispersion.

(a) Your source is an LED with a spectral width of 45 nm and a center wavelength of 900 nm. What is the maximum link length if you want the pulse spread to be 400 ns or less? (8 pts)

(b) You want to use a laser that operates at a center wavelength of 1.1 m on a fiber link that is 200 km long. If the maximum pulse spreading that the system can tolerate is 40 ns what is the maximum spectral width of the laser that you choose?

Problem #6 (5 pts.) You are designing a laser that uses an AlxGa1-xAs active layer What are the Al mole fraction and bandgap that you would need to achieve lasing at a wavelength of 750 nm?

Problem 7 (15 pts). A MMF has a core radius of 16.7 m and a numerical aperture of 0.10. The source emits at a wavelength of 1.5 m. The core attenuation, is 0.2 dB/km. What is the total attenuation in dB/km for the HE22 mode if the cladding attenuation is 3.0 dB/km?