Problems #1

(1) A point source with a wavelength of 810nm and a power of 0dBm is placed 1mm from the end face of a cleaved multimode optical fiber with $n_1$=1.46, $n_2=1.455$. The core diameter of the fiber is 50$\mu$m. Use a simple model to estimate the maximum amount of power that will be guided in the fiber. (2) For the fiber described in (1) use a simple ray model to estimate the number of modes that can propagate in the fiber at 810nm.

(3) For the $m=1$ mode in the fiber in question (1) what is the magnitude of the Goos-Haenchen shift?

(4) A light emitting diode has an angular emission pattern $I(\theta)=\cos^3(\theta)$, for $0\le\theta\le\pi/2$. The axial direction is $\theta$=0. This LED is placed 100$\mu$m from the end face of the fiber in question (1). If the total LED power is 0.1dBm, what amount of power is guided in the fiber? Assume that the emitting area of the LED is negligible compared to the other dimensions in the problem.

(5) Explain briefly the terms: 10-base T, 100-base T, SONET, FDDI, DWDM

(6) A laser operating at 810nm and being modulated at 100Mb/s in an RZ format enters the fiber in problem (1). Either analytically or by numerical simulation determine the maximum fiber length that could be used before serious communication errors occur. [Hint: this is a modal dispersion issue.]