1. A detector is placed on a screen onto which a bright red spot is observed. In calculation of the numerical aperture of the fiber, the diameter of the bright spot (W) and the distance of the screen from the fiber facet (L) have to be measured. The diameter was determined as 28mm and the distance between the screen and the fiber facet determined to be 100mm.

Calculate the numerical aperture of the fiber

2. A fiber is put into a fiber scrambler and the adjustment knob shifted until optical light is leaking out of the fiber. Numerous changes in pattern of the bright spot are observed on the screen until a stable pattern is established. The optical parameters can then be used to measure the fiber attenuation. The final power (P_f) measured by the power meter is 12.2microvolts. Once the final power has been recorded, the fiber is cut at about one meter after the fiber scrambler and plugged into the detector to measure the initial power (P_i) of the fiber. The difference between the initial and final power is used to calculate the attenuation of the fiber. The initial power is determined to be 1.09millivolts. The power meter records environmental noise of about 7microvolts. To obtain the initial and final powers, the environmental noise has to be subtracted. Calculate the optical fibre attenuation at 632nm.