S-108.3110 OPTICAL COMMUNICATIONS
Home exercise #3: Fiber-Optic Components 21.11.2009
exercise 1. Finesse of a Fabry-Pérot filter.
We consider a Fabry-Pérot filter with a free-spectral range of 1000 GHz.
a) What is the length of the Fabry-Pérot cavity? Assume a refractive index of 1.5 for the cavity
material.
b) The Fabry-Pérot filer is used to filter individual channels from a WDM system. The spectral
bandwidth of the channels is equal to 1 GHz. What should be the minimum Finesse of the FabryPérot in order to select exactly all the spectral content of the channels? What is the
corresponding mirrors reflectivity in the filter? Assume identical mirrors.
exercise 2.
Two 50/50 couplers are used in cascade as shown in the figure below. Calculate the power exiting
ports OUT1 and OUT2 as a function of input powers P1 and P2 at input ports 1 and 2, respectively.
exercise 3. Add/drop resonator.
We consider a ring resonator add/drop made from 3dB (50/50) couplers. What should the length of
the ring resonator so that a wavelength of 1.5 m is dropped (ie: reflected) by the resonator.
Assume that the ring resonator is made of fiber with refractive index n=1.5.