Hwk3:

This hwk is due on Thursday March 20th at the start of class.

(1) The purpose of this hwk is to help you understand how to choose
    the parameter that controls the step size used in the fiber propagation
    algorithm.

    Your simulations should be for the Tyco system modeled in MyApp.cc. 

    The hwk will require you to both adjust the parameters in the input
    parameter files, and to add some lines to the source code in MyApp.cc
    to output additional data. 

    Since you are going to be modeling a WDM system, use the WALK_OFF
    step-size selection criterion in the OptFiberLocalError class
    In this case the parameter that controls the step size is called
    WalkOffParameter.

(2) Choose a 50 GHz channel spacing. You are to
    look at the performance in the center channel. 

    First work out what the optimal FWHM of the demultiplexing
    optical filter should be in the back-to-back case. The idea
    is to maximize the eye opening. 

(3) Second, work out the minimum number of channels you need in the simulation
    so that the electrical eye diagram at the receiver does not visibly 
    change when you add more channels. 

    To do so you will need to propagate the signal through the system.
    What value should you choose for WalkOffParameter? You should
    pick a reasonable value and check that for a given number of channels
    the electrical eye diagram at the receiver does not visibly 
    change when you halve the value of WalkOffParameter.
    If it does change you will need to decrease WalkOffParameter!

(4) For the minimum number of channels you found in (3) 
    work out the smallest qtPoints you can use.

(5) For this part, use the values of qtPoints, NumChanns,
    and the demux filter FWHM you found above. 

    Your task is to study how the electrical eye diagram at the receiver
    changes as you change WalkOffParameter. To get a range of values
    of WalkOffParameter use the value you used in (3) and repeatedly
    double WalkOffParameter making the step sizes bigger and also
    repeatedly halve WalkOffParameter making the step sizes smaller.

    Your aim is to see that as WalkOffParameter (and the step sizes)
    get smaller there is some critical value of WalkOffParameter for which
    the eye diagrams no longer visibly change when you halve 
    WalkOffParameter. What is this critical value of WalkOffParameter?

(6) In addition to looking at the electrical eye diagram you should also
    look at the real and imaginary parts of the optically filtered 
    signal immediately prior to the receiver. What is the critical
    value of WalkOffParameter in this case? Why might it be different
    from the critical value value you found in (5) above?