obj = SFG(deff)
  obj = SFG(deff, Name, Value)
 
  Creates a process representing Sum Frequency Generation
 
  deff is the value of effective nonlinear coefficient in [m/V]
  most often the scalar value of deff is used. It is, however,
  possible to use a frequency dependent, and also direction
  dependent, deff.
  For the later case if:
     A = CEnvelope(...)
     vAF = A.realAF();
     vKx = A.realKX();
     vKy = A.realKY();  
  or
     vKr = A.realKR();
 
  one a matrix deff with size(deff) equal to:
  [length(vAF, length(vKX), 
 
 
  deff can be a scalar, a vector or a matrix.
 
  of frequency dependent values
  in such a case size(deff) should be [N, 1], where N is the
  number of frequencies and:
    A = CEnvelope(...);
    vAF = A.realAF();  % vAF are the angular frequences.
    
  Options:
   No options at this moment.