So, we are ready to make a photonic NOT circuit. We have the beam- 
    combining optics, namely the two holograms that produce images that 
    change depending on the binary states of the input beams shinning on 
    the two input holograms. 

       To make a photonic NOT circuit, we need only one more item...a 
    fringe component separating mask.  In very complex devices the masks 
    will be calculated using the various development programs just as we 
    have created the holograms. 

      Masks, in most cases, will also be photographs, just as the holo- 
    grams are merely photographs.  But this case is an easy one. Since 
    the calculated image we started with is simply a point, the mask  
    need to make a NOT circuit is simply a completely opaque mask with a 
    single hole in it right at the focus.