Thus if the EM wave travelling in a tapered waveguide is bounced between two reflectors, with a large velocity difference at the reflector surfaces, the force difference will give a resultant thrust to the waveguide linking the two reflectors.
er... I'm not too hot in relativistic physics, but as far as I understand it light ALWAYS has to travel at the speed of light relative to any reference frame. So where do they take the velocity difference from? The only way is to put the two reflectors in two different frames... i.e. one of them NOT on the ship.