The metering servovalve includes a valve body, a shutter, and an electromagnet, and is housed inside a casing of the injector. The flat panel display comprises a pixel array portion where a plurality of pixels are arranged, and a driving circuit portion for driving the pixels of the pixel array portion. Fiber birefringence encountered in propagation between a transmitter and a receiver rotates the great circle on the Poincar\xe9 sphere that represents the polarization bases used for modulation. Further provided is a method of stimulating the vagus nerve of a subject.