A He-Ne laser beam is guided through an optical fiber, with an audio modulating electric field directly applied to a small part of a relatively long optical fiber. The photodetected lightwaves are modulated by the modulating electric field. The effect of varying the length of the interaction region between the lightwaves inside the fiber and the applied electric field on the observed photodetected signal is investigated. The effect of varying the modulating electric field strength and frequency on the observed nonlinear interaction between the lightwaves and the applied modulating field is also investigated. Results and discussion of the observed effects are presented.