This paper describes a simple modal filtering method for one-dimensional structures using a two -mode optical fiber as a distributed-parameter sensor. In comparison to the method presented in a previous paper, which employs the longitudinal spatial variation of the sensor, this method only requires placing the sensor straight along the beam. A procedure is derived for the design of modal filters for a simply-supported beam, the most typical example of a one-dimensional structure. According to this procedure, the sensor is mounted on the lower and upper surfaces of the beam along the antinodes of the desired vibration-mode. The procedure is extended to the case of a cantilevered beam and a practical mode filtering method is discussed. Finally, experimental results confirm the predictions and demonstrate efficient vibration-mode filtering.