Improved method of loss measurement for optical waveguides by use of a rectangular glass probe

The use of a glass-plate probe of rectangular shape is proposed for the measurement of transmission loss in optical waveguides. The light-collecting window is of a thin, rectangular shape and is perpendicular to the light streak, while the conventional fiberglass probe has a small circular face. This transversely elongated form results in a great improvement of mechanical tolerance for the probe movement in the vertical as well as in the transverse direction. A theoretical investigation also presents a reasonable agreement with the experiments.