Field distribution of an electromagnetic wave at the open end of a microstrip waveguide

The field distribution of the surface waves at the open end of an optical microstrip is investigated experimentally and analytically, taking diffraction effects into account. In the devices studied, six strip modes of width 20 microns propagate at 632.8 nm with attenuation of less than 1 dB/cm in an optical microstrip fabricated from a single-mode planar waveguide of graded glass, and coupling prisms are used to input and output the light. The principal maxima of the higher strip modes are shown in a photograph and found to agree to within 10-20 percent with the calculated angular positions. These results are applicable to the design of optical-fiber/microstrip couplers for integrated optics.