PURPOSE: To stabilize capacity, by constituting the title analyser of a refractive index distribution type optical waveguide and a piezoelectric substrate having a refractive index lower than that of said waveguide.

CONSTITUTION: A slab lens having refractive index distribution only in an x-axis direction is laminated to a piezoelectric substrate 1 and the thickness thereof is reduced to a wavelength of a surface elastic wave 13 or less by cutting and grinding to form a waveguide 15. By properly setting a refractive index and a length etc., an input terminal 16 and an output terminal 17 can be mutually brought to image forming positional relation. The beam emitted from semiconductive laser 3 and guided is condensed to the point A at the terminal 17 when no high frequency electric signal is applied to a transducer (Tr)6 and the emitting region of the laser 3 is formed into an image. Tr6 is positioned at the almost middle between the terminals 16, 17 and, when a high frequency electric signal is applied to Tr6, the elastic wave 13 is excited and a part of the beam guided through the waveguide 15 is diffracted to be condensed to a point B. As mentioned above, by constituting the wave guide only by the processing of a plane without performing the cutting and grinding of a curved surface, the facilitation of manufacturing and the stabilization of capacity are attained.