Abstract: A discharge tube comprises a vessel containing rare gas; a plurality of electrodes (having a cathodic part and anodic part therein) and so arranged tandem in said vessel that a glow discharge is kept in a discharge gap between each said cathodic part and said anodic part of the preceding electrode, and that an optical path is allowed to let through each negative glow part of said glow discharge adjacent to said cathodic part; means to apply a dc voltage across every said discharge gap in series; and means to supply metal vapor to one of said glow discharge at the most low potential end of said means to apply dc voltage, whereby metal ions formed in said one of said glow discharge are carried down throughout said vessel.

Abstract: On a substrate is formed a crystalline electrooptic thin-film waveguide, on which are deposited interdigital electrodes extending in the y-direction and spaced apart from one to another in the z-direction. To the electrodes is applied a modulating signal voltage to form in the waveguide an electrostatic field which is spatially periodic in the z-direction having an intensity proportional to the modulating signal voltage and uniform in the y-direction. Coherent light is coupled into and out of the waveguide with prism couplers. As the light propagates through the waveguide in the y-direction, it suffers a spatially periodic phase variation in the z-direction. The emerging light is accordingly diffracted into orders. The crystalline waveguide is manufactured easily and the light propagates fully through the electrostatic field.