Abstract: An infrared light source is disclosed that comprises a layered semiconductor active region having a semimetal region and at least one quantum-well layer. The semimetal region, formed at an interface between a GaAsSb or GalnSb layer and an InAsSb layer, provides electrons and holes to the quantum-well layer to generate infrared light at a predetermined wavelength in the range of 2-6 .mu.m. Embodiments of the invention can be formed as electrically-activated light-emitting diodes (LEDs) or lasers, and as optically-pumped lasers. Since the active region is unipolar, multiple active regions can be stacked to form a broadband or multiple-wavelength infrared light source.

Abstract: The present invention provides an optical wavelength filter, in which the light of a particular wavelength in a first linear polarization inputted from the input end of an optical waveguide formed near the surface of a substrate is transformed into a second linear polarization perpendicular to the first linear polarization by means of an elastic surface wave generated by a reed screen type electrode composed of a plurality of finger electrode portions formed on the input end side of the optical waveguide, and said plurality of finger electrode portions formed in a circular arc shape are disposed each having an angle for correcting the deflection of the propagation direction of the elastic surface wave so that the elastic surface wave converges at a desired position.