Abstract: An optical isolator comprises a Faraday rotator for non-reciprocally rotating a polarization plane of light, and two polarizers joined to both sides of the Faraday rotator. Each of the polarizers is processed into a spherical surface to form a lens for converging or diverging light passing through the polarizer to form a real image or a virtual image. The optical isolator is formed by joining the two polarizers with the Faraday rotator interposed therebetween and has a generally spherical shape as a whole. The two polarizers may be made of materials different in refractive index from each other.

Abstract: An inexpensive polarization independent optical nonreciprocal circuit which does not require a use of expensive birefringent crystals, optical branching circuits, and a phase adjustment. The optical nonreciprocal circuit is formed by at least one lens through which a light propagating between two waveguides passes; and a polarization rotation circuit for sequentially applying a nonreciprocal rotation and a reciprocal rotation to a first half of the light propagating between two waveguides, and sequentially applying a reciprocal rotation and a nonreciprocal rotation to a second half of the light propagating between two waveguides, so that the first half and the second half of a light propagating forward are set to have an identical polarization to form an even guided mode and coupled, while the first half and the second half for a light propagating backward are set to have opposite polarizations to form an odd non-guided mode and dissipated.

Abstract: There is disclosed a method of fabrication of a Josephson tunnel junction device. A surface of a base electrode of Nb or Nb compound is subjected to sputter cleaning and then to plasma oxidation in an atmosphere of a diluent gas and oxygen to form thereon an oxide layer serving as a tunnel barrier. A counter electrode is then formed on the oxide layer to provide the Josephson tunnel junction.