Abstract: An optical device includes a Faraday rotator made of a bismuth substituted rare earth iron garnet single crystal (BIG) having a Faraday rotation of 45 degrees, and permanent magnets arranged beside the Faraday rotator to define two or more areas of a single domain structure in the Faraday rotator. Adjacent areas are magnetized in opposite directions to cause the polarization planes of light beams passing through the adjacent areas to rotate in opposite directions. The optical device satisfies the relation expressed by Hs/Br/DH>&Dgr;D/2>0 where Hs (Oe) is a saturation magnetic field of the BIG, DH (cm−1) is a rate of change in magnetic field in the proximity to a boundary between the adjacent areas, Br (Gauss) is a residual flux density of the permanent magnets, and &Dgr;D is a distance between the two light beams.

Abstract: An optical device includes a Faraday rotator made of a bismuth substituted rare earth iron garnet single crystal (BIG) having a Faraday rotation of 45 degrees, and permanent magnets arranged beside the Faraday rotator to define two or more areas of a single domain structure in the Faraday rotator. Adjacent areas are magnetized in opposite directions to cause the polarization planes of light beams passing through the adjacent areas to rotate in opposite directions. The optical device satisfies the relation expressed by Hs/Br/DH>&Dgr;D/2>0 where Hs (Oe) is a saturation magnetic field of the BIG, DH (cm−1) is a rate of change in magnetic field in the proximity to a boundary between the adjacent areas, Br (Gauss) is a residual flux density of the permanent magnets, and &Dgr;D is a distance between the two light beams.

Abstract: A method of manufacturing is used to manufacture a magnet-free Faraday rotator having a square hysteresis loop, the Faraday rotator being formed of a bismuth-substituted rare earth iron garnet single crystal that has a compensation temperature in the range of 10 to 40° C. and is grown on a non-magnetic garnet substrate by a liquid phase epitaxy. The method comprising the steps of placing the bismuth-substituted rare earth iron garnet single crystal film in an environment of a temperature at least 20° C. away from the compensation temperature; and applying an external magnetic field higher than 1000 Oe to the bismuth-substituted rare earth iron garnet single crystal film so that the bismuth-substituted rare earth iron garnet single crystal film is magnetized to have a square hysteresis loop.

Abstract: A method of manufacturing is used to manufacture a magnet-free Faraday rotator having a square hysteresis loop, the Faraday rotator being formed of a bismuth-substituted rare earth iron garnet single crystal that has a compensation temperature in the range of 10 to 40° C. and is grown on a non-magnetic garnet substrate by a liquid phase epitaxy. The method comprising the steps of placing the bismuth-substituted rare earth iron garnet single crystal film in an environment of a temperature at least 20° C. away from the compensation temperature; and applying an external magnetic field higher than 1000 Oe to the bismuth-substituted rare earth iron garnet single crystal film so that the bismuth-substituted rare earth iron garnet single crystal film is magnetized to have a square hysteresis loop.

Abstract: A high-energy laser Faraday rotator is used in an optical system in which the Faraday rotator absorbs laser light energy of more than 20 mW. The Faraday rotator includes a bismuth-substituted rare-earth iron garnet single crystal film grown as a Faraday rotator by using a liquid phase epitaxial method, and non-magnetic substrate having a side surface on which the bismuth-substituted rare-earth iron garnet single crystal film is formed.

Abstract: A reflection type magneto-optic sensor includes a light path assembly, a lens, a polarizer, a bismuth-substituted rare earth iron garnet single crystal film (BIG film), a non-magnetic garnet substrate, and a mirror, all being aligned in this order along the optical axis of the lens. The light path assembly has a light-inputting path and a light-outputting path parallel to each other. The lens has a focal point, the optical axis parallel to the light-inputting path and the light-outputting path, and first and second surfaces normal to the optical axis. The light-inputting path and the light outputting path are disposed in proximity to the focal point of the lens so that light exiting the light inputting path enters the lens and is then reflected back by the mirror into the light-outputting path.

Abstract: A low magnetic saturation type bismuth-substituted rare-earth iron garnet crystal film of the invention is grown on a substrate of (111) garnet single crystal (GdCa)3(GaMgZr)5O12 by using a liquid phase epitaxial method. This single crystal has a lattice constant of 1.2497.+-.0.0002 nm and has a chemical structural formula expressed byTb.sub.3-x Bi.sub.x Fe.sub.5-y-z Ga.sub.y Al.sub.z O.sub.12wherein x has the range 1.25<.times.<1.40, y+z has the range 0.50<y+z<0.65, and z/y has the range 0.45<z/y<0.75.

Abstract: A BIG film for a Faraday rotator is provided with a first antireflection film on the front surface and a second antireflection on the back surface. The first and second antireflection films differ in material or thickness and therefore differ in color. The difference in color makes it possible to visually distinguish the front surface from the back surface. The antireflection films of different colors may be applied to a BIG film with a square hysteresis which retains its magnetic saturation after an external magnetic field has been removed.

Abstract: A Faraday rotator is formed of a bismuth-substituted iron garnet single crystal film on which an antireflection film is formed. The antireflection film includes first, second, and third layers. The first layer is a layer of silicon dioxide. The second layer is a layer of tantalum pentoxide. The third layer is a layer of silicon dioxide. The first, second, and third layers are formed in this order from the atmosphere side on the bismuth-substituted iron garnet single crystal film. The antireflection film may be formed on both of opposing surfaces of the single crystal film.

Abstract: A Faraday rotator is formed of a bismuth-substituted iron garnet single crystal film grown by a liquid phase epitaxial method. The single crystal film is represented by a formula: Tb.sub.3-x Bi.sub.x Fe.sub.5-y-z Ga.sub.y Al.sub.z O.sub.12 wherein x has the range 1.1.ltoreq.x.ltoreq.1.5, y+z has the range 0.65.ltoreq.y+z.ltoreq.1.2, and z has the range z.ltoreq.y. The bismuth-substituted rare earth single crystal film is subjected to a magnetization process where the single crystal film is magnetized by an external magnetic field so that the film has a square magnetic hysteresis loop. The external magnetic field has a magnetic field strength of 1,000 Oe or higher and is applied in a direction normal to a surface of the bismuth-substituted rare earth iron garnet single crystal film.

Abstract: A method of manufacturing a bismuth-substituted rare-earth iron garnet single crystal film used for short wavelengths, includes the steps of: manufacturing a BIG-grown substrate in an LPE furnace by the LPE method, the BIG-grown substrate having a bismuth-substituted rare-earth iron garnet single crystal film grown on one surface of a non-magnetic garnet single crystal substrate, the film having a thickness in the range of 20-100 .mu.m; spinning the BIG-grown substrate at a high speed to remove a melt adhering thereto prior to taking the BIG-grown substrate out of the LPE furnace; and cooling the BIG-grown substrate to 300.degree. C. within one minute.

Abstract: A bismuth-substituted rare earth iron garnet single crystal film is represented by a general equation Tb.sub.x Lu.sub.y Bi.sub.3-x-y Fe.sub.5-z Al.sub.z O.sub.12 (where 0.09.ltoreq.y/x.ltoreq.0.23, 1.40.ltoreq.x+y.ltoreq.1.70, 0.20.ltoreq.z.ltoreq.0.38) grown on a non-magnetic garnet substrate (CaGd).sub.3 (MgZrGa).sub.5 O.sub.12 having a lattice constant of 12.490 .ANG.-12.500 .ANG. by a liquid phase epitaxial method. The bithmus-substituted rare earth iron garnet single crystal film satisfies three conditions that (1) the Faraday effect is large, i.e., the film thickness required for the Faraday rotator at a wavelength of 1.55 .mu.m is 450 .mu.m or less, (2) the saturated magnetic field is 800 (Oe) or less, and (3) the temperature coefficient .alpha. is 0.07 deg/.degree.C. or less.

Abstract: A Faraday rotator in which a portion of a rare-earth iron garnet single crystal film is exposed to a localized magnetic field to control hysteresis. In one embodiment, the field is applied by a permanent magnet positioned on a part of the film. As a result, it is possible to fabricate Faraday effect optical switches and magneto-optical sensors using rare-earth iron garnet films having small saturated magnetic field intensities.

Abstract: A bismuth-substituted rare earth iron garnet single crystal grown on a non-magnetic substrate having a lattice constant of 12.490 .ANG.-12.510 .ANG. by the liquid phase epitaxial method, and represented by a general equation:Gd.sub.x R.sub.y Bi.sub.3-x-y Fe.sub.5-z-w Ga.sub.z Al.sub.w O.sub.12where R denotes at least one element selected from the group consisting of yttrium (Y), ytterbium (Yb) and lutetium (Lu), and x, y, z and w are numerical values in the ranges 0.50.ltoreq.y/x.ltoreq.1.35, 1.40.ltoreq.x+y.ltoreq.1.90, 0.0.ltoreq.w/z.ltoreq.0.3 and 0.7.ltoreq.z+w.ltoreq.1.25. The magneto-optic optical switch or Faraday rotator constituted by the bismuth-constituted rare iron garnet is stably operable in a temperature range of -20.degree. C. to 60.degree. C. Because of the saturated magnetic field is 160 (Oe) or less, a magnetic field application device necessary to invert the magnetic field can be miniaturized.

Abstract: A reflection type magnetooptic sensor head. The respective structural elements are aligned in the order of a light source, light inputting/outputting path, polarizer, Faraday rotator, and reflecting film. The Faraday rotator is made of a (111) bismuth-substituted iron garnet single crystal film. The Faraday rotator is positioned such that the optical axis of the light incident upon the surface of the Faraday rotator makes an angle of 10 to 70 degrees with an axis normal to the surface of the Faraday rotator. The sensor head may further include two identical rectangular prisms positioned such that the Faraday rotator is sandwiched between the slanting surfaces of the prisms.

Abstract: A reflection type magnetooptic sensor head is disclosed. The respective structural elements are aligned following a light source in the order of a light inputting/outputting path, polarizer, Faraday rotator, and reflecting mirror. The Faraday rotator is made of a (111) bismuth-substituted iron garnet single crystal film having [111] axis at an angle of 5-60 degrees with an axis normal to the film surface. The reflecting mirror is positioned such that a light incident upon the reflecting mirror is substantially normal to the surface of the reflecting mirror.

Abstract: An optical isolator comprises two birefringent plates one of which separates two light components whose planes of polarization are perpendicular to each other to make the two light components spatially separate between the two birefringent plates and pass through two separate optical paths and the other of which thereafter combines the two separate light components, two Faraday rotators disposed between the two birefringent plates and having a Faraday rotation angle of approximately 45 degrees, a polarizer disposed between the two Faraday rotators and having a predetermined polarized-light transmitting angle, and a magnetic field device for applying an external magnetic field to the two separate optical paths in the two Faraday rotators to magnetize respective regions near the two optical paths in each of the rotators in opposite magnetization directions to each other.

Abstract: A high quality small-sized polarization independent optical isolator for use in an optical fiber communication system, wherein a pair of magneto-optical elements having Faraday rotation angle of 45.+-.5 are contained in permanent magnets and arranged between a pair of birefringent crystal plates for splitting and combining an optical path of a laser light, and two polarizers arranged in parallel as being bounded on the midpoint of separated optical paths are interposed between the pair of magneto-optical elements, whereby a degree of worsening the optical isolation can be kept minimum against variations of an environmental temperature and wave length.

Abstract: This invention provides a magneto-optic garnet grown by liquid phase epitaxy on a nonmagnetic garnet substrate and having a composition of the following formula (1)Ho.sub.x Tb.sub.y Bi.sub.3-x-y Fe.sub.5 O.sub.12 (1)wherein 0.3.ltoreq.y/x.ltoreq.1.0 and x+y<3.0.According to this invention there is provided a magneto-optic garnet as a Faraday rotator for use in an optical isolator, optical circulator, etc., utilizing Faraday effect, which has a very large Faraday rotation coefficient, a small difference in lattice constant from a nonmagnetic garnet substrate, exhibits a mirror face without causing a film defect (or so-called pit), and has a small temperature dependency.