An optical isolator includes a Faraday rotator including a trivalent ion exchange TAG (terbium-aluminum garnet), and arranged around the Faraday rotator, a central hollow magnet and a first and a second hollow magnet units arranged to sandwich the central hollow magnet in an optical axis direction. A magnetic flux density B [T] in the Faraday rotator and an optical path length L [mm] where the Faraday rotator is arranged satisfy

0<B  (1) and

14.0≤L≤24.0  (2).

The optical isolator, compared with a conventional Faraday rotator such as a terbium-gallium garnet (TGG) crystal, contributes to reduction of a thermal lensing effect, being a pending problem, in a high-output fiber laser.

A magnetic field sensor element 30 has a first polarization maintaining fiber 31 separating the linearly polarized light into a first linearly polarized wave propagated along the first slow axis and a second linearly polarized wave propagated along the first phase advance axis faster than the first linearly polarized wave, and propagating the first linearly polarized wave and the second linearly polarized wave, a second polarization maintaining fiber 32 having a second slow axis and a second phase advance axis, and connected to the first polarization maintaining fiber so that the second phase advance axis and the second slow axis are inclined 45 degrees with respect to the first phase advance axis and the first slow axis, a Faraday rotator 33 optically connected to the second polarization maintaining fiber, and shifting a phase of circularly polarized light emitted from the second polarization maintaining fiber in response to magnetic field at which the magnetic field sensor element is disposed, and a mirror element 34 connected to the Faraday rotator, and generating the return light.

A magnetic field sensor element 30 has a first polarization maintaining fiber 31 separating the linearly polarized light into a first linearly polarized wave propagated along the first slow axis and a second linearly polarized wave propagated along the first phase advance axis faster than the first linearly polarized wave, and propagating the first linearly polarized wave and the second linearly polarized wave, a second polarization maintaining fiber 32 having a second slow axis and a second phase advance axis, and connected to the first polarization maintaining fiber so that the second phase advance axis and the second slow axis are inclined 45 degrees with respect to the first phase advance axis and the first slow axis, a Faraday rotator 33 optically connected to the second polarization maintaining fiber, and shifting a phase of circularly polarized light emitted from the second polarization maintaining fiber in response to magnetic field at which the magnetic field sensor element is disposed, and a mirror element 34 connected to the Faraday rotator, and generating the return light.

The present invention discloses an encoding apparatus, including: a polarization splitter-rotator PSR, a polarization rotation structure, and a modulator, where the PSR is configured to receive an input signal light, split the input signal light into two parts whose polarization modes are the same, and send the two parts to the polarization rotation structure and the modulator respectively; the polarization rotation structure has functions of rotating, by 180 degrees, a polarization direction of an optical signal entering the polarization rotation structure from one end, and keeping a polarization direction of an optical signal entering the polarization rotation structure from the other end unchanged; the modulator is configured to modulate a light input to the modulator; and the PSR is further configured to receive signal lights sent by the polarization rotation structure and the modulator, combine the two signal lights to send the output signal light.

An optical element including a plate-shaped substrate with a light-entrance surface and a light-exit surface, a multiplicity of imaging elements formed on the light-exit surface and a multiplicity of diaphragms formed on the light-entrance surface. Each diaphragm includes a transparent geometric region in an opaque region. The optical element can be switched between two operating modes B1 and B2 such that some of the imaging elements change their focal length between values f1 and f2 and/or, some of the diaphragms change their aperture width and/or their position. Exactly one diaphragm is associated with each imaging element in mode B1 so that light passing through the diaphragm is imaged or collimated by the associated imaging element. Consequently, light arriving in the optical element through the diaphragms and then through the light-entrance surface has, after passing through the associated imaging elements in the two operating modes B1 and B2, different propagation angles.

In a bismuth-substituted rare earth iron garnet single crystal film production method, the bismuth-substituted rare earth iron garnet single crystal film expressed by the composition formula (Ln.sub.3-aBi.sub.a)(Fe.sub.5-bA.sub.b)O.sub.12 is grown using a substrate of paramagnetic garnet with a lattice constant of Ls. The method includes forming a buffer layer with an average lattice constant of Lb (where Lb > Ls) on the surface of the substrate with a thickness of 5 to 30 .Math.m, and growing a target bismuth-substituted rare earth iron garnet crystal film with an average lattice constant of Lf (where Lf > Lb) with a thickness of 100 .Math.m or more overlaid on the buffer layer. The rate of lattice constant change in the buffer layer is steeper than the rate of lattice constant change in the bismuth-substituted rare earth iron garnet crystal film.

An optical isolator device with minimized polarization mode dispersion includes a first polarization splitter/combiner, a non-reciprocal polarization rotator and a second polarization splitter/combiner. Only forward propagation of light is allowed to propagate in the device, with backward optical signal blocked due to non-reciprocal polarization rotation. The optical paths of o-ray and e-ray are arranged to achieve equal optical path lengths, which makes polarization mode dispersion minimal to nonexistent. When symmetrically configured, both polarization mode dispersion (PMD) and polarization dependent loss (PDL) become zero in principle.

A small integrated free space circulator, comprising a first polarizing beam splitter (1), a half-wave plate (2), a Faraday rotating plate (3), a beam splitter (4), a quarter-wave plate (5), and a pair of reflective plates (6, 7), wherein the first polarizing beam splitter (1), the half-wave plate (2), the Faraday rotating plate (3), and the beam splitter (4) are sequentially arranged, the quarter-wave plate (5) and the reflective plate (6) are sequentially attached to a side surface of the first polarizing beam splitter (1) adjacent to the half-wave plate (2), and the reflective plate (7) is arranged on a side surface of the beam splitter (4, 8) adjacent to or opposite to the Faraday rotating plate (3); when the reflective plate (7) is arranged on the side surface of the beam splitter (8) opposite to the Faraday rotating plate (3), the reflective plate (7) partially covers the side surface of the beam splitter (8) opposite to the Faraday rotating plate (3). By means of an organic combination of optical elements such as the polarizing beam splitters (1, 4), the wave plates (2, 5), the Faraday rotating plate (3), the reflectors (6, 7), and the birefringent crystal (8), the device has advantages such as small volume, high integration, easy production, and low cost, and has a good market prospect.

An optical device includes an optical amplifier that optically amplifies incident light, a first isolator that is arranged on an input stage of the optical amplifier and inputs the incident light to the optical amplifier, and a second isolator that is arranged on an output stage of the optical amplifier and receives input of incident light that has been optically amplified by the optical amplifier. The first isolator inputs, to the optical amplifier, first linearly-polarized incident light that is converted from randomly-polarized incident light and that has been transmitted. The second isolator, when reflected light of the first linearly-polarized incident light that has been optically amplified by the optical amplifier is input from a reverse direction, converts reflected light of the first linearly-polarized incident light to reflected light of second linearly-polarized light that is orthogonal to the reflected light of the first linearly-polarized incident light.

A magnetic erasing device including a magnet that includes an S pole and an N pole extending along an axial direction of the magnet, and a rotation mechanism for rotating the magnet in a housing around an axis of the magnet, wherein lines of magnetic force generated around the axis of the magnet during rotation of the magnet are designed to be applied to magnetic particles in the microcapsules to erase a visible image on a magnetic panel when the axis of the magnet is spaced from a surface of the magnetic panel by a predetermined distance.