Provided is a glass material having a high light transmittance in a short wavelength range and easily producible. A glass material contains, in terms of % by mole, 5 to less than 30% Pr.sub.2O.sub.3 and 0.1 to 95% B.sub.2O.sub.3.

An optical isolator has optical fibers arranged on a single side. The optical isolator includes an input optical fiber, an output optical fiber, an input splitting/combining device, an output splitting/combining device, an input optical rotation device, an output optical rotation device, a lens, a Faraday rotator, and a reflector. The input optical fiber and the output optical fiber are on a same side of each of the lens, the Faraday rotator, and the reflector. The optical isolator with input and output optical fibers arranged on a single side only needs to use one lens. The input and output splitting/combining devices are fixed on an end surfaces of input/output optical fibers, respectively.

The present disclosure relates to magnetization-free Faraday rotator systems, apparatuses, and related methods. One such system comprises a Faraday rotator device comprising a magneto-optical composite material having first and second magnetic component materials in a periodic or uniform pattern in an X-Y plane, wherein the first and second magnetic component materials are magnetized along a Z-axis in opposite directions and the Faraday rotator device produces nonzero magnetic Faraday rotation for the electromagnetic wave propagating in a Z-axis direction in the absence of an external bias magnetic field.

A paramagnetic garnet-type transparent ceramic characterized by being a sintered body of a terbium-containing composite oxide represented by formula (1) in which the linear transmittance at a wavelength of 1,064 nm at an optical path length of 15 mm is 83% or higher.
(Tb.sub.1-x-ySc.sub.xCe.sub.y).sub.3(Al.sub.1-zSc.sub.z).sub.5O.sub.12  (1)
(In the formula, 0<x<0.08, 0≤y≤0.01, 0.004<z<0.16.)

Embodiments of synthetic garnet materials having advantageous properties, especially for below resonance frequency applications, are disclosed herein. In particular, embodiments of the synthetic garnet materials can have high Curie temperatures and dielectric constants while maintaining low magnetization. These materials can be incorporated into isolators and circulators, such as for use in telecommunication base stations.

The present disclosure provides an optical circulator. The optical circulator includes a first integrated module, a second integrated module and a third integrated module which are sequentially connected from front to rear. The first integrated module includes a mating shell, an optical fiber ferrule received in the mating shell and a first birefringence crystal attached to a rear surface of the optical fiber ferrule; the second integrated module comprises a first tube fixed behind the mating shell, a magnetic ring received in the first tube, a Wollaston prism fixed in the magnetic ring, two Faraday rotators respectively provided to both sides of the Wollaston prism, and two collimating lenses respectively provided to both sides of the two Faraday rotators. The third integrated module includes a second tube fixed behind the first tube, a dual fiber pigtail received in the second tube, and a second birefringence crystal attached to a front surface of the dual fiber pigtail. The above-mentioned optical circulator is small in volume and convenient to manufacture.

A bismuth-substituted rare earth iron garnet single crystal suitable for Faraday rotators and optical isolators with reduced insertion loss due to suppressed valence fluctuation of Fe ions is provided. The bismuth-substituted rare earth iron garnet single crystal of the present invention is characterized by the composition formula (Gd.sub.aLn.sub.bBi.sub.cMg.sub.3−(a+b+c))(Fe.sub.dGa.sub.eTi.sub.fPt.sub.5−(d+e+f))O.sub.12. In the composition formula above, 0.02≤f≤0.05, 0.02≤{3−(a+b+c)}≤0.08, and −0.01≤{3−(a+b+c)}−{f+5−(d+e+f)}≤0.01. Ln is a rare earth element and may be selected from Eu, Dy, Gd, Ho, Tm, Yb, Lu, and Y.

Provided is a magnetic circuit which, with the use in an optical isolator, is less likely to cause the polarizer to be damaged even with higher laser output power. A magnetic circuit 1 includes first to third magnets 11 to 13 each provided with a through hole allowing light to pass through and is composed of the first to third magnets 11 to 13 arranged coaxially in this order in a front-to-rear direction, wherein one of the first and third magnets 11 and 13 is magnetized in a direction Y perpendicular to a direction X of an optical axis to have a north pole located toward the through hole 2, the other of the first and third magnets 11 and 13 is magnetized in a direction Y perpendicular to the direction X of the optical axis to have a south pole located toward the through hole 2, the second magnet 12 is magnetized in a direction parallel to the direction X of the optical axis to have a north pole located toward the one of the first and third magnets 11 and 13 having the north pole located toward the through hole 2, and a length L1 of the first magnet 11 along the direction X of the optical axis is different from a length L3 of the third magnet 13 along the direction X of the optical axis.

Nonreciprocal optical transmission devices and optical apparatuses including the nonreciprocal optical transmission devices are provided. A nonreciprocal optical transmission device includes an optical input portion, an optical output portion, and an intermediate connecting portion interposed between the optical input portion and the optical output portion, and comprising optical waveguides. A complex refractive index of any one or any combination of the optical waveguides changes between the optical input portion and the optical output portion, and a transmission direction of light through the nonreciprocal optical transmission device is controlled by a change in the complex refractive index.

A narrow linewidth laser in which an all-optical feedback line-up is used to improve the linewidth from a conventional laser source, such as a laser diode. The feedback line-up comprises an optical device having a controllable unbalanced optical coupler arranged on a cavity input path to couple a source signal from the laser source into the optical cavity, and to couple a seed signal received back from the optical cavity into the laser source. The seed signal has a lower power than the source signal. The unbalanced optical coupler may be an optical isolator arranged to couple the seed signal into the laser source at a power level selected to promote preferential stimulated emission within a narrower linewidth. By controlling the power of seed signal such that only a small portion thereof influences the lasing cavity, the narrowing effect of the preferential stimulated emission can be enhanced.