Lucent Technologies Inc.

At&t Bell Laboratories

American Telephone & Telegraph Co., At&t Bell Laboratories

American Telephone and Telegraph, Co.

Steven J Licht

Charles D Brandle, Jr

Vincent Jerome Fratello

Vincent J Fratello

George W Berkstresser

Robert Ralph Abbott

Ralph S Jameson

In an arrangement substantially like an optical isolator, appropriate choice of the composition of the magneto-optic element can result in a variable optical attenuator. The composition is selected to vary in the direction of light propagation, and also is selected such that the magneto-optic element comprises a compensation wall. The compensation wall is movable in response to a change in the temperature of the magneto-optic element, whereby the attenuation of the device is changed.

Article comprising a variable optical attenuator

Garnet material according to a particular embodiment of the invention exhibits a substantially rectangular magnetization loop, with .vertline.H.sub.S .vertline.&gt;.vertline.4.pi.M.sub.S .vertline.Oe and .vertline.4.pi.M.sub.s .vertline.&lt;100 G over a predetermined operating range (e.g., -40.degree. to +80.degree. C.), where H.sub.S is the switching magnetic field of the loop, and 4.pi.M.sub.S is the saturation magnetization. The material exhibits improved latching behavior. In a further embodiment of the invention the composition of the garnet material is selected such that the material exhibits hard latching behavior (.vertline.H.sub.s .vertline.&gt;500 Oe) at least at room temperature. Garnet materials according to the invention can advantageously be used in magneto-optic isolators and other magneto-optic devices. For instance, the material enables manufacture of isolators that do not contain a bias magnet. Garnet materials according to the invention generally contain at most relatively small amounts of Gd, Tb and Dy (less than 1.0, 2.1 and 2.5 atoms per formula unit, respectively; with Gd+(Tb/2.1)+(Dy/2.5)&lt;1.0), and generally contain Eu and/or Ho. In a departure from prior practice, compositions according to the invention can have a compensation temperature in the operating temperature range, e.g., at room temperature. An exemplary garnet according to the invention has nominal composition Bi.sub.0.75 Eu.sub.1.5 Ho.sub.0.75 Fe.sub.4.1 Ga.sub.0.9 O.sub.12.

Article comprising a magneto-optic material having low magnetic moment

Garnet material according to the invention exhibits a substantially rectangular magnetization loop, with .vertline.H.sub.S .vertline.&gt;.vertline.4.pi.M.sub.S .vertline.Oe, where H.sub.S is the switching magnetic field of the loop, and 4.pi.M.sub.S is the saturation magnetization. The material exhibits 'latching' behavior, and can advantageously be used in magneto-optic isolators and other magneto-optic devices. For instance, the material enables manufacture of isolators that do not contain a permanent magnet. An exemplary garnet according to the invention has nominal composition Bi.sub.0.75 Eu.sub.1.5 Ho.sub.0.75 Fe.sub.4.1 Ga.sub.0.9 O.sub.12.

An optical isolator is disclosed which comprises a Faraday rotator disposed between a pair of polarization selective elements (e.g., linear polarizers, birefringent wedges, birefringent plates, etc.). Improvement in isolation stability as a function of variations in temperature and/or signal wavelength are achieved in accordance with the teachings of the present invention by utilizing a Faraday device with a rotation .theta. less than the conventional 45.degree.. A linear reduction in .theta., while resulting in a some signal loss, provides a linear increase in both temperature and wavelength stability.

Optical isolator with improved stabiity

Apparatus according to the invention comprises a magneto-optic isolator. The isolator comprises a magneto-optic member that comprises a single crystal substrate and a single crystal garnet layer on the substrate. The garnet layer comprises a first and a second stratum. The composition of the former is chosen such that the lattice constant of the first stratum material is substantially equal to that of the substrate at a first temperature (e.g., room temperature), and is substantially larger than that of the substrate at a second temperature (e.g., the garnet growth temperature) that is higher than the first temperature. The composition of the second stratum is chosen such that the lattice constant of the second stratum is less than that of the substrate at the first temperature, and is less than that of the first stratum at the second temperature. Wafers according to the invention typically are less subject to fracture than analogous prior art wafers.

Apparatus comprising a magneto-optic isolator utilizing a garnet layer

Apparatus according to the invention comprises magneto-optic isolator means that utilize a novel temperature compensation scheme. The scheme involves the use of a composite magneto-optic member that comprises a first single crystal garnet layer that does not have a compensation temperature within the operating temperature range of the isolator, and further comprises a single crystal garnet layer (the 'compensation point layer') that has a compensation temperature within the operating temperature range of the isolator. Exemplarily, the compensation point layer has composition (Bi.sub.0.8; Tb.sub.1.1 Gd.sub.1.1)(Fe.sub.4.6 Ga.sub.0.4)O.sub.12, and is grown on an CMZ:GGG substrate, and the first garnet layer has composition (Bi.sub.1.2 Tb.sub.1.8)(Fe.sub.4.6 Ga.sub.0.4)O.sub.12 and is grown on the compensation point layer. The novel temperature compensation scheme can result in isolators having improved extinction ratio with relatively small additional path length in the magneto-optic material.

Epitaxial layers are grown from a body of molten material which includes flux and layer constituent components; included in the flux are lead oxide and a small amount of boron trioxide. As compared with prior-art processing in the absence of boron trioxide, enhanced yield is realized as believed to be due to reduced adhesion of solidifying material entrained upon withdrawal of a substrate after growth. The method is particularly useful in the manufacture of magnetic domain devices designed to operate at extreme temperatures, as well as in the manufacture of magneto-optic devices such as, e.g., switches, modulators, and isolators.

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Bridgewater, NJ, United States of America

Steven J Licht