Optical: systems and elements – Extended spacing structure for optical elements – Extension of tubular element adjustable
Reexamination Certificate
2000-08-14
2002-03-19
Schuberg, Darren (Department: 2872)
Optical: systems and elements
Extended spacing structure for optical elements
Extension of tubular element adjustable
C359S484010, C359S490020
Reexamination Certificate
active
06359733
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to composite optical elements, optical isolators, optical circulators, and optical switches for applications in optical communications and measurements, and also to processes for producing the same.
BACKGROUND OF THE INVENTION
In Japanese Patent Application Kokai No. 5-181088 the present inventors proposed a novel, polarization-insensitive optical isolator comprising a Faraday rotator positioned between a pair of birefringent diffraction grating elements. Known birefringent diffraction grating elements useful for the optical isolator are as follows. They are all diffraction grating polarizers. Each element of the present invention by itself does not function as, but is technically equivalent to, a polarizer.
(1) The element according to Japanese Patent Application Kokai No. 63-55501; an element in which a diffraction grating is formed by subjection of lithium niobate to proton ion exchange. The element has a problem of high-cost manufacture because of the expensive single crystal substrate of lithium niobate for the grating. Another problem is that the difficulty of precise control of the optical path difference for polarization obstructs the fabrication of the elements in a stable way with good reproducibility.
(2) The element according to Japanese Patent Application Kokai No. 2-156205; a polarizer having a dielectric layer at the bottoms of grooves formed at regular intervals on the principal surface of an optically anisotropic crystal plate. The polarizer can be made at low cost, but the difficulties in accurately controlling the depth of grooves and the thickness of the dielectric layer render it impossible to control the optical path difference for polarization with high precision. Consequently, as with (1), stable production with good reproducibility has not been attained. In addition, rough bottom surface of the grooves can cause scattering, leading to deteriorated characteristics.
The present invention, therefore, aims at solving the afore-described problems and providing diffraction grating elements, especially birefringent diffraction grating elements, which permit easy control of the optical path length, production scheme, and designing, exhibit high performance stability with time, and have reduced thickness and also providing processes for producing them, and further providing optical isolators, optical circulators, and optical switches using those elements, and processes for producing them.
BRIEF SUMMARY OF THE INVENTION
The composite optical element in one aspect of the present invention comprises a first optical material and a second optical material joined to one plane of a third optical material, the first and second optical materials being the same in thickness and having ground principal planes flush with each other on both sides of them. To be more concrete, either the first or second optical material is a birefringent material. Alternatively, both of the first and second optical materials are birefringent and have functions as wave plates. The optical element has a broad range of applications as a component member for polarizers, diffraction gratings, optical isolators, optical circulators, and optical switches.
The composite optical element of the structure described is produced by the process according to of the invention. The process is a process for producing a composite optical element comprising the steps of:
forming a plurality of first grooves at predetermined intervals in a first optical material;
forming a plurality of second grooves at predetermined intervals in a second optical material;
bonding the first optical material having the first grooves and the second optical material having the second grooves together, with their grooves and lands staggered to fit each other, through an adhesive to provide a composite block;
grinding one side of the composite block to a thickness where both surfaces of the first and second optical materials are exposed;
bonding a third optical material, with a first plane on one side thereof, to the first ground surface of the composite block, through an adhesive; and
grinding the side opposite to the first ground surface of the composite block to a given thickness where the surfaces of both the first and second optical materials are exposed.
The process of the invention facilitates the production control and designing as well as the control of the optical path lengths, and provides excellent composite optical elements.
A diffraction grating polarizer using a composite optical element according to the invention acts as a linear polarizer when the first optical element is made of a birefringent material and the second optical element is made of an isotropic material, and the component elements are combined so that a relation (ne
1
−no
1
)d=(M+1/2)&lgr;, in which d is the overall thickness of the resulting element, &lgr; is the wavelength of incident light, and M is an integer, holds between the refractive indexes no
1
, ne
1
of the first optical element with respect to two natural linear polarizations, or ordinary light and extraordinary light, and the refractive index n
2
of the second optical element.
The composite optical element is further combined with a Faraday rotator to make a composite optical element for optical isolator according to the invention. Thus the composite optical element for optical isolator formed from the optical element of the invention is a composite optical element comprising a Faraday rotator having a Faraday rotation angle of approximately 45°, first and second birefringent materials joined to one side of the rotator, and third and fourth birefringent materials joined to the other side of the rotator, wherein:
the light that has been transmitted through the first birefringent material passes through the third birefringent material;
the light that has been transmitted through the second birefringent material passes through the fourth birefringent material;
the optical axis of the first birefringent material and that of the second birefringent material intersect orthogonally;
the optical axis of the third birefringent material and that of the fourth birefringent material intersect orthogonally;
the optical axis of the first birefringent material and that of the third birefringent material make an angle of about 45° with respect to each other;
the first and second birefringent materials have the same ground principal planes flush with each other on both sides of them;
the third and fourth birefringent materials have the same ground prinicpal planes flush with each other on both sides of them;
the first, second, third, and fourth birefringent materials are of the same material and have approximately the same thickness d, substantially satisfying the equation
2(no−ne)d=(M+1/2)&lgr;
where no is the refractive index of the birefringent material to ordinary light, ne is the refractive index of the birefringent material to extraordinary light, M is an arbitrary integer, and &lgr; is the wavelength of the light.
A polarization-insensitive optical isolator according to the present invention that utilizes the composite optical element fabricated in accordance with the present invention comprises a first optical waveguide, a first lens, the said composite optical element, a second lens, and a second optical waveguide arranged in the order in which they have just been mentioned.
Light outgoing in the forward direction from the end of the first optical waveguide is converted by the first lens to parallel beams, the first light that has been transmitted through the first birefringent material passes through the third birefringent material, the second light that has been transmitted through the second birefringent material passes through the fourth birefringent material, and, after the passage through the third and fourth birefringent materials, the first light and second light, producing no optical path difference regardless of the optical path length difference, are combined by the second lens into the second optical wa
Hata Kenjiro
Iwatsuka Shinji
Prinker Biddle & Reath LLP
Schuberg Darren
TDK Corporation
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