Optical waveguides – Having nonlinear property
Reexamination Certificate
1999-02-12
2002-07-09
Healy, Brian (Department: 2874)
Optical waveguides
Having nonlinear property
C385S001000, C385S006000, C385S031000, C385S002000, C385S003000, C385S140000, C385S016000
Reexamination Certificate
active
06418255
ABSTRACT:
TECHNICAL FIELD
The invention concerns to area of nonlinear integrated and fiber optics, to be exact to area completely of optical modulators and switches.
BACKGROUND ART
Use of devices is heretofore-known on the basis of Faraday effect, including an optical element passing optical radiation, surrounded by the solenoid for creation of a variable magnetic field (e.g., M. Berwick, J. D. C. Jones, D. A. Jackson “Alternating-current measurement and noninvasive data ring utilizing the Faraday effect in a closed-loop fiber magnetometer”, “Optics letters”, v.12, p.4, 1987).
The heretofore-known modulator which is the closest to the suggested modulator is the modulator on the basis of Faraday effect or magneto-optical Kerr effect, containing consistently mounted in a course of a beam an optical element from magneto-optical material, on which the modulating magnetic field acts, and analyzer (S. Gonda, D. Seko “Optoelectronics in questions and answers”, Leningrad, Energoatomizdat, 1989, with pp.28-31). Shortcoming of this modulator is a small angle of turn of a polarization plane at small amplitude of a current, and in consequence a small level of modulation, or necessity, of use of a current with the large amplitude. For achievement enough large angles of the turn (of a polarization plane) ensuring an appreciable level of modulation (>20%), the solenoids with a plenty of coils, or large amplitudes of a current (about 1 A and more), or and that and another are required. A direct consequence of it is the low speed of operation. Use ferromagnetics in magneto-optical element s, as a rule, results in large losses. Shortcoming of modulators on the basis of magneto-optical Kerr effect is restriction on extreme small value of magnetization of domains determining maximal density of recording and/or reading the information. This results in impossibility of reduction of the sizes of the domains to below extreme allowable value, and thus limits density of record.
In the heretofore-known technical decisions the increase of a level of modulation (at moderate currents) is achieved by increase of the optical course of a beam within (magneto) optical element due to repeated reflection from end faces of the optical element (S. Gonda, D. Seko “Optoelectronics in questions and answers”, Leningrad, Energoatomizdat, 1989, pp. 126-127), or increase of length of the optical element as such made as fiber-optic waveguide (S. N. Antonov, S. N. Bulyuk, V. M. Kotov “Faraday optical fiber gauge of a magnetic field”, “Quantum electronics”, 18, No. 1, 1991, pp.139-141). Both in that, and in the other case optical radiation losses grow considerably; besides the modulating variable current, passed through the solenoid, should be strong enough.
DISCLOSURE OF THE INVENTION
The technical result of the invention is expressed in sharp amplification of Faraday effect and achievement of a high level of modulation of optical radiation at rather small amplitudes of a current, and consequently, high speed of operation and low losses, and also in a possibility of reading of the information at higher density of record.
The put task is solved by that the modulator on the basis of Faraday effect, containing optically connected magneto-optical element passing optical radiation and separator of radiations of various polarizations, thereto the magneto-optical element consists of an optical element made from magneto-optical material, and the means creating a variable magnetic field in it, in addition is provided with a nonlinear-optical element located between the magneto-optical element and the separator of radiations of various polarizations.
For the even greater increase of a level of modulation the nonlinear-optical element has a birefringence and/or is made from a magneto-optical material and/or is made from optically active material.
In specific case, most preferable for constructive performance, the nonlinear-optical element is made as the nonlinear-optical waveguide.
Nonlinear-optical waveguide must be made with possibility of propagation in it at least two unidirectional distributively coupled waves of orthogonal polarizations, So in the most preferable case the nonlinear-optical waveguide has a birefringence and/or is made from a magneto-optical material and/or is made from optically active material.
A length of the nonlinear-optical waveguide is not less than the length, which is necessary for switching or transfer at least 10% of a power from one of unidirectional distributively coupled waves with mutually orthogonal polarizations to other unidirectional distributively coupled wave with orthogonal polarization, thereto the length of the nonlinear-optical waveguide, which is necessary for switching or transfer at least 10% of a power of one of said unidirectional distributively coupled waves to another wave with orthogonal polarization, is not exceed the length at which a power of the most attenuated (absorbed) wave from the unidirectional distributively coupled waves of orthogonal polarizations, is attenuated in 20 times or less.
As a rule, a length of the nonlinear-optical waveguide is not less than the length, which is necessary for switching or transfer at least 50% of a power from one of unidirectional distributively coupled waves with mutually orthogonal polarizations to other unidirectional distributively coupled wave with orthogonal polarization, thereto the length of the nonlinear-optical waveguide, which is necessary for switching or transfer at least 50% of a power of one of said unidirectional distributively coupled waves to another wave with orthogonal polarization, is not exceed the length at which a power:of the most attenuated (absorbed) wave from the unidirectional distributively coupled waves of orthogonal polarizations, is attenuated in 10 times.
Thereto, as a rule, the nonlinear-optical waveguide is made as singlemoded.
As a rule, the entrance and/or out put ends (faces). of the nonlinear-optical waveguide have antireflection coverings, in particular, the antireflection coating at ends (faces) of the nonlinear-optical waveguide can be formed lowering factor of reflection of radiation from input and/or output end face up to value no more than 1%.
In a case, when the modulated optical radiation is not polarized, or for, increase of a degree of laser radiation polarization. the modulator in addition contains a polarizer placed before the magneto-optical element.
In special cases the polarizer, mounted before the magneto-optical element, and/or separator of radiations of various polarizations, mounted after the nonlinear-optical waveguide in the course of the radiation beam, is made as a polaroid, or a polarizing prism, or a birefringent prism, or a directional coupler, separating radiations of different polarization, or a polarizer on the basis of single optical waveguide.
For choice and maintenance of the optimum difference between phases of the orthogonally polarized waves, the modulator in addition contains a birefringent element located between said magneto-optical and nonlinear-optical elements. It operates as phase compensator or phase controller.
In special cases the birefringent element is made as an electrooptical crystal supplied with electrical contacts, or waveguide from an electro-optical material supplied with electrical contacts, or phase plate, or a birefringent waveguide, or acousto-optic crystal, or a waveguide from acousto-optic material. For elimination of return influence of the radiations reflected from ends faces of the nonlinear-optical waveguide and other optical elements of the device on the source of optical radiation and the nonlinear-optical waveguide, before the magneto-optical element or at the output of the modulator the optical isolator is mounted; in particular, the optical isolator is made as an optical waveguide.
In specific case the function of separator of waves of various polarizations the nonlinear-optical waveguide as such or the optical isolator mounted at the output of the nonlinear-optical waveguide carries out.
As a rule, the means creating variable magnetic fi
Cleomen Ltd.
Collard & Roe P.C.
Healy Brian
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