Optical waveguides – Integrated optical circuit
Patent
1997-08-29
1999-07-06
Ngo, Hung N.
Optical waveguides
Integrated optical circuit
385 37, 385 36, 385 10, 359322, 359323, G02B 610
Patent
active
059206624
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention concerns a planar electro-optical light-beam deflector with a line of prismatic deflectors arranged alongside each other, exhibiting electrodes to which an electrical voltage can be applied.
The invention concerns furthermore a process for producing such a light-beam deflector.
BACKGROUND
Electronically controlled light-beam diverters, so-called deflectors, are employed for example in the case of optical memories or laser TV displays and the like. An important property of such a deflector is the achievable number of resolvable points, i.e. of individual angularly separated light-beam positions which can be generated. Known is the construction of a deflector with the aid of a prism, whose refractive index can be changed electro-optically. With a single prism of this type it is however possible to generate only about from 10 to 20 resolvable points. This is inadequate for most applications. For example, approximately 1,000 resolvable points are needed for application in a laser TV display. The option of arranging several prisms one behind the other, to increase the number of resolvable points, entails the disadvantage that the length of such a composite deflector would be correspondingly large. Light deflectors with a line of prisms arranged side by side do not have this disadvantage. In that case, each prism deflects a part of the light-beam, and to be sure in such a way that the entire beam is oriented in the desired direction once it has passed the deflector. To prevent destructive interference of the partially deflected partial beams in the remote radiation field, means are also known which permit the phase of each partial beam to be controlled electro-optically. Used for this purpose are a number of control electrodes, which are respectively positioned in front of the prism electrodes, arranged in the shape of a wedge, which form the prismatic deflection fields (DE 3,025,096 A1).
Electro-optical light-beam deflectors with deflector prisms arranged side by side, i.e. in the shape of a prism array, have been constructed both with so-called volume prisms (Yuichi Ninomiya, Ultrahigh resolving electro-optic prism array light deflectors. IEEE Journal of Quantum Electronics, QE-9, No. 8, August, 1973, pp. 791-795) as well as with integrated-optics waveguide prisms (DE-3,025,096 A1). The main problem with prism-array deflectors is the generation of an ideal sawtooth curve development of the refractive index changes without roundings at the prism necks and without distortions between the prisms, from each deviation from an ideal curve development leads to amplified sidebands and worsening of the signal-noise ratio.
With volume prisms it is practically impossible to produce an ideal sawtooth curve development. Aside from the fact that it is technologically very inefficient to assemble such a deflector from individual crystal chips in order to achieve sharp boundaries between at least a few of the prisms, the thickness of the chips through which the light-beam passes is relatively large due to technological requirements and amounts to at least 200 .mu.m. The result of this is that the electrical field distribution in such a chip is very inhomogeneous. As a consequence, the refractive-index plot exhibits large deviations from the ideal curve. These deviations are greatest in the center of the chip, the deviations being smaller, on the other hand, near the electrodes. A further disadvantage caused by the thickness of the chip is the high control voltage that must be used, approximately 1 kV, if an acceptable number of resolvable points is to be achieved.
The solution with waveguide prisms has the advantage over that with volume prisms that the light is guided in a thin layer, permitting a reduction in the magnitude of the control voltage applied to the electrodes. Due to the unfavorable electrode geometry, this must still be about from 400 to 500 V. Even this solution does not present the possibility of producing an ideal saw-toothed distribution of the refractive-index chang
REFERENCES:
patent: 5093874 (1992-03-01), Hawkins et al.
patent: 5202790 (1993-04-01), Uchino et al.
patent: 5317446 (1994-05-01), Mir et al.
"Fabrication of Periodic Domain Grating in LiNbO.sub.3 by Electron Beam Wing for Application of Nonlinear Optical Processes", Electronics Letters, Jul. 4, 1991, vol. 27, No. 14, pp. 1221-1222.
"Modulation and Conversation of Light in Lithium Niobate Crystals with a Regular Domain Structure", A.A. Blistanov et al., Soviet Journal of Quantum Electronics, Dec. 16, 1986, No. 12, pp. 1678-1679.
"Ultrahigh Resolving Electrooptic Prism Array Light Deflectors", Yuichi Ninomiya, IEEE Journal of Quantum Electronics, Aug. 1973, No. 8, pp. 791-795.
Fraunhofer-Gesellschaft zur Forderung der ange-wandten Forschung
Ngo Hung N.
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