1984-10-05
1987-12-29
Sikes, William L.
350 9613, 350 9614, G02B 600
Patent
active
047156805
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an optical switch usable for optical circuits and more particularly to an optical switch of the type including an optical wave guide, branch optical wave guides and electrodes disposed in spaced relation along the optical wave guide, both the optical wave guide and the branch optical wave guides being made of electro-optical material so that transmission of light beams through the optical wave guides may be switched on or off as required.
DESCRIPTION OF THE PRIOR ART
The Mach-Zehder type optical switch has hitherto been known as a typical optical switch. The conventional optical switch of this type is constituted by a Ti-diffused LiNbO.sub.3 -based optical wave guide. The Ti-diffused LiNbO.sub.3 -based optical wave guide is divided into two branch optical wave guides in a Y-shaped configuration and light beams transmitted through the one branch optical wave guide are phase modulated under the influence of the electro-optical effect. Both the branch optical wave guides are united at another Y-shaped branch at which optical interference takes place whereby switching can be carried out.
However, it is found that the conventional Ti-diffused LiNbO.sub.3 -based optical wave guide has a refractive index which changes by a small amount under the influence of the electro-optical effect. For instance, the amount of change in refractive index was 0.2.times.10.sup.-3 when the electric field required for a normal switching operation had a rate of 2 KV/mm. Accordingly, to ensure that the switching operation is initiated by a voltage of about 5 V in the presence of phase interference, there is a necessity for designing elements with dimensions larger than 20 mm. For this reason the conventional optical switch cannot be practicably employed when it is to be mounted on an integrated circuit. For instance, when four optical switches are mounted on an integrated circuit, the latter requires a total length of more than 100 mm, inclusive of joint portions between adjacent optical switches where optical wave guides are jointed to one another.
With the foregoing problem in mind, proposals have been made to employ (Pb, La) (Zr, Ti) O.sub.3 (hereinafter referred to simply as PLZT) as an optical switch. Obviously, PLZT is a compound oxide material comprising lead oxide, titanium oxide, zirconium oxide and lanthalum oxide. However, a problem was found with respect to PLZT in that grinding of such a ceramic material to a very small dimension in the order of microns and adhesive connection of ground materials were achieved only with great difficulty. This is because of the fact that the body of an optical switch is required to have a thickness in the order of microns when an optical switch is used for an integrated optical circuit utilizing an excellently high electro-optical effect and the transparency of PLZT.
On the other hand, an optical switch has been proposed in which is used transparent PLZT produced by sintering a plurality of oxide materials comprising lead oxide, titanium oxide, zirconium oxide and tantalum oxide on a base plate made of sapphire. Obviously, it is impossible to grind this transparent material to a thickness in the order of microns as will be seen from the foregoing proposal.
Further, it is well known that material can be easily worked to a very thin thickness by employing a conventional deposition method, for instance, the vacuum deposition method. However, since a required composition cannot generally be obtained when a compound oxide material comprising lead oxide, titanium oxide and lanthanum oxide is processed by employing the conventional deposition method, it is believed that such kinds of compound oxide material cannot be worked to provide a thin thickness film for industrial use by means of presently available techniques.
On the other hand, research for obtaining a layer of epitaxial PLZT based thin film by employing the sputtering method have been reported. In this research, a single crystal cubic substrate of MgO and SrTiO.sub.3 was used
REFERENCES:
patent: 4136350 (1979-01-01), Tien
Kawaguchi et al; "PLZT Thin-Film Waveguides"; Applied Optics; vol. 23, No. 13, pp. 2187-2191; Jul. 1984.
Applied Physics Letters, vol. 31, No. 7, Oct. 1977, pp. 433-434, New York; M. Ishida et al., "Electro-Optic Effects of PLZT Thin Films".
Adachi Hideaki
Kawaguchi Takao
Ohji Kenzo
Setsune Kentaro
Wasa Kiyotaka
Matsushita Electric - Industrial Co., Ltd.
Sikes William L.
Wise Robert E.
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