Nonlinear optical silica material and nonlinear optical device

Details Nonlinear optical silica material and nonlinear optical device Nonlinear optical silica material and nonlinear optical device

1999-07-28

2002-04-23

Jones, Deborah (Department: 1775)

Stock material or miscellaneous articles

Composite

Of silicon containing

C428S448000, C428S450000, C428S469000, C428S697000, C501S154000, C423S335000

Reexamination Certificate

active

06376086

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a nonlinear optical silica material based on SiO
2
—GeO
2
, and more particularly to a nonlinear optical silica material having nonlinear optical properties which are exhibited readily, and which is very reliable. The invention also relates to an optical functional device using the nonlinear optical silica material and a method of producing it.
2. Description of the Related Art
It is almost inevitable that the field of optical communications will be the subject of major development in the future. A light-controlled switching device, a wavelength conversion device, an optical functional device such as an optical memory and an optical sensor are major components in an optical communication system. An optical material having nonlinear properties is also important to produce such optical functional devices.
As a nonlinear optical material, a crystalline material such as LiNbO
3
(lithium niobate) has been put to practical use.
However, when this nonlinear optical material LiNbO
3
is used as an optical device, its physical properties are very different from those of glass (e.g., optical glass fiber) used as a connecting member, and this difference in physical properties has a problem of causing a defect in the optical device. Also, LiNbO
3
is bulky and quite difficult to make thin film. Such a bulky optical functional part and a semiconductor device must be produced separately and then combined together, resulting in a disadvantage in view of production costs. Besides, it is difficult to form the bulky nonlinear optical device minutely, so that it can not easily be made highly functional.
Under such circumstances, SiO
2
—GeO
2
glass is now under development as a nonlinear material which can be formed into a thin film and is based on silicon glass having only slight differences in physical properties from silica glass or the like.
FIG. 1
is a schematic diagram showing a three-dimensionally configured bonded state of the SiO
2
—GeO
2
glass in a two-dimensional form. This SiO
2
—GeO
2
has less optical loss, a wider transmitted wavelength area and better processability and durability compared with a conventional material. Also, SiO
2
—GeO
2
material is considered to be readily formable into a thin film, and if the nonlinear optical material, SiO
2
—GeO
2
, can be formed into a thin film, it can be readily made into a hybrid with a semiconductor (electric) device such as an IC and LSI. It is well known that ICs and LSIs are produced by performing heat treatment and thin film formation while finely processing the surface of a substrate of Si, GaAs or the like. Therefore, a process of forming the nonlinear optical material can be incorporated into the process of manufacturing an IC or LSI using the SiO
2
—GeO
2
material formed into a thin film, so that a optical semiconductor hybrid element can be produced. In addition, development into a high-integrated optical device (optical IC) is also high. SiO
2
—GeO
2
has a material composition similar to those of a main semiconductor material Si and an oxide film (SiO
2
) which is formed when Si is processed and also has good applicability to a semiconductor production process compared with a conventional nonlinear optical material.
However, this proposed SiO
2
—GeO
2
film which can be made thin is still in a research stage and satisfactory nonlinear optical properties have not been obtained yet. Neither are its element composition and manufacturing method optimized, and so it has not been put to practical use. In order to impart nonlinear optical properties to this SiO
2
—GeO
2
film, its poling must be performed by applying a high electric field of about 10
5
V/cm. However, a high electric field causes breakage of the semiconductor element or degradation in performance when a hybrid element is configured by incorporating an IC, LSI or the like having other circuit elements (transistors, capacitors and the like) on a semiconductor substrate such as Si which is also used for the nonlinear optical material film. There is therefore a demand for satisfactory nonlinear optical properties to be obtainable by applying a low electric field so that an adverse effect owing to the application of the electric field to the SiO
2
—GeO
2
film is not applied to other semiconductor elements.
When the SiO
2
—GeO
2
film is formed on a semiconductor substrate of Si or the like, elements such as Ge of the SiO
2
—GeO
2
film are dispersed in the semiconductor substrate (Si), causing a breakage in the semiconductor substrate and also the transistors, capacitors and other elements formed on the semiconductor substrate or degradation in performance thereof. Furthermore, there is likely to be a problem that when the SiO
2
—GeO
2
film is formed on the semiconductor substrate, a defect in the crystal of the surface of the semiconductor substrate is increased.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a material which can exhibit satisfactory high nonlinear optical properties by applying a weak electric field which does not affect other elements even when an SiO
2
—GeO
2
film having physical properties somewhat different from silica glass is used as an optical material.
It is another object of the invention to lower an adverse effect on the other elements caused by the presence of a nonlinear optical silica film mainly consisting of SiO
2
—GeO
2
formed on a substrate such as an Si substrate which has other semiconductor elements formed thereon.
The present invention has been achieved to complete the aforesaid objects and has the following features.
First, the nonlinear optical silica material of the invention has Sio
2
—GeO
2
as a main component and is characterized by having a hydrogen or halogen element added to this silica material.
The invention is also characterized in that oxygen, which is bonded to Ge contained in the nonlinear optical silica material mainly consisting of SiO
2
—GeO
2
, is substituted by hydrogen.
The invention is also characterized in that oxygen bonded to Ge contained in the material is substituted by elemental halogen to totally or partly take the place of hydrogen.
In the nonlinear optical material mainly consisting of SiO
2
—GeO
2
, Si and Ge elements having four coordinates are bonded through O elements to form Si—O—Si, Si—O—Ge and Ge—O—Ge bonds. Among them, a part where the material exhibits nonlinearity is a part where all valence arms of Ge elements having four coordinates of the Ge—O bond do not bond with O elements but some valence arms have remained as nonvalence arms, namely a so-called dangling bond (unpaired electron) is present.
The nonlinear optical silica material according to the present invention has, for example, a structure indicated in a two-dimensional form as shown in FIG.
2
. It is seen in
FIG. 2
that H (hydrogen) is added to the material so to have Si—H and Ge—H bonds (Si—X and Ge—X bonds when halogen element X is added) in the material film. In the bonded state of points (Ge·) where nonlinearity is exhibited, the material of the present invention (see
FIG. 2
) has two Ge—O bonds and one Ge—H (Ge—X when halogen element X is added) bond with respect to one Ge while a conventional material (see
FIG. 1
) has three Ge—O bonds.
Thus, Ge—H bonds and Ge—X bonds which do not relate to bonding of crystal networks can be formed at points (Ge·)where nonlinearity is exhibited by adding hydrogen and halogen elements to the nonlinear optical silica material. In other words, since the Ge· points have a bond not related to the crystal network, the electric field applied can be lowered substantially compared with a conventional nonlinear optical silica material in processing for polarity orientation (poling) to cause the nonlinear optical silica material to exhibit nonlinearity.
As described above, the nonlinear optical silica material according to the present invention can be used as a thin film on a semiconductor substrate so to form, for example, a optical semiconductor hybrid element having a si

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