Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
2002-11-21
2004-10-19
Sugarman, Scott J. (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S282000
Reexamination Certificate
active
06806990
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an optical device of which optical elements are bonded without using adhesive, and a method for producing an optical device.
BACKGROUND ART
In recent years, an optical communication system has become of high integration according to increasing the number of wavelength in WDM (Wavelength Division Multiplex). Consequently, demand on miniaturization of an optical device used for it has also been increased. In many cases, optical devices are composed of combinations of bonded bodies formed by bonding optical elements such as a Faraday rotator and polarizers to a fixing member. However, according to this method, a fixing member is an obstacle, which hinders the miniaturization of optical devices. Accordingly, it has been considered a method such that a fixing member is omitted and optical elements are bonded to each other.
The easiest method for bonding optical elements each other is to bond them by using organic adhesive. For example, Japanese Patent Laid-open Publication No. 6-75189 discloses an optical isolator wherein optical elements are adhered each other using organic adhesive such as resin to be unified. However, it has a disadvantage that use of the organic adhesive causes generation of outgas, which adversely affects a laser diode. Furthermore, the organic adhesive is easily affected by irradiation of high energy laser and exposure to atmosphere of high temperature and high humidity, and therefore it may causes low reliability to the device.
Accordingly, there have been investigated various methods of bonding optical elements each other without using organic adhesive. For example, there is a method of bonding optical elements by using low-melting glass or solder as inorganic bonding material. Low-melting glass is a glass for bonding of which the main component is a low-melting point material such as B
2
O
3
, PbO, or the like. It is necessary to heat to higher temperature than the softening point of the glass at a time of bonding using it. Moreover, although it is effective to bond light transmissive surfaces of the optical elements each other in order to achieve miniaturization of an optical device, there may be caused a problem when bonding the light transmissive surfaces of the optical elements using such low-melting glass, an antireflection film formed on the optical elements may react with the low-melting glass during softening of the low-melting glass by heating, which may lead to lowering of antireflection function. For this reason, it has been considered that a practical application of the optical device obtained by using low-melting glass for bonding each light transmissive surface was difficult.
On the other hand, in the case of using solder, since solder has no transparency, it can not be disposed directly on each light transmissive surface Therefore, such a bonding method that each outer frame of light transmissive surfaces is selectively metalized to exist solder only on the metalized surface is employed. Such a bonding method suffers from a problem that a complicate metalizing process is required, and therefore, decrease in yield and increase in cost can not be avoided.
Moreover, a method that each optical element is directly bonded without using adhesive has been attempted. (See Japanese Patent Application Laid-open (kokai) No. 7-220923 and Japanese Patent Application Laid-Open Application (kokai) No. 2000-56265.) In these methods, after surfaces of optical elements are subjected to hydrophilic treatment, hydrophilic-treated surfaces are bonded each other. This method is practically used for a manufacturing process of an SOI (Silicon On Insulator) wafer in the semiconductor field. However, in the case of applying this method to an optical device, it suffers from problems as follows and therefore it is a difficult situation to put this method to practical use.
Namely, such a method wherein the optical elements are subjected to hydrophilic treatment and then bonded directly depends on a configuration and physical properties of the components to be bonded. For example, as for the warp, the curvature radius is desirably several hundreds meters or more. Moreover, it is said that surface roughness of components to be bonded is desirably Ra=0.3 nm or less. Furthermore, it is greatly influenced by difference in linear expansion coefficient of components to be bonded.
However, only few optical elements satisfy the above-mentioned requirements. For example, since an iron garnet crystal or the like which is one of optical elements generally used in the optical device has stress distribution in thickness direction, it often has large warp. Moreover, since a polarizing glass has the structure wherein metal particles such as silver, copper or the like are dispersed in glass, surface roughness thereof is hardly controlled. Furthermore, linear expansion coefficients of these optical elements often differ greatly depending on material, and thus there is a tendency that the difference in the linear expansion coefficient between components to be bonded becomes large. Therefore, the optical elements bonded directly as mentioned above are easily delaminated at the bonded surface when they are subjected to heat treatment, and adhesiveness and durability of the bonded surface are low.
Furthermore, there is a problem that when the materials of which linear expansion coefficient are different from each other are bonded directly as above, thermal stress is generated between different materials, and it is concentrated on the bonded surface, and thereby optical strain may easily generate, resulting in lowering of optical properties such as the extinction ratio. Therefore, it is very difficult to apply a direct bonding technique to an optical device.
As described above, it has been very difficult to bond optical elements without using organic adhesive, and to produce an optical device having high reliability easily at a low cost.
SUMMARY OF THE INVENTION
The present invention has been accomplished to solve the above-mentioned previous problems. An object of the present invention is to provide an optical device which has small size and has high reliability at a low cost by bonding optical elements each other without using organic adhesive.
To achieve the above mentioned object, the present invention provides a method for producing an optical device by bonding optical elements each other without using adhesive wherein the optical elements are bonded each other
by using optical elements in which the relation between the linear expansion coefficient &agr;1 and &agr;2 (/° C.) of each of the optical elements to be bonded and the thickness t2 (m) of one of the optical elements satisfies the following formula; |(&agr;1−&agr;2)×t2|≦10
−9
and t2≧2×10
−5
;
and/or, by sticking the optical elements each other in the state of being heated, and then subjecting them to a heat treatment.
According to the method of producing an optical device having such features, optical elements can be bonded with sufficient bonding strength without using adhesive. Moreover, since organic adhesive is not used, there is caused neither generation of outgas nor degradation of the bonded surface due to atmosphere. Therefore, a small size optical device having excellent optical properties and high reliability can be produced at a low cost.
Moreover, in order to accomplish the above object, according to the first embodiment of the present invention, there is provided an optical device formed by bonding a polarizer to at least one surface of a magnetic garnet crystal without using adhesive which functions by transmitting light through the bonded surface, wherein the relation of the linear expansion coefficient &agr;1 (/° C.) of the magnetic garnet crystal, the linear expansion coefficient &agr;2 (/° C.) of the polarizer and the thickness t2 (m) of the polarizer satisfies the following formula: |(&agr;1−&agr;2)×t2|≦10
−9
and t2 ≧2×10
−5
.
As described above, if the rela
Ishii Masatoshi
Konishi Shigeru
Shirasaki Toru
Yoshikawa Hiroki
Hanig Richard
Hogan & Hartson LLP
Shin-Etsu Chemical Co. , Ltd.
Sugarman Scott J.
LandOfFree
Optical device and method for producing optical device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical device and method for producing optical device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical device and method for producing optical device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3297400