Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-09-18
2003-09-23
Wilson, D. R. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S379000, C525S382000
Reexamination Certificate
active
06624255
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to polymer material used for composing optical communication parts, optical waveguides using such polymer materials and a method of fabricating the optical waveguides.
2. Description of the Background Art
In the field of telecommunications, development of optical waveguide has been recognized as a critical issue to enable large capacity communications.
Prerequisites to the materials used for composing optical communication parts such as an optical waveguide include higher transparency at wavelengths in the near-infrared range to which the wavelength of optical signals belongs and less scattering. The materials are also required to have controllability in their refractive indices since they are used to compose optical transmission paths.
Glass or other inorganic crystalline materials have conventionally been used as materials for composing optical communication parts such as an optical waveguide. These materials, however, suffer from their expensiveness and difficulty in processing.
In recent years, polymer materials, such as PMMA (polymethyl methacrylate) and PS (polystyrene), became more popular thanks to their inexpensiveness and easier processing as compared with those of glass or other inorganic crystalline materials. Use of such material can provide a film-type optical waveguide with wider area and higher flexibility than the conventionals. It becomes also possible to obtain a functional optical waveguide by introducing functional compounds or functional groups into such polymer materials.
Fabricating such an optical waveguide essentially requires a method of processing the polymer materials into a desired form. Typical of such a method has been the reactive ion etching (RIE) method using oxygen plasma. The fabrication process of a polymer-made optical waveguide by the RIE method has to be proceeded as generally shown in
FIGS. 5A
to
5
E. Here,
FIGS. 5A
to
5
E show schematic cross-sectional views useful for understanding the major steps in sequence for fabricating a polymer-made optical waveguide using the RIE method.
First, on a base
101
, a polymer film
103
a
as an underclad, a polymer film
103
b
for forming a core, and a photoresist film
105
for forming an etching mask are formed in this order, FIG.
5
A.
To obtain the etching mask corresponded to a desired patterned shape by processing the photoresist film
105
, the photoresist film
105
is then subjected to selective light exposure through a photomask
107
,
FIG. 5B
, corresponding to the patterned shape. This results in forming a latent image of the pattern in the photoresist film
105
. The photoresist film
105
after exposed with the light is then developed to obtain a resist pattern
105
x
, FIG.
5
C. The example shown here relates to a case with negative photoresist.
RIE with an oxygen-base etching gas is then carried out using the resist pattern
105
x
as an etching mask
105
x
, and a portion of the polymer film
103
b
being exposed from the etching mask
105
x
is removed. A core
103
x
made of the residual portion of the polymer film
103
b
is thus formed on the underclad
103
a
, FIG.
5
D.
On the specimen on which the core
103
x
has been formed, a polymer film
111
for forming overclad is formed to obtain an optical waveguide
113
, FIG.
5
E. The overclad
111
can be formed by, for example, coating on the specimen a coating fluid containing material of the overclad, and is then allowed to dry.
As for PMMA and PS, some approaches have been taken to improve transparency in the near-infrared region. More specifically, these materials show absorption ascribable to C—H bonds in their molecules in the near-infrared region, and thus deuterated PMMA, that is, PMMA whose hydrogen atoms are substituted with deuterium atoms has been developed. Deuterated PMMA shows absorption in the far-infrared region as shifted from the near-infrared region.
The above-described PMMA, PS and deuterated PMMA composing the core of the optical waveguide, however, are low in glass transition temperature. For instance, both of the PMMA and deuterated PMMA have a glass transition temperature of 107° C., so that these materials may easily be softened due to heat treatment such as soldering, if they are used to compose electronic parts for computers or so.
These materials also suffer from relatively high water absorption. Both of the PMMA and deuterated PMMA have a value of water absorption as high as 2.0%. The materials composing optical communication parts may alter their refractive indices due to water absorption, which may cause undesirable transmission error in optical communications.
The PS further has a specific problem on birefringence. In the conventional fabrication process of optical waveguides based on the RIE method, a number of steps and a long process time are necessary for forming the pattern, as is clear from the description referring to
FIGS. 5A
to
5
E. Problems also reside in that apparatus used for the RIE method costs high and requires special skills in the operation.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide polymer material superior in transparency and free from scattering in the operating wavelength region.
It is another object of the present invention to provide an optical waveguide having a core made of material with higher heat resistance, lower water absorption and no birefringence.
It is still another object of the present invention to provide an optical waveguide simpler in structure and easier in fabrication process without using the RIE method.
The inventors of the present invention, after extensive studies, focused on the fact that imidated polymer material becomes higher in glass transition temperature and lower in water absorption as compared with those of the original material before imidation, which has led to the present invention.
A polymer material according to the present invention contains a repetitive unit having formula (1):
The material expressed by the formula (1) can be obtained by, for example, reacting deuterated PMMA having superior transparency in the near-infrared region with deuterated methylamine, where deuterated methylamine reacts with the ester bond portion of deuterated PMMA to effect intramolecular imidation. The resultant imide has a cyclic structure. The imidated deuterated PMMA, i.e. deuterated polymethyl methacrylimide, has a higher glass transition temperature and a lower water absorption as compared with those of deuterated PMMA, and has a transparency equivalent with that of deuterated PMMA. The material is thus favorable as the one for optical communication parts.
The present invention also claims a polymer material containing a repetitive unit having formula (2):
The material expressed by the formula (2) can be obtained by, for example, reacting deuterated PMMA with ethylenediamine, where etylenediamine reacts with the ester bond portion of deuterated PMMA. One repetitive unit and one amino group react each other. Since one ethylenediamine molecule has two amino groups, two repetitive units of deuterated PMMA and one ethylenediamine molecule can react. Thus the products (polymer material) of the reaction will have a structure in which two repetitive units of deuterated PMMA are crosslinked with ethylenediamine. The repetitive unit of this polymer material has two cyclic portions each of which being similar to the above-described deuterated polymethyl methacrylimide. Also this polymer material has a higher glass transition temperature and a lower water absorption as compared with those of deuterated PMMA, and has a transparency equivalent with that of deuterated PMMA. The material is thus favorable as the one for optical communication parts.
An optical waveguide of the present invention comprises a clad and a core, and the core is made of polymer material containing a repetitive unit having formula (1), (2) or (3):
A polymer material, e.g. polydimethyl glutarimide (PMGI) expressed by the formula (3), can be obtained
Kaifu Katsuaki
Koyano Takeshi
Maeno Yoshinori
Mita Juro
Frank Robert J.
Oki Electric Industry Co. Ltd.
Venable LLP
Wells Ashley J.
Wilson D. R.
LandOfFree
Polymer material for use in optical communication parts does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Polymer material for use in optical communication parts, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Polymer material for use in optical communication parts will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3074584