Stock material or miscellaneous articles – Composite – Of quartz or glass
Reexamination Certificate
2000-08-02
2002-10-15
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Composite
Of quartz or glass
C501S072000, C501S134000
Reexamination Certificate
active
06465105
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an optical filter used in a field of optical communication to select a light beam of a specific wavelength from multiple wavelength light components. This invention also relates to a glass substrate for the above-mentioned optical filter. In particular, this invention relates to a WDM (wavelength division multiplexing) optical filter. This invention also relates to a glass substrate for use in such optical filter.
In such WDM (wavelength division multiplexing) communication, communication is carried out by combining light beams having wavelengths slightly different from one another into a combined light beam and, inversely, by splitting or demultiplexing the combined light beam to selectively derive a specific wavelength light beam from the combined light beam. Herein, it is to be noted that the optical filter used for light combination and separation has been called a WDM (Wavelength Division Multiplexing) optical filter. As such a WDM optical filter, there are known WDM optical filters described in JP-A H10-339825 and JP-A H10-512975.
Each of the optical filters described in these publications comprises a glass substrate with a dielectric multilayer film of SiO
2
, TiO
2
, Ta
2
O
5
, or the like formed thereon. Such a dielectric multilayer film is operable as a band-pass filter (BPF) by giving a function which transmits a particular wavelength light beam or which reflects the particular wavelength light beam. As a rule, the substrate on which the dielectric multilayer film is deposited is formed by a glass material, such as silica.
In the meanwhile, it is recently reported that, in the optical filter of the type, a center wavelength in a pass band is drifted due to variation in temperature. It is also reported that such temperature drift depends upon a thermal expansion coefficient of each of the glass substrate and the dielectric multilayer film (Haruo Takahashi, Applied Optics, Vol. 34[4], pp. 667-675, 1995).
In the above-referenced article, description is made about the fact that a center wavelength within the pass band is drifted or shifted towards a positive direction (namely, a longer wavelength direction) when the thermal expansion coefficient of the glass substrate is smaller than a range determined for thermal properties of the dielectric multilayer such as an expansion coefficient. On the other hand, in case where the thermal expansion coefficient of the glass substrate is excessively large, the drift of the filter center wavelength occurs in a negative direction (shorter-wavelength direction).
If the drift is undesirably large, a filter characteristic, i.e., a transmission wavelength unfavorably varies following the change in operation temperature. In particular, if the bandpass filter is used as a narrow band filter, for example, in an optical multiplexer/demultiplexer used in a wavelength multiplexing transmission technique of optical communication, the influence becomes serious because such a narrow band constraint inevitably restricts a transmission density. Following an increase in a degree of wavelength multiplexing, there arises an increasing demand for an optical filter having a more stable characteristic over the variation in temperature as well as an optical multiplexer/demultiplexer using the same. In order to increase a thermal stability, proposal is made of a technique of controlling the temperature of the optical filter. However, this technique requires a complicated structure. Therefore, the difficulty in assuring a long-term reliability is increased and devices and apparatuses become more expensive.
As described above, the temperature drift of the bandpass peak wavelength constitutes one of factors that obstructs a high density optical communication.
In addition, conventional optical filters are disadvantageous in that peeling off of the multilayer from the glass substrate is liable to occur due to a temperature variation.
SUMMARY OF THE INVENTION
Taking the above-mentioned background into consideration, this invention has been created so as to reduce a temperature drift at a center wavelength of a pass band and to thereby avoid peeling off of the dielectric multilayer. More specifically, it is an object of this invention to provide a novel glass substrate which has a desired thermal expansion coefficient and a desired composition. It is another object of this invention to provide an optical filter and an optical multiplexer/demultiplexer both of which has a high reliability and which can reduce a temperature drift at a center wavelength within a pass band.
It is another object of this invention to provide a method of manufacturing glass which has a thermal expansion coefficient pertinent to a substrate material for a wavelength multiplexing/demultiplexing optical filter. Such glass can be obtained by controlling an amount of specific glass components.
According to a first aspect of this invention, a glass substrate is for use in a wavelength multiplexing/demultiplexing optical filter and is formed by glass which includes SiO
2
and which has a thermal expansion coefficient between 100×10
−7
and 130×10
−7
/K within a temperature range between −30 and +70° C.
According to a second aspect of this invention, a glass substrate is used for an wavelength multiplexing/demultiplexing optical filter and is formed by glass which includes SiO
2
, R
2
O (wherein R is representative of an alkali metal element), and TiO
2
as essential components and which comprises a total of the essential components not smaller than 60 mol %.
According to a third aspect of this invention, a glass substrate for the wavelength multiplexing/demultiplexing optical filter and is formed by glass which includes SiO
2
, R
2
O (wherein R is representative of an alkali metal element), and TiO
2
as essential components a total amount of which is greater than an amount of each of the remaining components.
According to a fourth aspect of this invention, the glass mentioned in connection with each of the first through the third aspects comprises, by mol %,
SiO
2
38-58%
TiO
2
7-30%
Al
2
O
3
0-12% and
R
2
O
15-40% in total.
According to a fifth aspect of this invention, the glass mentioned in connection with the fourth aspect comprises, by mol %, as R
2
O,
Na
2
O
10-25% and
K
2
O
4-15%.
According to a sixth aspect of this invention, the glass mentioned in connection with each of the second and the third aspects of this invention comprises, by mol %,
SiO
2
38-55%
Na
2
O
13-25%
K
2
O
2-15%
TiO
2
10-25%
Al
2
O
3
0.5-8%.
According to a seventh aspect of this invention, the glass mentioned in conjunction with each of the second through the sixth aspects comprises at least one species of oxides RO selected from a group consisting of alkaline earth metal oxides and zinc oxide.
According to an eighth aspect of this invention, the glass mentioned in the seventh aspect comprises, by mol %, a total of RO between 2 and 15%.
According to a ninth aspect of this invention, the glass mentioned in each of the seventh and the eighth aspects comprises, as RO, by mol %
MgO
0-13%
CaO
0-10%
SrO
0-8%
BaO
0-6%, and
ZnO
0-10%.
According to a tenth aspect of this invention, the glass mentioned in each of the seventh through the ninth aspects comprises, by mol %,
MgO
1-13%
ZnO
0.5-10%, and
Sb
2
O
3
0-1%.
According to an eleventh aspect of this invention, the glass mentioned in each of the second through the tenth aspects comprises, by mol %,
ZrO
2
0-2%
HfO
2
0-2%
La
2
O
3
0-2%, and
Y
2
O
3
0-2%.
According to a twelfth aspect of this invention, the glass mentioned in each of the second through the eleventh aspects has an average thermal expansion coefficient between 100×10
−7
and 130×10
−7
at a temperature range between −30 and +70° C.
According to a thirteenth aspect of this invention, the glass mentioned in the twelfth aspect has an average thermal expansion coefficient between 105×10
−7
Hashimoto Kazuaki
Johnson Robert W.
Yanagita Hiroaki
Blackwell-Rudasill Gwendolyn
Hoya Corporation
Jones Deborah
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