JP2020019659A - Crystallized glass - Google Patents

Abstract

To provide a glass ceramic substrate for an optical filter, which has a stable coefficient of thermal expansion and a temperature coefficient dn/dT of a refractive index so as to prevent refractive index variation in a use temperature range of a filter member having a monolayer or multilayer film formed therein and which has a good ray transmittance so as to suppress an insertion loss as much as possible.SOLUTION: A crystallized glass is provided, which has the following composition of a raw glass: the composition contains components of, in terms of a percentage by mass on an oxide basis, SiOby 70 to 80%, LiO by 5 to 15%, KO by 0.5 to 5%, MgO+ZnO+SrO+BaO by 0.1 to 10%, POby 0.1 to 5%, ZrOby 0.1 to 7%, AlOby 1 to 11%, and SbOby 0 to 2%. The crystallized glass contains lithium disilicate and α-quartz as the main crystalline phase, has a coefficient of thermal expansion of 100 to 140×10/°C in the temperature range from -30 to +70°C, and a temperature coefficient of the refractive index dn/dT of -1 to +1 (10/K) in the temperature range from 40 to 60°C.SELECTED DRAWING: None

Description

  The present invention relates to a crystallized glass, and more particularly, to a crystallized glass for an optical filter substrate material, whose properties and quality are very stable.

Crystallized glass is also called glass ceramics, and refers to glass in which crystals are precipitated by heat-treating amorphous glass. Crystallized glass can exhibit physical properties not found in original glass due to precipitated crystals, and can be used for structural members, zero-expansion members, hard disk substrate materials, crown materials, WDM (wavelength division multiplexing) optical communication systems It is used for various applications such as optical filter substrate materials.
Above all, at present, the information amount of the optical communication system does not stop increasing, and is expected to increase further in the future. With the rapid spread of new information communication services such as cloud computing data services, mobile communication services, and high-definition video communication services, the amount of communication flowing on optical networks will increase, and autonomous vehicles and connected cars will be connected. If this happens, an explosive increase is expected.
Accordingly, it is required to further increase the optical fiber communication capacity. Naturally, individual module members used in the system are required to cope with the increase in capacity.

One of the members in the optical communication system is an optical filter for multiplexing / demultiplexing, and ordinary amorphous glass or crystallized glass is used. Optical filters include those that cut a specific wavelength, those that transmit light, and those that reduce light intensity regardless of wavelength.
Among these, as a band-pass filter that transmits a specific wavelength, a large compressive stress is applied to the dielectric multilayer film to be formed due to the large thermal expansion coefficient and high mechanical strength of crystallized glass, and the transmitted light Has been used to increase the temperature stability of the center wavelength of the light. As a response to the recent increase in communication capacity, narrowing of the communication wavelength bandwidth is also considered. For this purpose, it is necessary to provide more stable center wavelengths to be used. It is necessary to minimize the insertion loss, which is the ratio of the output light to the output light.
Regarding the temperature stability at the center wavelength, it is very important to control the film by the stress of the dielectric multilayer film, but the temperature stability related to the optical performance of the glass itself is also greatly affected.
It is desirable that the temperature stability of glass and the temperature coefficient of refractive index dn / dT change little in the temperature range of use environment. Regarding the insertion loss, not only the transmittance of the glass but also the configuration as a filter and the state of the interface are determined. It works great including it.
In addition, when it is used as an optical / mechanical precision member, its quality stability is very important. That is, it is important to have uniform physical properties in any part of the crystallized glass member or in different production lots.
In order to obtain uniform physical properties of the crystallized glass, it is necessary that the crystallized glass has high homogeneity. In the case of crystallized glass, it is the crystals that precipitate in the glass phase that greatly contribute to the physical properties, so in order to increase the homogeneity of the crystallized glass, the crystal size should be as uniform as possible, and evenly. Preferably, the crystals are dispersed.

BACKGROUND ART As a crystallized glass for an optical filter substrate material for a WDM (wavelength division multiplexing) optical communication system, for example, a glass composition represented by Patent Document 1 is known.
The glass described in Patent Document 1 does not consider the temperature coefficient of the refractive index of the glass itself as a substrate material for an optical filter for further large-capacity communication and narrowing of the band. It was very difficult to obtain a filter with higher temperature stability and a lower insertion loss using the filter.

JP 2001-48584 A

  The present invention, with the increase in the accuracy of the multiplexing / demultiplexing optical filter for an optical communication system, a stable thermal expansion coefficient for preventing the refractive index fluctuation in the operating temperature range of the filter member formed of a single layer or a multilayer film, the refractive index of the An object of the present invention is to provide a glass-ceramic substrate for an optical filter having a temperature coefficient dn / dT and good light transmittance capable of suppressing insertion loss as much as possible.

In view of the above problems, the present inventor has conducted extensive studies and found that a crystallization having a specific thermal expansion coefficient range, a specific temperature coefficient of refractive index, light transmittance, surface roughness, and a stable thermal expansion coefficient. It has been found that glass is suitable, and the present invention has been achieved. The specific configuration is as follows.

(1) The composition of the raw glass is a mass percentage based on oxides.
SiO ₂ 70~80%,
Li ₂ O 5 to 15%,
K ₂ O 0.5~5%,
MgO + ZnO + SrO + BaO 0.1-10%,
P ₂ O ₅ 0.1~5%,
ZrO ₂ 0.1-7%,
Al ₂ O ₃ 1 to 11%,
Sb ₂ O ₃ 0~2%,
Which is a crystallized glass containing the following components: lithium disilicate and α-quartz as main crystal phases; a coefficient of thermal expansion at −30 to + 70 ° C. of 100 to 140 × 10 ⁻⁷ / ° C .; A crystallized glass having a temperature coefficient dn / dT of a refractive index at 〜60 ° C. of −1 to +1 (10 ⁻⁶ / K).
(2) The crystallized glass according to (1), wherein the material having a thickness of 1 mm at a wavelength of 950 to 1600 nm has a light transmittance of 85% or more.
(3) The crystallized glass according to (1) or (2), wherein the polished surface has a center line average roughness Ra of 5 ° or less.
(4) The crystal grain size distribution of the main crystal phase is in the range of 0.05 μm or less, and the distribution width of the average linear expansion coefficient on the plane having the maximum area and the plane in the direction orthogonal to each other is 0 to 3 × 10 ⁻⁷ / (1) The crystallized glass according to any one of (1) to (3), wherein
(5) An optical filter comprising a dielectric film formed on the crystallized glass according to any one of (1) to (4).

  The reasons for limiting the thermal expansion coefficient, the temperature coefficient of the refractive index, the composition, the main crystal phase, the light transmittance, the surface roughness, and the distribution width of the average linear expansion coefficient of the glass ceramic for an optical filter of the present invention will be described below.

In the case of a band-pass filter, the thermal expansion coefficient is set to narrow the band width of the passing wavelength, and if an attempt is made to achieve a higher density and a narrower band, the temperature stability of the band center wavelength becomes a problem. In order to avoid a change in the refractive index of the filter member formed with a single layer or a multilayer film at the operating temperature, the substrate material is expanded, thereby applying a compressive stress to the film, thereby improving the temperature stability of the refractive index of the film.
When the substrate material has a coefficient of thermal expansion of 100 to 140 × 10 ⁻⁷ / ° C. at −30 to + 70 ° C., a sufficient compressive stress can be applied to the multilayer film. Further, the formed multilayer film varies depending on the communication wavelength and the multiplicity used, and the temperature stability of the film can be enhanced by selecting from within this range depending on the film configuration.
Accordingly, the coefficient of thermal expansion at −30 to + 70 ° C. is preferably 100 × 10 ⁻⁷ / ° C. or more, more preferably 102 × 10 ⁻⁷ / ° C. or more, and most preferably 105 × 10 ⁻⁷ / ° C. or more, It is preferably at most 140 × 10 ⁻⁷ / ° C., more preferably at most 138 × 10 ⁻⁷ / ° C., most preferably at most 135 × 10 ⁻⁷ / ° C.

As described above, it is important to provide the multilayer film itself with temperature stability, but the temperature stability of the refractive index of the substrate material itself is also important. Therefore, it is preferable that the temperature coefficient dn / dT of the refractive index of the substrate material be −1 to +1 (10 ⁻⁶ / K), whereby the temperature stability of the center wavelength from both the film and the substrate to the transmitted light is reduced. improves.
Therefore, the temperature coefficient dn / dT of the refractive index of the substrate material is preferably -1 ( ^10-6 / K) or more, more preferably -0.95 ( ^10-6 / K) or more, and most preferably -0. 90 (10 ⁻⁶ / K) or more, preferably 1 (10 ⁻⁶ / K) or less, more preferably 0.95 (10 ⁻⁶ / K) or less, and most preferably 0.90 (10 ⁻⁶ / K). K) The following is true.

In the present invention, if the light transmittance is low, the signal is reduced. Therefore, the value is preferably large. The wavelength used for the bandpass filter is 950 to 1600 nm, and the light transmittance at this wavelength in a 1 mm-thick material is preferably 85% or more, more preferably 88% or more, and most preferably 90% or more.

The aforementioned signal reduction and insertion loss often cause not only light absorption by the material but also scattering on the substrate surface. Therefore, the center line average roughness of the surface polished to prevent surface scattering is preferably 5 ° or less, more preferably 4 ° or less, most preferably 3 ° or less in Ra.

In the glass ceramics for an optical filter of the present invention, the main crystal phases are preferably lithium disilicate and α-quartz. By precipitating these crystals, the mechanical strength and chemical stability can be remarkably enhanced. By controlling the amount of α-quartz deposited, the thermal expansion coefficient is 100 in the temperature range of -30 to + 70 ° C. 140 × 10 ⁻⁷ / ° C., and the temperature coefficient dn / dT of the refractive index can be set to −1 to +1 (10 ⁻⁶ / K).

In the crystallized glass article of the present invention obtained by the production method of the present invention, the value of the crystal grain size distribution of the main crystal phase is preferably within 0.05 μm, more preferably within 0.045 μm, and most preferably 0.04 μm. Within. "Crystal grain size distribution" refers to a value measured by the following procedure. That is, an image of an arbitrary portion at a magnification of 100,000 to 500,000 times is acquired by a TEM (transmission electron microscope), and the longest distance when a crystal appearing in the obtained image is sandwiched between two parallel straight lines. Is the grain size of the crystal. This is measured for 100 randomly selected crystals, and the absolute value of the difference between the crystal grain size values of 95% and 5% based on the number is defined as the crystal grain size distribution value.

In the crystallized glass article of the present invention obtained by the production method of the present invention, the distribution width of the average linear expansion coefficient on the surface having the maximum area and the surface in the direction orthogonal to each other is preferably 0 to 3 × 10 ^−7. / ° C., more preferably 0 to 2.5 × 10 ⁻⁷ / ° C., and most preferably 0 to 2 × 10 ⁻⁷ / ° C.
The coefficient of expansion is determined by the amount of precipitated crystals in the case of crystallized glass. Therefore, according to JOGIS (Japan Optical Glass Industry Association Standard) 16-2003, "Method of measuring average linear expansion coefficient of optical glass near room temperature", one-sided pressing is performed. By measuring the expansion coefficient measured using a thermal dilatometer (temperature range -30 ° C. to 70 ° C.) and correlating this with the integrated intensity value of the crystal peak by an X-ray diffractometer (XRD), the value of XRD is obtained. Was used as an expansion coefficient. The difference between the maximum value and the minimum value obtained by converting the value of XRD into an expansion coefficient was defined as the distribution width.
These make it possible to improve the glass quality and the accuracy of the filter.
With respect to the characteristics of an optical filter obtained by finally forming a dielectric multilayer film, various values are taken depending on the film configuration, but the coefficient of thermal expansion of the substrate glass in the present invention, the temperature coefficient of the refractive index, etc. are stable. This makes it easier to achieve high center wavelength temperature stability. The temperature stability of the center wavelength of the filter is preferably -1 to +1 (pm / C), more preferably -0.5 to +0.5 (pm / C), and most preferably 0.

  Next, the reasons for limiting the composition range of the raw glass will be described below. In order to obtain a crystallized glass containing the above crystal phase, the composition range of the raw glass is preferably set as follows. In addition, the content of each component is shown by mass% based on the oxide. Here, the “oxide standard” means that the oxide or nitrate used as a raw material of the constituent components of the glass or the crystallized glass is completely decomposed at the time of melting and changes to the oxide, and the glass or the crystallized glass is used. This is a method of expressing the composition of each component contained in the glass, and the amount of each component contained in the glass or crystallized glass is described with the total mass of the produced oxide being 100% by mass.

The SiO ₂ component is a very important component that generates lithium disilicate and α-quartz which are precipitated as a main crystal phase by heat treatment of the raw glass, but if the amount is less than 70%, the obtained glass ceramics will be precipitated. The crystals are unstable and the structure is likely to be coarse, and if it exceeds 80%, the melting and forming properties of the raw glass become difficult. Therefore, the content is preferably at least 70%, more preferably at least 72%, most preferably at least 74%, preferably at most 80%, more preferably at most 79%, most preferably at most 78%.

The Li ₂ O component is a very important component that generates lithium disilicate precipitated as a main crystal phase by heat treatment of the raw glass. However, if the amount is less than 5%, precipitation of the crystal becomes unstable, and This makes it difficult to melt the raw glass. On the other hand, if it exceeds 15%, the obtained crystals are unstable, the structure is likely to be coarse, and the chemical durability is deteriorated. Therefore, the content is preferably at least 5%, more preferably at least 6%, most preferably at least 7%, preferably at most 15%, more preferably at most 14%, most preferably at most 13%.

The K ₂ O component is a component that improves the meltability of the glass and at the same time prevents coarsening of precipitated crystals, and can be optionally contained. However, if it is contained excessively, the precipitated crystals become coarse, the crystal phase changes, and the chemical durability deteriorates. Therefore, the content is preferably at least 0.5%, more preferably at least 0.6%, most preferably at least 0.7%, preferably at most 5%, more preferably at most 4%, most preferably at most 3%. % Or less.

  The MgO, ZnO, SrO, and BaO components improve the melting property of the glass, prevent coarsening of the precipitated crystals, and adjust the light transmittance by adjusting the refractive index of the glass phase as a matrix. However, if the total amount is too small, the above effects cannot be obtained, and if the total amount is excessive, the obtained crystals are unstable and the structure tends to be coarse. Therefore, their total content is preferably at least 0.1%, more preferably at least 0.2%, most preferably at least 0.3%, preferably at most 10%, more preferably at most 8%, most It is preferably at most 6%.

In the present invention, the P ₂ O ₅ component is indispensable as a nucleating agent for precipitated crystals, but to obtain its effect, it is preferably 0.1% or more, more preferably 0.3% or more, and most preferably 0.1% or more. It is 5% or more, preferably 5%, more preferably 4% or less, and most preferably 3% or less in order to prevent devitrification of the raw glass and maintain mass production stability.

Like the P ₂ O ₅ component, the ZrO ₂ component not only functions as a nucleating agent for precipitated crystals, but also has a remarkable effect on refinement of precipitated crystals, improvement in mechanical strength of a material, and improvement in chemical durability. Is found, and can be optionally contained. In order to obtain these effects, ZrO ₂ is contained preferably at least 0.1%, more preferably at least 1%, most preferably at least 2%. However, if it is added excessively, it becomes difficult to melt the raw glass and, at the same time, residual melting of ZrSiO ₄ or the like occurs. Therefore, the content is preferably 7% or less, more preferably 6% or less, and most preferably 5% or less.

The Al ₂ O ₃ component is a component for improving the chemical durability and mechanical strength, particularly the bending strength, of the glass ceramic. To obtain this effect, the amount is preferably 1% or more, more preferably 2%. Above, most preferably 4% or more. If the Al ₂ O ₃ component is excessive, the meltability and the devitrification resistance deteriorate, and β-spodumene and β-cristobalite are precipitated as precipitated crystal phases. Therefore, the Al ₂ O ₃ component is preferably at most 11%, more preferably at most 10%, most preferably at most 9%.

The Sb ₂ O ₃ component can be added as a fining agent when the glass is melted, but the content of each component is preferably 2% or less, more preferably 1% or less. However, the Sb ₂ O ₃ component can be substantially not included in consideration of the effect on the human body and the environment.
Similarly, As ₂ O ₃ and PbO are components that are environmentally unfavorable and should be avoided as much as possible.

Next, with respect to the production of the glass ceramic for an optical filter according to the present invention, after melting the glass having the above composition and performing hot forming and / or cold working, the temperature is in the range of 600 ° C to 650 ° C. Heat treatment is performed at a temperature for 1 to 5 hours to form crystal nuclei, and then heat treatment is performed at a temperature in the range of 700 to 780 ° C. for 1 to 5 hours to perform crystallization.
Thus, the main crystal phase of the glass ceramic crystallized by the heat treatment can contain lithium disilicate and α-quartz.

This heat-crystallized glass ceramic is wrapped by a conventional method and then polished to obtain a glass ceramic for an optical filter having a surface roughness Ra of 5 ° or less. The glass ceramic of the present invention is suitable for an interference type optical filter in which a dielectric multilayer film is formed on the substrate surface. In particular, as the dielectric multilayer film, a dielectric film having a high refractive index and a dielectric film having a low refractive index are used. It is suitable for a bandpass filter having a structure in which body films are alternately stacked and formed.
As the dielectric, inorganic oxides such as TiO ₂ , Ta ₂ O ₅ , Nb ₂ O ₅ , and SiO ₂ are preferable.

Next, a preferred embodiment of the present invention will be described.
Table 1 shows crystallized glasses of Examples of the present invention and Comparative Examples. It should be noted that the following examples are for illustrative purposes only, and are not limited to only these examples.

A method for producing the crystallized glass of the above embodiment will be described.
Raw materials such as oxides, carbonates, and nitrates are mixed, melted at a temperature of about 1350 to 1450 ° C. using a normal melting apparatus, homogenized by stirring, and then a glass molded body is obtained through a molding and cooling process. Was. Thereafter, this was heat-treated at 600 to 650 ° C. for 1 to 5 hours to form a crystal nucleus, and then heat-treated and crystallized at 700 to 780 ° C. for 1 to 5 hours to obtain a desired crystallized glass. Next, the crystallized glass was wrapped with diamond pellets of 800 # to 2000 # for 5 to 30 minutes, and then polished with a cerium oxide abrasive having a particle size of 0.02 to 3 [mu] m for 30 to 60 minutes to finish.

The precipitated crystal phase was identified with an X-ray diffractometer.
The coefficient of thermal expansion is determined according to JOGIS (Japan Optical Glass Industry Association Standard) 16-2003 “Method of measuring average linear expansion coefficient of optical glass near room temperature”, and the average linear expansion coefficient at −30 to + 70 ° C. is determined. Was measured at 40 to 60 ° C.
The transmittance was measured at a wavelength of 950 to 1600 nm, the light transmittance of a 1 mm-thick plate, and the surface roughness was measured with an atomic force microscope at the center line average roughness (Ra) in a 10 μm visual field.
The crystal particle size was measured with a transmission electron microscope (TEM). Since the distribution width of the expansion coefficient is determined by the amount of precipitated crystals in the case of crystallized glass, the measured expansion coefficient is measured using a one-sided dilatometer (temperature range −30 ° C. to 70 ° C.). The XRD value was converted and used as an expansion coefficient by correlating with the integrated intensity value of the crystal peak by a line diffractometer (XRD). The difference between the maximum value and the minimum value obtained by converting the value of XRD into an expansion coefficient was defined as the distribution width.

Further, a dielectric multilayer film of TiO ₂ / SiO ₂ is formed on these glass substrate materials to produce an interference type dielectric multilayer filter in a narrow band, and the temperature stability (thermal drift) of the center wavelength of the filter is reduced. It was measured.

Comparing Examples 1-4 of the present invention with Comparative Examples 1 and 2, the crystallized glass of Comparative Example 1 has a thermal expansion coefficient of 122 × 10 ⁻⁷ / ° C. Although stress was applied, the value of dn / dT was large, resulting in inferior temperature stability of the central wavelength as a whole. Further, the transmittance was also poor due to the influence of α-cristobalite precipitation as a precipitated crystal phase, resulting in a poor filter. In Comparative Example 2, amorphous glass for an optical filter was used. Both the thermal expansion coefficient and dn / dT had sufficient values and good temperature stability, but the formed glass substrate was significantly deformed and substrate cracks occurred. The Young's modulus of this glass substrate was about 75 GPa. On the other hand, the crystallized glass of the present invention has a sufficient thermal expansion coefficient, dn / dT, good temperature stability, a Young's modulus of 95 GPa or more, and an optical filter without deformation. Suitable for use as a substrate material.
All the polished surfaces were low in surface roughness and good, but the distribution width of the average linear expansion coefficient was large in Comparative Example 1, and the quality as a bulk material was inferior.

As described above, according to the present invention, it is possible to provide a glass-ceramic substrate for an optical filter having excellent temperature stability at the center wavelength while eliminating the above-mentioned disadvantages of the related art. It could be used as an optical filter that could be fully adapted to high-speed, large-capacity optical communication systems expected in the future.

Claims (5)

The composition of the raw glass is a mass percentage based on oxide,
SiO ₂ 70~80%,
Li ₂ O 5 to 15%,
K ₂ O 0.5~5%,
MgO + ZnO + SrO + BaO 0.1-10%,
P ₂ O ₅ 0.1~5%,
ZrO ₂ 0.1-7%,
Al ₂ O ₃ 1 to 11%,
Sb ₂ O ₃ 0~2%,
Which is a crystallized glass containing the following components: lithium disilicate and α-quartz as main crystal phases; a coefficient of thermal expansion at −30 to + 70 ° C. of 100 to 140 × 10 ⁻⁷ / ° C .; A crystallized glass having a temperature coefficient dn / dT of a refractive index at 〜60 ° C. of −1 to +1 (10 ⁻⁶ / K).   The crystallized glass according to claim 1, wherein the light transmittance of a 1 mm-thick material at a wavelength of 950 to 1600 nm is 85% or more.   The crystallized glass according to claim 1 or 2, wherein the polished surface has a center line average roughness Ra of 5 ° or less. The crystal grain size distribution of the main crystal phase is within the range of 0.05 μm, and the distribution width of the average linear expansion coefficient on the plane having the maximum area and the plane in the direction perpendicular to the plane is 0 to 3 × 10 ⁻⁷ / ° C. The crystallized glass according to claim 1. An optical filter comprising a dielectric film formed on the crystallized glass according to claim 1.