WO2015141465A1 - Glass substrate for dielectric multilayer film filter - Google Patents

Abstract

The provided glass substrate for a dielectric multilayer film filter has a high thermal expansion coefficient and Young's modulus and can improve mass productivity by having excellent workability. This glass substrate for a dielectric multilayer film filter is characterized by comprising amorphous glass which contains, in mass%, 5-30% Li₂O+Na₂O+K₂O and 0-2% TiO₂ (exclusive of 2%), and which has a thermal expansion coefficient between 95×10^-7 and 130×10^-7/K from -30°C to +70°C.

Description

Glass substrate for dielectric multilayer filter

The present invention relates to a glass substrate for a dielectric multilayer filter used for optical fiber communication or the like.

In optical fiber communication, electrical information such as voice data, image data, or text data on the sender side is converted into optical information mainly by an LD (laser diode), via an optical fiber network including base stations and relay stations. The receiver side receives the optical information and converts the received optical information into electrical information again, whereby information is communicated from the sender to the receiver. In the base station, a prism, a mirror, an optical filter (a band pass filter, an edge filter, an etalon, etc.), etc. are used in order to collect optical information from various terminals and sort sent information to each terminal. On the other hand, an EDFA (Erbium Doped optical Fiber Amplifier) or the like is used in the relay station to amplify optical information attenuated in the optical fiber.

In recent years, communication speed and capacity have been increased, and a method called wavelength division multiplexing (hereinafter referred to as WDM) is used in optical fiber communication. In the WDM system, in a certain wavelength band, a plurality of lights having different wavelengths to which information is added are simultaneously transmitted through one optical fiber, and then each information is demultiplexed to each wavelength and received. Here, since the wavelength band is determined in advance, the smaller the difference between the wavelengths, the more information can be transmitted simultaneously.

For demultiplexing in the WDM system, an optical filter that selectively reflects or transmits only light of a specific wavelength is used. In general, an optical filter has a structure in which a dielectric multilayer film is formed on a substrate surface (hereinafter referred to as a dielectric multilayer film filter). Since a laser beam with strong energy is incident on the substrate, glass is used as the material because of its excellent heat resistance and low light absorption at the corresponding wavelength.

In a dielectric multilayer filter, the refractive index of the dielectric multilayer tends to change due to density changes caused by expansion and contraction due to temperature changes. As a result, the wavelength of the light reflected or transmitted by the dielectric multilayer filter may change and communication may not be performed correctly. In order to solve this problem, a method has been proposed in which a compressive stress is applied to the dielectric multilayer film in advance to suppress a wavelength change caused by a temperature change.

A dielectric multilayer filter is generally manufactured as follows. (1) A glass substrate having a thermal expansion coefficient larger than that of the dielectric multilayer film is prepared. (2) A dielectric multilayer film is formed by laminating a dielectric film on the surface of a glass substrate heated to several hundred degrees Celsius. (3) After cooling to room temperature, post-processing such as polishing and cutting is performed as necessary. Here, since the glass substrate having a larger thermal expansion coefficient than the dielectric multilayer film contracts more greatly during cooling, compressive stress is applied to the dielectric multilayer film.

In order to improve the demultiplexing accuracy, it is necessary to precisely control the thickness of each layer in the dielectric multilayer film and increase the number of layers. If the number of layers of the dielectric multilayer film increases, the thickness of the entire film increases. Therefore, it is necessary to increase the compressive stress applied to the dielectric multilayer film. Therefore, a high thermal expansion coefficient of the glass substrate is required. In that case, since the stress applied to the glass substrate also increases, it is necessary to increase the Young's modulus in order to suppress deformation such as warpage. In order to satisfy such a requirement, a glass substrate for a dielectric multilayer filter having a large thermal expansion coefficient and Young's modulus has been proposed (for example, see Patent Document 1).

JP 2001-66425 A

With the rapid expansion of the optical communication market in recent years, attempts have been made to reduce the price by improving mass productivity while maintaining performance. Specifically, by increasing the workability of the glass substrate, that is, by increasing the polishing rate and cutting speed of the glass substrate, it is possible to shorten the processing time and increase the production efficiency. However, since the glass substrate disclosed in Patent Document 1 is inferior in workability, there is a problem that it is poor in mass productivity.

In view of the above, an object of the present invention is to provide a glass substrate for a dielectric multilayer filter that has a large coefficient of thermal expansion and Young's modulus and is excellent in workability and can be improved in mass productivity.

The dielectric multilayer filter glass substrate of the present invention contains, by mass%, Li ₂ O + Na ₂ O + K ₂ O 5-30% and TiO ₂ 0-2% (excluding 2%), − It is characterized by being made of an amorphous glass having a thermal expansion coefficient of 95 × 10 ⁻⁷ to 130 × 10 ⁻⁷ / K at 30 to + 70 ° C.

According to the investigation by the present inventors, it has been found that the workability such as polishing and cutting is improved by containing an alkali metal oxide in the glass composition. On the other hand, it was found that when TiO ₂ was contained in the glass composition, the glass structure was strengthened and the workability was decreased. Therefore, it has been found that workability can be improved by containing an appropriate amount of alkali metal oxide in the glass substrate and regulating the upper limit of the content of TiO ₂ . In addition, since the processing process is shortened by improving the workability, it becomes difficult to cause defects such as undesired processing scratches on the glass substrate and the dielectric multilayer film, and to be corroded by the polishing liquid, etc., and the yield is improved. Can also be expected.

In addition, since the glass substrate of this invention consists of amorphous glass, it is excellent in workability markedly compared with the glass substrate which consists of crystallized glass.

The glass substrate for dielectric multilayer filter of the present invention preferably has a Young's modulus of 75 GPa or more.

The glass substrate for a dielectric multilayer filter of the present invention preferably has a polishing rate by a lapping method of 20 μm / min or more.

The dielectric multilayer filter glass substrate of the present invention contains, by mass%, SiO ₂ 30 to 60%, Al ₂ O ₃ 0 to 10%, MgO + CaO + SrO + BaO + ZnO 3 to 35%, and ZrO ₂ 0 to 10%. Is preferred.

The glass substrate for a dielectric multilayer filter of the present invention preferably has an internal transmittance of 98% or more at a wavelength of 1550 nm in terms of a thickness of 1 mm.

A dielectric multilayer filter of the present invention comprises the above-mentioned dielectric multilayer filter glass substrate, and a dielectric multilayer film formed on the dielectric multilayer filter glass substrate. .

According to the present invention, it is possible to provide a glass substrate for a dielectric multilayer film filter that has a large coefficient of thermal expansion and Young's modulus and is excellent in workability, so that mass productivity can be improved.

The glass substrate for a dielectric multilayer filter of the present invention is amorphous, containing 5-30% of Li ₂ O + Na ₂ O + K ₂ O and TiO ₂ 0-2% (excluding 2%) by mass%. Made of quality glass. The reason for specifying the content of each component in this way will be described below. In the following description regarding the content of each component, “%” means “% by mass” unless otherwise specified.

Li ₂ O, Na ₂ O, and K ₂ O are components that improve workability and increase the coefficient of thermal expansion. The content of Li ₂ O + Na ₂ O + K ₂ O is 5-30%, preferably 5-22%. When _{Li 2 O + Na 2 O +} K 2 O content is too small, the effect is difficult to obtain. On the other _hand, when the _{Li 2 O + Na 2 O +} K 2 O content is too large, there tends to be inferior in weather resistance.

TiO ₂ is a component that strengthens the glass structure and lowers workability. The content of TiO ₂ is 0 to 2% (however, not including 2%), preferably 0 to 1%, more preferably 0 to 0.5%, and still more preferably not containing. .

The glass substrate for multilayer filter of the present invention can contain various components in addition to the above components. For example, the glass substrate for multilayer filter of the present invention contains, by mass%, SiO ₂ 30-60%, Al ₂ O ₃ 0-10%, MgO + CaO + SrO + BaO + ZnO 3-35%, and ZrO ₂ 0-10%. Is preferred. The reason for specifying the content of each component in this way will be described below.

SiO ₂ is a component constituting a glass skeleton and has an effect of improving weather resistance. The content of SiO ₂ is preferably 30 to 60%, more preferably 40 to 55%. When the content of SiO ₂ is too small, the weather resistance tends to lower. On the other hand, if the content of SiO ₂ is too large, processability tends to decrease. Also, melting and molding tend to be difficult.

Al ₂ O ₃ is a component constituting a glass skeleton similarly to SiO ₂ and has an effect of improving weather resistance. In particular, it is a component having a high effect of suppressing elution of alkali components in glass. The content of Al ₂ O ₃ is preferably 0 to 10%, more preferably 1 to 8%. When the content of Al ₂ O ₃ is too large, processability tends to decrease. Also, melting and molding tend to be difficult.

MgO, CaO, BaO, SrO and ZnO are components that act as fluxes and aid melting. Further, like the alkali metal oxide, it has an effect of improving workability. The content of MgO + CaO + SrO + BaO + ZnO is preferably 3 to 35%, more preferably 5 to 34%, still more preferably 10 to 33%, particularly preferably 15 to 32%, and more preferably 20 to Most preferably, it is 30%. When there is too little content of MgO + CaO + SrO + BaO + ZnO, workability will fall easily. On the other hand, if the content of MgO + CaO + SrO + BaO + ZnO is too large, the weather resistance tends to be lowered.

ZrO ₂ is a component that increases the coefficient of thermal expansion while maintaining weather resistance. The content of ZrO ₂ is preferably 0 to 10%, more preferably 1 to 8%. When the content of ZrO ₂ is too large, it tends to be devitrified.

In addition to the above components, a clarifying agent such as Sb ₂ O ₃ , Y ₂ O ₃ , La ₂ O ₃ , Nb ₂ O _5, Gd ₂ O _3, or the like is included in order to improve Young's modulus or weather resistance. Is also possible. However, As ₂ O ₃ is not preferable in view of the environment, so it is preferable not to include it.

The dielectric multilayer film filter glass substrate of the present invention has a thermal expansion coefficient of 95 × 10 ⁻⁷ to 130 × 10 ⁻⁷ / K at −30 to + 70 ° C., and 100 × 10 ⁻⁷ to 130 × 10 ^−7. / K is preferable, and 103 × 10 ⁻⁷ to 125 × 10 ⁻⁷ / K is more preferable. If the thermal expansion coefficient is too small, the application of compressive stress to the dielectric multilayer film tends to be insufficient. As a result, the temperature dependency of the transmitted light center wavelength of the dielectric multilayer filter increases, and the demultiplexing accuracy tends to decrease. On the other hand, when the thermal expansion coefficient is too large, the dielectric multilayer film is easily peeled from the glass substrate.

The temperature dependency of the transmitted light center wavelength of the dielectric multilayer filter is preferably 1 pm / K or less.

The Young's modulus of the glass substrate for a dielectric multilayer filter of the present invention is preferably 75 GPa or more, and more preferably 80 GPa or more. If the Young's modulus is too small, the glass substrate may be deformed by the stress received from the dielectric multilayer film.

The glass substrate for a dielectric multilayer filter of the present invention preferably has a polishing rate by a lapping method of 20 μm / min or more. If the polishing rate by the lapping method is too low, the processing time becomes long and the productivity tends to decrease. In addition, the glass substrate and the dielectric multilayer film are liable to suffer from problems such as unwanted processing flaws or being corroded by the polishing liquid, etc., and the yield tends to decrease. Note that the polishing rate by the lapping method depends on the measurement conditions described in the examples described later.

In the glass substrate for a dielectric multilayer filter of the present invention, the internal transmittance at a wavelength of 1550 nm is preferably 98% or more, more preferably 99% or more in terms of thickness of 1 mm. If the internal transmittance is too low, the light propagation efficiency tends to decrease. Further, the temperature may be unduly increased by the absorbed light energy.

The glass substrate for a dielectric multilayer filter of the present invention preferably has a mass loss of less than 0.25% and more preferably less than 0.1% in water resistance evaluation according to JOGIS.

The dielectric multilayer filter glass substrate of the present invention preferably has a strain point of 380 ° C. or higher. According to the said structure, even if it heats at each process, such as film-forming, washing | cleaning, and drying, it becomes difficult to deform | transform.

A dielectric multilayer filter of the present invention comprises the above-mentioned dielectric multilayer filter glass substrate, and a dielectric multilayer film formed on the dielectric multilayer filter glass substrate. .

Examples of the constituent components of the dielectric layer constituting the dielectric multilayer film include SiO ₂ , Al ₂ O ₃ , La ₂ O ₃ , TiO ₂ , and Nb ₂ O ₅ . Generally, a dielectric multilayer film is formed by alternately laminating low refractive index films (SiO ₂ , Al ₂ O ₃ etc.) and high refractive index films (La ₂ O ₃ , TiO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ etc.). It has the structure formed.

The dielectric multilayer filter of the present invention is manufactured as follows. First, a glass substrate having a size capable of producing a large number of target dielectric multilayer filters (for example, about 2 mm × 2 mm × 1 mm) is prepared. If necessary, a polishing process (preferably mirror polishing) is performed on the surface of the glass substrate on which the film is formed. A dielectric multilayer film is formed on a glass substrate by laminating dielectric materials in a predetermined order and with a predetermined film thickness at 200 to 300 ° C. using various film forming methods. After cooling to room temperature, cutting and polishing are performed to obtain a dielectric multilayer filter having a predetermined size. When both cutting and polishing are performed, either may be performed first. In addition, in order to improve the homogeneity of the dielectric multilayer film, heat treatment may be further performed as necessary.

Examples of the method for forming the dielectric layer include sputtering, PVD (Physical Vapor Deposition), CVD (Chemical Vapor Deposition), aerosol deposition, spin coating, dipping, and vacuum deposition. Among these, a sputtering method, a CVD method, a vacuum deposition method, or the like that can easily form a predetermined film material in a predetermined order and with a predetermined film thickness is preferable.

Examples of cutting means include a wire saw, a rotary blade cutter, a water jet, and a laser cutting.

In addition, as a raw material glass substrate, it is preferable to use a relatively thick glass substrate (for example, a thickness of 10 mm or more) so that deformation such as warpage does not occur due to stress from the dielectric multilayer film. In this case, after the dielectric multilayer film is formed, the surface on which the dielectric multilayer film is not formed is polished until a desired thickness (for example, about 1 mm) is obtained. In this case, it is preferable that the polished surface has a high degree of parallelism with the surface on which the dielectric multilayer film is formed and is a mirror surface.

Hereinafter, the dielectric multilayer filter glass substrate of the present invention will be described based on examples, but the present invention is not limited to the following examples.

Table 1 shows examples (Nos. 1 to 4) and comparative examples (Nos. 5 to 8) of the present invention.

(1) Fabrication and characteristic evaluation of glass substrate for dielectric multilayer filter A raw material was prepared so as to have the glass composition shown in Table 1, and was melted at 1300 to 1500 ° C. for 4 hours using a platinum crucible. The molten glass was poured onto a carbon plate and annealed to obtain an amorphous glass molded body. Next, the obtained glass compact is lapped with an alumina powder for 10 to 20 minutes using a flat polishing machine, and then polished with a cerium oxide powder for 30 to 60 minutes to form an amorphous glass. A glass substrate for a dielectric multilayer filter was prepared.

The obtained glass substrate was measured for thermal expansion coefficient, Young's modulus, polishing rate, water resistance and internal transmittance.

The thermal expansion coefficient was determined in the temperature range of −30 to + 70 ° C. using a dilatometer.

The Young's modulus was measured by a bending resonance method at room temperature using a plate-like sample of 20 mm × 40 mm × 2 mm.

The polishing rate by the lapping method was measured as follows. A plate sample of 25 mm x 30 mm x 1.8 mm is held in place on a horizontally rotating cast iron lap plate, processed while supplying a polishing agent with a load applied vertically, and the sample thickness after processing is measured. And evaluated. The test conditions were as follows.

Lap load: 37kPa
Wrap plate rotation speed: 110 rpm
Distance from center of lap plate to center of plate sample: 10cm
Abrasive: Slurry in which No. 1200 alumina powder and water are mixed at a mass ratio of 1:20 Abrasive supply rate: 10 mL / min

Water resistance was measured according to Japan Optical Glass Industry Association Standard JOGIS “Measurement Method of Chemical Durability of Optical Glass (Powder Method) 06-1975”. For the evaluation, pure water adjusted to pH 6.5 to 7.5 was used.

The internal transmittance was obtained after measuring transmittance at a wavelength of 1550 nm for two samples having different thicknesses of 2 mm and 4 mm using a V-670 ultraviolet visible near infrared spectrophotometer manufactured by JASCO Corporation. Based on the measured values, the internal transmittance in terms of 1 mm thickness was obtained by calculation.

(2) Result No. which is an example. Glass substrates 1 to 4 have a thermal expansion coefficient of 103 × 10 ⁻⁷ / K or more, a Young's modulus of 78 GPa or more, a polishing rate of 21 μm / min or more, a mass loss of 0.13% or less in water resistance evaluation, and an internal transmission The rate was 100%.

On the other hand, No. which is a comparative example. The glass substrates of 5 to 8 had a polishing rate as small as 15 μm / min or less and a thermal expansion coefficient as small as 94 × 10 ⁻⁷ / K or less.

Claims (6)

1. By _{mass%, Li 2 O + Na 2} O + K 2 O 5-30% and containing _TiO 2 0 ~ 2% (but not including 2%), -30 thermal expansion coefficient at ~ + 70 ° C. is 95 × 10 ^{- A} glass substrate for a dielectric multilayer filter comprising an amorphous glass having a ^{density of 7} to 130 × 10 ⁻⁷ / K.
2. The glass substrate for a dielectric multilayer filter according to claim 1, wherein Young's modulus is 75 GPa or more.
3. The glass substrate for a dielectric multilayer film filter according to claim 1 or 2, wherein a polishing rate by a lapping method is 20 µm / min or more.
4. The composition according to any one of claims 1 to 3, characterized by containing, in mass%, SiO ₂ 30 to 60%, Al ₂ O ₃ 0 to 10%, MgO + CaO + SrO + BaO + ZnO 3 to 35%, and ZrO ₂ 0 to 10%. A glass substrate for a dielectric multilayer filter according to the item.
5. The glass substrate for a dielectric multilayer filter according to any one of claims 1 to 4, wherein the internal transmittance at a wavelength of 1550 nm in terms of 1 mm thickness is 98% or more.
6. A dielectric multilayer film filter glass substrate according to any one of claims 1 to 5, and a dielectric multilayer film formed on the dielectric multilayer film filter glass substrate. Dielectric multilayer filter.