JP2005187215A - Glass composition for wavelength division multiplexing optical filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a glass composition for a wavelength division multiplexing (WDM) optical filter having average thermal expansion coefficient almost same as that of a dielectric thin film, excellent water resistance and ≤500 °C transition point. <P>SOLUTION: The glass composition for the WDM optical filter has (120-135)×10<SP>-7</SP>/°C average thermal expansion coefficient in 50-150°C and comprises 50-60% SiO<SB>2</SB>, 1-10% Al<SB>2</SB>O<SB>3</SB>, 1-5% Na<SB>2</SB>O, 20-35% K<SB>2</SB>O, 1-5% MgO and 92-97% in total of (SiO<SB>2</SB>+Al<SB>2</SB>O<SB>3</SB>+Na<SB>2</SB>O+K<SB>2</SB>O+MgO) by weight. The glass composition contains also 0-4% Li<SB>2</SB>O, 0-6% CaO, 0-6% BaO, 0-6% ZnO, 0-4% ZrO<SB>2</SB>and 3-8% in total of (Li<SB>2</SB>O+CaO+BaO+ZnO+ZrO) and has 0.75 mg/cm<SP>2</SP>alkali elution in a water resistant test by dipping in water at 95°C for 40 hr. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a glass for a WDM optical filter used as a WDM optical filter material that passes only a specific wavelength band and is used for wavelength division multiplexing (hereinafter referred to as WDM) of light in the optical communication field. Relates to the composition.

  The so-called optical filter includes one that cuts a specific wavelength, one that transmits light, and one that reduces transmission of light. The former optical filter includes a bandpass filter that transmits only a specific wavelength, a notch pass filter that cuts only a specific wavelength, a lowpass filter that transmits only waves shorter than a specific wavelength, and a specific wavelength. There is also a high-pass filter that transmits only the wave on the long wavelength side. A typical example of the latter optical filter is an ND filter.

  In wavelength multiplexing optical communication, light with slightly different wavelengths is multiplexed, or conversely, demultiplexing is performed to selectively extract specific wavelength light from light containing multiple wavelength components. A filter is used.

A narrow bandpass filter associated with the development of such a wavelength division multiplexing WDM system is called a WDM optical filter, and its structure is a dielectric multilayer made of SiO ₂ , TiO ₂ , Ta ₂ O _5, etc. on a quartz substrate. A film is formed (see, for example, Patent Document 1).

  Wavelength division multiplexing With the high accuracy of WDM systems, it is required to narrow the bandwidth of transmission wavelengths of WDM optical filters in order to perform wavelength multiplexed optical communication with higher density than before. If the bandwidth of the transmission wavelength is narrowed, the allowable range of the shift of the center wavelength of the band is also narrowed. Therefore, the shift of the wavelength center due to a slight temperature change also greatly affects. For this reason, it is required to avoid the refractive index fluctuation due to the fluctuation of the operating temperature of the WDM optical filter member and to bring the temperature shift of the wavelength close to zero.

It is known that the temperature shift depends on the thermal expansion coefficients of the glass and the dielectric multilayer film. As a method for bringing the temperature shift close to zero, a glass that takes into account the difference between the thermal expansion coefficient of glass and the thermal expansion coefficient of a dielectric multilayer film is known (for example, see Patent Document 2). Among such glasses, a glass having a particularly low thermal expansion coefficient corresponding to a dielectric film having a smaller thermal expansion coefficient than usual can be seen (see, for example, Patent Document 3).
Moreover, the invention which tried to solve this problem by using crystallized glass instead of normal glass is also seen (for example, refer patent document 4).

  Furthermore, as a filter with better performance, the total number of dielectric multilayer films has been increasing recently, and higher transmittance and refractive index control has been demanded for the base glass.

Japanese National Patent Publication No. 10-512975 JP 2001-89184 A JP 2001-66425 A JP 2001-48584 A

  Crystallized glass as described in Japanese Patent Application Laid-Open No. 2001-48584 described above is more advantageous than ordinary glass in terms of processing, but requires heating for a long time to crystallize, resulting in high costs. There was a problem.

  In addition, in the glass having the glass composition described in Japanese Patent Application Laid-Open No. 2001-89184, a part of the alkali component introduced in order to reduce the difference between the thermal expansion coefficient of the glass and the thermal expansion coefficient of the dielectric multilayer film. There was a phenomenon that it was lost due to a change with time and reaction with moisture during glass processing. As a result, there is a problem that the refractive index of the glass surface is slightly reduced, resulting in a minute change in reflectance.

  These minute changes in optical coefficients have not been so much a problem in the past, but they are a problem with respect to the recent demand for higher functionality of filters. In other words, in order to obtain the performance required by the filter, it is necessary to design the refractive index and thickness of the dielectric multilayer film finely, but this requires the reflectance of the base glass as a parameter, and the reflectance of the glass changes. Then, there was a problem that the desired filter performance could no longer be obtained.

The present invention is a glass for a WDM optical filter for forming a bandpass optical multilayer film on the surface, and an average thermal expansion coefficient at 50 to 150 ° C. is (120 to 135) × 10 ⁻⁷ / ° C., Furthermore, expressed as wt%, SiO ₂ is 50 to 60%, Al ₂ O ₃ is 1 to 10%, Na ₂ O is 1 to 5%, K ₂ O is 20 to 35%, MgO is 1 to 5%. , (SiO ₂ + Al ₂ O ₃ + Na ₂ O + K ₂ O + MgO) is a glass composition for a WDM optical filter, which is a glass composed of 92 to 97%.

Also, expressed in terms of% by weight, Li ₂ O is 0 to 4%, CaO is 0 to 6%, BaO is 0 to 6%, ZnO is 0 to 6%, ZrO ₂ is 0 to 4%, and (Li ₂ O + CaO + BaO + ZnO + ZrO ₂ ) is the above glass composition for a WDM optical filter having a content of 3 to 8%.

Furthermore, it is said glass composition for WDM optical filters whose alkali elution amount in the water resistance test immersed in 95 degreeC distilled water for 40 hours is 0.75 mg / cm < ² > or less.

  By taking the above means, it has suitable physical property values for WDM optical filters, does not require long-time heat treatment at the time of glass production, has good workability even after glass, Can obtain a glass with little change in surface shape due to aging.

  According to the present invention, it is possible to obtain a glass having physical property values suitable for a WDM optical filter, having little change in surface shape due to aging, and capable of being processed at a lower temperature than conventional.

The present invention is a glass for a WDM optical filter for forming a bandpass optical multilayer film on the surface, and an average thermal expansion coefficient at 50 to 150 ° C. is (120 to 135) × 10 ⁻⁷ / ° C., Furthermore, expressed as wt%, SiO ₂ is 50 to 60%, Al ₂ O ₃ is 1 to 10%, Na ₂ O is 1 to 5%, K ₂ O is 20 to 35%, MgO is 1 to 5%. , (SiO ₂ + Al ₂ O ₃ + Na ₂ O + K ₂ O + MgO) is a glass composition for a WDM optical filter, which is a glass composed of 92 to 97%.

  It is known that an optimum range exists for the thermal expansion coefficient in the glass for WDM optical filters. That is, when the thermal expansion coefficient is small, sufficient compressive stress cannot be applied to the optical multilayer film, and the temperature shift of the center wavelength of the filter increases in the positive direction. In addition, when the thermal expansion coefficient is large, the temperature shift increases in the negative direction, causing problems such as peeling of the multilayer film or destruction of the substrate.

However, the appropriate value depends on the target filter. Accordingly, the present inventors to prepare a 3 cavity band-pass filter of the _SiO 2 / _Ta 2 _{O 5} system by a vapor deposition method, was confirmed, the preferred average thermal expansion coefficient at 50 to 150 ° C. (120 to 135) × It was found to be 10 ⁻⁷ / ° C. Within this range, an appropriate compressive stress can be applied to the multilayer film, and the temperature dependence of the filter characteristics can be brought close to zero as much as possible depending on the film forming method. Therefore, the preferable average thermal expansion coefficient of the glass for WDM optical filters of the present invention is (120 to 135) × 10 ⁻⁷ / ° C. at 50 to 150 ° C. More preferably, it is (125-130 * 10 < ^-7 > / degreeC).

In the present invention, expressed by weight%, SiO ₂ is 50 to 60%, Al ₂ O ₃ is 1 to 10%, Na ₂ O is 1 to 5%, K ₂ O is 20 to 35%, MgO is 1 to 1%. It is preferably a glass composition for a WDM optical filter, which is 5% and is a glass composed of 92 to 98% of the total of (SiO ₂ + Al ₂ O ₃ + Na ₂ O + K ₂ O + MgO).

SiO ₂ is an essential component and is introduced into the glass to form a glass skeleton. Expressed in weight%, the content of SiO ₂ is preferably 50 to 60%. If the glass composition of SiO ₂ is less than 50%, the glass state becomes unstable and devitrification is likely to occur, and the glass is not stable. Also, the density becomes too high due to additional components such as alkaline earth components to be introduced instead of SiO ₂ . On the other hand, if it exceeds 60%, the thermal expansion coefficient becomes too low. More preferably, it is 55 to 58% of range.

Al ₂ O ₃ is an essential component, has an effect of stabilizing the glass state, and is introduced into the glass in order to adjust the thermal expansion coefficient and Young's modulus by adjusting the glass composition. Expressed in weight%, the content of Al ₂ O ₃ is preferably 1 to 10%. If the glass composition is less than 1%, the effect cannot be expected. On the other hand, if it exceeds 10%, the thermal expansion coefficient becomes too low and the Young's modulus becomes too high.

Na ₂ O is an essential component and is introduced into the glass in order to increase the thermal expansion coefficient. Expressed in weight%, the content of Na ₂ O is preferably 1 to 5%. If the glass composition is less than 1%, the effect of increasing the thermal expansion coefficient of the glass cannot be obtained. On the other hand, if it exceeds 5%, the glass state becomes unstable and the glass tends to devitrify, and the water resistance is impaired and burns are likely to occur. More preferably, it is 2 to 4.5% of range.

K ₂ O is an essential component and is introduced into the glass in order to increase the thermal expansion coefficient. Expressed in weight%, the content of K ₂ O is preferably 20 to 35%. If the glass composition is less than 20%, the effect cannot be expected. On the other hand, when it exceeds 35%, a problem that water resistance is impaired occurs. More preferably, it is 25 to 33% of range.

  MgO is an essential component and is introduced into the glass for adjusting the thermal expansion coefficient and Young's modulus. Expressed in weight%, the MgO content is preferably 1 to 5%. If the glass composition is less than 1%, the effect cannot be expected. On the other hand, if it exceeds 5 wt%, the expansion coefficient becomes too small. More preferably, it is 1 to 4.5% of range.

Furthermore, it is preferable that the glass is composed of 92 to 98% of the total sum of (SiO ₂ + Al ₂ O ₃ + Na ₂ O + K ₂ O + MgO). If the sum of (SiO ₂ + Al ₂ O ₃ + Na ₂ O + K ₂ O + MgO) is outside the above range, it is difficult to clear the physical properties required for the glass for a WDM optical filter. More preferably, it is 92 to 97% of range.

Also, expressed in terms of% by weight, Li ₂ O is 0 to 3%, CaO is 0 to 6%, BaO is 0 to 6%, ZnO is 0 to 6%, ZrO ₂ is 0 to 4%, (Li ₂ O + CaO + BaO + ZnO + ZrO ₂ ) is preferably 2 to 8%.

Li ₂ O is not necessarily essential, but is preferably introduced for adjusting the thermal expansion coefficient and Young's modulus. However, if it exceeds 4%, the glass becomes unstable and devitrification tends to occur. More preferably, it is 0.1 to 3% of range.

  CaO is not necessarily essential, but is preferably introduced into the glass for adjusting the thermal expansion coefficient and Young's modulus. However, if it exceeds 6%, the tendency to devitrification becomes stronger and the expansion coefficient becomes too small. More preferably, it is 0.1 to 3% of range.

  BaO is not necessarily essential, but is an additional component introduced into the glass for adjusting the thermal expansion coefficient and Young's modulus. However, if it exceeds 6%, the density becomes too large and the water resistance of the glass is lowered. Preferably, it is 3% or less.

  ZnO is not necessarily essential, but is an additional component that is introduced into the glass to stabilize the glass with a small content and adjust the thermal expansion coefficient and Young's modulus. However, if it exceeds 6%, the water resistance of the glass decreases. Preferably, it is 3% or less.

ZrO ₂ is not necessarily essential, but if it is introduced in a small amount, it has the effect of stabilizing the glass state and is an additional component that is introduced into the glass in order to improve the water resistance of the glass. However, when the glass composition exceeds 4%, the tendency of devitrification of the glass is conversely increased and the thermal expansion coefficient is too small. Preferably, it is 2% or less.

Further, (Li ₂ O + CaO + BaO + ZnO + ZrO ₂ ) is preferably 3 to 8%. If the total sum of (Li ₂ O + CaO + BaO + ZnO + ZrO ₂ ) is outside the above range, it is difficult to clear the physical properties required for the WDM optical filter glass. More preferably, it is 3 to 7% of range.

Furthermore, it is preferable that the Na ₂ O elution amount in a water resistance test immersed in distilled water at 95 ° C. for 40 hours is 0.75 mg / cm ² or less. Water resistance is closely related to glass polishing. The glass polishing is competitively performed by mechanical polishing that mechanically removes the surface layer and chemical polishing that chemically dissolves the surface layer. If the water resistance is extremely poor, chemical polishing proceeds excessively and a smooth surface cannot be obtained, and the polished surface is burned. Therefore, the preferable water resistance of the glass for a WDM optical filter of the present invention is 0.75 mg / cm ² or less as an alkali amount in a water resistance test immersed in distilled water at 95 ° C. for 40 hours. With this weight reduction amount, the reflectance is hardly reduced.

In addition, the preferable density of the glass for WDM optical filters of this invention is 2.7 g / cm < ³ > or less under the working temperature at the time of cutting.

  Hereinafter, the present invention will be described with reference to examples. Using oxides, carbonates, nitrates and the like corresponding to the raw materials of each component of the glass, the resulting glass has the composition described in Examples 1 to 5 in Table 1 and Comparative Examples 1 to 4 in Table 2. And weighed and mixed at a predetermined ratio.

  The mixed raw materials are put in a platinum crucible containing 2000 ml in capacity and 10 wt% rhodium, and are melted for 5 hours in an electric furnace heated to 1400 ° C. Then, fine bubbles contained in the molten glass are removed. After cooling in a furnace to an appropriate temperature for removal, it is poured into a graphite mold, put into an electric furnace previously held near the glass transition point, held for 2 hours, and then cooled to room temperature. A glass block having a thickness of 30 mm and a size of 200 mm × 300 mm was obtained.

Next, the glass block was sliced thinly, ground into a cylindrical shape, further polished on both sides, and Ta ₂ O ₅ and SiO ₂ were alternately deposited on one polished surface to obtain a dielectric multilayer film. As a method for producing the dielectric multilayer film and the antireflection film, for example, there are an RF ion plating method, a magnetron sputtering method, a plasma ion plating method, a vapor deposition method, and the like. In this example, the vapor deposition method was used. Thereafter, grinding and polishing were performed from the side where the film was not formed until the thickness reached 1 mm, and an antireflection film was formed on the polishing surface opposite to the multilayer film.

  Next, by rotating a diamond cutter with diamond powder attached to a metal disk and applying it to the glass substrate on which the dielectric multilayer film is formed from the non-film-forming surface side, a so-called dicing process is performed to obtain a thickness of 1 mm, a size of 1 Cut into 5 mm square chips.

The glass thus produced was measured for coefficient of thermal expansion, density and water resistance. The coefficient of thermal expansion was measured by a differential thermal dilatometer with a temperature range of 50 ° C. to 150 ° C. and silica glass as a standard sample. The density was measured by the Archimedes method using distilled water as an immersion liquid. The water resistance was evaluated based on the weight loss when immersed in distilled water at 95 ° C. for 40 hours, that is, the amount of alkali elution, using glass polished to 20 × 50 × 2 mm ^t as a sample. This water resistance test condition conforms to the concepts of JIS R3502 and JOGIS 06-99, and is used, for example, for evaluation of display substrates.

  For the transmittance, a self-recording spectrophotometer (manufactured by Hitachi, U4000 type) was used, and the internal transmittance was determined according to the Japan Optical Glass Industry Association Standard (JOGIS 17-82). It was confirmed that the internal transmittance at a plate thickness of 1 mm was 99% or more in a region of 1300 nm or more, and it was confirmed that this glass was suitable for a WDM filter.

Table 1 relates to the WDM optical filter of the present invention, and shows the glass composition, average thermal expansion coefficient (α _50-150 ), alkali elution amount and density at 50 to 150 ° C. expressed in weight% of Examples 1 to 5. It is shown.

Table 2 relates to the WDM optical filter of the present invention, and shows the glass composition, average thermal expansion coefficient (α _50-150 ), alkali elution amount and density at 50 to 150 ° C. expressed in weight% of Comparative Examples 1 to 4. It is shown.

Claims (3)

A glass for a WDM optical filter for forming a bandpass optical multilayer film on the surface, wherein an average coefficient of thermal expansion at 50 to 150 ° C. is (120 to 135) × 10 ⁻⁷ / ° C. And SiO ₂ is 50-60%, Al ₂ O ₃ is 1-10%, Na ₂ O is 1-5%, K ₂ O is 20-35%, MgO is 1-5%, (SiO ₂ + Al ₂ O ₃ + Na ₂ O + K ₂ O + MgO) is a glass composed of 92 to 97%, and a glass composition for a WDM optical filter. Expressed in weight%, Li ₂ O is 0-4%, CaO is 0-6%, BaO is 0-6%, ZnO is 0-6%, ZrO ₂ is 0-4%, (Li ₂ O + CaO + BaO + ZnO + ZrO). _The glass composition for a WDM optical filter according to claim 1, wherein ₂ ) is 3 to 8%. 3. The glass composition for a WDM optical filter according to claim 1, wherein an alkali elution amount in a water resistance test immersed in distilled water at 95 ° C. for 40 hours is 0.75 mg / cm ² or less.