JP2002311201A - Substrate for optical filter and optical filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a glass substrate for an optical filter having little elution of alkalis, excellent temperature stability of films and high transmittance and to provide an optical filter. SOLUTION: The substrate for an optical filter satisfies the conditions of Ar<=0.1, 70<=α<=150 and T>=90, wherein Ar [μg/cm<2> ] is the eluted amount of the alkali metal component per 1 cm<2> , α[×10<-7> / deg.C] is the coefficient of linear thermal expansion at 25 deg.C to 100 deg.C, and T [%] is the minimum transmittance of the substrate having 1 mm thickness at 500 to 1700 nm wavelength.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical filter substrate and an optical filter. In particular, the present invention relates to an optical filter substrate and an optical filter using crystallized glass.

[0002]

2. Description of the Related Art Some optical filters attenuate the amount of light, selectively transmit / reflect incident light, and rotate a plane of polarization. Among them, wavelength-selective optical filters include band-pass filters that transmit and reflect only specific wavelength regions, notch-pass filters that cut only specific wavelengths, light at shorter wavelengths than specific wavelengths, and light at longer wavelengths. There are high-pass filters and low-pass filters that transmit only light. Usually, these optical filters use a dielectric multilayer film formed by alternately laminating a dielectric thin film having a high refractive index and a dielectric thin film having a low refractive index on a substrate such as glass. I have. For such an optical filter substrate, ordinary amorphous glass having excellent transmittance, durability and low cost is often used.

[0003]

As described above, when an amorphous glass is used for a substrate of an optical filter, there is a problem that an alkali metal component of the substrate moves to a multilayer film formed on the substrate. That is, the alkali metal component diffuses into the film, causing a decrease in transmittance, an increase in surface scattering, a wavelength shift, and the like. In particular, when obtaining a high expansion characteristic with a glass substrate, it is necessary to contain a large amount of an alkali metal component, and the problem of alkali elution becomes important. The alkali elution occurs during film formation and over time.

Further, amorphous glass has a problem that the coefficient of thermal expansion is not sufficiently high, a compressive stress is not given to a film deposited at the time of film formation, and a uniform and high-density film cannot be obtained. If the film is not compressed, the density of the film remains sparse at the time of film formation, and the temperature dependence of the refractive index of the film increases. For example, when amorphous glass is used for the substrate of the bandpass filter, the refractive index of the film fluctuates greatly,
Since the center wavelength of the band pass shifts greatly, the bandwidth cannot be set narrow.

[0005] In view of the above problems, an object of the present invention is to provide a glass substrate for an optical filter and an optical filter, which have low alkali elution, have excellent film temperature stability, and have high transmittance.

[0006]

To achieve the above object, the invention described in claim 1 is characterized in that an optical filter satisfies the following conditions.

Ar ≦ 0.1 70 ≦ α ≦ 150 T ≧ 90 where Ar: elution amount of alkali metal component per 1 cm ² [μg / c
m ^2] α: coefficient of linear thermal expansion at ^{25 ℃ ~100 ℃ [× 10- 7} / ℃] T: is the lowest value of the light transmittance with respect to wavelength 500-1,700 nm of the substrate having a thickness of 1 mm [%].

[0008] The invention described in claim 2 is the crystallized glass according to the invention described in claim 1, wherein at least one of cristobalite, cristobalite solid solution, quartz, and quartz solid solution is a main crystal. It is characterized by.

Further, the invention described in claim 3 is a crystallized glass containing the following components in% by weight described in claim 1 or 2. Or the optical filter substrate described in 2 above: SiO _{2 at} 60 w% or more, 70 w% or less, Al ₂ O _{3 3} w% or more, 10 w% or less, Li ₂ O 4 w% or more, 8 w% or less, ZrO ₂ 1 w% or more, 5 w%. % or less, 5w% in P ₂ O ₅ 1 w% or more.

Further, the invention according to claim 4 is the optical filter substrate according to claim 3, wherein the weight percent is 0.1% by weight.
As described above, it is characterized by containing ZnO of 15 w% or less.

Further, the invention according to claim 5 provides the optical filter substrate according to claim 3, wherein the substrate is substantially ZnO.
Is not contained.

Further, the invention described in claim 6 is characterized in that in the optical filter substrate according to any one of claims 1 to 5, the Young's modulus is 75 GPa or more.

Further, according to the invention described in claim 7, the optical filter substrate according to any one of claims 1 to 6, wherein Vickers hardness is 600 or more.

An eighth aspect of the present invention is an optical filter using the optical filter substrate according to any one of the first to seventh aspects, wherein the optical filter has a wavelength at a temperature change of 0 ° C. to 100 ° C. shift amount TS _{0 ℃ / 100 ℃} is equal to or less than ± 0.1 nm.

Further, the invention described in claim 9 is an optical filter using the optical filter substrate according to any one of claims 1 to 7, wherein the optical filter has a wavelength at a temperature change of 0 ° C. to 100 ° C. shift amount TS _{0 ℃ / 100 ℃} is characterized expressed that the following equation.

[0016] _{TS 0 ℃ / 100 ℃ = -1.45} × 10 5 α S + 1.721 × 1
0 ¹⁰ α _f2 + 2.921 × 10 ⁵ α _f +1.376 where α _{S is the} coefficient of linear thermal expansion of the substrate in the range of 0 ° C. to 100 ° C., α _{f is} the average linear heat of the multilayer film in the range of 0 ° C. to 100 ° C. The coefficient of expansion,

Further, the invention described in claim 10 is characterized in that it is manufactured by laminating a thin film on the optical filter substrate according to any one of claims 1 to 7.

[0018]

Embodiments of the present invention will be described below. The optical filter substrate of the present embodiment satisfies the following conditional expression (1).

Ar ≦ 0.1 70 ≦ α ≦ 150 T ≧ 90 where Ar: elution amount of alkali metal component per 1 cm ² [μg / c
m ^2] α: coefficient of linear thermal expansion at ^{25 ℃ ~100 ℃ [× 10- 7} / ℃] T: is the lowest value of the light transmittance with respect to wavelength 500-1,700 nm of the substrate having a thickness of 1 mm [%].

Conditional expression (1) defines the range of the transfer amount of the alkali metal component from the substrate to water. The movement amount Ar is
FIG. 9 shows the amount of alkali component eluted per 1 cm ² of the substrate surface when the substrate in a mirror state is kept in pure water at 80 ° C. for 24 hours. If the value of the moving amount Ar exceeds 0.1 [μg / cm ² ], the transmittance formed by the erosion of the alkali metal component of the substrate on the film formed on the substrate, the surface scattering increases, the wavelength shift, etc. Become remarkable, which is not desirable.

Conditional expression (2) defines the range of the coefficient of thermal expansion of the substrate. If the coefficient of linear thermal expansion is less than 70 [× 10 ⁻⁷ / ° C.], no compressive stress is generated in the film deposited on the substrate, and a uniform and high-density film cannot be obtained. Therefore, the temperature stability of the refractive index of the film is deteriorated, and the wavelength characteristic changes due to the temperature change. On the other hand, if the coefficient of linear thermal expansion exceeds 150 [× 10 ⁻⁷ / ° C.], the difference in expansion coefficient between the substrate and the film becomes too large, and problems such as peeling of the film are likely to occur, which is not desirable.

Conditional expression (3) defines the range of the light transmittance T of the substrate. The higher the light transmittance, the better.
%, The signal of laser light used in optical communication
S / N may not be sufficient, which is not desirable.

The optical filter substrate of the present embodiment is a crystallized glass having at least one of cristobalite, cristobalite solid solution, quartz, and quartz solid solution as a main crystal phase. By precipitating these crystal phases, alkali elution can be suppressed, the coefficient of linear thermal expansion can be significantly increased, and the light transmittance of a 1 mm thick substrate in the wavelength region of 700 nm to 1700 nm can be reduced by 90%. %.

The substrate for an optical filter of the present embodiment contains the following components by weight.

SiO ₂ 60 w% or more, 70 w% or less, Al ₂ O _{3 3} w% or more, 10 w% or less, Li ₂ O 4 w% or more, 8 w% or less, ZrO ₂ 1 w% or more, 5 w% or less, P ₂ O ₅ 1w% or more and 5w% or less.

In the system having the above glass component, SiO ₂
Is a glass-forming oxide, which is a component of cristobalite, cristobalite solid solution, quartz, and quartz solid solution precipitated as a main crystal phase. However, in the present embodiment, SiO ₂
Is less than 60% by weight, the above-mentioned crystals are difficult to precipitate, which is not desirable. On the other hand, if the content of SiO ₂ exceeds 70% by weight, the melting temperature is increased and the devitrification is increased.

Al ₂ O ₃ is a glass intermediate oxide, and when lithium aluminum silicate or lithium aluminosilicate solid solution is precipitated as a sub-crystal phase, it is a component of these crystal phases. However, in the present embodiment, Al ₂ O ₃ is 3
If less than w%, mechanical strength and chemical durability cannot be obtained. On the other hand, if the content of Al ₂ O ₃ exceeds 10% by weight, the melting temperature increases, and the meltability and devitrification deteriorate.

Since Li ₂ O works as a flux, it improves the stability during production. Also, lithium aluminosilicate,
When a lithium aluminosilicate solid solution, lithium zinc silicate, or lithium zinc silicate solid solution precipitates, it becomes a constituent component of these crystal phases. However, in the present embodiment, if Li ₂ O is less than 4% by weight, the meltability deteriorates. On the other hand, when Li ₂ O exceeds 8% by weight, crystal phases such as lithium monosilicate (Li ₂ O · SiO ₂ ) and lithium disilicate (Li ₂ O · 2SiO ₂ ) are precipitated as crystal phases. This is not desirable because the corrosion value of the alkali metal component increases and elution of the alkali metal component from the substrate occurs.

ZrO ₂ effectively functions as a crystal nucleating agent and also functions as a glass-modified oxide. However, in this embodiment, if ZrO ₂ is less than 1% by weight, necessary crystal nuclei are not formed. In addition, chemical durability and migration resistance are reduced, adversely affecting the film on the substrate. On the other hand, if it exceeds 5% by weight, the melting temperature becomes high and the glass tends to be devitrified, so that melt molding becomes difficult. Further, the crystal grains become coarse or the precipitated crystal phase changes, making it difficult to obtain the required characteristics. Further, a fine and uniform crystal structure cannot be obtained, and a smooth surface required as an optical filter substrate cannot be obtained in polishing.

P ₂ O ₅ is a nucleating agent that functions as a flux and precipitates silicate-based crystals, and is an important component for uniformly depositing crystals throughout the glass. However, in the present embodiment, if P ₂ O ₅ is less than 1% by weight, necessary crystal nuclei are not formed. In addition, chemical durability and migration resistance are reduced, adversely affecting the film on the substrate. On the other hand, if it exceeds 5% by weight, the melting temperature becomes high and the glass tends to be devitrified, so that melt molding becomes difficult. Further, the crystal grains become coarse, the precipitated crystal phase changes, and the desired characteristics are hardly obtained, and a smooth surface required as a substrate for an optical filter in polishing processing cannot be obtained. Further, the reactivity with the furnace material at the time of melting increases, and the devitrification also increases, so that the productivity at the time of melt molding decreases. In addition, the stability of the glass structure is reduced, and the elution of the alkali metal component is likely to occur.

In this embodiment, the composition can be substantially free of ZnO. By not adding ZnO, it becomes possible to increase the value of the coefficient of thermal expansion.

On the other hand, when ZnO is added, ZnO acts as a flux and assists in uniform crystal deposition. When lithium zinc silicate or lithium zinc silicate solid solution precipitates, it becomes a constituent component of these crystal phases. However, in the present embodiment, if ZnO is less than 0.1% by weight, the above-mentioned effect of ZnO cannot be obtained. If ZnO exceeds 15% by weight, the glass becomes stable, crystallization is suppressed, and the desired strength is hardly obtained.

The optical filter substrate of this embodiment has a Young's modulus of 75 GPa or more. If the rigidity of the optical filter is at the above-described level, the optical filter can be held without relatively paying attention to bending or cracking of the substrate. If the Young's modulus is less than 75 GPa, the rigidity of the substrate is insufficient, and the filter characteristics may be changed by holding, which is not desirable.

The optical filter substrate of the present embodiment has a Vickers hardness of 600 or more. If the hardness of the optical filter is within the above range, the handling of the optical filter becomes easy, which is desirable. If the Vickers hardness is less than 600, the hardness of the substrate is insufficient, and if carelessly applied to a jig or the like, the substrate may be damaged, which is not desirable.

The optical filter of the present embodiment has a film configuration in which high-refractive-index dielectric thin films (H layers) and low-refractive-index dielectric thin films (L layers) are alternately laminated, and has a temperature change of 0 ° C. to 100 ° C. wavelength shift amount TS _{0 ℃ / 100 ℃} in is less than ± 0.1 nm. If the amount of wavelength shift is kept within the above range, wavelength separation can be performed stably with respect to wavelength multiplexed light. If it exceeds ± 0.1 nm, the S / N ratio is lowered because it is mixed with signals of adjacent wavelengths, which is not desirable.

The optical filter of the present embodiment has a temperature of 0 ° C. to 100 ° C.
Wavelength shift TS due to temperature change _{0 ° C / 100 ° C}Is
Can be expressed.

[0037] _{TS 0 ℃ / 100 ℃ = -1.45} × 10 5 α S + 1.721 × 10 10 α f 2 + 2.921 × 10 5 α f +1.376 (4) However, α _S: 0 ℃ ~100 ℃ Coefficient of linear thermal expansion of the substrate in the range α _f : Average coefficient of linear thermal expansion of the multilayer film in the range of 0 ° C to 100 ° C.

Conditional expression (4) is an expression derived from the distribution of data obtained from the experiment, and shows the relationship between the linear thermal expansion coefficient of the substrate and the multilayer film deposited on the substrate and the wavelength shift amount. . According to the conditional expression (4), the expansion of the substrate contributes to suppress the wavelength shift, but the expansion of the multilayer film increases the wavelength shift. In addition, since the coefficient of linear expansion of the multilayer film is effective as a square, it is understood that it is preferable to use a substrate having a considerably large coefficient of linear expansion. Using this equation, if the linear expansion coefficients of the substrate and the multilayer film are known, the wavelength shift amount of the optical filter composed of the combination can be calculated. In addition, a combination that reduces the amount of wavelength shift can be found.

Hereinafter, the manufacturing method will be described. Raw materials containing the composition of the main components of the finally produced glass substrate are sufficiently mixed at a predetermined ratio, and the mixture is put into a platinum crucible or a brick crucible and melted. After melting, it is poured into a mold to form a rough shape. This is annealed to room temperature. Then, 50
The temperature is maintained at a primary heat treatment temperature of 0 to 600 ° C. and a primary treatment time (heat treatment), and a crystal nucleus is generated. Continue to 6
The crystal nucleus is grown while maintaining the temperature at the secondary heat treatment temperature of 00 to 750 ° C. and the secondary treatment time. By cooling this, the desired crystallized glass is obtained.

By subjecting this to grinding and polishing to a desired shape and thickness, it can be used as a crystallized glass substrate.

Next, a dielectric multilayer film is formed into an optical filter. A method of manufacturing the optical filter will be described with reference to FIG. The substrate is fixed to a rotating dome that rotates at the top of the vacuum device. During film formation,
By rotating the substrate in the dome, a uniform film can be formed. The substance to be deposited on the substrate is in a crucible located on the bottom inside the vacuum device and is evaporated by an adjacent electron source. In addition, an ion source method is used in which ions are generated by an ion source arranged in the apparatus and applied to a substrate in a dome to give energy to the film and make the film dense.

As examples of the dielectric multilayer film, two types of films having sharp bandpass characteristics were formed.

In the film configuration A, Ta ₂ O ₅ is deposited on the substrate as a high-refractive-index dielectric thin film (H layer), and a low-refractive-index dielectric thin film (L
SiO ₂ was laminated as a layer). As shown in Fig. 2, the film configuration A is composed of an H layer and an L layer alternately formed on the substrate, each having an optical thickness.
Up to 43 layers were formed at 0.25λ. As the last two layers, an H layer and an L layer were laminated with an optical thickness of 0.325λ. Thus, a bandpass filter having a center wavelength of 1.55 μm was obtained. The half width at design is 0.4 nm.

In the film configuration B, HfO ₂ is formed on the substrate as a high-refractive-index dielectric thin film (H layer), and a low-refractive-index dielectric thin film (L layer) is formed on the substrate.
And SiO ₂ was laminated. Film configuration B is shown in FIG.
The H and L layers are alternately formed on the substrate with an optical thickness of 0.25
Up to 47 layers were formed at λ. As the last two layers, an H layer and an L layer were laminated with an optical thickness of 0.325λ. Thus, a bandpass filter having a center wavelength of 1.55 μm was obtained. The half width at design is 1 nm.

Tables 1 to 4 show the glass compositions of the crystallized glass substrates of Examples 1 to 28 in terms of% by weight, together with the respective production conditions. Table 5 shows comparative examples. In the description in the column of main precipitated crystal phase, Crist is cristobalite, Quartz SS (s
olid solution) means quartz solid solution, and Quartz means quartz. The transmittance showed values for wavelengths of 1.55 μm and 1.3 μm.

[0046]

[Table 1]

[0047]

[Table 2]

[0048]

[Table 3]

[0049]

[Table 4]

[0050]

[Table 5]

Next, Table 6 shows a comparison of alkali elution from the substrate. On a substrate surface by cerium oxide was polished to mirror surface of Ra = 10 Å, the coefficient of linear expansion 1 la 10 ^{- 7} / ° C. high temperature and high humidity RH for light filters 90 ° C. -90% where the film A is deposited in For 200 hours, and the change in light transmittance at a wavelength of 1.55 μm including the substrate was measured.

[0052]

[Table 6]

In this embodiment, since the coefficient of thermal expansion is adjusted in accordance with the coefficient of thermal expansion of the film, the amount of wavelength shift due to a change in temperature is kept very small. Furthermore, in this example, the alkali component elution Ar from the substrate is sufficiently small,
The light transmittance hardly deteriorates with time, indicating excellent durability (stability) close to that of a quartz glass substrate containing no alkali.

[0054]

As described in detail above, it is an object of the present invention to provide a glass substrate and an optical filter for an optical filter, which have a small alkali elution, an excellent film temperature stability, a small temperature wavelength shift, and a high transmittance. Aim. According to the present invention, it is possible to provide a crystallized glass substrate having a high expansion coefficient and good workability while reducing the elution amount of an alkali metal component.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a film forming apparatus for forming a dielectric multilayer film of an optical filter.

FIG. 2 shows a film configuration A of an embodiment.

FIG. 3 shows a film configuration B of an embodiment.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Hiroshi Yugame, Inventor Hiroshi Yugame 2-3-1, Azuchicho, Chuo-ku, Osaka City, Osaka International Building Minolta Co., Ltd. F-term (reference) 2H048 GA07 GA09 GA13 GA35 GA51 GA60 2K009 BB04 CC03 CC42 DD03 DD07 EE00 4G062 AA04 AA11 BB02 DA06 DB03 DC01 DD03 DE02 DE03 DE04 DF01 EA03 EB01 EC01 ED01 EE01 EF01 EG01 FA01 FB01 FC03 FD01 FE01 FF01 FG01 FH01 FJ01 FK01 FL01 H01 H01 H01 H01 H01 H01 H01 H01 H01 H01 H01 H01 H01 H01 H01 H01 H01 H01 JJ01 JJ03 JJ05 JJ07 JJ10 KK01 KK03 KK05 KK07 KK10 MM04 NN01 NN30 NN33 NN34 NN40 QQ02 QQ03

Claims (10)

[Claims] An optical filter substrate characterized by satisfying the following conditions: Ar ≦ 0.170 ≦ α ≦ 150 T ≧ 90, where Ar: elution amount of alkali metal component per 1 cm ² [μg / c
m ^2] α: coefficient of linear thermal expansion at ^{25 ℃ ~100 ℃ [× 10- 7} / ℃] T: is the lowest value of the light transmittance with respect to wavelength 500-1,700 nm of the substrate having a thickness of 1 mm [%]. 2. The optical filter substrate according to claim 1, wherein the substrate is a crystallized glass having at least one of cristobalite, cristobalite solid solution, quartz, and quartz solid solution as a main crystal phase. 3. A light filter substrate according to claim 1 or 2, characterized in that a crystallized glass containing the following components in weight%: 70 w% or less SiO ₂ 60 w% or more, Al ₂ O ₃ w% or more and 10 w% or less, Li ₂ O 4 w% or more 8 w% or less, ZrO ₂ 1 w% or more 5 w% or less, P ₂ O ₅ 1 w% or more ₅ w% or less. 4. The composition according to claim 1, wherein said Z is not less than 0.1% by weight and not more than 15% by weight.
4. The optical filter substrate according to claim 3, comprising nO. 5. The optical filter substrate according to claim 3, wherein the substrate does not substantially contain ZnO. 6. The optical filter substrate according to claim 1, wherein the Young's modulus is 75 GPa or more. 7. The optical filter substrate according to claim 1, wherein the substrate has a Vickers hardness of 600 or more. 8. An optical filter using the optical filter substrate according to any one of claims 1 to 7, wherein the optical filter has a temperature of 0 ° C. to 100 ° C.
The wavelength shift amount TS _{0 ° C / 100 °} C in the temperature change of _{° C} is ± 0.
An optical filter having a thickness of 1 nm or less. 9. An optical filter using the optical filter substrate according to claim 1, wherein the optical filter has a temperature of 0 ° C. to 100 ° C.
Light filter wavelength shift amount TS _{0 ℃ / 100 ℃} in temperature change ° C. is characterized expressed that the following _{equation: TS 0 ℃ / 100 ℃ =} -1.45 × 10 5 α S + 1.721 × 10 10 α f2 +2.9
21 × 10 ⁵ α _f +1.376, where α _{S is the} coefficient of linear thermal expansion of the substrate in the range of 0 ° C. to 100 ° C., and α _{f is} the average coefficient of linear thermal expansion of the multilayer film in the range of 0 ° C. to 100 ° C. 10. An optical filter manufactured by laminating a thin film on the optical filter substrate according to claim 1.