JPH0948631A - Optical glass for polarizing optics - Google Patents

Abstract

(57) [Summary] [Purpose] Light polarization even under mechanical external stress or thermal stress
Optical glass for polarization optics that transmits without impairing optical characteristics
Provide the service. [Composition] B in mol% display in terms of oxide₂O_Three  0 to
57.0%, Al₂O_Three0 to 13.0% (B₂O_Three+ A
l₂O_Three  0.1-57.0%), SiO₂  0-54.
0% (However, SiO₂+ B₂O_Three+ Al₂O_Three  43.0 ~
57.0%), PbO 43.0 to 45.5%, R₂O
(R: Li, Na, K) 0-3.5%, R'O
(R ': Mg, Ca, Sr, Ba) 0 to 12.0%,
As₂O_Three+ Sb ₂O_Three  It is in the range of 0-1.5%,
T, (F₂/ F₂+ O₂) Fluorine in the range of 0-0.1
An optical glass for a polarizing optical system, which is characterized by being introduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical glass for a polarization optical system having a small photoelastic constant C used in a polarization optical system using a spatial light modulator for performing polarization modulation, a polarization beam splitter and the like.

[0002]

2. Description of the Related Art In recent years, the number of means for controlling the polarization characteristics of optical information has increased, and the field of application of optical systems utilizing polarized light, that is, polarization optical systems, is acceleratingly expanding. For example, as the element for controlling the polarization, there is a polarization modulation type spatial light modulation element which spatially modulates the polarization, or a polarization beam splitter which separates the S polarization and the P polarization, and a device using them, for example, a projection type display. The device has been put to practical use.

Under these circumstances, it is important to control the polarization characteristics with high precision in the polarization optical system, and it is desired to further improve the precision.
Among optical components such as various substrates and prism bases that constitute a polarization optical system, a light transmissive material having optical isotropy should be used in a place where polarization property retention is required. If a material with optical anisotropy is used, the phase difference (optical path difference) between the chief ray and the extraordinary ray orthogonal to it will change in the transmitted light compared to before it passed through the material. , Because the polarization characteristics cannot be preserved. That is,
Even if the element has the ability to control the polarization with high precision, if the characteristics should be impaired by the substrate or the substrate that should maintain the polarization characteristics, it is impossible to obtain high characteristics as a whole. Become.

Generally, fully annealed glass has optical isotropy and is superior to other materials in terms of durability, strength, transmittance, refractive index and price.
Such glass is often used in optical parts where the polarization characteristics should be preserved. In particular, borosilicate glass (for example, BK7 = a symbol of Schott GmbH, Germany) is inexpensive, has excellent durability, and has a small dispersion, so that it is widely used for polarizing optical systems.

[0005]

However, even when the above-mentioned conventional optical glass is used for the optical component of the polarization optical system, the optical difference caused by the photoelastic effect is caused under the mechanical external stress or the thermal stress. Induction is induced. As a result, there is a problem that the polarization characteristics of light change due to this optical anisotropy, and it becomes difficult for the polarization optical system to obtain desired performance.

It is considered that these mechanical external stress and thermal stress mainly occur under the following conditions. The mechanical external stress is mainly due to the glass processing steps (cutting, joining with other materials, film formation on the surface, etc.) and operations for incorporating the glass into the optical system (holding with a jig, bonding, etc.). It occurs later. Also,
The thermal stress is generated by heat generated inside the glass (such as absorption of light energy) or heat generated outside (such as heat generated by peripheral devices). Further, when heat is generated, stress is generated even when glass and a material having a different coefficient of thermal expansion are contact bonded. Therefore, when the polarization optical system is composed of optical components, it is unavoidable that mechanical external stress or thermal stress acts, and when conventional general optical glass is used in the polarization optical system, optical anisotropy is induced. It was unavoidable to be done.

An object of the present invention is to find an optical glass for a polarizing optical system which transmits light without impairing the polarization characteristics of light even under mechanical external stress or thermal stress.

[0008]

Generally, when a force is applied to an isotropic transparent body such as glass to generate a stress, an optical anisotropy is generated in the transparent body and a certain crystal is produced. It becomes birefringent like the body. This is called the photoelastic effect. The refractive index of the transparent body when stress is generated can be represented by a so-called refractive index ellipsoid, and at this time, the main refractive index axis of the refractive index ellipsoid coincides with the main stress axis. The main refractive index is n
Assuming that 1, n2, n3 and principal stresses are σ1, σ2, σ3 (those having common subscripts in the same direction), the following relationship is established between them.

[0009]

[Equation 1]

When light is incident on such a transparent body, if coordinates are taken so that the direction is the same as σ3, the incident light will have two σ1 and σ2 directions, that is, two vibrating surfaces orthogonal to each other. Divided into linearly polarized light. When light is emitted from the transparent body, the difference in refractive index (n1, n2) in each principal stress direction
Therefore, an optical path difference (phase difference) Δφ represented by the following equation is generated between these two linearly polarized lights.

[0011]

[Equation 2]

The value of the photoelastic constant C of the optical glass conventionally used in the polarization optical system is large.
In the case of 7, 2.78 [10 ⁻⁸ cm ² / N] (wavelength λ = 633
The value of (nm) is obtained. Therefore, the optical anisotropy induced by thermal stress or mechanical external stress, and the optical path difference Δφ based on the optical anisotropy are values that cannot be ignored. The present inventors have previously noted that if the glass having a photoelastic constant C is substantially zero, optical anisotropy hardly occurs even under thermal stress or mechanical external stress, and a certain amount of lead is obtained. The inventors have found an optical glass for a polarizing optical system in which a photoelastic constant C is substantially zero in a composition system containing ions. Further, by adding fluorine to the above composition system, the photoelastic constant C
We have found an optical glass for a polarizing optical system, which has improved transmittance in the visible short wavelength range while maintaining substantially zero. However, in the case of a highly accurate polarization optical system, there are some applications in which the transmittance of the glass according to the above-mentioned invention is not yet sufficient, and a material having a further excellent transmittance is required.

Generally, when melting high quality optical glass, a stable platinum crucible is used as a glass melt.
However, depending on the composition system, coloring due to elution of platinum is a problem, and even in the lead-based glass of the present invention, glass having excellent transmittance in which the coloring due to elution of platinum is sufficiently suppressed has not been obtained. It was A glass using only SiO ₂ as an oxide for forming a glass has a problem that it requires a high temperature for melting. Usually, addition of an alkali metal oxide or the like lowers the viscosity of the glass melt to lower the melting temperature. However, the present inventors have experimentally found that the elution of platinum is greatly promoted by an alkali metal oxide or the like which often acts as a flux of SiO ₂ . After extensive research, SiO ₂ which is an oxide capable of forming glass is converted into oxides B ₂ O ₃ and Al ₂ O _{3 which} are capable of forming glass.
It has been found that by substituting with, the meltability of glass is increased and the content of alkali metal oxides and the like is suppressed.

Therefore, the present inventors have found that platinum elution is small and the transmittance in the visible short wavelength region to the ultraviolet region is improved,
Moreover, the glass having a composition range in which the photoelastic constant C of the glass can be kept substantially zero, "B ₂ O ₃ 0 to 57.0% Al ₂ O ₃ 0 to 13.0% in terms of oxide% mol% B ₂ O ₃ + Al ₂ O ₃ 0.1 to 57.0% SiO ₂ 0 to 54.0% However, SiO ₂ + B ₂ O ₃ + Al ₂ O ₃ 43.0 to 57.0% PbO 43.0 to 45. 5% R ₂ O (R: Li, Na, K) 0 to 3.5% R′O (R ′: Mg, Ca, Sr, Ba) 0 to 12.0% As ₂ O ₃ + Sb ₂ O ₃ 0 To 1.5%, and (F ₂ / F ₂ + O ₂ ) 0 to 0.1 is introduced in the range of fluorine. is there.

The above composition range is preferably B ₂ O ₃ 0 to 19.0% Al ₂ O ₃ 0 to 13.0%, expressed as mol% in terms of oxide, where B ₂ O ₃ + Al ₂ O ₃ 2 _{.0 ~ 19.0% SiO 2 38.0 ~} 54.0% , however _{SiO 2 + B 2 O 3 +} Al 2 O 3 43.0 ~ 57.0% PbO 43.0 ~ 45.5% R 2 O (R : Li, Na, K) 0 ~ 3.5% R'O (R ': Mg, Ca, Sr, Ba) 0 ~ 12.0% As 2 O 3 + Sb 2 O 3 0 ~ 1.5% of the range And (F ₂ / F ₂ + O ₂ ) 0 to 0.1.

However, the wavelength of the incident light of the glass of the present invention is
The range is preferably 0.4 μm to 3.0 μm. Note that the photoelastic constant C referred to here is substantially zero,
When the glass is used in a polarization optical system, the influence of the optical path difference due to optical anisotropy is not a problem in the entire system. For example, the photoelastic constant C is -0.8 to 0.8 with respect to the incident light.
It is considered to be within the range of [10 ⁻⁸ cm ² / N]. Preferably, the photoelastic constant C is −0.1 to 0.1 [10 for incident light in the entire visible region (for example, 0.4 to 0.7 μm).
^-8 cm ² / N].

[0017]

In the optical glass for a polarizing optical system of the present invention, the composition range of each component has been experimentally found.
The reasons for limiting them are as follows. The oxides that can form the glass of the present invention are SiO ₂ , B ₂ O ₃ , and Al ₂ O _3.
It is. If the sum of them is 43.0 mol% or less, the devitrification tendency becomes strong, and if it exceeds 57.0 mol%, the content of lead ions, which will be described later, falls out of a predetermined range and decreases, resulting in a desired photoelastic constant. The value of C cannot be obtained.

B ₂ O ₃ is a glass-forming oxide and is excellent in meltability, but if it exceeds 57.0 mol%, the content of lead ions, which will be described later, falls out of a predetermined range and decreases, so that the desired light is emitted. The value of the elastic constant C cannot be obtained. Further, in consideration of chemical durability, it is preferably 19.0 mol% or less. Al ₂ O ₃ is an intermediate oxide and is an oxide capable of forming glass. It is used to replace SiO ₂ to enhance the meltability, but if it exceeds 13.0 mol%, deterioration of the transmittance due to platinum elution is also observed.

B₂O_ThreeAnd Al₂O_ThreeIs SiO₂Replace from
By doing so, it is possible to obtain S without impairing the stability of the glass.
iO₂The melting temperature can be lowered compared to when only
When the platinum crucible is dissolved, platinum is prevented from elution and the transmittance is improved.
It can be possible. B ₂O_ThreeAnd Al₂O_ThreeIs 5
It can be introduced up to 7.0mol%, and its effect is sufficient.
2.0 mol% or more is preferable in order to exhibit
If it exceeds 9.0 mol%, the chemical durability is significantly impaired.
It is.

When SiO ₂ exceeds 54.0 mol%, the meltability becomes poor. Further, in order to obtain good moldability and chemical durability, it is preferably 38.0 mol% or more. As described above, PbO is used to control the photoelastic constant C. Lead ion content of 43.0-45.5m
If it is ol%, the value of the photoelastic constant C becomes substantially zero.

Alkali metal oxides such as Li ₂ O, Na ₂ O and K ₂ O are used to lower the melting temperature and glass transition temperature of the glass and increase the stability of the glass against devitrification. If it exceeds, coloring due to elution of platinum becomes extremely severe. Similarly, MgO, CaO, Sr
Alkaline earth oxides such as O and BaO also have the effect of lowering the melting temperature and glass transition temperature of the glass and increasing the stability of the glass against devitrification, and are thought to promote platinum elution, but compared with alkali metal oxides. Weakly effective, 1
It can be introduced up to 2.0 mol%.

As a defoaming agent₂O_Three+ Sb₂O_ThreeIs necessary
However, if it exceeds 1.5 mol%,
The devitrification resistance and spectral transmission characteristics are impaired. In addition, the above
When fluorine is introduced into the glass composition, the short wavelength side of the spectral transmission curve
The absorption edge of can be moved to the shorter wavelength side. Fluorine
Is KF, K₂SiF₆, PbF ₂With fluoride such as
Can be introduced into the composition of
Ratio of substitution with fluoride (F₂/ F₂+ O₂) Is 0.1
If it exceeds, the glass stability is impaired and devitrification occurs.

As described above, according to the present invention, an optical glass for a polarizing optical system having a photoelastic constant C within the range of substantially zero with respect to the wavelength of incident light can be obtained. Optical glass for polarizing optical system of the present invention, as a raw material of each component constituting each glass composition, corresponding oxides, fluorides, carbonates, nitrates, etc. are prepared, in a box set to room temperature, those The mixture was weighed and mixed at a desired ratio to prepare a blended raw material. The raw material thus prepared was heated to 1000 to 1300 ° C. in an platinum furnace under an air atmosphere using an electric furnace to dissolve the raw material, followed by clarification and stirring by a conventional method to homogenize the raw material. Mold (stainless steel) preheated to 300-450 ° C
It can be easily manufactured by casting in and cooling slowly.

The optical glass for a polarizing optical system of the present invention can be applied to many optical parts, but in particular, it is transparent for reading a polarizing beam splitter or a spatial light modulator which requires highly accurate polarization characteristics. It can be used as a substrate. The polarization beam splitter is, for example, as shown in FIG. 2, composed of two dielectric multilayer films formed between two translucent substrates. In FIG. 2, two prisms 1 and 2 are formed by using the optical glass for polarizing optical system of the present invention as a translucent substrate, and the dielectric multilayer films 3 and 4 are held by the adhesive layer 5 between them. There is.

Since the light loss due to absorption and scattering when light passes through the glass increases as the light transmission thickness of the prisms 1 and 2 increases, the optical glass for polarizing optical system according to the present invention having improved transmittance. It can be used for such a polarizing beam splitter having a long light transmission thickness. Hereinafter, the optical glass for a polarizing optical system of the present invention will be described in detail with reference to examples.

[0026]

EXAMPLE As a raw material of each component constituting each glass composition, corresponding oxides, fluorides, carbonates, nitrates, etc. were prepared, and they were shown in Table 1 in a box set at room temperature.
The proportions described in 2 and 3 were weighed (total weight of each batch: 100 to 500 g) and mixed to prepare a raw material.

The raw material thus prepared was heated to 1000 to 1300 ° C. in an atmosphere of air in a platinum crucible using an electric furnace.
After heating to dissolve the inside, clarification and stirring by a conventional method to homogenize, and then cast into a mold (made of stainless steel) preheated to 300 to 450 ° C. and slowly cooled,
Eight types of polarizing optical system optical glass were manufactured. Tables 1, 2 and 3 show the component ratios in terms of mol% and wt% conversion, and each totals 100%.

With respect to each of the glasses produced as described above, the wavelength at which the refractive index nd is 10 mm and the internal transmittance (internal transmittance of a 10 mm thick sample excluding surface reflection) is 80%,
The photoelastic constant C for light with a wavelength λ = 633 nm was measured. It should be noted that the photoelastic constant C is the light transmission wavelength l = 1 of the light having the wavelength λ = 633 nm in the formula (1) and the formula (2).
Calculation was performed using a 0 mm sample. The measurement results are shown in Tables 1, 2, 3
And 4. However, as a comparison, an optical glass (A) for a polarizing optical system containing a certain amount of lead ions is placed.

[0029]

[Table 1]

[0030]

[Table 2]

[0031]

[Table 3]

[0032]

As described in detail above, the optical glass for a polarizing optical system of the present invention does not substantially cause an optical path difference due to optical anisotropy when mechanical external stress or thermal stress occurs. . In addition, compared with conventional optical glass for polarizing optics, the transmittance in the entire visible range is improved by suppressing the coloring caused by the elution of platinum that occurs when the platinum crucible is melted, so it can be applied to many optical components. become. In particular, it can be used as a reading transparent substrate of a polarization beam splitter or a spatial light modulator that requires highly accurate polarization characteristics.

[Brief description of drawings]

FIG. 1 is 10 m of Examples 2, 5, 6 and Comparative Example (A).
It is a spectrum transmission curve figure of optical glass inside m.

FIG. 2 is a schematic view showing an example of a polarization beam splitter to which the optical glass of the present invention can be applied.

[Explanation of symbols]

 2 ... Spectral transmission curve diagram of Example 2 5 ... Spectral transmission curve diagram of Example 5 6 ... Spectral transmission curve diagram of Example 6 21, 22 ... Prism 23, 24 ... Dielectric Body multilayer film 25 ・ ・ ・ Adhesive layer

Claims (3)

[Claims] 1. B ₂ O ₃ 0 to 57.0% Al ₂ O ₃ 0 to 13.0% in terms of oxide equivalent mol% where B ₂ O ₃ + Al ₂ O ₃ 0.1 to 57.0% SiO ₂ 0 to 54.0% However, SiO ₂ + B ₂ O ₃ + Al ₂ O ₃ 43.0 to 57.0% PbO 43.0 to 45.5% R ₂ O (R: Li, Na, K) 0 to 3.5% R′O (R ′: Mg, Ca, Sr, Ba) 0 to 12.0% As ₂ O ₃ + Sb ₂ O ₃ 0 to 1.5%, and (F ₂ / F ₂ + O ₂ ) 0 to 0.1 Introducing fluorine in the range, An optical glass for a polarizing optical system. 2. B ₂ O ₃ 0 to 19.0% Al ₂ O ₃ 0 to 13.0%, but B ₂ O ₃ + Al ₂ O ₃ 2.0 to 19.0% in mol% in terms of oxide. SiO ₂ 38.0 to 54.0% However, SiO ₂ + B ₂ O ₃ + Al ₂ O ₃ 43.0 to 57.0% PbO 43.0 to 45.5% R ₂ O (R: Li, Na, K) 0 to 3.5% R′O (R ′: Mg, Ca, Sr, Ba) 0 to 12.0% As ₂ O ₃ + Sb ₂ O ₃ 0 to 1.5%, and (F ₂ / F ₂ + O ₂ ) 0 to 0.1 in which fluorine is introduced, an optical glass for a polarizing optical system. 3. The optical glass for a polarizing optical system according to claim 1 or 2, wherein the wavelength of incident light on the glass is 0.
An optical glass for a polarizing optical system, wherein the photoelastic constant C is substantially zero in the range of 4 μm to 3.0 μm.