JPH08259259A - Optical glass for polarizing optical system and method for controlling its refractive index - Google Patents

Abstract

PURPOSE: To make the photoelasticity constant C of optical glass practically zero to a common wavelength range of incident light by incorporating SiO2 , R2 O (R is Li, Na or K), RF, R2 SiF6 , PbO, PbF2 , As2 O3 and Sb2 O3 . CONSTITUTION: Oxides, fluorides, carbonates, nitrates, etc., of the components of optical glass as starting materials are weighed and mixed so as to give a compsn. consisting of, by mol, 40.0-54.0% SiO2 , 0.5-9.0% R2 O (R is Li, Na or K), 0-16.0% RF, 0-3.3% R2 SiF6 , 43.0-45.5%, in total, of PbO and 0-10.0% PbF2 and 0-1.5%, in total, of As2 O3 and Sb2 O3 and satisfying 0.1<=F/O<=18.0. The resultant starting material mixture is melted by heating to 1,000-1,300 deg.C, refined, homogenized by stirring, cast in a preheated metal mold and slowly cooled to obtain the objective optical glass whose photoelasticity constant C is practically zero to 0.4-3.0μm wavelength of incident light.

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 such as a spatial light modulator for polarization modulation or a polarization beam splitter.

[0002]

2. Description of the Related Art In recent years, polarization characteristics of optical information have been used in various fields including liquid crystals. Accordingly, it is important to control the polarization characteristics of optical information with high accuracy in an optical system using polarized light, that is, a polarizing optical system.
Therefore, it is desired to further improve the accuracy.

Of optical components such as a substrate and a prism that constitute a polarization optical system, an optical component having optical isotropy is used for an optical component which is required to maintain polarization characteristics. 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.

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 components for which polarization characteristics should be preserved. In particular, borosilicate glass (eg BK7
= Symbol of Schott GmbH in Germany) is inexpensive, has excellent durability, and has a small dispersion, so it is widely used in polarization optical systems.

[0005]

However, even when the above-mentioned conventional optical glass for a polarization optical system is used for an optical component, under optical external stress or thermal stress, an optical difference caused by a photoelastic effect is caused. Induction is induced. As a result, there is a problem that the polarization characteristics of optical information 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 mainly caused by heat generated inside the glass (such as absorption of light energy) or heat generated outside (such as heat generated from 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 in the conventional polarization optical system optical glass, it is avoided that optical anisotropy is induced. I couldn't do it.

The object of the present invention is to find an optical glass for a polarizing optical system which does not impair the polarization characteristics of optical information even under mechanical external stress or thermal stress, and further control the refractive index of the optical glass to achieve optical design. To expand the possibilities.

[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. Generally, assuming that the main refractive indices are n ₁ , n ₂ , and n ₃ and the main stresses are σ ₁ , σ ₂ , and σ ₃ (the ones having common subscripts are in the same direction), the following is obtained between them. The relationship is established.

[0009]

[Equation 1]

When light is incident on such a transparent body, if the coordinates are taken so that the direction is the same as σ ₃ , the incident light is in the σ ₁ and σ ₂ directions, that is, the vibrating planes are orthogonal to each other. It is divided into two linearly polarized lights. When light is emitted from the transparent body, the difference in refractive index (n ₁ , n ₂ ) 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 No. 7, a value of 2.78 [10 ⁻⁸ cm ² / N] (wavelength λ = 633 nm) is obtained. Therefore, the optical anisotropy induced by the thermal stress or the mechanical external stress and the optical path difference Δφ based on the optical anisotropy.
Is a value that cannot be ignored. In addition, Japanese Patent Application No. 6-13
At 570, the inventors of the present invention 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. We have found an optical glass for a polarizing optical system in which a photoelastic constant C is substantially zero in a composition system containing lead ions. However, the optical glass having the photoelastic constant C in the above invention is substantially zero only when it has a specific refractive index, and is shorter than other incident light when used as an optical component in the visible region. It cannot be said that the transmittance in the wavelength range (for example, about 400 nm to 480 nm) is sufficient.

Therefore, as a result of earnest research, the present inventors have found that
In the composition system of the previous invention, the inventors have found a composition that improves the transmittance by further introducing fluorine and keeps the photoelastic constant C of glass substantially zero, and a method of controlling the refractive index thereof. As a result, the present invention firstly states that, in an optical glass for a polarizing optical system having a photoelastic constant C within a range of substantially zero with respect to a wavelength of incident light, the glass is an oxide-equivalent mol% display. SiO ₂ 40.0 to 54.0% R ₂ O (R: Li, Na, K) 0.5 to 9.0% PbO 43.0 to 45.5% As ₂ O ₃ + Sb ₂ O ₃ 0 to 1.5%, and fluorine / Oxygen (F / O) 0.1 to 18.0% fluorine in the range of glass for polarizing optics, or "photoelastic constant C for the wavelength of incident light.
Is in the range of substantially zero, in the optical glass for a polarizing optical system, the glass is SiO ₂ 40.0 to 54.0% R ₂ O (R: Li, Na, K) 0.5 to 9.0% RF 0 to 16.0% R ₂ SiF _{60 to} 3.3% PbO + PbF ₂ 43.0 to 45.5% PbF _{20 0 to} 10.0% As ₂ O ₃ + Sb ₂ O ₃ 0 to 1.5% composition range and fluorine / oxygen (F / O) 0.1 to 18.0% of fluorine in the range. The wavelength of incident light is preferably in the range of 0.4 μm to 3.0 μm.

Secondly, the present invention relates to an "optical glass for a polarizing optical system in which a photoelastic constant C is substantially zero with respect to a wavelength of incident light, in which the fluorine / oxygen (F
The method for controlling the refractive index of the optical glass for polarizing optical systems is characterized in that the refractive index is controlled by changing the ratio of / O).

It is to be noted that the photoelastic constant C here being substantially zero means that the influence of the optical path difference due to the optical anisotropy when glass is used in a polarizing optical system can be ignored in the entire system. Yes, for example, the photoelastic constant C for incident light is -0.1 to
It is considered to be within the range of 0.1 [10 ^-8 cm ² / N].

[0016]

FUNCTION FIG. 1A shows an example of a composition in which the photoelastic constant C becomes substantially zero with respect to the wavelength of incident light (633 nm) F /
The relationship between O and the refractive index is shown. In addition, FIG. 1B shows the fluctuation of the photoelastic constant C with F / O. As described above, the refractive index of the glass is linear with respect to the ratio of fluorine / oxygen (F / O), and its photoelastic constant C is substantially independent of the ratio of fluorine / oxygen (F / O). Becomes zero. The photoelastic constant C
Is dependent on the content of lead ions and not on the amount of fluorine introduced, this phenomenon is considered to hold in the composition system of the present invention.

Further, FIG. 2 shows a spectral transmission curve within 10 mm of the composition system of the present invention. The optical glasses for polarizing optical systems, which the present inventors have previously found, did not have sufficient transmittance in the short wavelength region, but the introduction of fluorine into the composition system improves the transmittance in the short wavelength region. This tendency becomes remarkable when the ratio of fluorine / oxygen (F / O) is increased, and the absorption edge is also shifted to the short wavelength side accordingly.

The reasons for limiting the composition range of each component in the optical glass for polarizing optical system of the present invention are as follows. Lead ions are used to control the photoelastic constant C. Generally, the photoelastic constant C of a composition system containing lead ions
Is known to depend on its content. When the content of lead ions is 43.0 to 45.5 mol%, the value of photoelastic constant C becomes substantially zero.

Refractive index when fluorine is introduced into the glass composition
Lower the absorption edge on the short wavelength side of the spectral transmission curve to a shorter wavelength.
Has the effect of moving to the side. Fluorine is KF, K₂SiF₆, P
bF ₂Introduced into the glass composition by fluoride such as
Can be. Also, KF, K₂SiF₆And PbF₂Then
It is possible to introduce up to 16.0, 3.3, 10.0 mol% respectively,
If it exceeds that, crystals are deposited due to excess fluorine. Well
In addition, when multiple fluorides are mixed, fluorine / oxygen (F / O)
The ratio can be up to 18.0%.

SiO ₂ is a glass-forming oxide in the glass of the present invention, and 40.0 mol% or more is necessary, but 54.
If it is 0 mol% or more, the content of the lead ion falls outside the predetermined range and decreases, and the photoelastic constant C increases. Alkali metal oxides such as Li ₂ O, Na ₂ O and K ₂ O have the effect of lowering the melting temperature and glass transition temperature of glass and increasing the stability of glass against devitrification, so the total amount is 0.5 mol% or more. It is necessary, but if it exceeds 9.0 mol%, the chemical durability is significantly impaired.

As ₂ O ₃ + Sb ₂ O ₃ as a defoaming agent is introduced as needed, but if it exceeds 1.5 mol%, the devitrification resistance and the spectral transmission characteristics of the glass are impaired. As described above, according to the present invention, an optical glass for a polarization optical system having a photoelastic constant C within the range of substantially zero with respect to the wavelength of incident light is obtained,
Further, the refractive index can be arbitrarily adjusted within the above composition range.

The optical glass for a polarizing optical system of the present invention uses corresponding oxides, fluorides, carbonates, nitrates, etc. as raw materials for each component, and weighs and mixes them in a desired ratio to prepare a compounding raw material. It can be easily produced by heating it to 1000 to 1300 ° C. to melt it, clarifying it, stirring it to homogenize it, then casting it in a preheated mold and slowly cooling it. However, if the nitrate is used in excess, the effect of introducing fluorine in the present invention is reduced.

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. 3, composed of two dielectric multilayer films formed between two translucent substrates. In FIG. 3, 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.

Spatial Light Modulato
r: SLM) is a device that converts optical information by utilizing the photoconductive effect of a photoconductive material and the electro-optical effect of liquid crystal. The spatial light modulator includes at least a photoconductive layer, a liquid crystal layer, and a voltage applying unit that applies a voltage to the two layers. For example, as shown in FIG. 4, it has two transparent substrates, and the transparent substrate 6, the transparent electrode 8, the photoconductive layer 10, the light absorption layer 11, the dielectric mirror 12, and the liquid crystal layer 1 from the writing side.
3, a transparent electrode 9 and a transparent substrate 7. The optical glass of the present invention can be used as a transparent substrate for reading out such a spatial light modulator.

The optical glass for polarizing optical system of the present invention will be described in detail below with reference to examples.

[0026]

EXAMPLE A corresponding oxide, fluoride, carbonate, nitrate or the like was prepared as a raw material for each component,
Weigh and mix the ingredients in the proportions described in 3 and 4 to prepare a blended raw material, heat it to 1000 to 1300 ° C, melt it in an electric furnace, clarify, stir and homogenize it, then preheat it beforehand. A polarizing optical system optical glass was manufactured by casting in the die and gradually cooling.

Tables 1, 2, 3 and 4 show mol% and wt.
Shows the component ratio by% conversion, each is 100% in total
become. For each glass thus obtained, the photoelastic constant C and the refractive index nd, 1 for light with a wavelength λ = 633 nm
The transmittance inside 0 mm (wavelength at a transmittance of 80%) was measured.
The photoelastic constant C was calculated by using a sample having a wavelength of λ = 633 nm and a glass light transmission thickness 1 = 10 mm in the formulas (1) and (2). The measurement results are shown in Tables 1, 2, 3 and 4.

[0028]

[Table 1]

[0029]

[Table 2]

[0030]

[Table 3]

[0031]

[Table 4]

[0032]

As described above in detail, the optical glass for a polarizing optical system of the present invention substantially causes an optical path difference due to optical anisotropy when mechanical external stress or thermal stress occurs. Absent. Furthermore, by selecting the ratio of fluorine / oxygen (F / O), it is possible to increase or decrease the refractive index within a certain range while keeping the photoelastic constant C substantially zero, which greatly contributes to the optical design. To do. For example, the selection of the optical thin film, which is determined by the refractive index of the glass, can be facilitated.
Furthermore, since the transmittance in the short wavelength region is also improved, it can be applied to many optical components. In particular, it can be used as a reading transparent substrate for a polarization beam splitter or a spatial light modulator that requires highly accurate polarization characteristics.

[Brief description of drawings]

FIG. 1 is a diagram showing changes in the physical properties of glass with the ratio of fluorine / oxygen (F / O) according to the present invention. It is a figure which shows (A) refractive index nd. (B) It is a figure which shows the fluctuation | variation of the photoelastic constant C.

FIG. 2 is a spectral transmission curve diagram of optical glasses having a 10 mm inside of Examples 1, 3, and 5.

FIG. 3 is a schematic view showing an example of a polarization beam splitter to which the optical glass of the present invention can be applied.

FIG. 4 is a schematic view showing an example of a spatial light modulator to which the optical glass of the present invention can be applied.

[Explanation of symbols]

 1, 2 ... Prism 3, 4 ... Dielectric multilayer film 5 ... Adhesive layer 6, 7 ... Transparent substrate 8, 9 ... Transparent electrode 10 ... Photoconductive layer 11 ... Light absorption layer 12 ... Dielectric mirror 13 ... Liquid crystal layer

Claims (4)

[Claims] 1. An optical glass for a polarizing optical system having a photoelastic constant C within a range of substantially zero with respect to the wavelength of incident light, wherein the glass is SiO ₂ 40.0 to 54.0 in terms of oxide equivalent mol%. % R ₂ O (R: Li, Na, K) 0.5 to 9.0% PbO 43.0 to 45.5% As ₂ O ₃ + Sb ₂ O ₃₀ 0 to 1.5% composition range and fluorine / oxygen (F / O ) An optical glass for a polarizing optical system, which has fluorine in the range of 0.1 to 18.0%. 2. An optical glass for a polarizing optical system having a photoelastic constant C within a range of substantially zero with respect to a wavelength of incident light, wherein the glass is SiO ₂ 40.0 to 54.0% R ₂ O expressed in mol%. (R: Li, Na, K) 0.5 to 9.0% RF 0 to 16.0% R ₂ SiF _{60 to} 3.3% PbO + PbF ₂ 43.0 to 45.5% PbF _{20 to} 10.0% As ₂ O ₃ + Sb ₂ O ₃ 0 An optical glass for a polarizing optical system, which has a composition range of ˜1.5% and a fluorine / oxygen (F / O) content of 0.1˜18.0%. 3. In an optical glass for a polarizing optical system having a photoelastic constant C within a range of substantially zero with respect to the wavelength of incident light, the ratio of fluorine / oxygen (F / O) of the glass is changed. A refractive index control method for an optical glass for a polarizing optical system, characterized in that the refractive index is controlled thereby. 4. The polarizing optical system optical glass according to claim 1, wherein the incident light has a wavelength in the range of 0.4 μm to 3.0 μm. System optical glass.