JPH11199269A - Optical glass having low photoelastic constant - Google Patents

Abstract

PROBLEM TO BE SOLVED: To precisely control polarizing characteristics in a polarizing optical system by imparting a specified photoelastic constant at a specified wavelength to a BaO-contg. phosphate glass having a specified refractive index and a specified Abb's number as optical constants. SOLUTION: This optical glass is a BaO-contg. phosphate glass having a refractive index of 1.55-1.65, an Abbe's number of 55-65 and <=1.0×10<-5> nm/cm/ Pa photoelastic constant (β) at 0.4-0.7 μm wavelength. The compsn. of the optical glass consists of, by weight, 0.1-4% B2 O3 , 0-5% Al2 O3 , 35-60% P2 O5 , 0-4% MgO, 0-30% CaO, 0-30% SrO, 31-6% BaO (41%<=MgO+CaO+SrO+BaO<=60%), 0-5% ZnO, 0.5-7% La2 O3 , 0-7% Y2 O3 , 0-7% Gd2 O3 , 0-5% Nb2 O5 , 0-10% Ta2 O5 , 0-10% WO3 (0%<=Nb2 O5 +Ta2 O5 +WO3 <=10%), 0-4% Li2 O, 0-4% K2 O (0.1%<=Li2 O+Na2 O+K2 O<=4%) and 0-4% Na2 O, 0-4% Sb2 O3 .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical glass having a small photoelastic constant (.beta.) Suitable for use in a polarization optical system such as a spatial light modulator for performing polarization modulation or a polarization beam splitter.

[0002]

2. Description of the Related Art In recent years, an optical system using polarized light, that is, a polarized optical system, has been used in various fields such as a liquid crystal projector. For example, a spatial light modulator that spatially modulates polarized light, a polarizing beam splitter that separates S-polarized light and P-polarized light, and the like are used in liquid crystal projectors and the like.
In these polarization optical systems, it is desired to control the polarization characteristics with higher accuracy.

When optically anisotropic materials are used for optical components such as a substrate and a prism in a polarization optical system which are required to maintain polarization characteristics, the transmitted principal ray is orthogonal to the principal ray. Since the phase difference (optical path difference) between the extraordinary ray and the extraordinary ray changes compared with that before passing through the material, it becomes impossible to maintain the polarization characteristics, and therefore, a material having optically isotropic properties is used for those parts. There is a need.

[0004] A sufficiently strain-reduced glass, particularly an optical glass, is optically isotropic, and is superior to other materials in terms of durability, strength, light transmittance, and the like. Since there are various types of optical glasses having various optical constants and a wide range of choices in optical design, they have been conventionally used for polarizing optical systems. Above all, S-BSL7 (trade name of OHARA CORPORATION) is inexpensive, has excellent durability, and has a small dispersion.
It is frequently used in polarization optics.

However, even when the above-mentioned conventional optical glass having optical isotropy is used for an optical component of a polarizing optical system,
When mechanical stress or thermal stress is applied to those components, optical anisotropy due to the photoelastic effect, that is, birefringence, is exhibited, and as a result, there is a problem that it is difficult to obtain desired polarization characteristics. .

The mechanical stress is caused, for example, by bonding a material having a different coefficient of thermal expansion from that of glass to glass, and the thermal stress is caused, for example, by heat generation of peripheral equipment and transmission light. It is caused by the heat generated by the glass itself by absorbing energy. When these stresses are applied to the glass, the magnitude of the birefringence of the glass can be indicated by the optical path difference. Assuming that the optical path difference is δ (nm), the thickness of the glass is d (cm), and the stress is F (Pa), the following equation (1) is established. The larger the optical path difference, the greater the birefringence.

[0007]

(Equation 1)

The proportionality constant (β) in the above equation (1) is called a photoelastic constant, and its value differs depending on the type of glass. As shown in the above equation, when the stress (F) applied to the glass and the thickness (d) of the glass are the same, the smaller the photoelastic constant (β), the smaller the optical path difference (δ), that is, the birefringence. In the above-described S-BSL7 (trade name of OHARA CORPORATION), the value of β at a wavelength of 546 nm is 2.79.
As described above, a glass having a smaller photoelastic constant (β) is required in order to more precisely control the polarization characteristics in the polarization optical system as described above.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a liquid crystal display having a refractive index (Nd) of 1.55 to
The present invention is to provide a glass having a small photoelastic constant (β) having an optical constant in the range of 1.65 and Abbe number (νd) of 55 to 65.

[0010]

Means for Solving the Problems To achieve the above object, the present inventors have conducted intensive studies and found that the refractive index (Nd) of a phosphate glass containing BaO is 1.55. The present inventors have found that an optical glass having an optical constant in the range of from 1.65 to 1.65 and an Abbe number (νd) of from 55 to 65 and having a small value of the photoelastic constant (β) can be obtained.

In order to achieve the above object, according to the present invention, the refractive index (Nd) is 1.5.
It is a phosphate glass containing BaO and having an optical constant of 5 to 1.65 and an Abbe number (νd) of 55 to 65, and a photoelastic constant (β) at a wavelength of 0.4 μm to 0.7 μm. Is 1.0 × 10 ⁻⁵ nm / cm / Pa or less.

According to a second aspect of the present invention, when the wavelength is 0.1.
The photoelastic constant (β) at 4 μm to 0.7 μm is 0.9.
× 10 ⁻⁵ nm / cm / Pa or less.

The optical glass according to a preferred embodiment of the present invention has a B ₂ O ₃ content of 0.1% by weight as described in claim ₃ .
_{1~4%, Al 2 O 3 0~5} %, P 2 O 5 35~60%,
MgO 0-4%, CaO 0-30%, SrO 0
30%, BaO 31-60%, provided that MgO + Ca
O + SrO + BaO 41-60%, ZnO 0-5
_{%, La 2 O 3 0.5~7%} , Y 2 O 3 0~7%, Gd
_{2 O 3 0~7%, Nb 2} O 5 0~5%, Ta 2 O 5 0~10
%, WO _{30 to} 10%, provided that Nb ₂ O ₅ + Ta ₂ O <sub>5
+ WO 3 0~10%, Li 2</sub> O 0~4%, Na 2 O
0~4%, K ₂ O0~4%, however, Li ₂ O + Na ₂ O
+ K ₂ O 0.1~4%, characterized by comprising the components of Sb ₂ O ₃ 0~4% range.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The reasons for limiting the composition ranges of the components of the optical glass according to the preferred embodiment of the present invention are as follows.
The P ₂ O ₅ component is an essential component for constituting glass, and is preferably added in an amount of 35% or more. In order to maintain the chemical durability of the glass, the amount is preferably up to 60%. preferable.

The Al ₂ O ₃ component is effective for improving the chemical durability of the glass, and can be added arbitrarily, but is preferably up to 5% for maintaining the devitrification resistance.

The B ₂ O ₃ component is an effective component for stabilizing the glass, and is preferably added in an amount of 0.1% or more. In order to maintain the chemical durability of the glass, the amount is 4%. %.

In the present invention, the BaO component is an important component which has been found to have an effect of greatly reducing the value of the photoelastic constant (β) of the glass. However, in order to exert the above effect, it is added in an amount of 31% or more. In order to maintain the devitrification resistance of the glass, the upper limit is preferably 60%.

The CaO and SrO components have the effect of reducing the photoelastic constant (β) and can be added arbitrarily. However, in order to maintain the target optical constant and the chemical durability of the glass, their amounts are reduced. It is preferable that each is up to 30%.

The MgO component is preferably arbitrarily added up to 4% in order to adjust the target optical constant and improve the meltability.

However, BaO, CaO, SrO and M
The total amount of one or more of each component of gO is 41 to 6 in order to maintain the target optical constant and the devitrification resistance of the glass.
It is preferable to set the range to 0%.

The La ₂ O ₃ component is effective for improving the chemical durability of the glass. However, if the content is less than 0.5%, the effect is small, and if it exceeds 7%, the devitrification tendency is exhibited. Increase.

[0022] Y ₂ O ₃ and Gd ₂ O ₃ component, the La ₂
It has the same effect as the O ₃ component and can be added arbitrarily, but the amount of each is sufficient up to 7%.

The components Nb ₂ O ₅ , Ta ₂ O ₅ and WO ₃ are preferably arbitrarily added up to 5%, 10% and 10%, respectively, for adjusting optical constants. However,
When the total amount of one or more of these three components exceeds 10%, the devitrification resistance of the glass deteriorates.

Each of the components Li ₂ O, Na ₂ O and K ₂ O has the effect of promoting the melting property of the glass and improving the devitrification resistance. One or two of these three components are effective. It is preferable that the total amount is 0.1 to 4%.

The Sb ₂ O ₃ component is a fining agent for melting the glass and has an effect of reducing the photoelastic constant (β), and can be added arbitrarily, but its amount should be 4% or less. Is more preferred.

In addition, a small amount of a component other than the above, for example, a SnO ₂ component may be added as a fining agent to the optical glass of the preferred embodiment of the present invention. In addition, SiO ₂ , Bi ₂ O ₃ and I
Components such as n ₂ O ₃ may be added as necessary to adjust the optical constant up to about 5% and to improve the melting property and devitrification resistance of the glass.

[0027]

EXAMPLES Next, examples of composition (No. 1 to No. 9) of the optical glass according to a preferred embodiment of the present invention and a comparative example (No. A) of the conventional optical glass will be described. The results are shown in Table 1 together with the measurement results of Nd), Abbe number (νd) and photoelastic constant (β). The photoelastic constant (β) is 0.8 cm for the light transmission thickness of the glass sample.
Wavelength 5 with constant stress applied to glass sample from outside
The optical path difference due to birefringence generated when transmitting light of 46 nm was measured, and the difference was obtained by the above equation (1).

[0028]

[Table 1]

As is evident from Table 1, the refractive index (Nd) of each of the optical glasses of Examples of the present invention is 1.0.
It has an optical constant in the range of 55 to 1.65 and an Abbe number (νd) of 55 to 65, and has a photoelastic constant (β) smaller than that of the conventionally known glass of the comparative example, which is further improved. .

All of the optical glasses of these examples have excellent devitrification resistance, good chemical durability, and
Easy to homogenize. The optical glasses of these working compositions are:
Raw materials for optical glass, such as oxides, carbonates, nitrates, and hydroxides, are weighed and mixed at a predetermined ratio, and then charged into a platinum crucible.
After melting at a temperature of about 2 to 4 hours, stirring and homogenizing,
It can be easily obtained by casting into a mold or the like and slowly cooling.

[0031]

As described above, the optical glass of the present invention having a small photoelastic constant has a refractive index (Nd) of 1.55 to 1.55.
1.65, a phosphate-based glass having an Abbe number (νd) having an optical constant in the range of 55 to 65 and containing BaO,
Photoelastic constant (β) at a wavelength of 0.4 μm to 0.7 μm
Is 1.0 × 10 ⁻⁵ nm / cm / Pa or less, and is useful for optical components such as lenses and prisms used in polarization optical systems such as spatial light modulators and polarization beam splitters that perform polarization modulation. It is.

Claims (3)

[Claims] 1. a refractive index (Nd) of 1.55 to 1.65;
It is a phosphate-based glass having an Abbe number (νd) in the range of 55 to 65, containing BaO, and having a wavelength of 0.1.
An optical glass having a small photoelastic constant, wherein the value of the photoelastic constant (β) at 4 μm to 0.7 μm is 1.0 × 10 ⁻⁵ nm / cm / Pa or less. 2. The light according to claim 1, wherein the photoelastic constant (β) at a wavelength of 0.4 μm to 0.7 μm is 0.9 × 10 ⁻⁵ nm / cm / Pa or less. Optical glass with small elastic constant. 3% by weight of B ₂ O ₃ 0.1-4%, Al
₂ O ₃ 0-5%, P ₂ O ₅ 35-60%, MgO 0-4
%, CaO 0-30%, SrO 0-30%, BaO
31-60%, but MgO + CaO + SrO + B
aO 41-60%, ZnO 0-5%, La ₂ O _{3
0.5~7%, Y 2 O 3 0~7} %, Gd 2 O 3 0~7%,
_{Nb 2 O 5 0~5%, Ta} 2 O 5 0~10%, WO 3
0 to 10%, provided that Nb ₂ O ₅ + Ta ₂ O ₅ + WO _{30
~10%, Li 2 O 0~4%} , Na 2 O 0~4%, K
₂ O 0 to 4%, provided that Li ₂ O + Na ₂ O + K ₂ O
_{0.1~4%, Sb 2 O 3 0~4} % of photoelastic constant is small optical glass according to claim 1 or 2, characterized in that it consists of the components in the range.