JP2000034132A - Glass having low photoelastic coefficient and optical glass - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a glass having specific low photoelastic constant and transmittance without using harmful PbO, exhibiting improved chemical resistance and producible in a mass by specifying a composition composed of P2O5, BaO and Al2O3 and, as necessary, adding specific amount of La2O3, ZnO, B2O3, Sb2O3, etc. SOLUTION: The objective glass contains 41-52 wt.% of P2O5, 47-57 wt.% of BaO and 0.5-5 wt.% of Al2O3 (provided that P2O5+BaO+Al2O3 is 95-100 wt.%) and is optionally incorporated with 0-3 wt.% of La2O3, 0-3 wt.% of ZnO, 0-3 wt.% of CaO, O-3 wt.% of B2O3, 0-3 wt.% of WO3, 0-3 wt.% of Nb2O5, 0-3 wt.% of MgO, 0-3 wt.% of SrO 0-2 wt.% of Sb2O3 and 0-2 wt.% of As2O3 to get a composition falling in the range surrounded by A-B-G-H-I-J-K-F-A in the triangular diagram of P2O5-BaO-Al2O3 composition. A glass having a photoelastic constant of +0.5×10-12 Pa or below and an outer transmittance of >=80% (10 mm thick) at 400 nm, exhibiting negative temperature coefficient of refractive index and having low liquid crystal temperature is produced by the use of the above composition.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low photoelastic constant glass or the like for an optical polarization controlling element which does not substantially contain PbO. Further, in the glass composition range of the present invention, since the photoelastic constant is small and birefringence is unlikely to occur, it can be used as a general optical glass as an application example, for example, a highly reliable lens, prism, and optical window. It can be used as a material.

[0002]

2. Description of the Related Art A low photoelastic constant glass is, for example, an optical polarization control element (optical component) such as a substrate or a prism base constituting a polarization beam splitter, or an optical polarization control element such as a spatial light modulation element for performing polarization modulation. Optical products).

[0003] Low photoelastic constant glass means that the birefringence, that is, the photoelastic constant generated when an external force is applied to the glass thermally and mechanically is small. The low photoelastic constant glass used for the light polarization control element, etc. has a low photoelastic constant, a low liquidus temperature, easy production and mass production, a predetermined wavelength for a predetermined wavelength. It is necessary to satisfy required characteristics such as having a transmittance, no concern about environmental pollution, and having a predetermined refractive index. Among these, the required numerical values for the refractive index, the transmittance and the like differ depending on the application.

The problem of birefringence (photoelastic constant) in a liquid crystal projector is as follows.

In the case of a transmissive liquid crystal projector, the following reasons apply. The number of pixels in the liquid crystal tends to increase year by year due to higher definition of images and matching with the number of pixels of a personal computer. VGA is 640 × 480 pixels, SVGA is 8
00 × 600 pixels, XGA is 1024 × 768 pixels,
At present, the XGA type is going to occupy the mainstream. The trend toward higher pixel counts tends to progress further, and SXGA (1
080 x 1024 pixels) is coming soon. One pixel includes an opening for transmitting light and a transistor portion for driving the pixel. A transistor portion for driving a pixel does not transmit light. As the number of pixels increases, the area of one pixel in the liquid crystal decreases. However, there is a limit to reducing the size of a transistor occupying one pixel. Therefore, as the number of pixels increases, the proportion of the transistor portion that does not transmit light increases (see FIG. 2).
(See (a) to (c)). As a result, the rate at which the liquid crystal transmits light (aperture ratio) decreases, and in order to prevent a decrease in brightness, a lamp having a strong light (high output) must be used. As a result, heat distribution due to light occurs in the PBS prism that polarizes the P wave and S wave of light,
Distortion is caused by the difference in thermal expansion, and thermal stress acts on the glass.
Thermal stress is generated by heat generation inside the glass (due to absorption of light energy, etc.) and heat generation outside (e.g., heat generated by a light source).

In the case of a reflection type liquid crystal projector, the following reasons are given. FIG. 3 is a simple configuration diagram of a reflection type liquid crystal projector. The reflective type differs from the transmissive type in that the transistor that drives the liquid crystal is located below the reflective surface, so it has the characteristic that the aperture ratio does not decrease even if the pixel is oriented toward higher definition. This is advantageous for increasing the number of pixels of the liquid crystal projector. However, a drawback of the reflection type structure is that the light path reciprocates in the PBS prism 1 and the cross prism 2 and thus the optical path length becomes long. When the optical path difference due to birefringence is δ (nm), the following relationship is established. δ = B × σ × d In the above equation, σ (10 ⁵ Pa) is the internal stress when heat or a mechanical force is applied, d (cm) is the optical path length, and B is the photoelastic constant (10 ⁻¹² Pa). Is shown. That is, if the photoelastic constant B is constant, the birefringence increases as the internal stress σ and the optical path length d increase. When the birefringence increases, the resolution of the P-polarized light and S-polarized light is disturbed. In particular, light that should have been converted from P-polarized light to S-polarized light in the OFF state of expressing black as a pixel remains as P-polarized light. This causes non-uniformity on the screen (the internal stress σ in the case of the transmission type and the optical path length d in the case of the reflection type increase, which is a problem). Birefringence is B, σ, d
Because of the product of σ and d, it is possible to reduce B for the amount of increase in σ and d to relatively reduce birefringence. Extremely speaking, if B is 0, δ is 0 even if σ and d are large.

[0007]

SUMMARY OF THE INVENTION Japanese Patent Application Laid-Open No. 9-48631
No. In Japanese, low photoelastic constant glass _{B 2 O 3 -A1 2 O 3} -PbO system is described. In this glass, Pb
O has the strongest effect of reducing the photoelastic constant among the components that can be added to glass, and B ₂ O ₃ and A1 ₂ O ₃ have the effect of increasing the photoelastic constant. It is possible to make the photoelastic constant close to zero. However, since PbO is highly toxic, it is difficult to use glass containing PbO in an area where environmental regulations are severe.

Japanese Patent Application Laid-Open No. 9-48633 discloses that
Although a low photoelastic constant glass based on hydrofluoric acid is described, since this glass contains fluorine, the volatilization of fluorine during melting is large, and the photoelastic constant and the reproducibility of optical characteristics such as dispersion are high. High glass is difficult to obtain. In addition, the striae inside the glass become strong, and the yield of non-defective products is extremely reduced. In addition, even if F is contained, the photoelastic constant does not always decrease. In particular, when a large amount of F is added, the homogeneity inside the glass deteriorates.

Japanese Patent Application Laid-Open No. Hei 2-188442 discloses that P ₂ O ₅ -A ₁₂ O ₃ -B ₂ O ₃ -RO (R = Mg, C
a, Sr, Ba, Pb) -based phosphoric acid-based optical glass is described, but this glass is intended to obtain an optical glass having a high transmittance in an ultraviolet region, and is used for a low photoelastic constant glass. It is not intended to be used for Therefore, P ₂ O ₅ is out of the range of 41 to 52% or B
When the content of aO is less than 47%, the photoelastic constant is +
It exceeds 0.5 × 10 ⁻¹² Pa or does not vitrify. In the case where BaO is in the range of 48 to 53%, A
1 ₂ O ₃ is not suitable for the liquidus temperature because it contains more than 6% (LT) is increased production, and P ₂ O ₅ is vitrified for less than 41% Zuraku, liquidus temperature is increased .

Japanese Patent Laid-Open Publication No. Sho 50-71708 discloses a P ₂ O ₅ —PbO—Nb ₂ O ₅ system phosphate optical glass. The purpose of the present invention is to obtain an optical glass having a low photoelastic constant. Therefore, in Examples therein, Nb ₂ O ₅ was 5% by weight.
The photoelastic constant is + 0.5 × 10
^{Exceeds -12} Pa. In the examples in which Nb ₂ O ₅ is less than 5%, since PbO is contained in 50% or more, 400%
The transmittance near nm is deteriorated.

SUMMARY OF THE INVENTION The present invention has been made under the above-mentioned background, and solves the above-mentioned various problems and provides harmful PbO.
The photoelastic constant, transmittance, etc. are within the specified range without using, excellent in chemical durability such as weather resistance, low liquidus temperature,
It is an object of the present invention to provide a low photoelastic constant glass that can be mass-produced.

[0012]

SUMMARY OF THE INVENTION The present applicant basically proposes PbO as a low photoelastic constant glass capable of achieving the above object.
The P ₂ O ₅ -BaO based low photoelastic constant glass free (P
₂ O _{5: 30~60} weight%, BaO: 40~60 weight%
Etc.) and already filed an application (Japanese Patent Application No. 10-1)
00101). The present inventors have further simplified the main composition of the P ₂ O ₅ —BaO-based low photoelastic constant glass to a simple composition of substantially three components with Al ₂ O ₃ as an essential component. They have found that the photoelastic constant can be reduced, and have completed the present invention.

That is, the low photoelastic constant glass of the present invention has the following constitution.

(Structure 1) P ₂ O ₅ is 41 to 52% by weight.
%, BaO is 47-57%, and Al ₂ O ₃ is 0.5-
5%, contains, _{and, P 2 O 5 + BaO +} Al 2 O 3 of the total amount is low photoelastic constant glass for optical polarization control element, characterized in that 95 to 100%.

(Structure 2) P ₂ O ₅ is 42 to 50% by weight.
%, BaO 48-56%, and Al ₂ O ₃ 1-4.
%, And the total amount of P ₂ O ₅ + BaO + Al ₂ O ₃ is 97 to 100%. A low photoelastic constant glass for a light polarization controlling element.

(Structure 3) The low photoelastic constant glass according to Structure 1 or 2, wherein La ₂ O ₃ is 0 to 3% by weight and Z is
nO 0-3% 0-3% of CaO, B ₂ O ₃ 0 to 3
% WO ₃ 0 to 3% Nb ₂ O ₅ 0-3% of MgO 0-3%, 0-3% of SrO, and Sb ₂ O ₃ 0~2%, A
0 to 2% of s ₂ O ₃ , and P ₂ O ₅ + BaO + A
l ₂ O ₃ + La ₂ O ₃ + ZnO + CaO + B ₂ O ₃ + WO ₃ +
_{Nb 2 O 5 + MgO + SrO} + Sb 2 O 3 + As 2 O 3 in the total amount is low photoelastic constant glass for optical polarization control element which is a 98% to 100%.

(Constitution 4) The low photoelastic constant glass according to constitutions 1 to 3, wherein SiO ₂ , GeO ₂ , Li ₂ O, Na ₂
O, K ₂ O, Cs ₂ O, Y ₂ O ₃ , Gd ₂ O ₃ , Yb ₂ O ₃ , G
a ₂ O ₃ , ZrO ₂ , Ta ₂ O ₅ , TiO ₂ , TeO ₂ , Bi ₂
A low photoelastic constant glass for a light polarization controlling element, comprising at least one component selected from O ₃ .

(Structure 5) P ₂ O ₅ -BaO-A shown in FIG.
In the triangular diagram of the composition of l ₂ O ₃ , A → B → G → H → I →
A low photoelastic constant glass for a light polarization controlling element, which has a composition in a range of J → K → F → A.

(Structure 6) The low photoelastic constant glass according to structures 1 to 5, wherein the photoelastic constant is + 0.5 × 10 ^−12.
A low photoelastic constant glass for a light polarization controlling element, wherein the glass is Pa or less.

(Structure 7) The low photoelastic constant glass according to Structures 1 to 6, wherein the external transmittance at 400 nm is 8
A low photoelastic constant glass for a light polarization controlling element, wherein the glass is higher than 0% (10 mm thickness).

(Structure 8) An optical component produced using the low photoelastic constant glass described in Structures 1 to 7.

(Structure 9) The light polarization controlling element according to Structure 8, wherein the optical component is a polarization beam splitter.

(Structure 10) A liquid crystal projector comprising the polarizing beam splitter according to Structure 9.

(Structure 11) Photoelastic constant The intrinsic photoelastic constant value per mol of each component constituting the glass (unit is 1)
0 ^-12 Pa / mol), respectively, P ₂ O ₅ : 0.02
_{9, BaO: -0.021, La 2} O 3: -0.01, P
_{bO: -0.036, B 2 O 3} : 0.05, Al 2 O 3:
_{0.01, Nb 2 O 5: 0.11} , WO 3: 0.05, M
gO: 0.04, CaO: 0.016, SrO: 0.0
08, ZnO: 0.037, Ti ₂ O: 0.03, Li _{2
O: 0.015, Na 2 O:} 0.025, K 2 O: 0.0
3, Cs ₂ O: 0.03, Sb ₂ O ₃ : 0.04, Bi ₂ O
₃ : Set to 0.05, calculate the sum of intrinsic photoelastic constant value × molar amount, determine the components constituting the photoelastic constant glass based on the calculated value, and determine the desired photoelastic constant. And manufacturing a photoelastic constant glass having characteristics.

(Structure 12) P ₂ O ₅ is 41 to ₅ % by weight.
2%, a BaO 47-57% and the Al ₂ O ₃ 0.5
An optical glass characterized by containing 〜5%, and the total amount of P ₂ O ₅ + BaO + Al ₂ O ₃ is 95-100%.

(Structure 13) P ₂ O ₅ is 40 to 4% by weight.
6%, BaO 52-58%, and Al ₂ O ₃ 0.5
An optical glass characterized by containing 〜5%, and the total amount of P ₂ O ₅ + BaO + Al ₂ O ₃ is 95-100%.

(Arrangement 14) Temperature change amount dT of optical glass
14. The optical glass according to configuration 12 or 13, wherein a temperature coefficient of refractive index (dn / dT) indicating a change amount dn of refractive index with respect to a negative value has a negative value and has athermal property.

(Arrangement 15) A structure represented by the following equation (1)
Partial dispersion ratio P on the short wavelength side of visual light _g,_FAre equal
Shows a large value compared to the optical glass having an Abbe number of
Short-wavelength visible light compared to optical glass with equivalent Abbe number
Unique wavelength dependence with large change in refractive index in the long range
Configurations 12 to 14 characterized by having
Optical glass. P_g,_F= (N_g-N_F) / (N_F-N_c(1) (in the formula (1), n_gIs the refractive index at 436 nm, n_FIs
Refractive index at 480 nm, n_cAt 656 nm
Each shows a refractive index. )

[0029]

According to the structure 1, even if the glass is subjected to a thermal or mechanical stress, it has a low photoelastic constant enough to sufficiently exhibit the function as a light polarization controlling element, and has a light transmittance. In addition, it is possible to produce a lead-free low photoelastic constant glass which does not contain PbO and has good weather resistance such as chemical durability and long-term use. Further, the composition of the low photoelastic constant glass is P ₂ O ₅ —BaO—Al
_The photoelastic constant can be further reduced by simplifying the composition to a simple composition of substantially _two components of ₂ O ₃ . In particular, P ₂
O ₅ to a low photoelastic constant glass -BaO system by adding a predetermined amount of for Al ₂ O ₃ essential components, it is possible to increase the BaO allowable amount in the low photoelastic constant glass P ₂ O ₅ -BaO-based , The photoelastic constant can be further reduced. This is P
_This is because the photoelastic constant of ₂ O ₅ is positive and the photoelastic constant of BaO is negative. Therefore, the photoelastic constant can be made closer to zero by increasing the amount of BaO.
Further, Al ₂ O ₃ is effective for improving weather resistance.

According to the constitution 2, by setting each composition range to a more preferable range, the effect of the constitution 1 is further improved. For example, the photoelastic constant can be reduced, vitrification is facilitated, and weather resistance such as chemical durability is also improved. In particular, Al ₂
By setting O ₃ to 2% by weight, the photoelastic constant can be minimized.

According to the configuration 3, La_TwoO_Three, ZnO and C
Addition of aO improves weather resistance such as chemical durability
Has the effect of causing B_TwoO_Three, WO_Three, Nb_TwoO_Five, MgO,
It is possible to adjust to a predetermined refractive index by adding SrO.
Is possible, Sb_TwoO_Three, As _TwoO_ThreeBy adding
Foam and clarification effects are obtained. Of these components, La
_TwoO_Three, ZnO, Sb_TwoO_ThreeAnd the like in a substantially three-component system (P_TwoO_Five
-BaO-Al_TwoO_ThreeSystem) and compatibility with the three-component system
The addition effect is large even in a very small amount. In particular, La_TwoO_Three
Is preferable because the photoelastic constant is negative, the transmittance,
It is possible to lower the photoelastic constant while maintaining weather resistance.
it can. Also, the total amount of the above components is 98 to 100%.
, The value of the photoelastic constant is + 0.5 × 10^-12Pa
It can be:

According to the constitution 4, by adding these components in a range that does not impair the effect of the present invention, the photoelastic constant value, the liquidus temperature, the refractive index, the transmittance, the stability, the light resistance, and the chemical durability are obtained. It is possible to improve various characteristics by controlling various characteristics such as characteristics.

According to the configuration 5, by using FIG. 1,
Adjustment of each effect and selection of a composition suitable for production become easy.

According to the configuration 6, the photoelastic constant value is set to +0.5.
By setting the pressure to 10 ^-12 Pa or less, the substrate can be suitably used, for example, as a substrate, a lens, or a prism base constituting a polarizing beam splitter in a liquid crystal projector.

According to the configuration 7, by setting the external transmittance at 400 nm to 80% or more (thickness: 10 mm), it can be suitably used as a substrate, a lens, or a prism base constituting a polarizing beam splitter in a liquid crystal projector.

According to the constitutions 8 to 10, by forming them using the low photoelastic constant glass of the present invention, an optical component or an optical product having excellent performance can be obtained.
In particular, even in a liquid crystal projector having a structure in which the prism receives much heat from transmitted light or a structure in which the optical path length of transmitted light is long, by using the prism made of the low photoelastic constant glass of the present invention, It is possible to obtain a liquid crystal projector free from image distortion due to birefringence.

According to the eleventh aspect, an arbitrary intrinsic photoelastic constant value is applied to each component constituting the photoelastic constant glass, a sum of intrinsic photoelastic constant value × molar amount is calculated, and based on the calculated value, By determining the components constituting the photoelastic constant glass and the content thereof, it becomes possible to produce a photoelastic constant glass having desired photoelastic constant and various characteristics.

According to configuration 12, glass of this composition is:
Change d in refractive index with respect to temperature change dT of optical glass
The temperature coefficient of the refractive index (dn / dT) and / or the partial dispersion ratio, which indicate n, show specific values, respectively, and are therefore effective as general optical glass for camera lenses and the like. In addition, since it has a small photoelastic constant and hardly generates birefringence, it is suitable as a lens material. Further, since it is resistant to thermal stress, it is suitable as a lens material used in an environment with a rapid temperature change.

According to the structure 13, the glass of this composition is:
dn / dT and / or partial variance ratio show specific values,
Therefore, it is effective as general optical glass for camera lenses and the like. In addition, since it has a small photoelastic constant and hardly generates birefringence, it is suitable as a lens material. Further, since it is resistant to thermal stress, it is suitable as a lens material used in an environment with a rapid temperature change.

According to the fourteenth aspect, the temperature coefficient of refractive index (dn / dT) indicating the change amount dn of the refractive index with respect to the temperature change amount dT of the optical glass shows a negative value and has athermal properties. It has the following effects.
The refractive index n of the optical glass changes when the temperature T changes.
The amount of change in the refractive index with respect to this amount of temperature change is the temperature coefficient of the refractive index (dn / dT). When the temperature of the glass changes, the optical path length also changes. The temperature coefficient (ds / dT) of the optical path length indicating the degree of this change is expressed by the following equation. ds / dT = (n-1) α + dn / dT (In the above formula, n indicates the refractive index of glass and α indicates the thermal expansion coefficient of glass.) In general optical glass, dn / dT has a positive value. On the other hand, since α is also positive, the optical path length changes due to the normal temperature change. However, the glass having the composition shown in the structure 12 or 13 has a characteristic that the refractive index decreases with an increase in temperature. This is indicated by the fact that dn / dT is a negative value (this is called athermal property). A lens or prism made of such glass has a small amount of change in the optical path length even when used in an optical system with a rapid temperature change, so that the focal length does not shift and a stable image without defocus is obtained. It is possible.

According to the fifteenth aspect, the values of the partial dispersion ratios P _g and _F on the short wavelength side of the visible light are larger than those of the optical glass having the same Abbe number, and the optical glass having the same Abbe number. By having a unique wavelength dependency that the change in the refractive index in the short wavelength region of visible light is larger than that of the above, the following effects are provided in detail. The partial dispersion ratios P _g and _F on the short wavelength side of visible light are represented by the following equation (1). _{P g, F = (n g} -n F) / (n F -n c) (1) ( in the formula (1), n _g is the refractive index at 436 nm, n _F is the refractive index at 480 nm, n _c is 656nm The glass having the composition shown in the above configuration 12 or 13 is, for example, as follows.
_{P g, F = 0.544, νd} = a 63.7, glass BSC7 (P _g having substantially the same Abbe number (νd), _F =
0.534, νd = 64.2) as compared to large P _g, shows a value of _F. As described above, the glass having the composition shown in the above-described configuration 12 or 13 is characterized in that the change in the refractive index in the short wavelength region of visible light is larger than that of the optical glass having the same Abbe number. In designing an optical lens, a plurality of lenses having different refractive indices and different wavelength dependences of the refractive index are combined in order to correct chromatic aberration. BSC7 above
Is a glass type frequently used in the design of an optical lens. By using such a glass having a unique wavelength dependency instead of the BSC7, the degree of freedom in optical design is expanded, and a more advanced chromatic aberration correcting lens is used. Can be created.

Since the photoelastic constant glass and the optical glass of the present invention do not substantially contain PbO, the environmental safety can be improved. Here, “substantially” means that it is not intentionally included. When it is contained as an impurity, or when PbO is contained in ppm or ppb order,
Is intentionally excluded.

Hereinafter, the present invention will be described in detail.

The low photoelastic constant glass of the present invention is characterized in that it is substantially composed of three components of P ₂ O ₅ —BaO—Al ₂ O ₃ . Here, "substantially" means that the total amount of these three components is 95% by weight or more, and means that the image is substantially composed of these three components.

The reason for limiting the content will be described below.

P ₂ O ₅ is an essential component as a glass forming component. Further, another glass-forming component, SiO.
_{(2) The} photoelastic constant becomes smaller with the same amount as compared with B ₂ O ₃ .
However, when the content of P ₂ O ₅ is less than 41% by weight, vitrification does not occur. If the content exceeds 52% by weight, the photoelastic constant exceeds + 0.5 × 10 ⁻¹² Pa. Therefore, the content of P ₂ O ₅ is preferably in the range of 41 to 52% by weight. A preferred range is 42 to 50% by weight, and a more preferred range is 4 to 50% by weight.
2.5 to 46% by weight.

BaO is a component which is indispensable for the present invention because it has a large effect of making the photoelastic constant negative after PbO. If BaO is less than 47% by weight, the photoelastic constant exceeds + 0.5 × 10 ⁻¹² Pa.
On the other hand, if it exceeds 57% by weight, vitrification does not occur. Therefore Ba
The content of O is preferably in the range of 47 to 57% by weight. A preferred range is 48 to 56% by weight, and a more preferred range is 51 to 5%.
5.5% by weight.

Al_TwoO_ThreeIncreases BaO by adding appropriate amount
Has the effect of expanding the vitrification range in the included area,
In addition, it has the effect of increasing chemical durability
It is an indispensable ingredient. Al_TwoO_ThreeContent of 0.5% by weight
If it is less than this, the chemical durability deteriorates. Conversely, 5% by weight
If the content exceeds 47% by weight when BaO is contained, it becomes vitrified.
Absent. Therefore Al_TwoO_ThreeIs in the range of 0.5 to 5% by weight.
The surroundings are good. In addition, Al _TwoO_ThreeContains BaO at 2% by weight
You can get the most. That is, the photoelastic constant
Can be minimized. Al_TwoO_ThreePreferred content of
The preferred range is 1 to 4% by weight, and the more preferred range is 1.5 to
3.5% by weight.

When the total amount of P ₂ O ₅ , BaO and Al ₂ O ₃ is less than 95% by weight, the photoelastic constant is + 0.5 × 10 ⁻¹² Pa.
Or the glass does not vitrify, or the chemical durability deteriorates, and white polishing occurs when polishing the glass, which is a problem. Therefore, the total amount of P ₂ O ₅ , BaO, and Al ₂ O ₃ is 95-1.
The range of 00% by weight is good. The preferred range is 97-100
%, More preferably 98 to 100% by weight.

La as an optional component_TwoO_Three, ZnO, CaO
Can improve the chemical durability of glass by adding an appropriate amount.
It has the effect of improving. However, these are each 3
If it exceeds 10% by weight, the photoelastic constant is + 0.5 × 10^-12Pa
La_TwoO _ThreeOf ZnO, ZnO and CaO
The amounts are each preferably in the range of 0 to 3% by weight. Preferred range
Is 0 to 2% by weight, respectively.

Optional components B ₂ O ₃ , WO ₃ , Nb
_The refractive index can be adjusted by adding an appropriate amount of ₂ O ₅ , MgO, and SrO. However, these are each 3
When the content exceeds% by weight, the photoelastic constant is + 0.5 × 10 ⁻¹² Pa
B ₂ O ₃ , WO ₃ , Nb ₂ O ₅ , Mg
The addition amounts of O and SrO are each preferably in the range of 0 to 3% by weight. The preferred ranges are each 0 to 2% by weight.

[0052] Defoaming is _{Sb 2 O 3, As 2 O} 3 is an optional component by adding an appropriate amount has an effect of refining. However, if each of them exceeds 2% by weight, the photoelastic constant exceeds + 0.5 × 10 ⁻¹² Pa. Therefore, S
b ₂ O _3, As ₂ amount of O ₃ is a good range of 0-2 wt%, respectively. The preferred ranges are each 0 to 0.5% by weight.

In the low photoelastic constant glass of the present invention, P
₂ O ₅ + BaO + Al ₂ O ₃ + La ₂ O ₃ + ZnO + CaO +
B ₂ O ₃ + WO ₃ + Nb ₂ O ₅ + MgO + SrO + Sb ₂ O ₃
If the total amount of + As ₂ O ₃ is less than 98% by weight, the photoelastic constant exceeds + 0.5 × 10 ⁻¹² Pa. Therefore, the total amount of these is preferably 98 to 100% by weight. A more preferred range is 99 to 100% by weight.

SiO ₂ , GeO ₂ , Li ₂ O, Na ₂ O, K
₂ O, Cs ₂ O, Y ₂ O ₃ , Gd ₂ O ₃ , Yb ₂ O ₃ , Ga
₂ O ₃ , ZrO ₂ , Ta ₂ O ₅ , TiO ₂ , TeO ₂ , Bi ₂ O
₃ can be added within the range of the present invention and within the range that does not impair the effects of the present invention.

FIG. 1 shows a triangular diagram of the composition of P ₂ O ₅ —BaO—Al ₂ O ₃ . FIG. 1 shows three components P ₂ O ₅ , BaO, A
FIG. 4 is a triangular diagram using a triangle having a composition point of l ₂ O ₃ as a vertex. In this figure, the glass composition at which the total amount of these three components becomes 100% can be represented by a point within a triangle, and the glass composition range can be represented by a plane. P ₂ O ₅ , BaO, A
Each component of l ₂ O ₃ is represented by the height of each vertex from the opposite side. For example, A point in FIG. 1, P ₂ O ₅ is 52 wt%, B
aO is 47% by weight and Al ₂ O ₃ is 1% by weight (see the scale shown in FIG. 1). In FIG. 1, A → B → C → D →
The composition in the range surrounded by the straight line in the path of E → F → A is P ₂ O ₅ : 41 to 52% by weight and BaO: 47 to
57% by weight and Al ₂ O ₃ : within the range of 0.5 to 5% by weight, which is consistent with the range of 100% for the three components.
The composition range surrounded by a straight line along the route of A → B → G → H → I → J → K → F → A is a range of composition suitable for manufacturing (mass productivity). In addition, point B indicates that P ₂ O ₅ is 52% by weight, Ba
O is 47.5% by weight, Al ₂ O ₃ is 0.5% by weight,
Point G is 47.5% by weight of P ₂ O ₅ , 52% by weight of BaO, and 0.5% by weight of Al ₂ O _3. Point H is 43% by weight of P ₂ O _{5 and} 56% of BaO. % By weight, 1% by weight of Al ₂ O ₃
The point I was that P ₂ O ₅ was 41.5% by weight and BaO was 5% by weight.
6.5% by weight and ₂ % by weight of Al ₂ O _3.
41% by weight of ₂ O ₅ , 56% by weight of BaO, ₃ % of Al ₂ O 3
Percent by weight, the point K is, P ₂ O ₅ is 46% by weight, BaO is 49 percent by weight are Al ₂ O ₃ is 5% by weight, point F, P ₂
O ₅ is 48% by weight, BaO is 47% by weight, and Al ₂ O ₃ is 5% by weight.
% By weight.

In the present invention, P ₂ O ₅ , BaO, Al ₂
La ₂ O ₃ other than O ₃ , ZnO, CaO, B ₂ O ₃ , WO ₃ ,
When Nb ₂ O ₅ , MgO, SrO, Sb ₂ O ₃ , and As ₂ O ₃ are added, 0.5% by weight of Al ₂ O ₃ is included in the frame of FIG.
Is less than + 0.5 × 10
It is possible to replace up to 5% by weight of any one of P ₂ O ₅ , BaO and Al ₂ O ₃ or the total amount within a range not ^{exceeding −12} Pa.

In the present invention, the liquidus temperature is preferably less than 900 ° C., more preferably 880 ° C. or less.

In the present invention, an arbitrary intrinsic photoelastic constant value is applied to each component constituting the photoelastic constant glass, and the photoelastic constant glass or the like of the present invention is determined based on a value calculated from these intrinsic photoelastic constant values. Can be manufactured.

Specifically, for example, the intrinsic photoelastic constant value (unit: 10 ⁻¹² Pa / mol) per mol of each component constituting the photoelastic constant glass is expressed by P
_{2 O 5: 0.029, BaO:} -0.021, PbO: -
0.036 (Effect utilized to calculate the case as _{impurity), La 2 O 3: -0.01} , B 2 O 3:
_{0.05, Al 2 O 3: 0.01} , Nb 2 O 5: 0.11,
WO ₃ : 0.05, MgO: 0.04, CaO: 0.0
16, SrO: 0.008, ZnO: 0.037, Ti
₂ O: 0.03, Li ₂ O: 0.015, Na ₂ O: 0.
025, K ₂ O: 0.03, Cs ₂ O: 0.03, Sb ₂
O ₃ : 0.04, Bi ₂ O ₃ : 0.05, the sum of intrinsic photoelastic constant value × molar amount was calculated, and the components constituting the photoelastic constant glass and the content thereof were calculated based on the calculated values. Is determined to produce a photoelastic constant glass having a desired photoelastic constant. At this time, the components and their contents can be determined in consideration of not only the photoelastic constant value but also the refractive index, transmittance, liquidus temperature, meltability, chemical durability, coloring, and the like.

The intrinsic photoelastic constant (per unit: 10 ^-12) per mol of each component constituting the photoelastic constant glass.
Pa / mol) is not limited to the above value.
₂ O ₅ : 0.029 ± 0.01, BaO: −0.021 ±
0.01, PbO: -0.036 ± 0.01, La
₂ O ₃ : -0.01 ± 0.01, B ₂ O ₃ : 0.05 ± 0.
01, Al ₂ O ₃ : 0.01 ± 0.01, Nb ₂ O ₅ : 0.1.
11 ± 0.01, WO ₃ : 0.05 ± 0.01, Mg
O: 0.04 ± 0.01, CaO: 0.016 ± 0.0
1, SrO: 0.008 ± 0.01, ZnO: 0.03
7 ± 0.01, Ti ₂ O: 0.03 ± 0.01, Li
₂ O: 0.015 ± 0.01, Na ₂ O: 0.025 ±
_{0.01, K 2 O: 0.03 ±} 0.01, Cs 2 O: 0.
03 ± 0.01, Sb ₂ O ₃ : 0.04 ± 0.01, Bi
₂ O ₃ : 0.05 ± 0.01, and the components constituting the photoelastic constant glass and the content thereof are determined based on the intrinsic photoelastic constant to obtain a desired photoelastic constant. Photoelastic constant glass can also be manufactured.

When a component other than the above is added, the intrinsic photoelastic constant of the component can be easily obtained from the actually measured value of the photoelastic constant, and can be used in the same manner as described above.

In producing the low photoelastic constant glass of the present invention, P ₂ O ₅ is used as a raw material in orthophosphoric acid (H ₃ P
O ₄ ), metaphosphate, diphosphorus pentoxide and the like, and as other components, carbonates, nitrates, oxides and the like can be appropriately used. These raw materials are weighed to a desired ratio and mixed to obtain a mixed raw material, which is put into a melting furnace heated to 900 to 1200 ° C., melted, clarified, stirred, homogenized, and then cast into a mold and gradually cooled. By doing so, the low photoelastic constant glass of the present invention can be obtained.

The low photoelastic constant glass of the present invention can be used as an optical element for controlling polarization (a substrate or a prism base constituting a polarization beam splitter, a spatial light modulation element for performing polarization modulation, an electro-optic glass substrate, an electro-optic Glass parts) and other optical components and products. In particular,
It is most suitable when used in a high-temperature device such as a projection color display device (such as a liquid crystal projector). Examples of the method of manufacturing the prism include a method of cutting a glass lump cast into a mold by the above method into a desired shape, a method of preparing a mold of a desired shape in advance, and casting the mold into the mold. Examples of the shape of the prism include a prism having a triangular or trapezoidal side surface.

[0064]

The present invention will be described below in more detail with reference to examples.

Examples 1 to 17, Comparative Examples 1 to 5, and Reference
Examples 1 to 4 Low photoelastic constant glasses were prepared by a conventional method in accordance with the prepared compositions (% by weight) shown in Tables 1 to 3. As raw materials for the preparation, for P ₂ O ₅ , orthophosphoric acid (H ₃ PO ₄ ), metaphosphate, diphosphorus pentoxide and the like are used, and for other components, carbonate,
Nitrate, oxide and the like were used. These raw materials are weighed in a desired ratio and mixed to obtain a compounded raw material.
The mixture was poured into a melting furnace heated to 300 ° C., melted, clarified, stirred, homogenized, and then cast into a mold and slowly cooled to obtain Examples 1 to 17, Comparative Examples 1 to 5, and Reference Examples 1 to 4. A low photoelastic constant glass was obtained.

With respect to the low photoelastic constant glass obtained above, the photoelastic constant, transmittance, and L.P. T (liquidus temperature), Dw
(Water resistance) was measured. Table 1 shows the results of Examples 1 to 8,
Table 2 shows the results of Examples 9 to 17, and Table 3 shows the results of Comparative Examples 1 to 5 and Reference Examples 1 to 4.

[0067]

[Table 1]

[0068]

[Table 2]

[0069]

[Table 3]

The "photoelastic constant" is the optical path difference generated at the center of a glass when a compressive load is applied in a straight line direction to a face-polished glass having a diameter of 20 mm and a height of 15.8 mm using a He-Ne laser beam. Was measured and determined.

“LT (liquidus temperature)” is 700
The glass was allowed to stand in a furnace with a temperature gradient of １1100 ° C., taken out after 30 minutes, and observed with a microscope for the presence or absence of crystals of the softened glass. The lowest temperature at which no crystals were observed was shown. "No LT" in the table means that there was no crystal in any temperature range.

“Dw (water resistance)” means that a glass powder (particle size: 420 to 590 μm) having a weight corresponding to the specific gravity is placed in a platinum basket, and 80 ml of pure water (pH: 6.5 to 7.5) is added.
In a quartz glass round-bottomed flask, treated in a boiling water bath for 60 minutes, and represented by the weight loss rate (% by weight).

The low photoelastic constant glasses of Evaluation Examples 1 to 17 have a photoelastic constant of +
0.5 × 10 ⁻¹² Pa or less, low liquidus temperature and 4
This is a glass having an external transmittance at 00 nm exceeding 80% (10 mm thickness). Also, it has good water resistance.

Comparative Examples 1 and 2 are described in
The glass described in Examples 20 and 26 of No. 8442. In Comparative Example 1, since BaO was less than 47% by weight, the photoelastic constant ^exceeded + 0.5 × 10 ⁻¹² Pa. Comparative Example 2 contains less than 41% by weight of P ₂ O ₅ and
Liquid phase temperature is high because it contains 3% by weight or more of ₂ O ₃ .

Comparative Examples 3 and 4 correspond to the above-mentioned JP-A-50-7
These are glasses described in 2 of Table 3 and 21 in Table 1 in Examples of No. 1708. Since they contain harmful PbO, they have low environmental safety. Further, since Comparative Example 3 contains PbO in an amount of 50% by weight or more, the transmittance at 400 nm is a very low value of 65% by weight. Comparative Example 4 contains more than 3% by weight of Nb ₂ O ₅ , so that the photoelastic constant is + 0.5 × 10 ⁻¹² P
a has been exceeded.

In Comparative Example 5, since a large amount of F was contained, the photoelastic constant ^exceeded + 0.8 × 10 ⁻¹² Pa and the liquidus temperature was high.

[0077] Reference Examples 1 to 4, carried out in the P ₂ O ₅ -BaO based low photoelastic constant glass that applicant does not contain PbO which was previously filed (Japanese Patent Application No. Hei 10-100101) Example 4
7. The glass according to any one of Items 1 to 6. Reference Example 1 is composed of P ₂ O ₅ and BaO
Is 98.5% by weight, but the chemical durability (Dw) is lower than that of the glass obtained by the present invention because Al ₂ O ₃ which is an essential component of the present invention is not contained. Reference Example 2 is P
_{Since the} total amount of ₂ O ₅ and BaO is 92% by weight, the photoelastic constant exceeds + 0.5 × 10 ⁻¹² Pa. In Reference Example 3, since BaO was less than 47% by weight, the photoelastic constant ^exceeded + 0.5 × 10 ⁻¹² Pa. In Reference Example 4, since P ₂ O ₅ exceeded 52% by weight, the photoelastic constant exceeded + 0.5 × 10 ⁻¹² Pa. As described above, the low photoelastic constant glass of the present invention is disclosed in Japanese Patent Application No. 10-1.
Compared with the low photoelastic constant glass described in No. 00101 (photoelastic constant is + 0.8 × 10 ⁻¹² Pa or less), the photoelastic constant is +
0.5 × 10 ⁻¹² Pa or less, low photoelastic constant,
In addition, the glass is more suitable for practical use because of its excellent chemical durability such as water resistance.

Examples 18 to 41 In order to examine the effects of adding a small amount of La ₂ O ₃ and ZnO, a low photoelastic constant glass was prepared in the same manner as in Example 1 according to the composition (% by weight) shown in Tables 4 to 6. Was prepared and evaluated. The results are shown in Tables 4 to 6. From Tables 4 to 6, L
It can be seen that a small amount of a ₂ O ₃ and ZnO has a great effect of improving durability and the like.

[0079]

[Table 4]

[0080]

[Table 5]

[0081]

[Table 6]

Example 42 A substrate and a prism base constituting a polarizing beam splitter in a liquid crystal projector were manufactured using the low photoelastic constant glasses of Examples 1 to 41, and these were incorporated to obtain a liquid crystal projector. When using a liquid crystal projector, the temperature on the heating side of the prism substrate is 150 ° C and the temperature on the cooling side is 50 ° C.
And the temperature difference was 100 ° C., but no effect due to birefringence was observed.

Application Example When the characteristics of the glass having the composition of the above-described embodiment were examined in detail, the temperature coefficient (dn / dT) of the refractive index indicating the change amount dn of the refractive index with respect to the temperature change amount dT of the optical glass.
And the partial dispersion ratio show specific values, respectively, and proved to be effective as general optical glass for camera lenses and the like.

For example, a glass having the composition shown in Example 3 (P
₂ O ₅ : 43.0% by weight, BaO: 55.0% by weight, Al
_{The characteristics of 2} O ₃ : 2.0% by weight, the total amount of P ₂ O ₅ + BaO + Al ₂ O ₃ = 100% by weight) were as follows. The refractive index nd was 1.6063, and the Abbe number (νd) was 63.7. Further, the temperature coefficient of refractive index (dn / dT) indicating the change amount dn of the refractive index with respect to the temperature change amount dT of the optical glass.
Shows a negative value as shown in Table 7 and was found to have athermal properties. Further, the partial dispersion ratio P _g , _F = (n
_g− n _F ) / (n _F −n _c ) = 0.544. The photoelastic constant was + 0.36 × 10 ⁻¹² Pa, and the external transmittance at 400 nm was 88.2% (10 mm thickness). In addition, the liquidus temperature was low and the water resistance was good.

[0085]

[Table 7]

Among the above characteristics, the following can be said for dn / dT. The refractive index n of the optical glass changes when the temperature T changes. The amount of change in the refractive index with respect to this amount of temperature change is the temperature coefficient of the refractive index (dn / dT). When the temperature of the glass changes, the optical path length also changes. The temperature coefficient (ds / dT) of the optical path length indicating the degree of this change is expressed by the following equation. ds / dT = (n-1) α + dn / dT (In the above formula, n indicates the refractive index of glass and α indicates the thermal expansion coefficient of glass.) In general optical glass, dn / dT has a positive value. On the other hand, since α is also positive, the optical path length changes due to the normal temperature change. On the other hand, the glass having the composition shown in this application example (for example, the glass having the composition shown in Example 3) has a characteristic that the refractive index decreases as the temperature rises. This is d
This is indicated by a negative value of n / dT (this is called athermal property). A lens or prism made of such glass has a small amount of change in the optical path length even when used in an optical system with a rapid temperature change, so that the focal length does not shift and a stable image without defocus is obtained. It is possible.

The following can be said of the partial dispersion ratios P _g and _F among the above characteristics. The partial dispersion ratios P _g and _F on the short wavelength side of visible light are represented by the following equation (1). _{P g, F = (n g} -n F) / (n F -n c) (1) ( in the formula (1), n _g is the refractive index at 436 nm, n _F is the refractive index at 480 nm, n _c is 656nm The glass having the composition shown in this application example (for example, the glass having the composition shown in Example 3) has, for example, P _g , _F = 0.544, and νd =
63.7, glass BSC7 having substantially the same Abbe number (νd) (P _g , _F = 0.534, νd = 64.
The values of P _g and _F are larger than those of 2). As described above, the glass having the composition shown in this application example has a feature that the change in the refractive index in the short wavelength region of visible light is larger than that of the optical glass having the same Abbe number. In designing an optical lens, a plurality of lenses having different refractive indices and different wavelength dependences of the refractive index are combined in order to correct chromatic aberration. The BSC 7 is a glass type that is frequently used in the design of an optical lens. By using a glass having a specific wavelength dependence as in this application example instead of the BSC 7, the degree of freedom in optical design is increased, It is possible to create an advanced chromatic aberration correction lens.

The composition of the optical glass shown in this application example is as follows: P ₂ O ₅ is 41-52% and BaO is 4% by weight.
7 to 57%, and 0.5 to 5% of Al ₂ O ₃ ,
And, the total amount of _{P 2 O 5 + BaO + Al} 2 O 3 is 95 to 100
% Optical glass, or 4% P ₂ O ₅ by weight.
0-46%, 52-58% of BaO, and, the Al ₂ O ₃ 0.5 to 5% contained, _{and, P 2 O 5 + BaO +} Al 2
It has been found that an optical glass having a total amount of O ₃ of 95 to 100% is preferable.

As described above, the optical glass shown in this application example has a temperature coefficient of refractive index (dn / dT) and / or a partial dispersion ratio that indicates the change amount dn of the refractive index with respect to the temperature change amount dT of the optical glass. Exhibit specific values, and are therefore effective as general optical glass for camera lenses and the like. In addition, since it has a small photoelastic constant and hardly generates birefringence, it is suitable as a lens material. Further, since it is resistant to thermal stress, it is suitable as a lens material used in an environment with a rapid temperature change. As an application example, for example, a general optical glass such as a highly reliable lens or prism and an optical window material can be manufactured. In particular, the optical glass described in this application example is suitable as a glass material for correcting chromatic aberration in cameras, VTR camera lenses, and various other optical devices, and is further resistant to thermal stress. It is suitable as a lens material used for devices and the like.

Although the present invention has been described with reference to the preferred embodiments, the present invention is not limited to the above embodiments and the like.

For example, components other than those listed in the examples and application examples can be added within a range that does not lose the characteristics of the present invention.

[0092]

As described above, the low photoelastic constant glass of the present invention has the following effects. 1) the photoelastic constant is + 0.5 × 10 ⁻¹² Pa or less;
Low photoelastic constant. 2) Since it does not contain PbO, it is highly safe for the environment. 3) The glass is more suitable for practical use because of its excellent chemical durability such as water resistance. 4) Since the liquidus temperature is low, mass production is possible. 5) Since the transmittance at 400 nm is 80% or more, it is suitable for optical applications. 6) For optical applications where the refractive index is limited, it is possible to adjust the refractive index to a predetermined value by adding a refractive index adjusting component within the scope of the present invention.

Such a photoelastic constant is + 0.5 × 10
^The low photoelastic constant glass which has a transmittance at 400 nm of 80% or more at ^-12 Pa or less, and has a low liquidus temperature, is particularly suitable for applications such as a polarizing beam splitter in a liquid crystal projector.

Further, in addition to the effect of the low photoelastic constant glass of the present invention, the optical glass of the present invention has a temperature coefficient of refractive index (dn / dn / dn) indicating a change in refractive index dn with respect to a temperature change dT of the optical glass. dT) and / or the partial dispersion ratio show specific values, respectively, and are therefore effective as general optical glasses for camera lenses and the like. In addition, since the photoelastic constant is small and birefringence hardly occurs, it is suitable as a lens material. Further, since it is resistant to thermal stress, it is suitable as a lens material to be used in an environment accompanied by a rapid temperature change.

[Brief description of the drawings]

FIG. 1 is a diagram showing a composition range of P ₂ O ₅ —BaO—Al ₂ O ₃ .

FIG. 2 is a plan view showing the relationship between the number of pixels and the aperture ratio.

FIG. 3 is a plan view showing a schematic configuration of a reflection type liquid crystal projector.

[Explanation of symbols]

 1 PBS prism 2 Cross prism

Claims (15)

[Claims] 1. The composition according to claim 1, comprising 41 to 52% of P ₂ O ₅ , 47 to 57% of BaO, and 0.5 to 5% of Al ₂ O ₃ , and P ₂ O ₅ + BaO + Al. _A low photoelastic constant glass for a light polarization controlling element, wherein the total amount of ₂ O ₃ is 95 to 100%. 2. The composition contains 42 to 50% of P ₂ O ₅ , 48 to 56% of BaO, and 1 to 4% of Al ₂ O ₃ by weight, and contains P ₂ O ₅ + BaO + Al ₂ O. _3. A low photoelastic constant glass for a light polarization controlling element, wherein the total amount of ₃ is 97 to 100%. 3. The low photoelastic constant glass according to claim 1, wherein 0 to 3% of La ₂ O ₃ , 0 to 3% of ZnO and 0 to 0% by weight.
_3%, B ₂ O 3 and 0 to 3%, WO ₃ and 0~3%, Nb ₂ O ₅
0-3%, MgO 0-3%, SrO 0-3%, S
b ₂ O ₃ 0-2% the As ₂ O ₃ 0 to 2%, contains, _{and, P 2 O 5 + BaO +} Al 2 O 3 + La 2 O 3 + ZnO + CaO
+ B ₂ O ₃ + WO ₃ + Nb ₂ O ₅ + MgO + SrO + Sb ₂ O
₃ + As ₂ O ₃ in the total amount is low photoelastic constant glass for optical polarization control element which is a 98% to 100%. 4. The low photoelastic constant glass according to claim 1, wherein the glass is SiO ₂ , GeO ₂ , Li ₂ O, Na ₂ O, K ₂ O, Cs.
₂ O, Y ₂ O ₃ , Gd ₂ O ₃ , Yb ₂ O ₃ , Ga ₂ O ₃ , Zr
A low photoelastic constant glass for a light polarization controlling element, comprising at least one component selected from O ₂ , Ta ₂ O ₅ , TiO ₂ , TeO ₂ , and Bi ₂ O ₃ . 5. In the triangular diagram of the composition of P ₂ O ₅ —BaO—Al ₂ O ₃ shown in FIG. 1, A → B → G → H → I → J → K →
A low photoelastic constant glass for a light polarization controlling element, which has a composition in a range surrounded by a straight line when connected by a straight line along a path of F → A. 6. The low photoelastic constant glass according to claim 1, wherein the photoelastic constant is + 0.5 × 10 ⁻¹² Pa or less. Constant glass. 7. The low photoelastic constant glass according to claim 1, wherein an external transmittance at 400 nm is 80%.
(10 mm thick), a low photoelastic constant glass for a light polarization controlling element. 8. An optical component produced using the low photoelastic constant glass according to claim 1. 9. The light polarization control device according to claim 8, wherein the optical component is a polarization beam splitter. 10. A liquid crystal projector comprising the polarization beam splitter according to claim 9. 11. An intrinsic photoelastic constant value (unit: 10 ⁻¹² P) per 1 mol of each component constituting the photoelastic constant glass.
a / mol) were calculated as follows: P ₂ O ₅ : 0.029, Ba
_{O: -0.021, La 2 O 3} : -0.01, PbO: -
_{0.036, B 2 O 3: 0.05} , Al 2 O 3: 0.01,
Nb ₂ O ₅ : 0.11, WO ₃ : 0.05, MgO: 0.
04, CaO: 0.016, SrO: 0.008, Zn
O: 0.037, Ti ₂ O: 0.03, Li ₂ O: 0.0
_{15, Na 2 O: 0.025,} K 2 O: 0.03, Cs 2
_{O: 0.03, Sb 2 O 3} : 0.04, Bi 2 O 3: 0.0
5, the sum of the intrinsic photoelastic constant value × the molar amount is calculated, and the components constituting the photoelastic constant glass and the content thereof are determined based on the calculated value to obtain the desired photoelastic constant and properties. A method for producing a photoelastic constant glass, comprising producing a photoelastic constant glass. 12. P ₂ O ₅ is 41 to 52% by weight and B is
The aO-47-57%, and the Al ₂ O ₃ 0.5~5%,
It contained, and optical glass the total amount of _{P 2 O 5 + BaO + Al} 2 O 3 is characterized in that 95 to 100%. 13. The method according to claim 1, wherein the content of P ₂ O ₅ is 40 to 46% by weight,
The aO-52 to 58%, and the Al ₂ O ₃ 0.5~5%,
It contained, and optical glass the total amount of _{P 2 O 5 + BaO + Al} 2 O 3 is characterized in that 95 to 100%. 14. A temperature coefficient of refractive index (dn / d) indicating a change amount dn of the refractive index with respect to a temperature change amount dT of the optical glass.
14. The optical glass according to claim 12, wherein T) has a negative value and has athermal property. 15. The values of the partial dispersion ratios P _g and _F on the short wavelength side of visible light represented by the following formula (1) are larger than those of optical glass having the same Abbe number, 15. The optical glass according to claim 12, wherein the optical glass has a peculiar wavelength dependency such that a change in a refractive index in a short wavelength region of visible light is larger than that of an optical glass having an Abbe number. _{P g, F = (n g} -n F) / (n F -n c) (1) ( in the formula (1), n _g is the refractive index at 436 nm, n _F is the refractive index at 480 nm, n _c is 656nm Are shown respectively.)