JP3426488B2 - Optical glass with small photoelastic constant - Google Patents

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 (β) suitable for use 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 Recently, an optical system utilizing polarized light, that is, a polarizing 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 polarization 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 an optically anisotropic material is used for a component such as a substrate or a prism in a polarization optical system, which is required to maintain polarization characteristics, the principal ray transmitted is orthogonal to the principal ray. The phase difference (optical path difference) between the extraordinary ray and the extraordinary ray will change compared to before transmission through the material, and the polarization characteristics will not be retained. Therefore, use materials with optical isotropy for these parts. There is a need.

Glass that has been sufficiently strained, particularly optical glass, has optical isotropy and is superior to other materials in terms of durability, strength and light transmittance, and There are various types of optical glass having various optical constants, and the range of choices in optical design is wide. Therefore, they have been conventionally used for polarization optical systems. Among them, S-BSL7 (trade name of OHARA CORPORATION) is cheap, has excellent durability, and has a small dispersion,
Widely used in polarization optics.

However, even when the above-mentioned conventional optical glass having optical isotropy is used as an optical component of a polarization optical system,
When mechanical stress or thermal stress is applied to these parts, they exhibit optical anisotropy due to the photoelastic effect, that is, birefringence, and as a result, it is difficult to obtain desired polarization characteristics. .

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

[0007]

[Equation 1]

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

[0009]

SUMMARY OF THE INVENTION The object of the present invention is to have a refractive index (Nd) of 1.55 to 5 in view of the above-mentioned prior art.
It is to provide a glass having a small photoelastic constant (β) having an optical constant in the range of 1.65 and an Abbe number (νd) of 55 to 65.

[0010]

In order to achieve the above object, the inventors of the present invention have conducted extensive studies to find that BaO-containing phosphate glass has a refractive index (Nd) of 1.55. It was found that an optical glass having an optical constant in the range of ˜1.65 and an Abbe number (νd) in the range of 55 to 65 and a small photoelastic constant (β) can be obtained, and the present invention has been completed.

The structure of the present invention for achieving the above object has a refractive index (Nd) of 1.5 as described in claim 1.
5 to 1.65, Abbe number (νd) has an optical constant in the range of 55 to 65, and contains BaO 31 to 60% by weight.
And by weight% MgO + CaO + SrO + BaO 4
It is a phosphate-based glass containing 1 to 60% and has a wavelength of 0.
The value of the photoelastic constant (β) at 4 μm to 0.7 μm is 1.0 × 10 ⁻⁵ nm / cm / Pa or less. Further, the present invention provides refraction as described in claim 2.
The ratio (Nd) is 1.55 to 1.65 and the Abbe number (νd) is
Having an optical constant in the range of 55 to 65, and MgO0 in% by weight.
~ 4%, CaO 0-30%, SrO 0-30%, B
aO 31 to 60%, but MgO + CaO + SrO
A phosphate-based glass containing 41 to 60% of BaO.
, The photoelastic constant at a wavelength of 0.4 μm to 0.7 μm
The value of (β) is 1.0 × 10 ⁻⁵ nm / cm / Pa or less.
It is characterized by The present invention also relates to claim 3.
As shown in the figure, the refractive index (Nd) is 1.55 to 1.65, and Abbe
The number (νd) has an optical constant in the range of 55 to 65, and the weight
%, B ₂ O ₃ 0.1-4%, P ₂ O ₅ 35-60%, Mg
O 0-4%, CaO 0-30%, SrO 0-30
%, BaO 31 to 60%, but MgO + CaO +
_{SrO + BaO 41~60%, La 2} O 3 0.5~7
%, Li ₂ O 0 to 4%, Na ₂ O 0 to 4%, K ₂ O
0-4%, provided that Li ₂ O + Na ₂ O + K ₂ O 0.1
It is a phosphate-based glass containing ~ 4% and has a wavelength of 0.4μ.
The value of photoelastic constant (β) at m-0.7 μm is 1.0
Be characterized by × is less than 10 ^-5 nm / cm / Pa
It

Further , according to the present invention , as described in claim 4 , 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. Characterize.

The optical glass of a preferred embodiment of the present invention, as defined in claim 5, has a weight percentage 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 + Ca
O + SrO + BaO 41-60%, ZnO 0-5
%, La ₂ O ₃ 0.5 to 7%, Y ₂ O ₃ 0 to 7%, Gd
₂ O ₃ 0 to 7%, Nb ₂ O ₅ 0 to 5%, Ta ₂ O ₅ 0 to 10%
%, WO ₃ 0 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 to 4% and Sb ₂ O ₃ 0 to 4%.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The reasons for limiting the composition range of each component of the optical glass of the preferred embodiment of the present invention are as follows.
The P ₂ O ₅ component is an essential component for constituting the glass, and it is preferable to add it in an amount of 35% or more. Also, in order to maintain the chemical durability of the glass, the amount thereof should be up to 60%. preferable.

The Al ₂ O ₃ component is effective in improving the chemical durability of the glass, and may be optionally added, but it is preferably up to 5% to maintain devitrification resistance.

The B ₂ O ₃ component is an effective component for stabilizing the glass, and it is preferable to add it in an amount of 0.1% or more, and the amount thereof should be 4 to maintain the chemical durability of the glass. It is preferably up to%.

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

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

It is preferable that the MgO component is arbitrarily added up to 4% for the purpose of adjusting the target optical constant and improving the melting property.

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

The La ₂ O ₃ component is effective in improving the chemical durability of the glass, but if its amount is less than 0.5%, its effect is small, and if it exceeds 7%, it tends to devitrify. Increase.

The Y ₂ O ₃ and Gd ₂ O ₃ components are the above La ₂
It has the same effect as the O ₃ component and can be optionally added, but the amount of each is up to 7%.

Each component of Nb ₂ O ₅ , Ta ₂ O ₅ and WO ₃ is preferably added up to 5%, 10% and 10%, respectively, in order to adjust the optical constants. However,
If 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 meltability of the glass and improving the devitrification resistance, and 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 at the time of melting the glass and also has the effect of reducing the photoelastic constant (β), and can be added arbitrarily, but the amount is 4% or less. Is more preferable.

A component other than the above, for example, SnO ₂ component may be added in a small amount 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
Ingredients such as n ₂ O ₃ may be added as necessary to adjust the optical constants up to about 5% and improve the meltability and devitrification resistance of the glass.

[0027]

EXAMPLES Next, the composition examples (No. 1 to No. 9) of the optical glass of the preferred embodiment of the present invention and the comparative example (No. A) of the conventional optical glass are shown as the refractive index ( Table 1 shows the measurement results of Nd), Abbe number (νd) and photoelastic constant (β). The photoelastic constant (β) is defined as 0.8 cm for the light transmission thickness of the glass sample,
Wavelength 5 with constant stress applied to the glass sample from the outside
It was determined by the above formula (1) by measuring the optical path difference due to birefringence that occurred when light of 46 nm was transmitted.

[0028]

[Table 1]

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

Further, all of the optical glasses of these composition examples have excellent devitrification resistance and good chemical durability, and
Easy to homogenize. Optical glass of these example compositions,
Ordinary optical glass raw materials such as oxides, carbonates, nitrates and hydroxides are weighed and mixed at a predetermined ratio and then charged into a platinum crucible, and 1100-1300 depending on the meltability depending on the composition.
After melting at a temperature of ℃ for about 2 to 4 hours, stirring and homogenizing,
It can be easily obtained by casting in 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.
1.65, which has an optical constant of Abbe number (νd) in the range of 55 to 65 and is BaO-containing phosphate glass,
Photoelastic constant (β) at a wavelength of 0.4 μm to 0.7 μm
Value of 1.0 × 10 ⁻⁵ nm / cm / Pa or less, it is useful for optical parts such as prism and prism used in polarization optical system such as spatial light modulator for polarization modulation and polarization beam splitter. Is.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A 61-40839 (JP, A) JP-A 60-171244 (JP, A) JP-A 9-48633 (JP, A) JP-A 7- 215732 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) C03C 1/00-14/00

Claims (5)

(57) [Claims] 1. A refractive index (Nd) of 1.55 to 1.65,
The Abbe number (νd) has an optical constant in the range of 55 to 65, contains 31 to 60% by weight of BaO , and has a weight of
% MgO + CaO + SrO + BaO 41-60%
It is a phosphate-based glass contained and has a wavelength of 0.4 μm to 0.
The value of photoelastic constant (β) at 7 μm is 1.0 × 10 ⁻⁵
An optical glass having a small photoelastic constant, which is not more than nm / cm / Pa. 2. A refractive index (Nd) of 1.55 to 1.65,
Abbe number (νd) has an optical constant in the range of 55 to 65
% By weight, MgO 0-4%, CaO 0-30%,
SrO 0-30%, BaO 31-60%,
Contains MgO + CaO + SrO + BaO 41-60%
Is a phosphate-based glass with a wavelength of 0.4 μm to 0.7 μm
The value of photoelastic constant (β) at m is 1.0 × 10 ^-5 nm
/ Cm / Pa or less, the photoelastic constant is
A small optical glass. 3. A refractive index (Nd) of 1.55 to 1.65,
Abbe number (νd) has an optical constant in the range of 55 to 65
And, in _{weight%, B 2 O 3 0.1~4%} , P 2 O 5 35~6
0%, MgO 0-4%, CaO 0-30%, SrO
0-30%, BaO 31-60%, but MgO
+ CaO + SrO + BaO 41-60%, La ₂ O _{3
0.5~7%, 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
A phosphate glass containing 0.1 to 4% of O,
Of the photoelastic constant (β) at a length of 0.4 μm to 0.7 μm
The value is 1.0 × 10 ^-5 nm / cm / Pa or less
An optical glass with a small photoelastic constant. 4. Any of the claims 1 to 3, photoelastic constant at wavelength 0.4μm~0.7μm (β) is characterized in that it is a less value ^{0.9 × 10 -5 nm / cm /} Pa photoelastic constant is small optical glass according to any. 5. B ₂ O ₃ 0.1-4% by weight, 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 to 60%, ZnO 0 to 5%, La ₂ O ₃
0.5 to 7%, Y ₂ O ₃ 0 to 7%, Gd ₂ O ₃ 0 to 7%,
_{Nb 2 O 5 0~5%, Ta} 2 O 5 0~10%, WO 3
0 to 10%, but 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%, but Li ₂ O + Na ₂ O + K ₂ O
_{0.1~4%, Sb 2 O 3 0~4} % range photoelastic constant is small optical glass according to any one of claims 1 to 4, characterized in that it consists of the components of.