JP2003048746A - Optical glass - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical glass having a high refractive index suitable to be used for an optical element of a lens, prism or the like or for a substrate, in particular, suitable to be used for an optical element in a polarizing optical system or for a polarization controlling element of a PBS(polarizing beam splitter), SLM(spatial light modulator) or the like. SOLUTION: The optical glass contains SiO2 , PbO and B2 O3 and further contains >=0.1 mass% TeO2 and >=0.4 mass% Li2 O. Preferably, when the glass is 10±0.1 mm thick, the glass has 80% transmittance for light at <=420 nm wavelength, and the glass shows <=3.0% deterioration rate in the transmittance by the irradiation of rays in a UV region and/or visible region at 2.2 W.cm<-2> radiation illuminance for 10 minutes.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is suitable for use in optical elements such as lenses and prisms and substrates, and in particular, optical elements in a polarization optical system and a polarization beam splitter (hereinafter referred to as PBS).
), A spatial light modulator (hereinafter referred to as SLM), and a high refractive index optical glass suitable for use as a light polarization control element such as a polarization conversion element.

[0002]

2. Description of the Related Art Optical systems using polarized light, that is, polarizing optical systems are used in various optical devices such as liquid crystal projectors. For example, in a projection device such as a liquid crystal projector, the brightness has been increased in recent years, but with this, there arises a problem that the transmittance of the optical glass used in each part of the optical system of the projection device deteriorates with time. ing. Irradiation of optical glass with high intensity, high irradiance light often results in undesirable coloring phenomena, such as solarization, resulting in a reduction in glass transmission. Solarization generally refers to the coloring phenomenon of glass caused by irradiating glass with light in the ultraviolet region wavelength, but the coloring phenomenon due to light irradiation is not limited to solarization, and glass with light in the visible wavelength range is used. Various coloring phenomena have been reported, including the coloring phenomenon of glass due to the visible light two-photon absorption process that occurs when irradiated to the surface. In particular, when borosilicate glass containing lead is irradiated with light having a wavelength in the visible range, it is known that the glass is likely to be colored due to two-photon absorption. As described above, although the wavelength of the irradiation light that induces the coloring phenomenon and the mechanism of causing the coloring phenomenon are various, the coloring phenomenon of the glass by the light irradiation results in deterioration of the transmittance of the glass.

In order to prevent these various coloring phenomena, it is conceivable to incorporate a filter for cutting light of a harmful wavelength, which causes a decrease in the brightness (output) of the light source and a coloring phenomenon, into the optical system. In an optical system that needs to maintain high brightness (for example, an optical system of a high brightness liquid crystal projector), these means are not desirable because they directly lead to a decrease in the output light amount. Further, in a projection device such as a liquid crystal projector, since high-luminance light is projected without impairing the color rendering property, the optical glass used in the optical system has a wavelength range from the long wavelength side to the violet region of the visible range. It is required to have excellent transparency to light rays.
Further, the optical system of a projection device such as a liquid crystal projector is usually a polarization optical system, and it is desired to control the polarization characteristics with higher accuracy. Among the optical components in the polarization optical system, when a material having optical anisotropy is used for a member such as a prism or a substrate of a light polarization control element which needs to maintain polarization characteristics such as PBS and SLM, it is transmitted. The phase difference (optical path difference) between the chief ray and the extraordinary ray orthogonal to it changes compared to before transmission through the material, and the polarization characteristics cannot be maintained, so these elements are optically isotropic. It is necessary to use a material having properties.

Even when a conventional optical glass having sufficient optical anisotropy that has been sufficiently annealed and de-strained is used for an optical component which is required to maintain polarization characteristics in a polarization optical system, mechanical stress and When thermal stress is applied to these glasses, if the absolute value of the photoelastic constant of the glass is large, the glass will exhibit optical anisotropy due to the photoelastic effect, that is, birefringence, and as a result, the desired polarization There is a problem that it is difficult to obtain the 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 devices or energy of transmitted light. It is caused by heat generation of the glass itself due to absorption.

When these stresses are applied to the glass, the magnitude of birefringence exhibited by the glass can be indicated by the optical path difference. The optical path difference is δ (nm) and the glass thickness is d (c
m) and the stress is F (Pa), the following formula (1) is established, and the larger the optical path difference, the larger the birefringence. δ = β · d · F (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 (1), when the stress (F) applied to the glass and the thickness (d) of the glass are the same, the photoelastic constant (β)
The glass having a smaller absolute value of has a smaller optical path difference (δ), that is, birefringence.

[0006]

Conventionally, as a material for optical parts in a polarization optical system, S-BSL7 (manufactured by Co., Ltd.) has been mainly used.
OHARA brand name) and the equivalent products of other companies, for example, borosilicate glass such as BK7 (trade name of Shot Glass Co., Ltd.), has excellent transparency to light rays of wavelengths from the long wavelength side to the purple region of the visible range. It is used because it has low cost and is easily available. However, these optical glasses have a large absolute value of the photoelastic constant (β), for example, S-
BSL7 has a refractive index (nd) of 1.52 and a β value of 2.79 × 10 ^{−5 at} e-line (wavelength 546.07 nm).
nm / cm / Pa, and as described above, there is a strong demand for an optical glass having a smaller absolute value of photoelastic constant (β) in order to control the polarization characteristics in the polarization optical system with higher accuracy. In view of optical design, there is also a need for optical glass having a higher refractive index.

As a high-refractive-index optical glass having a small absolute value of photoelastic constant (β), high lead content glass has been known since the early 20th century. Representative SiO ₂ -PbO-based glasses that are still manufactured and sold as lead-rich glass, such as PBH53 (trade name of OHARA CORPORATION), and SF57 (having the same refractive index (nd) as PBH53). Due to the above-mentioned reasons, Shot Glass Co., Ltd.) is being used as a material for controlling the polarization characteristics with higher accuracy in the polarization optical system. For example, PBH5
3 has a refractive index (nd) of 1.85 and e-line (wavelength 546.
Photoelastic constant (β) at 0. 7 nm is 0.1 × 10 ^-5
It has a refractive index of less than nm / cm / Pa, a high refractive index, and a photoelastic constant (β) whose absolute value is small enough to control the polarization characteristics with higher accuracy, that is, a low photoelastic constant.

However, these conventional high lead content glasses have poor light transmittance from the short wavelength side of the blue region of the visible region to the violet region. For example PBH53 and SF57
Together, these glass with a thickness of 10 ± 0.1 mm,
The limit value of the wavelength of the light ray including the reflection loss and transmitting at the transmittance of 80% is 440 nm, and the transmittance is below 80% in the shorter wavelength region. When these glasses are used in a polarization optical system, for example, in a polarization optical system such as a liquid crystal projector, blue light (B light), green light (G light) and red light (R light) are used.
The intensity of the light decomposed into the three primary colors of light is different, and in order to maintain the color rendering of the projected light, the intensity of the blue light (B
It is necessary to reduce the intensity of the other two color lights in accordance with the light), and as a result, there is a problem that the amount of light projected from the projection device such as a liquid crystal projector becomes insufficient.

In addition to the above glasses, glass having a small absolute value of photoelastic constant (β) is disclosed in, for example, JP-A-7-215.
No. 732, SiO ₂ -alkali metal oxide-P.
An optical glass for a polarization optical system of bO type is disclosed. However, this glass has a large transmittance deterioration rate (the degree of decrease in the transmittance before and after transmitting light rays, which may be hereinafter referred to as a deterioration amount), and even before the deterioration of the transmittance occurs, The light transmittance from the short wavelength side of the region to the violet region is not sufficient, and the bubbles in the molten glass during melting and refining are poor, and the striae disappears by sufficiently stirring the molten glass to homogenize the glass. Although it can be made into a polymer, it is not suitable for optical parts because bubbles remain in the obtained glass.

Japanese Patent Laid-Open No. 9-48361 discloses PbO.
-B ₂ O ₃ and / or A1 ₂ O ₃ based polarizing optical glass for optical systems have been disclosed. This glass has a small amount of deterioration in transmittance, and although slightly better in light transmittance than the glass of the above-mentioned publication, again, the light transmittance from the short wavelength side of the blue region to the violet region before the deterioration of transmittance occurs. It is not sufficiently improved, and the melting and melting of the molten glass at the time of refining is poor, and it is possible to homogenize the glass by eliminating striae like the glass of the above publication, but in the obtained glass It is difficult to make an optical component because bubbles remain on the surface. Further, in Japanese Patent Laid-Open No. 8-259259, SiO
₂ -R ₂ O-PbO- fluorine-based polarizing optics for optical glass is disclosed. Although this glass has better defoaming than the glasses of the two publications, the deterioration amount of the transmittance is significantly larger than that of the glasses of the two publications, and it is considered that the cause is the fluorine component.

By the way, the optical glass is a container (platinum crucible or platinum-made container) in which at least a portion in contact with the molten glass is formed of platinum in order to improve the work efficiency during melting and refining of the glass and the yield of the glass to be produced. In a tank),
It is generally clarified, and in particular, the vessel for fining glass that needs to be melted at high temperatures is usually made of platinum. However, in a glass containing a large amount of PbO, such as the above-mentioned PBH53, SF57 and the glasses of the above three publications, the light transmittance is apt to be deteriorated because platinum in the container is easily dissolved in the glass during melting and refining.

Therefore, in the case of glass having poor bubble breakage, such as the glass disclosed in JP-A-9-48361 and JP-A-8-259259, if the temperature during fining is increased,
In some cases it may be possible to obtain a glass with better defoaming and less or no bubbles. However, when the temperature is increased, the amount of platinum dissolved in the glass from the container is increased, and the light transmittance of the obtained glass is further deteriorated. On the contrary, when the temperature during refining is lowered, the amount of platinum dissolved in the glass is reduced, and the light transmittance is considerably improved, but the bubble breakage is further deteriorated.

In the glass disclosed in Japanese Patent Laid-Open No. 8-259259, when the temperature at the time of refining is low, a glass having a good light transmittance can be obtained. Since the amount is small, the amount of deterioration in transmittance is significantly large. Further, when the temperature during refining is increased, defoaming is improved, and the amount of fluorine volatilized from the molten glass is increased, so that the deterioration amount of the transmittance is slightly reduced, but this glass is described in the same publication. As described above, since the transmittance of the short wavelength region is improved by introducing fluorine, the amount of platinum dissolved in the glass from the container increases, and the light transmittance of the obtained glass is extremely high. Get worse.

An object of the present invention is to solve the above-mentioned conventional problems in a comprehensive manner, to reduce the amount of transmittance deterioration due to irradiation with light rays in the ultraviolet range and / or the visible range, and to reduce the transmittance from the long wavelength side to the visible range. It has excellent transparency to light of wavelengths up to the violet region, and is a glass that has excellent clarity because of melting of bubbles in the molten glass during melting and refining. Therefore, it has a small photoelastic constant (β) and is suitable for use as an optical element such as a lens and a prism or a substrate, and particularly in an optical element in a polarization optical system or a PB.
An object of the present invention is to provide an optical glass having a high refractive index suitable for use in a light polarization control element such as S or SLM.

[0015]

In order to achieve the above-mentioned object, the inventors of the present invention have conducted extensive studies as a result, and as a result, have been a glass having a poor light transmittance on the short wavelength side of the visible region for many years. It is recognized as, moreover, coloring due to light irradiation, i.e., SiO _2, P transmittance degradation has been the prone
By adding TeO ₂ and Li ₂ O to a glass containing bO and B ₂ O ₃ , surprisingly, it has excellent light transmittance, little deterioration of transmittance, and melting and clarification. In the present invention, the inventors have found that a glass having good defoaming and having a low photoelastic constant in addition to these properties can be obtained, and thus completed the present invention.

That is, the optical glass according to claim 1 of the present invention contains SiO ₂ , PbO and B ₂ O ₃ , and further comprises by mass%.
With 0.1% or more of TeO ₂ and 0.4% or more of Li ₂
It is characterized by containing O.

According to a second aspect of the present invention, in the optical glass according to the first aspect, when the thickness is 10 ± 0.1 mm, the wavelength of light transmitted with a transmittance of 80% is 420 nm or less. Is characterized by. Here, the transmittance of 80% is a value including reflection loss.

According to a third aspect of the invention, in the optical glass according to the first or second aspect, the ultraviolet ray and / or the visible ray is irradiated for 10 minutes at an irradiance of 2.2 W · cm ^−2. The deterioration rate (deterioration amount) of the transmittance of light having a wavelength of 450 nm is 3.0% or less. Here, the deterioration rate of the transmittance means that the transmittance of a light beam having a wavelength of 450 nm before irradiation with light for 10 minutes is T (b) and the transmittance of a light beam having a wavelength of 450 nm after irradiation is T (a). , (T (b) −T (a)) / T (b) × 100.

According to a fourth aspect of the invention, in the optical glass according to the first or second aspect, the ultraviolet ray and / or the visible ray is irradiated for 10 minutes at an irradiance of 2.2 W · cm ^−2. The deterioration rate of the transmittance of light having a wavelength of 450 nm is 1.0% or less. here,
The deterioration rate of the transmittance is the same as in claim 3.

The invention described in claim 5 is the same as in claim 1, 2,
The optical glass as described in 3 or 4, 400 to 80.
The absolute value of the photoelastic constant (β) in the wavelength range of 0 nm is 1.0 × 10 ⁻⁵ nm / cm / Pa or less.

The invention according to claim 6 is the same as claim 1, 2 or
%, In the optical glass as described in 3, 4, or 5.
Then, SiO ₂ 18-29%, PbO 66-78%,
TeO ₂ 0.1-3.5%, B ₂ O ₃ 0.1-6%,
It is characterized by containing 0.4 to 5% of Li ₂ O and having a refractive index (nd) in the range of 1.75 to 1.90.

[0022] The invention according to claim 7, the optical glass according to claim 6, further containing, by mass%, Na ₂ O
_{0~8%, K 2 O 0~8%} , however, Li ₂ O + Na _{2
O + K 2 O 0.4~10%,} 0~5% MgO, Ca
O 0-5%, SrO 0-5%, BaO 0-10
%, ZnO 0 to 5%, but MgO + CaO + Sr
O + BaO + ZnO 0-10%, GeO ₂ 0-5
%, Al ₂ O ₃ 0 to 3%, Nb ₂ O ₅ 0 to 3%,
GeO ₂ + Al ₂ O ₃ + Nb ₂ O ₅ 0-5%, As ₂ O ₃
It is characterized by containing 0 to 1% and Sb ₂ O ₃ 0 to 1%.

The invention according to claim 8 is the invention according to claim 1, 2,
%, In the optical glass as described in 3, 4, or 5.
Then, SiO ₂ 18-29%, PbO 66-78%,
TeO ₂ 0.1 to 3.5%, B ₂ O ₃ 0.1 to less than ₂ %, Li ₂ O 0.4 to 5%, Na ₂ O 0 to 8%, K ₂
O 0-8%, provided that Li ₂ O + Na ₂ O + K ₂ O
0.4-10%, MgO 0-5%, CaO 0-5
%, SrO 0-5%, BaO 0-10%, ZnO
0-5%, but MgO + CaO + SrO + BaO +
ZnO 0-10%, GeO ₂ 0-5%, Al ₂ O ₃
0-3%, Nb ₂ O ₅ 0-3%, provided that GeO ₂ + A
1 ₂ O ₃ + Nb ₂ O ₅ 0 to 5%, As ₂ O ₃ 0 to 1% and Sb ₂ O ₃ 0 to 1% are contained, and the refractive index (nd) is 1.
It is characterized in that it is in the range of 75 to 1.90.

The invention described in claim 9 is the same as in claim 1,
The optical glass described in 3, 4, 5, 6, 7 or 8 is characterized in that the Abbe number (νd) is less than 28.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION Next, the reason why the composition range of each component is limited in the optical glass of the present invention will be explained. The SiO ₂ component is a glass-forming oxide,
It is an essential component in the glass of the present invention. The amount is 1
If it is less than 8%, it becomes difficult to vitrify the raw material in which the components of the glass of the present invention are mixed, and if the amount exceeds 29%, the meltability of the glass deteriorates and it must be melted at high temperature. Raw material does not vitrify. In particular, in order to improve the meltability of the glass, the amount is more preferably set to 27%.

The PbO component has the effect of increasing the refractive index of glass and is an essential component in the glass of the present invention.
Further, the PbO component also has the effect of reducing the absolute value of the photoelastic constant (β) of glass. When the amount of the PbO component is less than 66%, it is difficult to obtain these effects, and when the amount exceeds 78%, the light transmittance is deteriorated.
On the contrary, the absolute value of the photoelastic constant (β) becomes large.

The TeO ₂ component has the effect of reducing the viscosity of the glass containing a large amount of PbO during melting and refining, and is a very important component in the present invention. By introducing the TeO ₂ component, the clarity of the glass, that is, the defoaming of the glass becomes very good, and it is possible to obtain glass with very few bubbles or no bubbles, and also from the long wavelength side to the violet region of the visible region. It is possible to obtain a glass having excellent light transmittance for light rays of all wavelengths. It is considered that one of the reasons why the light transmittance of the glass is improved is that the content of platinum dissolved in the glass at the time of melting and refining is reduced by including TeO ₂ . However, when the amount of TeO ₂ component is less than 0.1%, it is difficult to obtain these effects, and when the amount exceeds 3.5%, the light beam of glass on the short wavelength side in the visible region is rather adversely affected. The transmittance deteriorates, and the amount of deterioration of the glass due to irradiation of the glass with ultraviolet light and / or visible light also increases. In particular, in order to obtain a glass having a good light transmittance and a small transmittance deterioration amount, it is preferable that the amount of the TeO ₂ component be up to 3.0%, and further up to 1.5%. More preferable.

B₂O₃Ingredient is SiO₂And PbO component
TeO on glass containing₂To introduce the ingredients,
It is an essential ingredient. TeO₂The ingredients are
The viscosity of lath melted and clarified is reduced, but SiO₂Oh
And glass containing PbO component, TeO₂Enter only
Then, TeO as a raw material₂Is easily melted and remains homogeneous
Difficult to obtain a good glass, and TeO₂Melted in
In order to increase the melting temperature and refining temperature of the glass
Get lost. However, B₂O₃When the ingredients are introduced, T
eO₂Becomes very easy to melt. That is, B₂O₃
The components include TeO in the glass of the present invention.₂Promote the melting of
Proper amount of TeO in the glass₂Introducing ingredients
Therefore, TeO described above₂Effect to fully exert the effect of the ingredients
There is a fruit, B₂O ₃When melting and refining glass, the ingredients themselves
It has the effect of reducing the viscosity. But B₂O₃Amount of ingredients
Is less than 0.1%, it is difficult to obtain these effects.
If the amount exceeds 6%, UV and / or visible light
The amount of deterioration of the transmittance of the glass caused by irradiating the glass is large.
I hear Also, especially chemical durability (water resistance, acid resistance,
To obtain glass with excellent weather resistance and detergent resistance)
Should be less than 2%.

The Li ₂ O component is an important component which has been found to have the effect of significantly reducing the amount of deterioration in transmittance caused by irradiating the glass with ultraviolet light and / or visible light in the optical glass of the present invention. There is also an effect of promoting the melting of the glass raw material, but if the amount is less than 0.4%, the above-mentioned various effects are very small. Also, the amount is 5
%, The chemical durability of glass (water resistance, acid resistance,
Weather resistance and detergent resistance) tend to deteriorate.

Na₂O and K₂O component is a glass raw material
It has the effect of accelerating melting, and it is optionally contained as needed.
However, the amount of each of these ingredients
If it exceeds 8%, the chemical durability of glass deteriorates. Well
Li₂O, Na₂O and K ₂The total amount of O component is 10
%, The chemical durability of glass (water resistance, acid resistance,
Weather resistance and detergent resistance) deteriorate. Part of PbO component
R′O component, that is, MgO, CaO, SrO,
Substituted with one or more of BaO and ZnO components
Then, while maintaining the photoelastic constant with a small absolute value,
These ingredients are needed because the rate can be lower
It can be optionally added depending on the type. But these
The amount of each component is MgO 5%, CaO 5%, Sr
If O5%, BaO10% and ZnO5% are exceeded, it will be
Devitrification tends to occur, and the total amount of these 5 components
However, if it exceeds 10%, the glass tends to devitrify and
It becomes difficult to maintain the photoelastic constant having a small absolute value.

The GeO ₂ component adjusts the optical constant (refractive index) to a high level and further improves the chemical durability (water resistance, acid resistance, weather resistance and detergent resistance) and devitrification resistance of the glass. Therefore, it can be added arbitrarily, but if the amount exceeds 5%, the melting temperature of the glass becomes high and the meltability deteriorates. The Al ₂ O ₃ component adjusts the viscosity of the glass to a high level according to various molding methods of molten glass, and improves the chemical durability of the glass (water resistance, acid resistance, weather resistance and detergent resistance). It is a component effective for keeping, and it can be optionally added if necessary, but if the amount exceeds 3%, the glass tends to devitrify, which is not preferable.
The Nb ₂ O ₅ component is effective in increasing the chemical durability of the glass (water resistance, acid resistance, weather resistance and detergent resistance) and adjusting the refractive index of the glass to a higher level, but the amount thereof is If it exceeds 3%, the light transmittance of the glass is deteriorated, the degree of coloring is increased, and the glass tends to devitrify, which is not preferable. Further, when the total amount of the GeO ₂ , Al ₂ O ₃ and Nb ₂ O ₅ components exceeds 5%, the devitrification resistance of the glass deteriorates, which is not preferable.

Since the As ₂ O ₃ and Sb ₂ O ₃ components both have the effect as a fining agent for glass, they can be optionally added, but in order to obtain the fining effect, their amounts are each 1% or less. Is enough. Particularly, in order to obtain a glass having a good light transmittance, it is preferable to add an As ₂ O ₃ component. Further, In ₂ O ₃ and Ga ₂ O ₃ components may be added to the optical glass of the present invention for the purpose of increasing the refractive index, but when the amount of each of these components exceeds 3.5%, the light transmittance is increased. It is not preferable because the glass deteriorates and the glass is easily devitrified, and it becomes difficult to obtain a homogeneous glass. Also, these 2
Even if the total amount of the components exceeds 3.5%, the same unfavorable result as described above is caused.

[0033]

The preferred embodiments of the present invention will be described below. The present invention is not limited to the examples below. First, the optical glass of the present invention having the composition ratios shown in Tables 1 to 3 was manufactured. Example N shown in Tables 1 to 3
o. 1-No. In each of the 20 glasses, raw materials for ordinary optical glass such as oxides, carbonates, nitrates, and hydroxides are weighed and mixed at a predetermined ratio, and charged into a platinum crucible,
It is melted at a temperature of 800 to 1000 ° C. for about 1 to 3 hours, and then clarified at a temperature of 900 to 1100 ° C. for 1 to 3 hours depending on the meltability depending on the composition to defoam the molten glass, that is, defoam. Further, the molten glass was stirred to eliminate the striae, and the molten glass was homogenized, and then cast into a mold and gradually cooled (annealed), which could be easily obtained.
Various physical properties of the obtained optical glass were evaluated as follows, and the results are shown in Tables 1 to 3. The evaluation item is the refractive index (n
d), Abbe number (νd), transmittance including reflection loss 80%
Is the wavelength of the light beam (T ₈₀ ) that is transmitted through at or the wavelength of the light beam that transmits at a transmittance of 70% (T ₇₀ ) including reflection loss, the measurement result of the photoelastic constant (β), the deterioration amount of the transmittance, and the evaluation of bubbles. .

Table 4 shows the composition ratios of Comparative Examples (Nos. A to C), which are conventional optical glasses for polarizing optical systems, in which the absolute value of the photoelastic constant (β) is small. 1-No.
20 is shown together with the evaluation results evaluated in the same manner. It should be noted that the Abbe number (νd) is not so important when the optical glass is used for the light polarization control element, and therefore only the composition examples (No. 1 to No. 20) of the present invention are described. The glass of the comparative examples (No. A to No. C) shown in Table 4 is a raw material for ordinary optical glass such as an oxide, a carbonate, a nitrate, and a hydroxide, which are weighed and mixed at a predetermined ratio, Put into a platinum crucible, 1000 ℃ depending on the meltability by composition
Melted at a temperature of about 1 to 3 hours, then clarified at a temperature of 1100 ° C. for about 1 to 3 hours, further stirring the molten glass to eliminate striae, homogenizing the molten glass, and then gold. It was obtained by casting in a mold and gradually cooling (annealing).

The evaluation method will be described. T ₈₀ and T
₇₀ indicates the result measured on a glass sample having a thickness of 10 ± 0.1 mm polished on both sides, and the photoelastic constant (β) is the light transmission thickness of the glass sample, that is, the thickness (d) in the above formula (1). ) Is 0.8 cm, and e-line (wavelength 546.07 nm) is applied with a constant stress applied to the glass sample from the outside.
The optical path difference due to the birefringence generated when the light of FIG. Also,
The amount of deterioration in transmittance was measured by first measuring the light transmittance T (b) at a wavelength of 450 nm including the reflection loss of a glass sample having a thickness of 40 ± 0.1 mm, which was polished on both sides, and then, from the ultraviolet region to the visible region of blue. The irradiance is 2.2 W
A wavelength of 450 nm including the reflection loss of the above glass sample after continuously irradiating the glass sample with a light beam of cm ^-2 for 10 minutes.
The light transmittance T (a) of is measured, and the transmittance deterioration amount (%) =
It is calculated as (T (b) -T (a)) / T (b) × 100. As a light source, a spot UV irradiation device whose lamp is an ultra-high pressure mercury lamp-250 W direct irradiation type (UIS-
25103AA manufactured by Ushio Electric Co., Ltd., the glass sample was placed at a position 110 mm away from the irradiation window of this device, and the glass sample was irradiated with light emitted from the irradiation device.

[0036] In addition, foam evaluation result (grade), the Japan Optical Glass Industry Association Standard: JOGIS 12- ^{199 4} in accordance with the "method of measuring the bubble of optical glass" bubbles in the glass obtained by using the microscope The diameter and number of the
The results are obtained by calculating the total sum of the cross-sectional areas and the total number of bubbles in 0 ml of glass, classifying them as follows, and displaying the grades. That is, when the total cross-sectional area (mm ² ) in 100 ml is less than 0.03, it is grade 1, when it is 0.03 or more and less than 0.1, it is grade 2, and when it is 0.1 or more and less than 0.25, it is grade 3. Grade, if 0.25 or more and less than 0.5, grade 4.
The case where the total number of bubbles in 100 ml is less than 10 is A class, the case where the total number of bubbles in 100 ml is less than 10 is B class, the case where 100 or more and less than 500 is C class, 500
The case of less than 1000 is classified as D class, and the case of 1000 or more is classified as E class. For example, the case where the sum of the cross-sectional areas is class 1 and the sum total is class A is displayed as class 1A.

[0037]

[Table 1]

[0038]

[Table 2]

[0039]

[Table 3]

[0040]

[Table 4]

[0041]

[Table 5]

As shown in Tables 1 to 3, all the glass of Examples (No. 1 to No. 20) of the optical glass of the present invention have comparative transmittance deterioration amounts shown in Table 4 (No. It can be seen that the value of T ₈₀ is smaller than that of the glasses of Comparative Examples (No. A to No. C) and the light transmittance is excellent. Furthermore, Example No. 1 of the optical glass of the present invention. 1-No. The glass of No. 20 has a photoelastic constant (β) whose absolute value is small enough to be used for a light polarization control element, 1.0 × 10 ⁻⁵ nm / cm.
It has β of less than / Pa.

The obtained Example No. of the present invention. 1-No.
As shown in Tables 1 to 3, all of the optical glasses of 20 had a bubble evaluation result of 1A class, and in particular, an optical element such as a prism or the like, which usually has a considerable thickness, or two prisms were combined. Sufficient optical glass was obtained for use in the PBS made by. On the other hand, the evaluation results of bubbles of the glass of Comparative Examples A to C are all Example No. 1 of the present invention. 1 to N
o. It is worse than the glass of No. 20, especially Comparative Example N
o. A, No. The result of C is bad. In addition, Comparative Example No. B
The glass of No. 1 had a relatively good bubble evaluation result, but the light transmittance (T ₈₀ ) was very poor, and the spectral transmittance including reflection loss did not reach 80% in the range of 400 to 500 nm. Indicates the T ₇₀ mentioned above. Further, Comparative Example No. A
And No. In the glass of B, the deterioration amount of the transmittance is the same as that of the example No. 1 of the present invention. 1-No. It was larger than 19 glass.

As described above, Comparative Example No. A and No.
The glass of C has a very poor bubble evaluation result, and Comparative Example No.
The glass of B had a very poor light transmittance, so that Comparative Example No. A and No. Regarding the glass of C, the refining temperature was raised to improve the breakage of bubbles, and Comparative Example No. Since it was expected that the light transmittance of the glass B was improved by reducing the amount of platinum dissolved in the molten glass, the refining temperature was lowered and the results of the experiment were shown in Table 5. Comparative Example No. A and No. In the glass of C, the bubble evaluation result was very good, but the light transmittance (T ₈₀ ) was further deteriorated, and the deterioration amount of the transmittance was also large. on the other hand,
Comparative Example No. Although the light transmittance of the glass B was improved (T ₈₀ ), the light transmittance was poor as compared with the glasses of Examples (No. 1 to No. 20) of the optical glass of the present invention. In addition, the deterioration amount of the transmittance was very large, and the bubble evaluation result was also very bad.

Next, in the polarization optical system of the three-plate type reflective liquid crystal projector, the embodiment No. 1 of the present invention was used. An example in which 20 glass is used as a prism of PBS which is an optical polarization control element will be described with reference to FIG. No. Twenty glasses were heated and softened and press-molded with a mold, and the obtained molded glass was polished to form six triangular prisms, and two prisms were made into a set to make three PBSs in total. . The PBS 4 shown in FIG. 1 is one of those PBSs. The PBS 4 uses the triangular prisms 1a and 1b out of the six triangular prisms, and a known dielectric multilayer film 2 is formed on the surface of the triangular prism 1a to which the prism 1a is attached.
Is formed, and the triangular prisms 1a and 1b are bonded to each other with the adhesive layer 3. The other two PBs
Similarly, S (not shown) was formed using the remaining four triangular prisms (not shown).

Next, the operation of the PBS 4 shown in FIG. 1 will be described. First, light emitted from an ultra-high pressure mercury lamp (not shown) is made into a plurality of partial light beams through a microlens array (not shown), and these partial light beams are made incident on a polarization conversion element (not shown). The partial light flux incident on the polarization conversion element becomes S-polarized light and is emitted from the polarization conversion element (not shown). This S-polarized light is condensed by a condenser lens (not shown) and is incident on a cross dichroic prism (not shown).

The S-polarized light incident on the cross dichroic prism is split into three primary colors of red, blue and green by this prism. Then, the S-polarized blue S-polarized light (not shown)
Through a relay lens (not shown) to be incident on the PBS 4 as indicated by the arrow in FIG. The incident S-polarized light has its optical path changed by 90 ° due to the dielectric multilayer film 2 and enters the reflective spatial light modulator 5. The incident S-polarized light is modulated by the image signal output from the liquid crystal drive (not shown) in the reflective spatial light modulator 5 and reflected to the PBS 4. In the case of the P-polarized light which is modulated and reflected, it goes straight without changing the optical path and passes through the PBS 4, but when it is the S-polarized light, it is reflected again by the dielectric multilayer film 2, so that the contrast corresponding to the image is obtained. give. The P-polarized light transmitted through the PBS 4 passes through a relay lens (not shown), enters a condenser lens (not shown), is condensed, and enters a cross dichroic prism (not shown).

Similarly to the blue light, the light paths of the other two color lights previously dispersed are changed by 90 degrees by the other two PBSs, and are polarized and modulated by the reflective spatial light modulator, and then reflected. Straight through the two PBSs, and enters a cross dichroic prism (not shown). The three primary color lights incident on the cross dichroic prism (not shown) are combined by this prism, emitted from the prism, transmitted through the projection lens, and projected and projected as an image. As shown in Table 2, Example No. Since 20 glass has a small amount of deterioration in transmittance, no decrease in the amount of projected light was observed even when light was continuously passed through PBS 4 for a long time. In addition, this glass, in the purple region of the visible range,
Since it has an excellent light transmittance, it is possible to obtain projection light with good color rendering properties without reducing the light amount. Furthermore, since this glass has a small absolute value of the photoelastic constant (β),
The portion of PBS4 did not cause birefringence leading to a decrease in light intensity. In addition, the embodiments of the present invention (No. 1 to No. 1)
When PBS was prepared from each of the glasses of 9) and used, the same effect as described above was obtained.

Next, Example No. 3 of the present invention. An example (application) of using 20 glasses as a polarization conversion element optical system will be described. In the same manner as above, a triangular prism was prepared, and PBS was prepared from the triangular prism. High-power light such as an ultra-high pressure mercury lamp is made into a uniform light flux through an optical integrator (not shown) composed of a fly lens array,
This light flux is made incident on the PBS. The light beam incident on the PBS is separated into two linearly polarized lights (P-polarized light and S-polarized light) whose polarization directions are orthogonal to each other. The P-polarized light transmitted through the PBS is converted into S-polarized light through a polarization rotation optical system (polarization rotation by reflection using a triangular prism), and is combined with the other S-polarized light reflected by the PBS. Comparing the polarization exchange efficiencies according to the conventional technology (using a polarizing plate, for example), the separated P polarized light is converted into S polarized light to be combined and used.
It has almost twice the conversion efficiency and is suitable for applications that use polarized light with high efficiency (high brightness liquid crystal projector).

As shown in Table 2, Example N of the present invention
o. Since the glass of No. 20 had a small amount of deterioration in transmittance, no decrease in the amount of projected light was observed even when high intensity light was continuously irradiated for a long time. Furthermore, since the absolute value of the photoelastic constant (β) of this glass is small, birefringence due to thermal stress due to temperature rise due to light irradiation and mechanical stress during optical system fabrication (film deposition or prism laminating) Since it does not occur, it has an excellent polarization maintaining property. In addition, the embodiment No. 1-No. PBS from 19 glass each
When the above was prepared and used, the same effects as described above were obtained.

[0051]

As described above, the optical glass of the present invention contains SiO ₂ , PbO and B ₂ O ₃ , and further contains the mass% of
With 0.1% or more of TeO ₂ and 0.4% or more of Li ₂
Since it is an optical glass characterized by containing O,
The deterioration rate of the transmittance caused by irradiating the glass with light in the ultraviolet range and / or visible range is small, and it has excellent light transmittance for light with wavelengths from the long wavelength side to the violet range in the visible range. And, the melting, the glass of high refractive index having a good photoelastic constant (β) with a small absolute value, which is excellent in the clarity of the molten glass during melting and clarification,
Suitable for use in optical elements such as lenses and prisms and substrates, especially optical elements in polarizing optical systems, PBS, SLM,
It is suitable for use in a light polarization control element such as a polarization conversion element.

[Brief description of drawings]

FIG. 1 is an enlarged view of a main part of a polarization optical system of a projection device including a PBS using an embodiment of the present invention.

[Explanation of symbols]

1a, 1b triangular prism 4 PBS

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] June 12, 2002 (2002.6.1)
2)

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0010

[Correction method] Change

[Correction content]

Japanese Unexamined Patent Publication No. 9-48631 discloses PbO.
-B ₂ O ₃ and / or A1 ₂ O ₃ based polarizing optical glass for optical systems have been disclosed. This glass has a small amount of deterioration in transmittance, and although slightly better in light transmittance than the glass of the above-mentioned publication, again, the light transmittance from the short wavelength side of the blue region to the violet region before the deterioration of transmittance occurs. It is not sufficiently improved, and the melting and melting of the molten glass at the time of refining is poor, and it is possible to homogenize the glass by eliminating striae like the glass of the above publication, but in the obtained glass It is difficult to make an optical component because bubbles remain on the surface. Further, in Japanese Patent Laid-Open No. 8-259259, SiO
₂ -R ₂ O-PbO- fluorine-based polarizing optics for optical glass is disclosed. Although this glass has better defoaming than the glasses of the two publications, the deterioration amount of the transmittance is significantly larger than that of the glasses of the two publications, and it is considered that the cause is the fluorine component.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0012

[Correction method] Change

[Correction content]

Therefore, in the case of a glass having poor bubble breakage, such as the glass disclosed in JP-A-9-48631 and JP-A- 8-259259 , if the temperature during fining is increased,
In some cases it may be possible to obtain a glass with better defoaming and less or no bubbles. However, when the temperature is increased, the amount of platinum dissolved in the glass from the container is increased, and the light transmittance of the obtained glass is further deteriorated. On the contrary, when the temperature during refining is lowered, the amount of platinum dissolved in the glass is reduced, and the light transmittance is considerably improved, but the bubble breakage is further deteriorated.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Masahiro Onozawa             1-15-30 Koyama, Sagamihara City, Kanagawa Prefecture             In ceremony company OHARA (72) Inventor Junko Ishioka             1-15-30 Koyama, Sagamihara City, Kanagawa Prefecture             In ceremony company OHARA F-term (reference) 2H049 BA05 BA43 BC10 BC22                 4G062 AA01 AA04 BB04 DA04 DB01                       DB02 DB03 DC02 DC03 DD01                       DE01 DE02 DE03 DF06 DF07                       EA02 EA03 EB01 EB02 EB03                       EC01 EC02 EC03 ED01 ED02                       ED03 EE01 EE02 EE03 EF01                       EF02 EF03 EG01 EG02 EG03                       FA01 FA10 FB01 FC01 FD01                       FD02 FD03 FE01 FF01 FG01                       FG02 FG03 FH01 FJ01 FK01                       FL01 GA01 GB01 GC01 GD02                       GD03 GE01 HH01 HH03 HH05                       HH07 HH09 HH11 HH13 HH15                       HH17 HH20 JJ01 JJ03 JJ04                       JJ05 JJ07 JJ10 KK01 KK03                       KK05 KK07 KK10 MM02 NN01                       NN02

Claims (9)

[Claims] 1. An optical system containing SiO ₂ , PbO and B ₂ O ₃ , and further containing 0.1% or more of TeO ₂ and 0.4% or more of Li ₂ O in mass%. Glass. 2. The optical glass according to claim 1, wherein, when the thickness is 10 ± 0.1 mm, the wavelength of light transmitted at a transmittance of 80% is 420 nm or less. 3. Light rays in the ultraviolet range and / or visible range are 2.
The optical glass according to claim 1 or 2, wherein the deterioration rate of the transmittance of a light beam having a wavelength of 450 nm is 3.0% or less when irradiated with irradiance of ² W · cm ^-2 for 10 minutes. 4. Light rays in the ultraviolet range and / or visible range are 2.
The optical glass according to claim 1 or 2, wherein the deterioration rate of the transmittance of a light beam having a wavelength of 450 nm is 1.0% or less after irradiation with irradiance of ² W · cm ^-2 for 10 minutes. 5. The absolute value of the photoelastic constant (β) in the wavelength range of 400 to 800 nm is 1.0 × 10 ⁻⁵ nm / cm /.
The optical glass according to claim 1, 2, 3 or 4, which is Pa or less. 6. Mass%, SiO ₂ 18-29%, Pb
O 66-78%, TeO ₂ 0.1-3.5%, B ₂ O
_3. 0.1 to 6% and Li ₂ O 0.4 to 5% are contained, and the refractive index (nd) is in the range of 1.75 to 1.90. The optical glass as described in 4 or 5. 7. Further, 0 to 8% by mass of Na ₂ O,
K ₂ O 0-8%, provided that Li ₂ O + Na ₂ O + K ₂ O
0.4-10%, MgO 0-5%, CaO 0-5
%, SrO 0-5%, BaO 0-10%, ZnO
0-5%, but MgO + CaO + SrO + BaO +
ZnO 0-10%, GeO ₂ 0-5%, Al ₂ O ₃ 0
~ 3%, Nb ₂ O ₅ 0-3%, provided that GeO ₂ + Al ₂
The optical glass according to claim 6, which contains O ₃ + Nb ₂ O ₅ 0 to 5%, As ₂ O ₃ 0 to 1%, and Sb ₂ O ₃ 0 to 1%. 8. SiO ₂ 18-29%, Pb in mass%
O 66-78%, TeO ₂ 0.1-3.5%, B ₂ O
₃ 0.1 to less than ₂ %, Li ₂ O 0.4 to 5%, Na ₂
O 0-8%, K ₂ O 0-8%, but Li ₂ O + N
a ₂ O + K ₂ O 0.4-10%, MgO 0-5%, C
aO 0-5%, SrO 0-5%, BaO 0-10
%, ZnO 0 to 5%, but MgO + CaO + Sr
O + BaO + ZnO 0-10%, GeO ₂ 0-5
%, Al ₂ O ₃ 0 to 3%, Nb ₂ O ₅ 0 to 3%, provided that GeO ₂ + Al ₂ O ₃ + Nb ₂ O ₅ 0 to 5%, As ₂ O
_{30 to 1} % and Sb ₂ O ₃ 0 to 1% are contained, and the refractive index (nd) is in the range of 1.75 to 1.90. 5. The optical glass according to item 5. 9. The Abbe number (νd) is less than 28, which is preferably 1, 2, 3, 4, 5, 6, 7, or 8.
Optical glass according to.