JPH075337B2 - Phosphoric acid glass protector - Google Patents

Description

TECHNICAL FIELD The present invention relates to a device for protecting an optical surface of a phosphate glass.

<Prior Art> For example, phosphoric acid glass has been widely used as an optical element for color sensitivity correction of an image pickup element of a video camera.
However, this phosphoric acid-based glass has weak weather resistance, and a so-called “burning” phenomenon occurs in which the transmittance is lowered by the action of moisture in the air. Therefore, in order to enhance the weather resistance without deteriorating the optical characteristics, after applying a coating treatment to the optical surface of the phosphoric acid-based glass, an optical glass, a hard optical element having high weather resistance such as crystal is adhered. Protects phosphate glass,
An antireflection film has been provided on the surface. Explaining this conventional example, after coating the optical surface of phosphoric acid glass with magnesium fluoride (MgF ₂ ) with a film thickness of λ / 4, an optical material such as quartz is prepared using an ultraviolet curable adhesive or the like. The element was bonded. The thickness λ / 4 of the coating layer in this conventional example is also commonly used as the thickness of the antireflection film.

<Problems to be Solved by the Invention> The light reflectance of such a conventional example is shown in FIG.
As shown in, reflection occurs for each coating film,
The total value of the reflectances at these four points is the reflectance of the entire device. The light reflectance of each coating film at the wavelength of 530 nm in the above conventional example is 0.3%,
, And 0.9%, respectively, resulting in a total reflectance of 2.4%, which was a cause of image quality deterioration. The wavelength characteristic of the total light reflectance of this conventional example is shown by the dotted line in FIG.

Further, the conventional example has a drawback that if there is a pinhole in the film, moisture in the air easily penetrates the phosphate glass through the pinhole and is poor in weather resistance. Fig. 6 shows the non-defective product 10
The test data of the non-defective product retention rate when a large number of 0% test objects are placed in a predetermined environment are shown. This test environment has a temperature of 60 ℃
It is in the air with a humidity of 90%. It can be clearly seen that some deteriorate after about 500 hours, then the number of deteriorated products rapidly increases, and all of them deteriorate within 1000 hours. When I examined this defective state, all of it
The surface of the phosphoric acid glass was dissolved by the water, and the light transmittance was lowered.

Therefore, it is an object of the present invention to provide a highly reliable phosphoric acid-based glass protective device that enhances light transmittance and weather resistance.

<Means for Solving the Problems> In order to solve the above problems, the phosphate glass protective device of the present invention has an optical film thickness on the front and back surfaces of the phosphate glass that is an integer multiple of λ / 2 (here, λ is the wavelength of the transmitted light) and a protective film is coated on each protective film, and an optical element such as crystal or glass is adhered to the protective film through an adhesive layer having a refractive index substantially the same as that of the optical element. Is characterized by

<Embodiment> FIG. 1 shows a schematic configuration diagram of an embodiment of the present invention. The optical surfaces 1a and 1b of the phosphoric acid-based glass plate 1 are coated with protective films 2 and 2, and the optical elements 3 and 3 made of a quartz plate are adhered onto the protective films 2 and 4, respectively.
And the surfaces of the optical elements 3, 3 are coated with antireflection films 5, 5 such as MgF ₂ . Protective film 2
Is composed of, for example, a group consisting of MgF ₂ , Al ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO _2, etc., and its optical film thickness is λ
Then, λ / 2 × K (where K is 1,2,3,4, ...). Here, the optical film thickness means (refractive index) × (thickness). The adhesive is, for example, an ultraviolet curable adhesive, and its optical refractive index is adjusted to be substantially the same as the optical refractive index of the optical element 3 or an approximate value within ± 0.02. The film thickness of the protective film 2 is most preferably K = 1, but may be K = 2 or more.

In FIG. ₂ , the solid line shows the wavelength characteristic of the total reflectance of the embodiment of the present invention using MgF ₂ as the film material. At a wavelength of 530 nm, the reflectance of the conventional example was 2.4%, whereas that of the present invention is reduced to about 0.6%, which is about 1/4.

The protective film 2 in the present invention is made of Al ₂ O ₃ , SiO ₂ , MgF ₂ , Zr.
It can be carried out using O ₂ , TiO ₂ or the like. FIG. 3 shows the wavelength characteristics of the reflectance at K = 1 when the material of the protective film 2 is changed.

As shown in FIG. 4, the test condition of the wavelength characteristic is that the optical film of the phosphoric acid-based glass 11 is provided with the protective film 12 having an optical film thickness of λ / 2, and the optical refractive index n = UV curable adhesive with the same refractive index as 1.54 was prepared and applied, and the adhesive layer 14
FIG. 3 is a diagram in which the light reflectance at the boundary surface between the crystal 13 and the phosphoric acid-based glass 11 is calculated for the device in which the crystal 13 is bonded via the. It should be noted here that the specific wavelength λ ₀ = 530n
At m, the light reflectance is substantially zero regardless of the material forming the protective film. Further, as shown in FIG. 5, when the present invention product having a film thickness K = 1 was tested under the same conditions as the weather resistance test of the conventional example,
No deterioration was observed even after the test time of 1,000 hours.

<Effect of the Invention> According to the present invention, the light reflectance is reduced to about 1/4 and the optical characteristics are improved. In addition, the product of the present invention maintained the good condition for all products even after 1,000 hours compared to the case where all products were defective after 1,000 hours, and the weather resistance could be improved while improving the optical characteristics.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention, FIG. 2 is a wavelength characteristic diagram comparing light reflectances of an embodiment of the present invention (solid line) and a conventional example (dotted line), and FIG. FIG. 4 is a wavelength characteristic diagram showing the light reflectance shown in FIG. 4 when the material of the protective film 2 is changed variously, FIG. 4 is an explanatory diagram of the test conditions of the characteristic diagram shown in FIG. 3, and FIG. It is a figure which shows the time-dependent characteristic of a prior art example and this invention Example. 1 ... Phosphate glass plate 2 ... Protective film 3 ... Optical element 4 ... Adhesive layer

Claims (1)

[Claims] 1. A protective film having an optical thickness of an integral multiple of λ / 2 (where λ is the wavelength of the transmitted light) is coated on each of the front and back surfaces of the phosphate glass, and a quartz crystal is formed on each protective film. An apparatus for protecting a phosphate glass, wherein an optical element such as glass is adhered via an adhesive layer having a refractive index substantially the same as that of the optical element.