JP4648813B2 - Infrared cut coat film, optical element having infrared cut coat film, and endoscope apparatus having the optical element - Google Patents

Description

  The present invention relates to an infrared cut coat film that transmits visible light and absorbs infrared light, and more specifically, can cut infrared light in a wide wavelength range and is suitable for a light source optical system of an endoscope. The present invention relates to an infrared cut coat film and an optical element having the infrared cut coat film.

  In many cases, a xenon lamp or a halogen lamp is used as an illumination light source of a light source optical system of an endoscope. Irradiation light of any lamp includes not only visible light required as illumination light but also infrared light having a wavelength of 750 nm or more. The light emitted from the illumination light source is guided to the incident end face of the light guide by the condensing lens, but if the light is condensed to the infrared light, the light guide is burnt. Recently, xenon lamps, which are frequently used for endoscope light sources, have a wavelength of 220 to 2000 nm, which includes infrared light with a wavelength of 750 nm or more at a high rate. It has become.

  Therefore, as shown in FIG. 6, an infrared cut filter 5 is provided between the illumination light source 3 and the condenser lens 1. Even if light including infrared light is irradiated from the illumination light source 3, it is necessary to prevent the light guide 4 from being overheated by cutting the infrared light in front of the condenser lens 1 and transmitting only visible light. Light can be guided to the endoscope. An optical member provided with a multilayer interference coating film that cuts infrared light by light interference is used as an infrared cut filter 5. A general multilayer interference coating film exhibits a spectral transmittance as shown in FIG. That is, it transmits visible light, reflects infrared light having a wavelength of 800 to 1100 nm, and transmits light having a wavelength of 1100 to 2000 nm. From the viewpoint of preventing the light guide 4 from being overheated, it is preferable not to transmit light having a wavelength of 1100 to 2000 nm. However, if interference is caused in this wavelength range to cause reflection, reflection also occurs in visible light. For example, when light having a wavelength of 1550 nm is reflected, the reflection of light having a wavelength of 1/3, that is, 517 nm is also increased (FIG. 9). Thus, from the viewpoint of preventing impairing the visible light transmission performance, the multilayer interference coating film is designed to have a transmittance that does not cut light having a wavelength of 1100 to 2000 nm.

A substrate that absorbs infrared light, such as infrared absorbing glass, can also function as an infrared cut filter. However, since the substrate that absorbs infrared light has a large thermal expansion coefficient of 70 × 10 ⁻⁷ ° C. ^{−1 at} 100 to 300 ° C., it is short when used as an infrared cut filter for an endoscope light source optical system. Over time, the surface temperature will rise to several hundred degrees. As a result, there is a problem that a rapid temperature distribution is generated between the light incident surface and the light emitting surface and / or the central portion and the peripheral portion of the substrate, and the substrate is cracked or chipped.

  Japanese Patent No. 2876998 (Patent Document 1) includes, as shown in FIG. 7, an infrared reflection filter 51 having a predetermined transmission energy amount and an infrared absorption filter 52 between the illumination light source 3 and the light guide 4. An endoscope light source optical system is described. In this endoscope light source optical system, the infrared absorbing filter 52 absorbs light having a wavelength of 1100 nm or more, the infrared reflecting filter 51 reflects infrared light having a wavelength of 750 to 1100 nm, and the infrared absorbing filter. Reduce the calorific value of 52. Therefore, if these filters 51 and 52 are provided between the illumination light source 3 and the light guide 4, the light guide 4 can be prevented from being burned out. However, the two members of the infrared reflection filter 51 and the infrared absorption filter 52 must be separated from each other, and there is a problem that it is difficult to reduce the size of the optical system.

Japanese Patent No. 2876998

  Accordingly, an object of the present invention is to provide an infrared cut material capable of cutting infrared light in a wide wavelength range with a single member without causing cracks or chips due to heat generation, and an endoscope apparatus having the same.

  As a result of diligent research in view of the above object, the present inventor has provided a film having a layer made of a material that transmits visible light and absorbs infrared light on the surface of a condensing lens or the like, thereby illuminating an endoscope. The present inventors have found that necessary visible light can be taken into the light guide while preventing burning by infrared light without separately providing an infrared cut filter in the optical path of the optical system.

That is, the infrared cut coat film of the present invention is formed by laminating layers that transmit visible light, and an infrared light absorption layer in which at least a part of the infrared cut coat film has absorption in the infrared light wavelength region. Non-absorbing layers that do not absorb infrared light are alternately laminated, and the infrared light absorbing layer contains zinc oxide as a main component, gallium as a subcomponent, and the content of the subcomponent is 0.1. It is characterized by having a transmittance of 0 to 5% in the infrared light wavelength region of 800 to 2000 nm .

The optical element of the present invention, rather is preferably of the infrared cut coating film of the present invention is formed on the surface of the substrate, the thermal expansion coefficient of the substrate is 1 × 10 ^-7 ~50 × 10 ^-7 C.- ¹ is preferred.

  The infrared cut coat film of the present invention transmits visible light and absorbs infrared light. A preferred infrared cut coat film exhibits a low transmittance of 5% or less for infrared light having a wavelength of 800 to 2000 nm. For this reason, when the infrared cut coat film of the present invention is formed on the surface of the condenser lens of the illumination optical system, even if a light source that irradiates light of a wide wavelength, such as a xenon lamp, is used, Even if a member such as a light cut filter is not separately provided, it is possible to prevent the light guide from being burned by infrared light. Thus, an optical element having an infrared cut coat film capable of cutting infrared light in a wide wavelength range is suitable for an illumination optical system that requires downsizing.

[1] Infrared cut coat film The infrared cut coat film has an infrared light absorbing layer having absorption in an infrared light wavelength region. In the present specification, “having absorption in the infrared light wavelength region” refers to showing a transmittance of 0 to 5% in the range of 800 to 2000 nm of so-called infrared light. A broadband infrared cut coat film capable of cutting light having a wavelength of 850 to 2000 nm is suitable for an illumination optical system of an endoscope.

  The infrared light absorbing layer transmits visible light and is transparent. The infrared light absorbing layer preferably has a wavelength of 400 to 700 nm and a spectral transmittance of 80% or more. A layer exhibiting such transmittance is substantially transparent.

The infrared light absorbing layer is preferably composed of a main component that transmits visible light and a subcomponent. When the subcomponent is contained, the crystal lattice of the main component is disturbed, and it is considered that infrared light is absorbed by this disorder. The content of subcomponents is 0.1 to 20% by mass . When the content is less than 0.1% by mass, the infrared light absorption layer is too difficult to exhibit a sufficient infrared light absorption rate. If it exceeds 20% by mass, it is difficult to exhibit sufficient transparency in the visible light region.

The main component of the infrared light absorbing layer is zinc oxide, the sub-component is gallium. The layer composed of these main components and subcomponents transmits visible light and absorbs infrared light with high efficiency .

In addition to the infrared light absorbing layer, the infrared cut coat film is made of a visible light transmitting material and has a non-absorbing layer that does not absorb infrared light . Moreover, it is preferable that layers having a high refractive index of about 1.7 to 2.5 and layers having a low refractive index of about 1.1 to 1.6 are alternately laminated. By alternately laminating the high refractive index layer and the low refractive index layer with an appropriate film thickness, an antireflection film capable of transmitting visible light in a wide wavelength range can be obtained. When the infrared light absorbing layer has a high refractive index, the non-absorbing layer preferably has a low refractive index, and when the infrared light absorbing layer has a low refractive index, the non-absorbing layer preferably has a high refractive index. For example, a gallium-doped zinc oxide layer, which is an infrared light absorbing layer, has a high refractive index of about 1.9, and therefore is alternately laminated with a non-absorbing layer having a low refractive index such as silicon oxide (refractive index: 1.48). Is preferred. Of course, a plurality of high refractive index layers and low refractive index layers may be provided, and only some of them may be infrared light absorbing layers. Examples of preferred materials for the non-absorbing layer include silicon oxide, tantalum oxide, titanium oxide, niobium oxide, zirconium oxide, cerium oxide, hafnium oxide, tin oxide, indium oxide, zinc oxide, yttrium oxide, aluminum oxide, and magnesium fluoride. Can be mentioned.

  The thickness and the number of layers of the infrared light absorbing layer and the non-absorbing layer may be appropriately determined depending on the refractive index of each layer, the wavelength range to be absorbed, and the like. In the case of an infrared cut coat film in which infrared light absorbing layers and non-absorbing layers are alternately laminated, generally, the optical film thickness (nd) of each layer is 50 to 650 nm, and the number of each layer is 20 It is about ~ 80.

  The infrared cut coat film has a low transmittance band in the infrared wavelength region. The light transmittance in the low transmittance band is preferably 5% or less, and more preferably 3% or less. When the light transmittance in the low transmittance band in the infrared wavelength region is 5% or less, overheating of the light guide can be effectively prevented when used in the illumination optical system of the endoscope apparatus. The short wavelength end of the low transmittance band is preferably 650 to 850 nm. If the short wavelength end is in this range, visible light transmission is not substantially prevented. The long wavelength end is preferably 1300 nm or more, and more preferably 1300 to 2300 nm.

[2] Optical Element FIG. 1 shows an example of an optical element having an infrared cut coat film. An optical element 10 shown in FIG. 1 includes a base material 1 and an infrared cut coat film 2 formed on a surface 11 of the base material 1. In the example shown in FIG. 1, the substrate 1 is a lens, but the substrate 1 of the optical element 10 of the present invention is not limited to a lens, and may be a flat plate, a prism, a diffraction grating, a polarizing element, an absorption filter, or the like.

Since the infrared cut coat film absorbs infrared light and becomes high temperature, the substrate 1 is preferably made of a material resistant to heat of 150 to 450 ° C. The coefficient of thermal expansion of the substrate 1 is preferably 1 × 10 ⁻⁷ to 50 × 10 ⁻⁷ ° C. ⁻¹ . When the thermal expansion coefficient is within this range, even if the infrared cut coat film 2 is heated when the optical element 10 is used, it is difficult to peel off from the substrate 1. Examples of a preferable material for the substrate 1 include heat-resistant glass such as Pyrex (registered trademark), low expansion glass, and transparent ceramics.

  As shown in the partially enlarged view, the infrared light absorbing layer 21 and the non-absorbing layer 22 are alternately laminated to form the infrared cut coat film 2. In the example shown in FIG. 1, an infrared light absorbing layer 21 is formed on the substrate 1, and the layer in contact with the medium is the non-absorbing layer 22, but depending on the refractive index of the substrate 1 and the layers 21 and 22, etc. In some cases, the non-absorbing layer 22 is formed on the substrate 1, or the layer in contact with the medium is the infrared light absorbing layer 21.

  The layers 21 and 22 of the infrared cut coat film 2 can be formed by a vacuum deposition method, an ion beam assist method, an ion plating method, a sputtering method, a pulse laser deposition method, or the like. Of these forming methods, the ion beam assist method is most preferable. A film formed by the ion beam assist method exhibits high adhesion to the substrate 1. Therefore, even if the infrared cut coat film 2 changes in temperature, it is difficult to peel off from the substrate 1.

  When light including infrared light Li and visible light Lv enters the optical element 10 from the infrared cut coat film 2 side, the infrared light Li is absorbed by the infrared cut coat film 2, and the visible light Lv is infrared cut coat. The light passes through the film 2 and is collected on the optical axis by the lens 1. The light transmittance in the infrared wavelength region is preferably 5% or less, and the light transmittance in the visible wavelength region is preferably 95% or more. When the optical element 10 having such a transmittance is provided on the optical path, the visible light Lv can be used while preventing other optical components from being overheated by effectively cutting the infrared light Li. .

[3] Endoscope Device FIG. 2 schematically shows an example of an illumination optical system of the endoscope device. A condensing lens 10 and a light guide 4 are provided on the optical path in this order on the optical axis of the light source 3 including the xenon lamp 31 and the reflecting mirror 32. The light emitted from the xenon lamp 31 reaches the condenser lens 10 directly and is reflected by the reflecting mirror 32 to enter the condenser lens 10. The effective diameter of the condenser lens 10 is preferably equal to or larger than the light diameter of the light source 3, and more preferably equal to the light diameter of the light source 3. If the effective diameter of the condensing lens 10 is smaller than the light diameter of the light source 3, visible light cannot be collected effectively, and there is much infrared light that is not cut, and the light guide 4 and the like are easily overheated.

  Of the light emitted from the xenon lamp 31, the visible light Lv passes through the infrared cut coat film 2, is condensed by the lens 1, and enters the light guide 4. Since the infrared light Li is absorbed by the infrared cut coat film 2, the light guide 4 is not overheated. That is, the optical element 10 having the infrared cut coat film 2 can incorporate the visible light Lv into the light guide 4 while cutting the infrared light Li to prevent the light guide 4 from being burned out.

  The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

Example 1
Infrared cut coat film shown in Table 1 on Pyrex (registered trademark) glass (thermal expansion coefficient 36 × 10 ⁻⁷ ° C ⁻¹ , refractive index 1.474) of 50 mm × 50 mm and thickness 1 mm by ion beam assist method Was deposited. At that time, the Ta ₂ O ₅ (refractive index 2.26) layer and the SiO ₂ (refractive index 1.48) layer were formed using a material having a purity of 99.9% or more. The material of the zinc oxide layer (ZnO + Ga, refractive index 1.92) to which gallium is added is mixed with 99.9% pure zinc oxide and 99.9% pure gallium oxide so that the gallium content is 2.7% by mass in advance. What was done was used. For the ion assist, a MARK-II ion source manufactured by Commonwealth was used, and the ionized gas was argon, the acceleration voltage was 100 V, and the ion current was 2A. O ₂ was introduced as a reaction gas into the vacuum chamber, and the degree of vacuum was 5 × 10 ⁻² Pa.

Comparative Example 1
Table 2 shows the optics shown in Table 2 using an ion beam assist method on an infrared absorption substrate (HA15, thermal expansion coefficient 67 × 10 ⁻⁷ ° C ⁻¹ , refractive index 1.524, manufactured by HOYA Corporation) with a thickness of 50 mm × 50 mm and thickness 1 mm. A film was formed. Ta ₂ O ₅ and SiO ₂ were the same as in Example 1, and the conditions for ion beam assist were the same as in Example 1.

Comparative Example 2
An optical element was produced in the same manner as in Example 1 except that the configuration of the optical film formed on the substrate was as shown in Table 3.

表３（続き）

Table 3 (continued)

  The spectral transmittances on the surfaces of the infrared cut coat films of Example 1, Comparative Example 1 and Comparative Example 2 are shown in FIGS. Example 1 showed a high transmittance in the visible region, and a low transmittance of 3% or less in the infrared region (wavelength 800 to 2000 nm).

  After holding the optical element of Example 1 and the optical element of Comparative Example 1 at 200 ° C. for 500 hours, a test was conducted by attaching and removing a cellophane tape (registered trademark), and the state of the film was observed. In Comparative Example 1, the film was peeled off together with the tape, but no change was observed in the infrared cut coat film of Example 1.

It is sectional drawing which shows the optical element which has the infrared cut coat film of this invention. It is a block diagram which shows the illumination optical system which has the optical element of this invention. 3 is a graph showing the film surface transmittance of Example 1. 5 is a graph showing the film surface transmittance of Comparative Example 1. 10 is a graph showing the film surface transmittance of Comparative Example 2. It is a block diagram which shows an example of the illumination optical system which has the conventional infrared cut filter. It is a block diagram which shows another example of the illumination optical system which has the conventional infrared cut filter. It is a graph which shows the film surface transmittance | permeability of the conventional infrared cut filter. It is a graph which shows the film surface transmittance | permeability of the conventional infrared cut filter.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Base material 2 ... Infrared cut coat film
21 ... Infrared light absorbing layer
22 ... Non-absorbing layer 3 ... Light source
31 ... Xenon lamp
32 ... Reflector 4 ... Light guide
Lv ・ ・ ・ Visible light
Li: Infrared light

Claims (4)

An infrared cut coat film formed by laminating layers that transmit visible light, wherein at least part of the infrared cut coat film has an infrared light absorption layer and an infrared light having absorption in an infrared light wavelength region. Non-absorbing non-absorbing layers are alternately laminated, the infrared light absorbing layer contains zinc oxide as a main component, gallium as a subcomponent, and the content of the subcomponent is 0.1 to 20% by mass An infrared cut coat film characterized by having a transmittance of 0 to 5% in an infrared light wavelength region of 800 to 2000 nm . An optical element formed by forming the infrared cut coat film according to claim 1 on the surface of a substrate. 3. The optical element according to claim 2, wherein the base material has a coefficient of thermal expansion of 1 * 10. ^-7 ~ 50 × 10 ^-7 ℃ ^-1 An optical element characterized by the above. An endoscope apparatus comprising the optical element according to claim 2 .

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