JP2006201697A - Light absorbing member and optical device having the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a light absorbing member effectively preventing incident light from being reflected or made to transmit to exit to the outside by absorbing the incident light. <P>SOLUTION: The light absorbing member (black reflection preventive film) 10 is provided on a transparent substrate 11 to absorb the incident light, and is constructed by providing a light absorbing part (absorption type multilayer reflection preventive film) 12, a light shielding part (light shielding film) 13, and a light absorbing part (absorption type multilayer reflection preventive film) 14 successively from the transparent substrate 11 side. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a light absorbing member and an optical element having the light absorbing member. For example, in an optical device such as a digital camera or a video camera, the light absorbing member absorbs a light beam incident on a region other than the light beam effective portion out of the light incident on the lens barrel. This is suitable for preventing reflected light or transmitted light from an area other than the luminous flux effective portion and preventing these lights (unnecessary light) from entering the image plane.

  In general, in an optical component (optical element) used in an optical device such as a lens barrel or a camera body, light incident on a portion other than the effective portion of the light beam is reflected or transmitted from there to become unnecessary light, and is incident on an image plane. In order to prevent the image quality from being deteriorated, a light absorbing member (light shielding film) is provided in a region other than the light flux effective portion of the optical element.

  Especially in an optical system where the distance between optical elements is close, if unnecessary light is not removed, it will cause multiple reflections, which will enter the image plane and cause flare due to ghost or scattered light, which will adversely affect optical performance. Effect.

  In recent years, the optical system has become particularly compact and the distance between the optical elements tends to approach. Therefore, it is desired to provide a light absorbing member with a high effect of removing unwanted light in a region other than the effective beam portion of the optical element. ing.

  Currently, there is a black organic paint as a material of a light absorbing member (light shielding film) formed for the purpose of unnecessary light absorption (light shielding) on a transparent substrate such as a lens or a glass substrate. The black organic paint is generally printed on a substrate by screen printing or the like to form a light shielding film.

  The light-shielding film prepared by screen printing has excellent characteristics such as high light-shielding properties, little residual reflection on the front and back surfaces, and easy processing. On the other hand, heat resistance and mechanical strength are generally inferior to light absorbing members used in optical components (optical elements), and a certain coating thickness is required for light shielding. For this reason, there are drawbacks that it is difficult to form a thin film of several μm or less, and that secondary processing involving heating or the like cannot be performed.

As a light-absorbing member that solves such a problem, a light-absorbing antireflection film by vacuum film formation is known (Patent Documents 1 to 5).
Japanese Patent No. 3359114 JP 2003-344612 A JP 2001-350003 A Patent No. 2691989 Japanese Patent Laid-Open No. 10-96801

  Patent Documents 1 and 2 disclose a thin-film ND filter using only a metal oxide such as titanium oxide as an absorption film.

  In Patent Documents 1 and 2, in order to obtain a complete light shielding effect, it is necessary to increase the thickness of the absorbing film or increase the number of absorbing films. As a result, the residual reflected light increases, Furthermore, the total film thickness tends to increase.

  Patent Document 3 discloses a black antireflection film comprising a black coating made of an inorganic substance and an antireflection coating formed on the black coating and having a refractive index different from that adjacent to each interface. Yes. In this configuration, back surface reflection occurs, and surface reflection occurs in the use wavelength region.

  Patent Document 4 discloses a neutral density filter in which an antireflection film composed of a transparent dielectric film and a metal thin film is formed on a metal film.

  As described above, the black antireflection film in which the transparent dielectric film is directly formed on the metal film is difficult to reduce the reflectance at a wavelength other than the specific wavelength, and it is difficult to prevent the reflection in a wide wavelength range.

  Patent Document 5 discloses a light-absorbing antireflection body comprising a light-absorbing film and a transparent dielectric film from the substrate side.

  Although Patent Document 5 discloses an antireflection film having a low reflectance and a wide wavelength range, dedicated equipment such as a plasma apparatus is required for manufacturing metal nitrides and the like.

  An object of the present invention is to provide a light absorbing member capable of effectively preventing incident light from being reflected or transmitted and emitted to the outside by absorbing incident light, and an optical element having the same. To do.

  In addition, the present invention has a sufficient absorption effect (light shielding effect) for transmitted light, front surface, and back surface reflected light in the entire visible region (wavelength: 400 nm to 700 nm) without requiring special gas introduction or a plasma apparatus. It is an object of the present invention to provide a light-absorbing member excellent in physical properties such as strength, heat resistance and flatness and having a thin physical film thickness and an optical element having the same.

  The light-absorbing member of the present invention is a light-absorbing member provided on a transparent substrate to absorb incident light, and the light-absorbing member is sequentially from the light-absorbing portion, the light-shielding portion, and the light-absorbing portion from the transparent substrate side. It is characterized by that.

  ADVANTAGE OF THE INVENTION According to this invention, the light absorption member which can prevent effectively that the incident light reflects or permeate | transmits and is radiate | emitted outside by absorbing the incident light is obtained.

  FIG. 1 is a cross-sectional view of an essential part of Example 1 of an optical element 100 to which a light absorbing member of the present invention is applied. FIG. 2 is an explanatory diagram of a film configuration of the light absorbing member according to the first embodiment. The light absorbing member (black antireflection film) 10 of Example 1 includes a light absorbing portion (absorbing multilayer antireflection film) 12 and a light shielding portion (light shielding film) 13 formed of a metal single layer film on a flat or curved surface of the transparent substrate 11. The light absorbing portion (absorbing multilayer antireflection film) 14 is provided.

Specifically, the transparent substrate 11 is made of optical glass (trade name S-BSL7 (BK7)), and the light absorption part 12 is made from the substrate 11 side from Al ₂ O ₃ / TiO / Al ₂ O ₃ / TiO / Al ₂ O _3. The light shielding part 13 is composed of four layers of TiO / Al ₂ O ₃ / TiO / _Mg F ₂ from the substrate 11 side. TiO is a light absorption layer.

  Here, the light-shielding portion 13 is formed of a multilayer film having a transmittance at a reference wavelength of 550 nm of 0% and a reflectance of about 60%, and the light absorbing portions 12 and 14 having a transmittance of 10% or less.

  The optical member of the present example realizes sufficient performance as a light-shielding film with a transmittance of zero in the entire visible region (wavelength of 400 nm to 700 nm) and a surface reflectance and a back surface reflectance of 0.6% or less. Yes. The total film thickness of Example 1 is 647.09 nm, and a reduction in thickness is achieved. The back surface reflected light refers to light that enters the optical element, passes through the inside of the optical element, is reflected at the light emission side interface (not shown in FIG. 1), and then returns to the incident side interface. Refers to that.

  The ratio with respect to the total film thickness of the chromium single layer film of the light shielding part 13 is set to about 10% to 20%, thereby constituting a good light absorbing member.

  In Example 1, the light absorption member 10 has a total physical film thickness of 1 μm or less.

  Further, the light absorbing member 10 has a film layer configured such that the light transmittance, the surface reflectance, and the back surface reflectance are all 1% or less in the entire visible region (wavelength 400 nm to 700 nm).

  The light absorbing member 10 of the first embodiment is provided with a light shielding portion (light shielding layer) 13 between the light absorbing portions 12 and 13 for completely blocking light reflection and light transmission.

  As a result, most of the light shielding effect is realized by the light shielding portion 13, thereby simplifying the entire film configuration and reducing the total film thickness.

  Further, as shown in FIG. 10, the light transmission in the light absorbing member 10 is transmitted by the light shielding film 13, and the transmitted light Tb in the light absorbing portion 12 on the substrate 11 side and the light absorbing portion 14 on the atmosphere side (light incident side). The transmitted light Ta is substantially divided.

  Here, as shown in FIGS. 10 and 11, the light that is incident from the atmosphere side (the drawing, the left side) and reflected by the light absorbing member 10 constituting the optical element 100 is the surface reflected light Ta, and is incident from the substrate 11 side. The light reflected by each surface of the light absorbing member 10 and reflected toward the substrate 11 side is the back surface reflected light Tb.

  The first embodiment has the above-described configuration in order to reduce the front surface reflected light Ta and the back surface reflected light Tb.

  FIG. 11 shows a state in which a light beam is incident on the light absorbing member 10 provided in a region other than the light beam effective portion on the surface of the lens using a lens as the optical element 100.

  In FIG. 11, the light that directly enters and reflects the light absorbing member 10 out of the incident light from the air is the surface reflected light Ta, and enters the effective region of the substrate 11 of the lens 100 and then enters the effective region of the light flux. The light reflected by the provided light absorbing member 10 is back surface reflected light Tb.

  In general, in an optical element provided with an antireflection film, the surface reflection on the film surface and the back surface reflection on the substrate surface at the boundary between the film and the substrate need to be optimized at the same time.

  In an actual film design, the surface reflection and the back surface reflection interfere with each other, so that the film design is difficult.

  On the other hand, in the film configuration of Example 1, as shown in FIG. 10, the light transmission in the light absorbing member 10 is divided by the light shielding portion 13 to prevent mutual interference between the front surface reflected light Ta and the back surface reflected light Tb. ing. For this reason, in the film design, the surface reflectance can be designed independently from the surface reflectance of the light absorbing portion 14 on the atmosphere side, and the back surface reflectance can be designed independently from the back surface reflectance of the light absorbing portion 12 on the substrate 11 side. As a result, the light absorbing member 10 can be further improved.

  The spectral characteristic diagram of Example 1 is shown in FIG. As a comparative example, a film configuration excluding the light shielding portion 13 is shown in FIG. 8, and a spectral characteristic diagram is shown in FIG. As shown in FIGS. 3 and 9, it can be confirmed that the light absorption member 10 of Example 1 has improved transmittance and reflectance compared to the comparative example.

  The light absorbing member 10 of the present invention is an absorption multilayer antireflection film including two or more light absorbing layers (light absorbing films) (TiO) each of the light absorbing portions 12 and 14 (front and rear) sandwiching the light shielding portion 13. It is composed.

Patent Document 4 discloses a neutral density filter in which an antireflection film composed of a transparent dielectric film and a metal thin film is formed on a metal film. The antireflection effect obtained by such a configuration is difficult to obtain a low reflectance over the entire visible range as shown in FIG. Although the anti-reflection film example by thin film having absorption as Cr ₂ O ₃ as Comparative Example 2 in this document are presented, it is difficult to realize a low reflectance in the entire visible range even in such a configuration .

  Further, in Patent Document 3, an example using a black film made of an inorganic substance as a light shielding film is used, and in Patent Document 5, an example using a gold alloy, silicon nitride oxide, or the like as a light-absorbing antireflective body and its manufacturing method. However, in order to obtain such a black coating, it is necessary to manage complicated elements such as processing equipment and gas introduction conditions, and a black antireflection film must be used unless a special gas introduction or plasma device is used. Can not get.

On the other hand, in the first embodiment, the light shielding portion 13 is composed of a metal single layer film. Further, as the light absorbing portions 12 and 14, TiO or Ti ₂ O ₃ or a mixture thereof is used as a light absorbing layer as a material capable of obtaining a stable light absorbing characteristic without using gas introducing means or the like, and further light absorbing. The light absorption layer is divided into two or more layers for the purpose of widening the bandwidth. In addition, a transparent dielectric layer made of Al ₂ O ₃ , SiO ₂ , _Mg F ₂ or the like is disposed before and after (between) the light absorption layers. Further, as the optimum value of the reduction of the reflected light from the metal single layer film constituting the light shielding portion 13 and the film thickness limit, the film configuration is such that the light transmittance of the light absorbing portions 12 and 14 alone is 10% or less. Yes.

  As a result, the amount of influence of the reflected light from the actual light shielding portion 13 is reduced to 10% × 10% = 1% or less. For example, when the light-shielding portion 13 is realized by a metal chrome single layer film, the reflectivity of the metal chrome single layer film itself is about 60%, so the actual reflectivity of the front surface reflected light Ta and the back surface reflected light Tb is 0.6. % Or less. The light shielding film 13 may be composed of a multilayer metal film.

  FIG. 4 shows a film configuration and spectral characteristics obtained by extracting only the light absorption part 14 on the atmosphere side from the film configuration presented in FIG. FIG. 5 shows the film configuration and spectral characteristics obtained by extracting only the light absorbing portion 12 on the substrate 11 side from the film configuration presented in FIG. Thus, when the light transmittance of each light absorption part 12 and 14 is 10% or less, if the light-shielding part 13 is provided between them, sufficient light absorption effect (antireflection effect) will be obtained.

FIG. 6 shows a film configuration and FIG. 7 shows a spectral characteristic diagram of the light absorbing member of Example 2 of the present invention. The film structure provided on the substrate is the same as in FIG. In Example 2, a transparent resin (polycarbonate) is used instead of the transparent substrate 11 made of glass as shown in FIG. The light absorbing portion 12 has a five-layer structure of SiO ₂ / TiO / SiO ₂ / TiO / SiO ₂ from the substrate side, the light shielding portion 13 is a chromium (Cr) single layer film, and the light absorbing portion 14 is TiO / from the substrate 11 side. It consists of four layers of Al ₂ O ₃ / TiO / _Mg F ₂ . The transmittance is zero in the entire visible region (wavelength 400 nm to 700 nm), and both the surface reflectance and the back surface reflectance are 0.6% or less, realizing a sufficient performance as a light shielding film.

  The total film thickness of Example 2 is 618.11 nm, which is 1 μm or less, and a reduction in thickness is achieved. The transparent substrate 11 can cope with either glass or resin, and of course, the film forming conditions can correspond to both heating / non-heating.

  As described above, according to each embodiment, a light absorbing member (black antireflection film) having a sufficient light blocking effect on transmitted light, front surface, and back surface reflected light in the entire visible region (wavelength 400 nm to 700 nm) can be obtained. Furthermore, all the film-forming materials used in each example are excellent in physical properties such as film hardness, heat resistance, and flatness, and are composed of only materials that can be easily formed, so that they are physically excellent. A quality light-absorbing member can be easily obtained only with a vacuum deposition apparatus. Further, a light absorbing member having a total thickness of 1 μm or less, which is difficult to realize by screen printing or the like, can be obtained.

Schematic view of essential parts of an optical element having the light absorbing member of Example 1 of the present application. Explanatory drawing of the film | membrane structure of the light absorption member of Example 1 of this invention Spectral characteristics of the light absorbing member of Example 1 of the present invention Film structure and characteristic diagram of light absorption part on substrate side used in Example 1 Film structure and characteristic diagram of light absorption part on surface side used in Example 1 Explanatory drawing of the film | membrane structure of the light absorption member of Example 2 of this invention Spectral characteristics of the light absorbing member of Example 2 of the present invention Explanatory drawing of the film | membrane structure of the comparative example 1 Spectral characteristics of Comparative Example 1 Explanatory drawing of the surface reflected light and back surface reflected light which arise with the optical element of this invention Explanatory drawing when a light beam enters the light absorbing member of the optical element of the present invention

Explanation of symbols

100: Optical element 10: Light absorbing member 11: Transparent substrate 12: Light absorbing portion 13: Light shielding portion 14: Light absorbing portion Ta: Front surface reflected light Tb: Back surface reflected light

Claims (8)

  A light absorbing member provided on a transparent substrate for absorbing incident light, wherein the light absorbing member comprises a light absorbing portion, a light shielding portion, and a light absorbing portion in order from the transparent substrate side. Element. The light absorbing portion, and two or more layers of the light absorbing layer, SiO _2, Al ₂ O _3, the light-absorbing member according to claim 1, characterized in that consists of one of the dielectric layer of MgF _2. The light-absorbing layer, the light-absorbing member according to claim 2, characterized in that consisting of TiO or Ti ₂ O ₃ or a mixture thereof.   4. The light absorbing member according to claim 1, wherein the light shielding portion is made of a single metal film.   5. The light absorbing member according to claim 1, wherein the light absorbing portion is made of a film layer having a light transmittance of 10% or less at a reference wavelength.   The light absorbing member according to claim 1, wherein the light absorbing member has a total physical film thickness of 1 μm or less.   The light-absorbing member has a film layer configured such that light transmittance, surface reflectance, and back surface reflectance are all 1% or less in the entire visible region (wavelength: 400 nm to 700 nm). Item 7. The light absorbing member according to any one of Items 1 to 6.   An optical element, wherein the light absorbing member according to claim 1 is provided on a transparent substrate.