JP5066644B2 - Multilayer ND filter - Google Patents

Description

  The present invention relates to a multilayer ND filter that can attenuate the amount of transmitted light uniformly and is used for applications such as a diaphragm for the amount of light of a camera.

Conventionally, a multilayer ND (Neutral Density) filter is used in a part of a photographing system (optical system) of a photographing device such as a camera or a video in order to attenuate the amount of transmitted light. The ND filter is an optical filter having a flat optical characteristic to transmit light in the visible range with almost uniform attenuation. For example, when there is too much light in fine weather, the ND filter can obtain an expected light amount only with the aperture. Its main purpose is to prevent overexposure when it is difficult to suppress, when it is desired to release the shutter at a low speed, or when it is desired to open the aperture. The ND filter needs to have flat optical characteristics and also have better antireflection characteristics.
Patent Documents 1 to 3 are shown as examples of such a multilayer ND filter. The multilayer ND filter of Patent Document 1 uses two or more kinds of metal oxides as a light absorption film. In addition, the multilayer ND filter of Patent Document 2 has one kind of metal oxide as a light absorbing film and a high refractive index film having a refractive index of 2.0 or more arranged at a position adjacent to the substrate, and has a transmittance of 10% or more 30 % And the reflectance is 3% or more. Japanese Patent Application Laid-Open No. H10-228561 is configured to form a multilayer ND filter from alternating layers of a light absorption film and a dielectric film mainly composed of nickel.
JP 7-63915 A JP 2003-344612 A JP 2006-58854 A JP 2007-235416 A

By the way, the conventional ND filter is mainly intended to attenuate light in the visible range almost uniformly as described above. Therefore, it is sufficient if the conventional ND filter has a flat characteristic around a wavelength of 400 to 700 nm in the visible range. there were.
However, in actuality, for example, CCTV (surveillance camera system) has come to shoot up to the vicinity of 1100 nm wavelength which is the near infrared region at night in addition to the normal visible region (for example, Patent Document 4). In the case of using an infrared projector for photographing in a dark place, there is a demand for an ND filter capable of dealing with light up to near 1100 nm wavelength, which is the near infrared region, for the purpose of suppressing the amount of infrared light.
However, conventionally, an ND filter having a flat characteristic in a wide band up to the near infrared region in addition to such a visible region has not been provided. For example, in a conventional ND filter composed of a light absorption film and a dielectric film as disclosed in the above-mentioned patent document, light with a wavelength in the near-infrared region near 1100 nm wavelength is sufficiently antireflection and still flat. Design was impossible.
For this reason, a conventional design that emphasizes the visible range is possible, and a high-performance ND filter that can provide flatness to the near-infrared range is required upon request.
The present invention has been made to solve the above-mentioned problems, and its purpose is to design a flat characteristic from the visible region to the near infrared region, and to cover not only the visible region but also the near infrared region. The object is to provide a possible multilayer ND filter.

In order to achieve the above object, according to the first aspect of the present invention, a multilayer structure is formed by laminating a plurality of light absorption films and a plurality of dielectric films on one or both surfaces of a transparent substrate. In the film ND filter, at least one of single germanium (Ge) and single silicon (Si) is used as the light absorption film, and as a light absorption film other than the single germanium (Ge) or the single silicon (Si) The gist is to use a mixture (Ni + NiO _x ) of nickel (Ni) and its oxide (NiO _x ) .
The gist of the invention described in claim 2 is that, in the invention described in claim 1, both the single germanium (Ge) and the single silicon (Si) are used as the light absorption film.
According to a third aspect of the present invention, in the first or second aspect of the present invention, the light absorption film composed of the single germanium (Ge) or the single silicon (Si) is located at a position adjacent to the substrate. The gist is that the light-absorbing film other than germanium (Ge) or the same silicon (Si) is disposed with at least one layer of the dielectric film interposed therebetween.
In the invention of claim 4, in the invention of any one of claims 1 to 3, the average reflectance is 4% or less in the wavelength band of 400 to 700 nm, and the flatness in this wavelength band is 4. The gist is that it is 0 or less.
In the invention of claim 5, in the invention of any one of claims 1 to 4, the average reflectance is 4% or less in the wavelength band of 400 to 1100 nm, and the flatness in this wavelength band is 8. The gist is that it is 0 or less.

The base material used in the present invention is not particularly limited, and glass materials and plastic materials can be used. For example, if it is a plastic substrate, polyimide, polymethyl methacrylate and its copolymer, polycarbonate, polydiethylene glycol bisallyl carbonate (CR-39), cellulose acetate, polyolefin, polyarylate, polyethylene terephthalate, polyvinyl chloride, polyurethane resin, Examples include polythiourethane, other sulfur-containing resins, and the like, or composites thereof. The substrate shape may be a film shape or a plate shape.
In the present invention, it is necessary to use at least one of simple germanium (Ge) and simple substance silicon (Si) as the light absorption film.
Table 1 shows the characteristics of the single layer film of single germanium (Ge) and single silicon (Si).
The transmittance of simple silicon (Si) with respect to simple germanium (Ge) is flatter in the vicinity of 400 to 700 nm in the visible region. Accordingly, it is considered that single silicon (Si) is more advantageous than single germanium (Ge) when designing a multilayer ND filter particularly for the visible region. However, single silicon (Si), on the other hand, has a characteristic that the rise in transmittance is steep compared to single germanium (Ge). The relationship between transmittance, reflectance and absorption is simple:
100 (%) − (transmittance + reflectance) = absorption can be evaluated, so that simple silicon (Si) has strong absorption only on the shorter wavelength side than simple germanium (Ge). Good.
When a multilayer ND filter is designed using single silicon (Si), the effect of this steepness is considered to occur on the long wavelength side. Therefore, it is considered that single germanium (Ge) is more advantageous when flatness is required not only in the visible range but also in the near infrared range.
In the case of “flatness”, in the present invention, the evaluation is based on the difference between the maximum value and the minimum value of transmittance, and the smaller the value, the higher the flatness, and the more suitable the ND filter is determined.

The multilayer ND filter of the present invention preferably has an average reflectance of 4% or less in the wavelength band of 400 to 700 nm and a flatness in this wavelength band of 4.0 or less. By providing such a condition, it is possible to obtain a suitable multilayer ND filter particularly in the visible range. Moreover, it is preferable that a reflectance is an average of 4% or less in the wavelength band of 400-1100 nm, and the flatness in this wavelength band is 8.0 or less. By providing such a condition, it is possible to obtain a suitable multilayer ND filter in a wide range from the visible range to the near infrared range. In the wavelength band of 400 to 1100 nm, it is more preferable that the reflectance is 4% or less on average and the flatness in this wavelength band is 4.0 or less.
It is also possible to use a light absorption film other than simple germanium (Ge) and simple silicon (Si). A metal material is generally used as such a light absorption film. Examples of the metal material used as the light absorption film include titanium (Ti), chromium (Cr), nickel (Ni), and the like. Of these, nickel (Ni), nickel alloys and oxides thereof are most preferable. Among metals added to nickel (Ni) as a nickel-based alloy, chromium (Cr), iron (Fe), and titanium (Ti) are preferable. In the present invention, semiconductors such as germanium (Ge) and silicon (Si) are not included in the category of metals.
Specific examples of the dielectric film include metal oxides such as TiO ₂ , Ta ₂ O ₅ , ZrO ₂ , Al ₂ O ₃ , Nb ₂ O ₅ , SiO ₂ , and MgF ₂ , and fluorides. Of these, SiO ₂ and Al ₂ O ₃ are particularly preferable as the dielectric film used in the present invention.

As the film configuration of the multilayer ND filter of the present invention, the light absorption film composed of single germanium (Ge) or single silicon (Si) is located adjacent to the substrate in the same single germanium (Ge) or single silicon (Si). It is preferable that the light absorbing film other than the above is disposed with at least one dielectric film interposed therebetween. In particular, when the substrate is a plastic material, it is preferable that a dielectric film intervenes rather than disposing single germanium (Ge) or single silicon (Si) directly on the substrate in terms of adhesion.
In addition, single germanium (Ge) and single silicon (Si) can be used in combination as the light absorption film. By using both in combination, it becomes possible to design a multilayer ND filter having more suitable characteristics over a wide band.
Further, as a film configuration, it is preferable that a dielectric film is disposed in the outermost layer, and it is preferable that the light absorption film has two or more layers, and these light absorption films are not adjacent to each other. The number of layers is not particularly limited, but at least five or more layers are required on one surface of the substrate in order to create flat characteristics. The film thickness is appropriately designed according to the filter characteristics.
The multilayer ND filter of the present invention can be formed by a known method such as a vapor deposition method, a sputtering method, an ion plating method, or an ion beam assist method.

  According to the inventions described in the above claims, the multilayer ND filter can be designed to have characteristics that place importance on the conventional visible region, and can be designed to flatten the infrared region in addition to the visible region. Can be provided.

Example 1
The multilayer ND filter of Example 1 was configured as an alternating multilayer film of 8 layers each composed of a light absorption film and a dielectric film on both sides of the base material. The film configuration of Example 1 is as shown in Table 2.
In Example 1, multilayer films were formed on both surfaces of a polyimide substrate having a thickness of 100 μm (refractive index 1.6 (wavelength: 589.3 nm)) by vacuum deposition. In this example, deposition was performed in an atmosphere of a substrate temperature of 100 ° C. and a vacuum degree of 8 × 10 ⁻⁴ Pa. As the light absorbing film, two kinds of single germanium (Ge) and a mixture of nickel (Ni) and its oxide (NiO _x ) (hereinafter referred to as nickel mixture (Ni + NiO _x )) were used. Since the nickel mixture (Ni + NiO _x ) is formed using nickel as a deposition material while introducing a mixed gas body containing oxygen, the exact mixing ratio of nickel alone and its oxide is unknown. In Example 1, the deposition rate of nickel and oxygen was set to a Ni deposition rate of 3 Å / s, and O ₂ gas was introduced at 20 sccm during deposition. SiO ₂ was used as the dielectric film. As a film configuration, a light absorption film and a dielectric film are basically alternately arranged, a single germanium (Ge) film is arranged at the innermost layer in contact with the substrate, and an SiO ₂ film is arranged as the outermost layer.
Table 3 is a graph showing optical characteristics regarding the transmittance and reflectance of the multilayer ND filter of Example 1. Example 1 is an example in which good optical characteristics were realized at a relatively low transmittance (average 2.6%) at 400 nm to 1100 nm. In Example 1, since the minimum value of the transmittance at 400 nm to 1100 nm was 2.3% and the maximum value was 3.3%, the flatness was evaluated as 1.0. Moreover, the reflectance of both front and back surfaces at 400 nm to 1100 nm showed the same characteristics as shown in Table 3. For example, on the first surface side, the maximum reflectance was 2.4% and the average reflectance was 0.8%.

(Example 2)
In Example 2, nine layers of alternating multilayer films each consisting of a light absorption film and a dielectric film on both surfaces of a glass substrate (refractive index 1.52 (at wavelength: 587.6 nm)) having a thickness of 1.0 mm under the same deposition conditions as in Example 1. Configured as. The film configuration of Example 2 is as shown in Table 4. In Example 2, as in Example 1, a film was composed of simple germanium (Ge), a nickel mixture (Ni + NiO _x ), and SiO ₂ . Example 2 differs from Example 1 in the positions of the single germanium (Ge) and nickel (Ni) films. In addition, SiO ₂ films were disposed on the innermost layer and the outermost layer in contact with the substrate, respectively.
Table 5 is a graph showing optical characteristics regarding the transmittance and reflectance of the multilayer ND filter of Example 2. Example 2 is an example in which a medium transmittance (average of 14.8%) and good optical characteristics at 400 nm to 1100 nm were realized. In Example 2, since the minimum value of the transmittance at 400 nm to 1100 nm was 14.2% and the maximum value was 15.6%, the flatness was evaluated as 1.4. Moreover, the reflectance of both front and back surfaces at 400 nm to 1100 nm showed the same characteristics as shown in Table 5. For example, on the first surface side, the maximum reflectance was 1.9% and the average reflectance was 1.3%.

(Example 3)
In Example 3, nine layers of alternating multilayer films each consisting of a light absorption film and a dielectric film on both surfaces of a glass substrate (refractive index 1.52 (at wavelength: 587.6 nm)) having a thickness of 1.0 mm under the same vapor deposition conditions as in Example 1. Configured as. The film configuration of Example 3 is as shown in Table 6. In Example 3, as in Example 1, a film was composed of simple germanium (Ge), a nickel mixture (Ni + NiO _x ), and SiO ₂ . Example 3 has the same film configuration as Example 2.
Table 7 is a graph showing optical characteristics regarding transmittance and reflectance of the multilayer ND filter of Example 3. Example 3 is an example where a relatively high transmittance (average 29.7%) and good optical characteristics were realized in the range of 400 nm to 1100 nm. In Example 3, since the minimum value of the transmittance at 400 nm to 1100 nm was 29.0% and the maximum value was 30.6%, the flatness was evaluated as 1.6. Moreover, the reflectance of both front and back surfaces at 400 nm to 1100 nm showed the same characteristics as shown in Table 7. For example, the maximum reflectance was 2.6% and the average reflectance was 2.1% on the first surface side.

Example 4
In Example 4, the same vapor deposition conditions as in Example 1 were configured as an alternating multilayer film of 9 layers each consisting of a light absorbing film and a dielectric film on both sides of a 1.0 mm thick glass substrate (refractive index 1.52 (wavelength 587.6 nm)). did. The film configuration of Example 4 is as shown in Table 8. In Example 4, unlike the above example, a nickel chromium alloy film was arranged instead of the light absorbing film of nickel mixture (Ni + NiO _x ). In Example 4, the NiCr deposition rate was 3 Å / s as the deposition conditions for the nickel chromium alloy and oxygen, and O ₂ gas was introduced at 20 sccm during the deposition.
Table 9 is a graph showing optical characteristics regarding the transmittance and reflectance of the multilayer ND filter of Example 4. Example 4 is an example having a medium transmittance (average of 14.7%) and good optical characteristics at 400 nm to 1100 nm. In Example 4, since the minimum value of transmittance at 400 nm to 1100 nm was 13.7% and the maximum value was 16.8%, the flatness was evaluated as 3.1. Moreover, the reflectance of both front and back surfaces at 400 nm to 1100 nm showed the same characteristics as shown in Table 9. For example, on the first surface side, the maximum reflectance was 1.9% and the average reflectance was 1.4%.

(Example 5)
Example 5 is configured as an alternating multilayer film of 9 layers each consisting of a light absorption film and a dielectric film on both surfaces of a glass substrate having a thickness of 1.0 mm (refractive index 1.52 (wavelength 587.6 nm)) under the same vapor deposition conditions as in Example 1. did. The film configuration of Example 5 is as shown in Table 10. In Example 5, a single silicon (Si) film was arranged in place of the single germanium (Ge) light absorption film in the same film configuration as in the above Example 2 or 3.
Table 11 is a graph showing optical characteristics regarding the transmittance and reflectance of the multilayer ND filter of Example 4. Example 5 is an example in which a medium transmittance (average of 14.8%) was achieved and good optical characteristics were realized at 400 nm to 1100 nm. In Example 5, since the minimum value of the transmittance at 400 nm to 1100 nm was 13.7% and the maximum value was 16.9%, the flatness was evaluated as 3.1. Moreover, the reflectance of both front and back surfaces at 400 nm to 1100 nm showed the same characteristics as shown in Table 11. For example, on the first surface side, the maximum reflectance was 2.8% and the average reflectance was 1.5%.

(Example 6)
In Example 6, the glass substrate (refractive index 1.52 (wavelength 587.6 nm)) having a thickness of 1.0 mm under the same vapor deposition conditions as in Example 1 is configured as an alternating multilayer film of 9 layers each consisting of a light absorption film and a dielectric film. did. The film configuration of Example 6 is as shown in Table 12. In Example 6, a single germanium (Ge) film was disposed in place of the light absorption film of the nickel mixture (Ni + NiO _x ) as the outermost layer in the same film configuration as in Example 5 above.
Table 13 is a graph showing optical characteristics regarding transmittance and reflectance of the multilayer ND filter of Example 6. Example 6 is an example in which a medium transmittance (average of 15.0%) was achieved and good optical characteristics were realized at 400 nm to 1100 nm. In Example 6, since the minimum value of the transmittance at 400 nm to 1100 nm was 14.0% and the maximum value was 16.0%, the flatness was evaluated as 2.0. Moreover, the reflectance of both front and back surfaces at 400 nm to 1100 nm showed the same characteristics as shown in Table 13. For example, on the first surface side, the maximum reflectance was 3.7% and the average reflectance was 1.9%.

(Example 7)
In Example 7, six layers of alternating multilayer films each consisting of a light absorbing film and a dielectric film on both surfaces of a glass substrate (refractive index 1.52 (at wavelength: 587.6 nm)) having a thickness of 1.0 mm under the same deposition conditions as in Example 1. Configured as. The film configuration of Example 7 is as shown in Table 14. In Example 7, as in Example 5, a film was made of simple silicon (Si), a nickel mixture (Ni + NiO _x ), and SiO ₂ . In the seventh embodiment, unlike the fifth embodiment, single silicon (Si) is directly formed on the substrate.
Table 15 is a graph showing optical characteristics regarding transmittance and reflectance of the multilayer ND filter of Example 7. Example 7 is an example in which a medium transmittance (average of 13.5%) and good optical characteristics at 400 nm to 700 nm were realized. In Example 7, the minimum value of transmittance at 400 nm to 700 nm was 13.4%, and the maximum value was 13.9%, so that the flatness was evaluated as 0.6. Moreover, the reflectance of both front and back surfaces at 400 nm to 700 nm showed the same characteristics as shown in Table 15. For example, on the first surface side, the maximum reflectance was 1.6% and the average reflectance was 0.8%.

(Comparative Example 1)
In Comparative Example 1, a PET substrate (refractive index: 1.59 (wavelength: 550 nm)) having a thickness of 0.1 mm was formed as an alternating multilayer film having five layers on one side consisting of a light absorption film and a dielectric film. The film configuration of Comparative Example 1 is as shown in Table 16. In Comparative Example 1, a mixture of titanium (Ti) and its oxide (TiO _x ) (hereinafter referred to as titanium mixture (Ti + TiO _x )) was used as the light absorption film. Since the titanium mixture (Ti + TiO _x ) is formed while introducing a mixed gas body containing oxygen using titanium as a vapor deposition material, the exact mixing ratio of titanium alone and its oxide is unknown. In this comparative example 1, as a deposition condition of titanium and oxygen, a Ti deposition rate was 3 Å / s, and a gas having a mixing ratio of N ₂ and O ₂ of 8: 2 was introduced at 55 sccm during deposition. SiO ₂ was used as the dielectric film.
Table 17 is a graph showing optical characteristics regarding transmittance and reflectance of the multilayer ND filter of Comparative Example 1. Comparative Example 1 is an example showing comparatively high transmittance (average 25.2%) and optical characteristics at 400 nm to 1100 nm. In Comparative Example 1, the design was designed with emphasis on flatness. In Comparative Example 1, the minimum value of transmittance at 400 nm to 1100 nm was 24.6%, and the maximum value was 26.0%, so the flatness was evaluated as 1.4. On the other hand, the maximum reflectance on the film formation surface side at 400 nm to 1100 nm was 12.9%, and the average reflectance was 4.3%.

(Comparative Example 2)
In Comparative Example 2, a glass substrate having a thickness of 1.0 mm (refractive index: 1.52 (wavelength: 587.6 nm)) was formed as an alternating multilayer film of seven layers including a light absorption film and a dielectric film on both surfaces under the same vapor deposition conditions as in Example 1. . The film configuration of Comparative Example 2 is as shown in Table 18. In Comparative Example 2, a nickel mixture (Ni + NiO _x ) formed under the same conditions as in Example 1 was used as the light absorbing film. SiO ₂ was used as the dielectric film.
Table 19 is a graph showing optical characteristics regarding the transmittance and reflectance of the multilayer ND filter of Comparative Example 2. Comparative Example 2 is an example showing moderate transmittance (average 13.3%) and optical characteristics at 400 nm to 1100 nm. In Comparative Example 2, the design was made with an emphasis on reflectance. In Comparative Example 2, the minimum value of transmittance at 400 nm to 1100 nm was 10.9%, and the maximum value was 21.0%, so the flatness was evaluated as 10.1. On the other hand, the reflectance of both front and back surfaces at 400 nm to 1100 nm showed the same characteristics. For example, on the first surface side, the maximum reflectance was 1.8% and the average reflectance was 1.2%.

<Result>
In any of the above Examples 1 to 6, it was confirmed that sufficient flatness was provided in the band from 400 nm to 1100 nm within the low reflectance required as an ND filter. In the above Examples 1 to 6, the evaluation value is within 4 even when the flatness of only the band of 400 nm to 700 nm is taken. Further, it was confirmed that by specializing in the band of 400 nm to 700 nm according to Example 7, an ND filter having very high flatness and low reflectance can be obtained. For light absorption films other than simple germanium (Ge) or simple silicon (Si), the nickel-based materials mentioned in this example were particularly better than other metals.
On the other hand, since the flatness was emphasized in Comparative Example 1, the reflectance was poor both in the average value and the maximum value, and it was confirmed that the design tends to be unreasonable, especially because it tends to become extremely high on the long wavelength side. . Further, in Comparative Example 2, it was confirmed that there was no flatness because importance was placed on the reflectance, and the amount of change in transmittance was particularly large on the short wavelength side, and it was still impossible to design.

Claims (5)

In a multilayer ND filter constituted by laminating a plurality of light absorption films and a plurality of dielectric films on one or both surfaces of a transparent substrate,
At least one of single germanium (Ge) and single silicon (Si) is used as the light absorption film, and nickel (Ni) is used as a light absorption film other than the single germanium (Ge) or the single silicon (Si). A multilayer ND filter using a mixture (Ni + NiO _x ) of the oxide (NiO _x ) . The elemental germanium (Ge) and the multilayer film ND filter of the serial placement in claim 1, characterized by the use of both the elemental silicon (Si) as the light absorbing film. The light absorbing film composed of the single germanium (Ge) or the single silicon (Si) is located at a position adjacent to the substrate, the light absorbing film other than the single germanium (Ge) or the single silicon (Si). 3. The multilayer ND filter according to claim 1, wherein the multilayer ND filter is disposed with at least one layer of the dielectric film interposed therebetween without intervening any of them. The multilayer film according to any one of claims 1 to 3, wherein a reflectance is an average of 4% or less in a wavelength band of 400 to 700 nm, and flatness in the wavelength band is 4.0 or less. ND filter. 5. The multilayer film according to claim 1, wherein a reflectance is an average of 4% or less in a wavelength band of 400 to 1100 nm, and flatness in this wavelength band is 8.0 or less. ND filter.