JP7261556B2 - Optical filters, imaging devices, optical sensors - Google Patents

Description

The present invention relates to an optical filter used in imaging devices, optical sensors, etc., such as digital cameras, video cameras, surveillance cameras, identification sensors for counterfeit banknotes (hereinafter referred to as banknote identification sensors), and particularly to visible light and near-ultraviolet light. or an optical filter that transmits or blocks light of specific wavelengths in visible light and near-infrared light. The present invention also relates to an imaging device and an optical sensor equipped with such an optical filter.

2. Description of the Related Art Solid-state imaging devices used in imaging devices such as video cameras are often used in combination with filters that adjust optical characteristics such as spectral transmittance so as to correspond to the sensitivity characteristics of the human eye. Specifically, there are an ultraviolet cut filter (UV cut filter), a near infrared cut filter (IR cut filter), or a UVIR cut filter realized by one filter.

In addition, banknote identification sensors irradiate banknotes with ultraviolet rays and detect the fluorescence from the fluorescent paint printed on the banknotes. Filters, UV pass filters (visible light cut filters), etc. are used.

JP-A-2003-153076

In Patent Document 1, an IR cut filter (infrared light cut filter) that blocks light in the near-infrared wavelength region and transmits only light in the visible wavelength region is used during daytime shooting when the amount of incident light is large. By reducing noise components in the near-infrared wavelength region that cause deterioration in color reproducibility, we aim to improve image quality.On the contrary, when shooting at night when the amount of incident light is low, the IR cut filter is removed and the solid-state image sensor is used. A method of taking a night vision image by positively using light in the near-infrared wavelength region with high sensitivity has been proposed.

However, it is necessary to shoot both day and night. For example, in imaging devices used for surveillance cameras, in addition to high image quality in shooting environments with strong external light such as during the day, it is also possible to shoot in situations where the amount of incident light is extremely low, such as at night. There is a strong demand for further improvement in the accuracy of captured images in . In addition, for bill identification sensors, etc., when the fluorescent paint is irradiated with UV light, visible light, which is a noise component, is reduced as much as possible. It is strongly demanded to reduce light as much as possible.

On the other hand, there is a strong demand for cost reduction, and there is a demand for optical filters, imaging devices, and optical sensors that can cope with cost reduction.

As described above, the object of the present invention is to solve the above-mentioned problems, and improve image quality under two or more types of imaging environments in which the wavelengths of the unnecessary component and the wavelength of the necessary component are in conflict with each other, and the wavelengths of the transmission band and the stop band are conflicting. To provide an optical filter capable of realizing a low cost. Another object of the present invention is to provide an imaging device and an optical sensor that achieve high accuracy by using such an optical filter.

In order to solve the above-mentioned problems, the present invention provides a visible wavelength to near-infrared wavelength region in which the wavelength is continuous with the visible wavelength. A near -infrared wavelength transmission film that blocks light and prevents reflection of light in the near-infrared wavelength region, and a near-infrared wavelength shield that blocks reflection of light in the visible wavelength region and blocks light in the near - infrared wavelength region and a film of light from visible wavelengths to the near -infrared wavelength region at a position facing the near- infrared wavelength transmitting film and the near-infrared wavelength shielding film on the other surface of the substrate. A single visible /near -infrared wavelength antireflection film that prevents reflection and has a transmittance of 90% or more over the visible wavelength to the near-infrared wavelength region on the substrate, and the near-infrared wavelength transmission If the wavelength at which the transmittance is 50% in the transmission-blocking transition region of the film is defined as the first half-value wavelength, and the wavelength at which the transmittance is 50% in the transmission-blocking transition region of the near-infrared wavelength shielding film is defined as the second half-value wavelength, , the first half-value wavelength and the second half-value wavelength are included in the visible wavelength to the near-infrared wavelength region.

In the optical filter of the present invention, a specific visible wavelength anti-reflection film that reduces reflection in a specific wavelength range from the visible wavelength is provided on the back side of the substrate on which the specific wavelength transmission film and the specific wavelength shielding film are provided. It is possible to increase the transmittance of the transmission band of the wavelength transmission film and the transmission band in the visible wavelength region formed by the specific wavelength shielding film. Is possible.

Further, by using such an optical filter of the present invention in an optical sensor such as a banknote identification sensor or a surveillance camera, or in an imaging device, it is possible to provide an optical sensor and an imaging device capable of achieving high image quality. .

In addition, two different types of functional films are combined into one sheet for use in shooting environments where the wavelengths used in the transmission band and stopband conflict, such as daytime and nighttime photography, UV light photography and fluorescence (visible light) photography. By forming on the substrate, each functional film is individually formed as a separate filter, and the number of drive mechanisms for driving the filters is reduced compared to the device configuration in which a plurality of optical filters are provided. Therefore, it is possible to reduce the cost of the entire apparatus. In addition, the transmission band formed by the specific wavelength shielding film and the specific wavelength transmission film are formed by one type of antireflection film provided on the back side of the substrate surface on which the specific wavelength shielding film and the specific wavelength transmission film are formed. Since the reflection in both the transmission bands in the visible wavelength region can be reduced, the manufacturing process can be reduced compared to the case where different antireflection films suitable for the specific wavelength shielding film and the specific wavelength transmission film are formed. It is possible to reduce the cost of filters, imaging devices, and optical sensors.

Spectral transmittance characteristic diagram of the IR pass filter in the present embodiment 1 Spectral transmittance characteristic diagram of the IR cut filter in the present embodiment 1 Sectional view of the optical filter in the first embodiment Spectral transmittance characteristic diagram of the IR cut filter and the NDIR filter in the second embodiment Cross-sectional view of the optical filter in the second embodiment Schematic configuration diagram of an imaging device in the present embodiment 4 Spectral transmittance characteristic diagram of the UV pass filter in Example 5 Spectral transmittance characteristic diagram of the UV cut filter in the fifth embodiment Cross-sectional view of the optical filter in the fifth embodiment Schematic configuration diagram of a banknote recognition sensor in the sixth embodiment

In the optical filter of this embodiment, a specific wavelength transmission film that blocks transmission of light in a predetermined visible wavelength range and transmits light in a specific wavelength range is formed on a part of one surface of a substrate, Forming a specific wavelength shielding film that transmits light in the visible wavelength region and shields light in the specific wavelength region in at least another region including a region different from the region where the specific wavelength transmission film is formed on the same substrate surface On the other side of the substrate, a specific visible wavelength anti-reflection film that prevents reflection of light in a specific wavelength range from the visible wavelength is formed, thereby functioning as a specific wavelength pass filter and as a specific wavelength cut filter. It is an optical filter having two functions in one filter.

As a substrate for such an optical filter, a substrate that has light transmittance at least in the respective transmission bands of the specific wavelength transmission film and the specific wavelength shielding film, that is, a substrate that has light transmittance in the visible wavelength range to the specific wavelength range is used. use. Such a visible specific wavelength transparent substrate may be a glass type, a resin type, or an organic-inorganic hybrid type, and a substrate that has the strength and optical properties required for an optical filter substrate and can function as a substrate is used. be done.

The functional films such as the specific wavelength transmission film, the specific wavelength shielding film, and the visible specific wavelength anti-reflection film formed on the substrate are produced by laminating one or more thin films on the substrate, and these thin films are physically, Alternatively, it may be formed by a chemical film forming method, or may be formed by a wet method such as spin coating. Among these film forming methods, from the viewpoint of reproducibility and environmental resistance of the film, a process capable of forming a film with relatively high energy, such as a sputtering method or a film forming method with some kind of assist, is preferable. More specifically, a sputtering method, an IAD method, an ion plating method, an IBS method, a cluster vapor deposition method, or the like can be applied, and the film thickness can be controlled relatively accurately, and a film with high reproducibility can be obtained. Any method may be used as long as it is a film method, and the optimum method may be selected in consideration of the properties, productivity, etc. required for the functional film.

The specific wavelength transmission film in this embodiment is composed of a plurality of layers of thin films, and the outermost layer is composed of one or more layers of thin films that block the reflection of light in a specific wavelength region, which is the transmission band. A specific wavelength anti-reflection film is formed. The film arranged as the outermost layer of the antireflection film has a central wavelength of the transmission band. A film thickness of about 1.0 qw at a certain wavelength of 800 to 1000 nm is preferable. If it is assumed that there is no wavelength dispersion of the refractive index, it can be rephrased as 2.0 qw at 400 to 500 nm. Here, qw is a unit representing the film thickness, and one wavelength λ is used as a reference, and λ/4 is used as one unit. Expressed as 0qw.

In the transmission band of an optical filter constructed by forming a specific wavelength transmission film on a substrate, it is ideally desirable to transmit 100% of the entire area, but in reality it is impossible to completely satisfy this. It is very difficult and is adjusted so as to obtain a transmittance as close to 100% as possible over the entire wavelength region of the transmission band. In order to realize such a transmittance, in this embodiment, the transmittance in the transmission band formed by the specific wavelength transmission film is maximized, and the transmission rate formed by the specific visible wavelength antireflection film provided on the back surface of the substrate is maximized. By maximizing the transmittance in the band and synthesizing the two transmission characteristics of the specific wavelength transmission film and the visible specific wavelength anti-reflection film, the transmittance in the transmission band of the optical filter as a whole is maximized.

Here, as the wavelength continuously changes, the transmittance in the transmission band changes not a little in a wavy manner, and this is called a ripple in the transmission band (transmission ripple). , is likely to occur as the film becomes thicker. If this transmission ripple becomes large, for example, the color balance will be disturbed, and the overall amount of light that enters the image sensor will decrease when shooting at night. As small as possible is desirable. Therefore, in order to reduce ripples in this transmission band, a transmission ripple adjustment layer for reducing ripples may be inserted between the substrate and the specific wavelength transmission film. The transmission ripple of the optical filter as a whole is determined by combining the transmission ripple in the transmission band formed by the specific wavelength transmission film and the transmission ripple in the transmission band formed by the visible specific wavelength anti-reflection film. In , even the single specific wavelength transmission film, which easily generates transmission ripples due to the large number of layers, has a flat transmission characteristic with little transmission ripple, and is arranged on the back side of the substrate on which the specific wavelength transmission film is formed. Even the specific visible wavelength anti-reflection film alone is configured to have a flat transmission characteristic with little transmission ripple. forming a characteristic. Apart from this, for example, the phase of the transmission ripple of the specific wavelength-antireflection film is adjusted with respect to the transmission ripple of the specific wavelength transmission film, and the ripples are canceled on both sides. Although it is possible to obtain a flat transmission characteristic with a small amount of light, if there is an error in the phase relationship between the specific wavelength transmission film and the specific wavelength anti-reflection film, there is a risk of increasing the transmission ripple. From the viewpoint of high image quality, the above configuration was selected in this embodiment. Such a transmission ripple adjustment layer is characterized by being thinner than the plurality of thin films forming the specific wavelength transmission film, and is the thinnest layer among all the layers. Two or more transmission ripple adjustment layers may be provided, but in that case also, all transmission ripple adjustment layers are thinner than the layer forming the specific wavelength transmission film.

The specific wavelength shielding film in this embodiment is composed of a plurality of layers of thin films, and the outermost layer is composed of one or more layers of thin films that block the reflection of light in the visible wavelength region, which is the transmission band. A visible antireflection film is formed on the surface. It is preferable that the film disposed as the outermost layer of the visible antireflection film has a film thickness of about 1.0 qw of the central wavelength of the transmission band.

The transmission band of an optical filter constructed by forming a specific wavelength shielding film on a substrate is adjusted so as to obtain a transmittance as close to 100% as possible in the entire wavelength range of the transmission band. In order to achieve such a transmittance, in this embodiment, the transmittance in the transmission band formed by the specific wavelength shielding film is maximized, and the transmittance formed by the specific visible wavelength antireflection film provided on the back surface of the substrate is maximized. By maximizing the transmittance in the band and synthesizing the transmission characteristics of the specific wavelength shielding film and the specific visible wavelength anti-reflection film, the transmittance of the entire optical filter in the transmission band is maximized.

Here, as with the specific wavelength transmission film, it is desirable that the transmission ripple in the specific wavelength shielding film is as small as possible. Therefore, in order to reduce ripples in this transmission band, a transmission ripple adjustment layer for reducing ripples may be inserted between the substrate and the specific wavelength transmission film. The transmission ripple of the optical filter as a whole is determined by combining the transmission ripple in the transmission band formed by the specific wavelength shielding film and the transmission ripple in the transmission band formed by the visible specific wavelength antireflection film. As with the transmission film, the specific wavelength shielding film tends to generate transmission ripples due to the large number of layers. Even the specific wavelength shielding film alone has flat transmission characteristics with little transmission ripple, and the specific wavelength shielding film is formed. Even the specific visible wavelength anti-reflection film alone disposed on the back side of the substrate is configured to have a flat transmission characteristic with little transmission ripple. By combining these two flat transmission bands, optical The filter as a whole has a flat transmission characteristic with little transmission ripple. Such a transmission ripple adjustment layer is characterized by being thinner than the plurality of thin films forming the specific wavelength shielding film, and is the thinnest layer among all the layers. Two or more transmission ripple adjustment layers may be provided, but even in that case, all the transmission ripple adjustment layers are thinner than the layer forming the specific wavelength shielding film.

By using the optical filter of the present invention as described above for an imaging device such as a surveillance camera or an optical sensor such as a banknote recognition sensor, an imaging device or an optical sensor capable of achieving high accuracy can be obtained.

Hereinafter, the optical filter of the present invention will be specifically described based on examples.

(Example 1)
A near-infrared transmissive film, a near-infrared shielding film, and a visible/near-infrared antireflection film, which are composed of multilayer thin films, are separately arranged on both sides of a single visible/near-infrared wavelength transparent substrate. An example in which an optical filter having the spectral transmission characteristic shown in 2 as a design value was manufactured will be described in detail below.

The visible and near-infrared transparent substrate 10 of the optical filter of Example 1 as shown in FIG. A 0.4 mm thick D263 Teco glass was used which had a spectral characteristic of transmitting .

Then, after forming the visible and near-infrared antireflection film 13 on one surface of the visible and near-infrared transparent substrate 10 by the IAD method, the visible and near-infrared transparent substrate 10 is turned over to form a visible and near-infrared transparent substrate. A near-infrared permeable film 11 is formed by the IAD method in a predetermined region on the other surface of the substrate 10, and a near-infrared permeable film is formed in a region different from the region where the near-infrared permeable film 11 is formed on the same surface of the substrate. A shielding film 12 was formed by the IAD method. The visible and near-infrared antireflection film 13 is formed first because it is thinner than the near-infrared transmissive film 11 and the near-infrared shielding film 12, and the film stress is low. This is because the effect of the film formation error is reduced depending on the position of the substrate at the time. As described above, the optical filter 14 in the first embodiment has the near-infrared transmissive film 11 and the near-infrared shielding film 12 on one side of the visible and near-infrared transparent substrate 10 as shown in FIG. A visible and near-infrared antireflection film 13 is disposed on the other surface of the opposing visible and near-infrared transparent substrate 10 .

The near-infrared transmissive film 11 of Example 1 formed on the visible and near-infrared transparent substrate 10, as shown in FIG. and the light in the wavelength region of about 750 to 1100 nm from the visible wavelength to the near-infrared wavelength region is suppressed to a small ripple, and most of the light except the reflected component on the back side of the substrate is transmitted. It has a clear transmission band. In addition, in the wavelength region of about 650 to 750 nm sandwiched between the transmission stop band and the transmission band, there is a transmission-block transition region where the transmission continuously changes from the transmission stop band to the transmission band. Furthermore, the wavelength at which the transmittance is 50% in the transmission-blocking transition region is defined as the IR half-value wavelength, and this value is set to 700 nm. Further, the near-infrared transmissive film 11 in Example 1 is composed of a 38-layer film in which TiO ₂ which is a high refractive index material and SiO ₂ which is a low refractive index material are alternately laminated, as shown in FIG. In addition, a transmission ripple adjusting layer 15a having a transmission ripple reduction function is arranged in the first layer of the near-infrared transmission film 11 directly above the visible and near-infrared transparent substrate 10 . Furthermore, the 38th layer, which is the outermost layer, is provided with a near-infrared antireflection structure 16a composed of a single layer having an antireflection function in the transmission band of near-infrared wavelengths. The transmission ripple adjustment layer 15a has the thinnest film thickness among all the film thicknesses constituting the near-infrared transmission film 11, and the near-infrared antireflection structure 16a has a wavelength band at the center of the antireflection band. It has a film thickness of about 1.0 qw at a wavelength of 800 to 1000 nm.

As shown in FIG. 2B, the near-infrared shielding film 12 of the present embodiment 1 formed on the visible and near-infrared transparent substrate 10 reduces the light in the wavelength region of about 400 to 600 nm in the visible wavelength region. While suppressing ripples, a transmission band that transmits most of the components except for the reflection components on the back side of the substrate, and a transmission blocking band that blocks light in the wavelength range of about 700 to 1100 nm from visible wavelengths to the near infrared wavelength range. have. In addition, in the wavelength region of about 600 to 700 nm sandwiched between the transmission band and the transmission stop band, there is a transmission-block transition region in which the transmission continuously changes from the transmission band to the transmission stop band. Furthermore, the wavelength at which the transmittance is 50% in the transmission-blocking transition region is defined as the IR half-value wavelength, and this value is set to 670 nm. The near-infrared shielding film 12 in Example 1 is composed of a 38-layer film in which TiO ₂ as a high refractive index material and SiO ₂ as a low refractive index material are alternately laminated, as shown in FIG. In addition, a transmission ripple adjusting layer 15b having a transmission ripple reduction function is arranged in the first layer of the near-infrared shielding film 12 directly above the visible and near-infrared transparent substrate 10. As shown in FIG. Furthermore, the 38th layer, which is the outermost layer, is provided with a visible antireflection structure 16b composed of a single layer having an antireflection function in the transmission band of near-infrared wavelengths. The transmission ripple adjustment layer 15b has the thinnest film thickness among all the film thicknesses constituting the near-infrared shielding film 12, and the visible antireflection structure 16b has a central wavelength of the wavelength band serving as the antireflection band. It has a film thickness of about 1.0 qw of 400 to 600 nm.

The visible and near-infrared antireflection film 13 of Example 1 formed on the visible and near-infrared transparent substrate 10 has a visible wavelength to a near-infrared wavelength as shown in FIG. 1(c) or FIG. 2(c). Most of the reflection of light in the wavelength region of about 400 to 1100 nm except for the reflection component on the back surface side of the substrate is blocked, that is, it has an optical characteristic that has a transmission band that transmits most of the light. there is Thus, the visible and near-infrared antireflection film 13 forms a transmission band at 700 nm, which is the IR half-value wavelength of the near-infrared transmissive film 11, and 670 nm, which is the IR half-value wavelength of the near-infrared shielding film 12. Even if the optical characteristics are shifted, for example, by about 10 nm to the short wavelength side or the long wavelength side due to film forming errors, the visible and near-infrared antireflection film 13 can maintain the transmission band at the IR half-value wavelength. Therefore, even if the optical characteristics of the visible and near-infrared antireflection film 13 change due to film formation errors during the formation of the visible and near-infrared antireflection film 13, the visible and near-infrared transparent The IR pass filter 17 or the IR cut filter 18 formed including the substrate 10 has an extremely small influence on each IR half-value wavelength. Since the transmission-blocking transition region of 17 or IR cut filter 18 is determined, the reproducibility can be further improved, and high precision of the optical filter as a whole can be realized.

The visible and near-infrared antireflection film 13 in Example 1 is composed of a 12-layer film in which high refractive index material TiO ₂ and low refractive index material SiO ₂ are alternately laminated. The twelfth layer, which is the outermost layer most influencing the function, has a film thickness of about 1.0 qw at 600 to 900 nm, which is the center wavelength of the wavelength range forming the antireflection band.

Furthermore, as shown in FIG. 1B, the transmission characteristics of the transmission band produced by the single near-infrared transmission film 11 formed on the visible and near-infrared transparent substrate 10 are flat with little transmission ripple and substantially It has a constant transmission characteristic, and has a characteristic of transmitting most of the light except for the reflection component on the back side of the substrate. Similarly, the transmission characteristics of the transmission band produced by the single visible and near-infrared antireflection film 13 formed on the visible and near-infrared transparent substrate 10 are flat with little transmission ripple as shown in FIG. It has a substantially constant transmission characteristic, and has a characteristic of transmitting most of the light except for the reflected component on the back side of the substrate. Strictly speaking, the transmittance of the visible and near-infrared antireflection film 13 is higher than that of the near-infrared transmitting film, as shown in FIGS. 1(b) and 1(c). Although the transmittance is slightly higher than that of No. 11, it has characteristics that can be regarded as substantially the same. By synthesizing the transmission characteristics of these two functional films, which are flat with little transmission ripple and have high transmission, the transmission band of the IR pass filter 17 is obtained as shown in FIG. , the transmission ripple is small, the film is flat, and the transmission is higher than that of the near-infrared transmission film 11 and the visible and near-infrared antireflection film 13 . Similarly, in the stop band of the IR pass filter 17, the transmission characteristics are determined by synthesizing the transmission characteristics produced by the two functional films. Therefore, the transmission characteristics of the IR pass filter 17 as a whole are determined by synthesizing the transmission characteristics produced by the two functional films of the near-infrared transmission film 11 and the visible/near-infrared antireflection film 13 .

Similarly, the transmission characteristics of the transmission band produced by the single near-infrared shielding film 12 formed on the visible and near-infrared transparent substrate 10 are flat with little transmission ripple as shown in FIG. It has a constant transmission characteristic, and has a characteristic of transmitting most of the light except for the reflected component on the back side of the substrate. Similarly, the transmission characteristics of the transmission band produced by the single visible and near-infrared antireflection film 13 formed on the visible and near-infrared transparent substrate 10 are flat with little transmission ripple as shown in FIG. It has a substantially constant transmission characteristic, and has a characteristic of transmitting most of the light except for the reflected component on the back side of the substrate. Strictly speaking, the transmittance of the visible and near-infrared antireflection film 13 is higher than that of the near-infrared shielding film, as shown in FIGS. Although the transmittance is slightly higher than that of 12, it has characteristics that can be regarded as substantially the same. By synthesizing the transmission characteristics of these two functional films, which are flat with little transmission ripple and have high transmission, the transmission band of the IR cut filter 18 is obtained as shown in FIG. , the transmission ripple is small, the film is flat, and the transmission is higher than that of the near-infrared shielding film 12 and the visible and near-infrared antireflection film 13 . Similarly, in the stop band of the IR cut filter 18, the transmission characteristics are determined by synthesizing the transmission characteristics produced by the two functional films. Therefore, the transmission characteristics of the IR cut filter 18 as a whole are determined by synthesizing the transmission characteristics produced by the two functional films of the near-infrared shielding film 12 and the visible/near-infrared antireflection film 13 .

Further, the imaging apparatus used for surveillance cameras and the like as in this embodiment is very sensitive to noise components, which greatly affect the image quality. Therefore, as in the filter of this embodiment, the average transmission in the stop band of the IR pass filter 17 is suppressed to 1% or less, more preferably 0.1% or less on average, while the transmission band has an average transmission of 80% or more. More preferably, it should have an average transmittance of 90% or more. Similarly, the IR cut filter 18 has an average transmission of 1% or less, preferably 0.1% or less in the stopband, and an average transmission of 80% or more, more preferably 90% or more in the transmission band. It is desirable to have transmissive properties.

In the near-infrared transmissive film 11, the near-infrared shielding film 12, and the visible and near-infrared antireflection film 13 in the first embodiment, TiO ₂ which is a high refractive index material and a low refractive index material configured as vapor deposition films In addition to SiO ₂ , Nb ₂ O ₅ , ZrO ₂ , Ta ₂ O ₅ and the like can be used as high refractive index materials, and MgF ₂ and the like can be used as low refractive index materials. In addition, it is also possible to use an intermediate refractive index material such as Al ₂ O ₃ in some layers for reasons of design and film formation. , Cr, Fe, Al, Mg, Ti, Si, Nb, Zr, Ta, In, Ag, Au, etc., and an optimum combination of materials may be selected depending on the situation.

The spectral transmission characteristics of the IR pass filter 17 manufactured as described above are approximately the design values shown in FIG. 1A, and the spectral transmission characteristics of the IR cut filter 18 are approximately the design values shown in FIG. I got the same properties. As a result, when photographing in the daytime when the amount of incident light is large, the area of the IR cut filter 18 is used to cut off the transmission of the near-infrared wavelength region, which is a noise component, thereby improving the quality of the color image. Furthermore, when shooting at night when the amount of incident light is small, the area of the IR pass filter 17 is used to block the transmission of the visible wavelength range, which is a noise component, thereby improving the quality of the night vision image. You can get a filter.

In addition, in the transmission bands of both the near-infrared transmitting film 11 and the near-infrared shielding film 12, the near-infrared transmitting film 11 and the near-infrared shielding film 12 are provided with the visible and near-infrared antireflection film 13 that exhibits an antireflection effect. Since it is not necessary to configure two different types of antireflection films optimized for the respective functional films of the infrared shielding film 12, the manufacturing process can be simplified and the cost of the optical filter can be reduced. can.

As described above, it is possible to obtain the optical filter 14 having the two functions of the IR pass filter 17 and the IR cut filter 18 and capable of achieving high image quality and low cost.

(Example 2)
In addition to the near-infrared transmissive film and near-infrared shielding film, which are composed of multilayer thin films, and the near-infrared antireflection film, an ND film that attenuates the transmission of light in the wavelength region including visible wavelengths is combined into a single visible and near-infrared film. An example in which an optical filter having the design values of the spectral transmission characteristics shown in FIGS. 1 and 4 by disposing them separately on both sides of an infrared wavelength transmitting substrate will be described in detail below.

The visible and near-infrared transparent substrate 20 of the optical filter of Example 2 has a spectral characteristic of transmitting most of the incident light, excluding the reflected component on the back side of the substrate, at least in the wavelength range of 400 to 1100 nm. A 0.4 mm thick B270i glass was used.

Then, after forming the visible and near-infrared antireflection film 23 on one surface of the visible and near-infrared transparent substrate 20 by the IAD method, the visible and near-infrared transparent substrate 20 is turned over to form a visible and near-infrared transparent substrate. A near-infrared permeable film 21 is formed in a predetermined region on the other surface of the substrate 20 by the IAD method, and a near-infrared permeable film is formed in a region different from the region where the near-infrared permeable film 21 is formed on the same surface of the substrate. A shielding film 22 was formed by the IAD method. In addition, an ND film 29 was formed on the near-infrared shielding film 22 by a normal EB vapor deposition method. As described above, the optical filter 24 in the second embodiment has the near-infrared transmissive film 21 and the near-infrared shielding film 22 on one side of the visible and near-infrared transparent substrate 20 as shown in FIG. A visible and near-infrared wavelength antireflection film 23 is disposed on the other surface of the infrared transparent substrate 20 , and an ND film 29 is disposed on a partial region of the near-infrared shielding film 22 .

The near-infrared transmissive film 21 of the second embodiment formed on the visible and near-infrared transparent substrate 20, as shown in FIG. and the light in the wavelength region of about 750 to 1100 nm from the visible wavelength to the near-infrared wavelength region is suppressed to a small ripple, and most of the light except the reflected component on the back side of the substrate is transmitted. It has a clear transmission band. In addition, in the wavelength region of about 650 to 750 nm sandwiched between the transmission stop band and the transmission band, there is a transmission-block transition region where the transmission continuously changes from the transmission stop band to the transmission band. Furthermore, the wavelength at which the transmittance is 50% in the transmission-blocking transition region is defined as the IR half-value wavelength, and this value is set to 700 nm. The near-infrared transmissive film 21 in Example 2 is composed of a 38-layer film in which TiO ₂ which is a high refractive index material and SiO ₂ which is a low refractive index material are alternately laminated, as shown in FIG. In addition, a transmission ripple adjusting layer 25a having a transmission ripple reduction function is disposed in the first layer of the near-infrared transmission film 21 directly above the visible and near-infrared transparent substrate 20. As shown in FIG. Furthermore, the 38th layer, which is the outermost layer, is provided with a near-infrared antireflection structure 26a composed of a single layer having an antireflection function in the transmission band of near-infrared wavelengths. The transmission ripple adjustment layer 25a has the thinnest film thickness among all the film thicknesses constituting the near-infrared transmission film 21, and the near-infrared antireflection structure 26a has the wavelength band centered in the antireflection band. It has a film thickness of about 1.0 qw at a wavelength of 800 to 1000 nm.

As shown in FIG. 4B, the near-infrared shielding film 22 of the present embodiment 2 formed on the visible and near-infrared transparent substrate 20 reduces the light in the wavelength region of about 400 to 600 nm in the visible wavelength region. While suppressing ripples, a transmission band that transmits most of the components except for the reflection components on the back side of the substrate, and a transmission blocking band that blocks light in the wavelength range of about 700 to 1100 nm from visible wavelengths to the near infrared wavelength range. have. In addition, in the wavelength region of about 600 to 700 nm sandwiched between the transmission band and the transmission stop band, there is a transmission-block transition region in which the transmission continuously changes from the transmission band to the transmission stop band. Furthermore, the wavelength at which the transmittance is 50% in the transmission-blocking transition region is defined as the IR half-value wavelength, and this value is set to 670 nm. The near-infrared transmissive film 21 in Example 2 is composed of a 38-layer film in which TiO ₂ which is a high refractive index material and SiO ₂ which is a low refractive index material are alternately laminated, as shown in FIG. In addition, a transmission ripple adjusting layer 25b having a transmission ripple reduction function is arranged in the first layer of the near-infrared shielding film 22 directly above the visible and near-infrared transparent substrate 20. As shown in FIG. Further, the 38th layer, which is the outermost layer, is provided with a visible antireflection structure 26b composed of a single layer having an antireflection function in the transmission band of near-infrared wavelengths. The transmission ripple adjustment layer 25b has the thinnest film thickness among all the film thicknesses constituting the near-infrared shielding film 22, and the visible antireflection structure 26b has a central wavelength of the wavelength band serving as the antireflection band. It has a film thickness of about 1.0 qw of 400 to 600 nm.

Next, on the near-infrared shielding film 22, an SiO2 film and a TiO2 film are laminated in this order as an interference condition adjusting layer for adjusting the interference condition with the near-infrared shielding film 22, and then a dielectric layer is formed. and TiOx (x is about 1.0 to 2.0), which is a light absorption layer. The ND film 29 composed of a total of 11 layers was formed by a normal EB vapor deposition method with no particular assist added so as to have the arrangement configuration shown in FIG. Also, the ND concentration of the ND film 29 was adjusted to about 1.0.

The antireflection film disposed on the outermost layer of the ND film 29 is not limited to MgF2, but may be an SiO2 film, or may be a one-layer SiO2 film produced by the IAD method. Furthermore, it may have a multilayer film structure formed of, for example, a plurality of SiO2 films and TiO2 films. The thin film material forming the ND film 29 is not limited to the material formed in the second embodiment, and may be dielectric layers such as SiO2 or Al2O3, materials with different acid values, Ni, W, Mo, Cu, Various materials such as single metals such as Cr, Fe, Al, Mg, Ti, Si, Nb, Zr, Ta, In, Ag, and Au, alloys and metal compounds thereof, and layers in which these are mixed are appropriately used. It is possible to choose.

The ND film 29 in Example 2 thus formed attenuates transmission in the entire visible wavelength range of 400 to 1100 nm, particularly 400 to 700 nm, including the IR half-value wavelength of 670 nm formed by the near-infrared shielding film 22. , has optical characteristics with substantially uniform transmission characteristics. Therefore, even if the spectral transmission characteristic of the ND film 29 shifts to the longer wavelength side or the shorter wavelength side due to a film formation error, the effect on the IR half-value wavelength described above is extremely small, and it is formed according to the characteristics of the substrate. It has almost no effect on the NDIR half-value wavelength as an NDIR filter. By adjusting the optical characteristics of the ND film 29 in this way, it is possible to obtain high reproducibility in the optical characteristics of the NDIR filter 30 as a whole.

The visible and near-infrared antireflection film 23 of Example 2 formed on the visible and near-infrared transparent substrate 20 has a visible wavelength to a near-infrared wavelength as shown in FIG. 1(c) or FIG. 4(c). Most of the reflection of light in the wavelength region of about 400 to 1100 nm except for the reflection component on the back surface side of the substrate is blocked, that is, it has an optical characteristic that has a transmission band that transmits most of the light. there is Thus, at 700 nm, which is the IR half-value wavelength of the near-infrared transmissive film 21, and at 670 nm, which is the IR half-value wavelength of the near-infrared shielding film 22, the visible and near-infrared antireflection film 23 forms a transmission band. Reproducibility can be improved, and high precision of the optical filter as a whole can be realized.

The visible and near-infrared antireflection film 23 in Example 2 is composed of a 12-layer film in which high refractive index material TiO ₂ and low refractive index material SiO ₂ are alternately laminated. The twelfth layer, which is the outermost layer most influencing the function, has a film thickness of about 1.0 qw at 600 to 900 nm, which is the center wavelength of the wavelength range forming the antireflection band.

Furthermore, as shown in FIG. 1B, the transmission characteristics of the transmission band produced by the single near-infrared transmission film 21 formed on the visible and near-infrared transparent substrate 20 are flat with little transmission ripple and substantially It has a constant transmission characteristic, and has a characteristic of transmitting most of the light except for the reflected component on the back side of the substrate. Similarly, the transmission characteristics of the transmission band produced by the single visible and near-infrared antireflection film 23 formed on the visible and near-infrared transparent substrate 20 are flat with little transmission ripple as shown in FIG. It has a substantially constant transmission characteristic, and has a characteristic of transmitting most of the light except for the reflected component on the back side of the substrate. As shown in FIGS. 1(b) and 1(c), the respective transmission characteristics in the transmission bands produced by these two functional films have characteristics that can be regarded as substantially the same. By synthesizing the transmission characteristics of these two functional films, which are flat with little transmission ripple and have high transmission, the transmission band of the IR pass filter 27 is obtained as shown in FIG. , the transmission ripple is small, the film is flat, and the transmission is higher than that of the near-infrared transmission film 21 and the visible and near-infrared antireflection film 23 . Similarly, in the stop band of the IR pass filter 27, the transmission characteristics are determined by synthesizing the transmission characteristics produced by the two functional films. Therefore, the transmission characteristics of the IR pass filter 27 as a whole are determined by synthesizing the transmission characteristics produced by the two functional films of the near-infrared transmission film 21 and the visible/near-infrared antireflection film 23 .

Similarly, the transmission characteristic of the transmission band produced by the single near-infrared shielding film 22 formed on the visible and near-infrared transparent substrate 20 is flat with little transmission ripple as shown in FIG. It has a constant transmission characteristic, and has a characteristic of transmitting most of the light except for the reflected component on the back side of the substrate. Similarly, the transmission characteristics of the transmission band produced by the single visible and near-infrared antireflection film 23 formed on the visible and near-infrared transparent substrate 20 are flat with little transmission ripple as shown in FIG. It has a substantially constant transmission characteristic, and has a characteristic of transmitting most of the light except for the reflected component on the back side of the substrate. Furthermore, as shown in FIG. 4( e ), the transmission characteristic produced by the ND film 29 alone formed on the near-infrared shielding film 22 is flat with few transmission lip from the visible wavelength to the near-infrared wavelength. It has a transmission characteristic that is relatively constant. Strictly speaking, the respective transmission characteristics in the transmission bands created by the near-infrared shielding film 22 and the visible/near-infrared antireflection film 23 are shown in FIGS. is slightly higher than the transmittance of the near-infrared shielding film 22, but they have substantially the same characteristics. By synthesizing the transmission characteristics of these two functional films, which are flat with little transmission ripple and have high transmission, the transmission band of the IR cut filter 28 is obtained as shown in FIG. , the transmission ripple is small and flat, and the transmission characteristics are higher than those of the near-infrared shielding film 22 and the visible and near-infrared antireflection film 23 . Similarly, in the stopband of the IR cut filter 28, the transmission characteristics are determined by synthesizing the transmission characteristics produced by the two functional films. Therefore, the transmission characteristics of the IR cut filter 28 as a whole are determined by synthesizing the transmission characteristics produced by the two functional films of the near-infrared shielding film 22 and the visible/near-infrared antireflection film 23 . Furthermore, in addition to the near-infrared shielding film 22 and visible/near-infrared antireflection film 23, the respective transmission characteristics in the transmission band created by the ND film 29 are shown in FIGS. By synthesizing the flat transmission characteristics with little ripple, a flat transmission characteristic with little transmission ripple is created in the transmission band of the NDIR filter 30, as shown in FIG. 4(e).

As in the present embodiment, the average transmission in the blocking band of the IR pass filter 27 is suppressed to 1% or less, preferably 0.1% or less on average, while the transmission band has an average transmission of 80% or more, more preferably an average of 80% or more. It is desirable to have a transmission characteristic of 90% or more. Similarly, the IR cut filter 28, like the filter of this embodiment, has an average transmission of 1% or less in the stopband, more preferably 0.1% or less on average, and an average of 80% or more in the transmission band. More preferably, it is desirable to have an average transmittance of 90% or more. Furthermore, like the filter of this embodiment, the NDIR filter 30 also preferably has a characteristic of suppressing transmission to 1% or less on average, more preferably 0.1% or less on average in the stopband.

The spectral transmission characteristics of the IR pass filter 27 produced as described above are the design values shown in FIG. 1A, the spectral transmission characteristics of the IR cut filter 28 are the design values shown in FIG. 4A, As for the spectral transmission characteristics of the NDIR filter 30, substantially the same characteristics as the design values shown in FIG. 4(e) could be obtained.

As a result, noise can be reduced by using the area of the IR cut filter 28 in FIG. 5 during daytime shooting when the amount of incident light is large, and by using the area of the NDIR filter 30 in FIG. By blocking the transmission of the component near-infrared wavelength region, it is possible to improve the quality of the color image. In addition to this, when photographing at night when the amount of incident light is small, the area of the IR pass filter 27 is used to cut off the transmission of the visible wavelength range, which is a noise component, thereby improving the image quality of the night vision image. It is possible to obtain an optical filter capable of

In addition, in the transmission band of both the near-infrared transmitting film 21 and the near-infrared shielding film 22, the near-infrared transmitting film 21 and the near-infrared shielding film 22 are provided with the visible and near-infrared antireflection film 23 that exhibits an antireflection effect. Since it is not necessary to form two different antireflection films optimized for each of the infrared shielding films 22, the manufacturing process can be simplified and the cost of the filter can be reduced.

As described above, the optical filter 24 having the three functions of the IR pass filter 27, the IR cut filter 28, and the NDIR filter 30 and capable of achieving high image quality and low cost can be obtained.

(Example 3)
Another configuration example of an optical filter having two functions of an IR pass filter and an IR cut filter, such as those manufactured in the present embodiment 1 and the present embodiment 2, will be described.

The adjustment is determined by various factors such as the sensitivity characteristics of the image sensor and the arrangement position in the optical system as shown in FIG. 1 and FIG. It is also possible to have an IR pass filter that differs from the optical properties of edge filter types that transmit most of the light in the entire required near-infrared wavelength range.

In other words, the same effect as the optical filters produced in Examples 1 and 2 can be obtained by using a band-pass type IR pass filter that transmits only light in a specific wavelength region in the near-infrared wavelength region that requires adjustment. It is possible to form a filter with For example, the transmission characteristics of the transmission band of the near-infrared transmission film in FIG. Other wavelength regions have the same characteristics as in FIG. 1(b). The optical characteristics of the near-infrared antireflection film are assumed to be the same as those in FIG. 1(c). From the above, it can be concluded that by synthesizing the respective transmission characteristics of these two functional films, which have low transmission ripple and high transmission, the transmission band has low transmission ripple, flatness, and very high transmission. An IR pass filter having transmission characteristics can be formed as a bandpass type that transmits light only in a specific region of 800 to 900 nm in the near-infrared wavelength region. Such band-pass type transmission characteristics can be obtained by adjusting the film thickness, the number of layers, the thin film material, etc. of the multiple layers of thin films that constitute the near-infrared transmissive film. Similarly, it is possible to form a bandpass type IR pass filter that transmits only various intended wavelength regions such as 800-1000 nm and 750-850 nm.

As another example, in Example 1 and Example 2, the antireflection structure disposed on the outermost layer of the near-infrared transmissive film, the near-infrared shielding film, the visible and near-infrared antireflection film, and the ND film was 1 Although the thin film structure of the layer was mentioned, it is also possible to structure with multiple layers. By adopting such a configuration, it may be possible to further reduce the reflection of light in the wavelength region required by each of the functional films described above.

5 described in the second embodiment, the stacking order of the near-infrared shielding film 22 and the ND film 29 can be reversed. In this case, together with the fabrication of the IR cut filter 28, the formation of the near-infrared shielding film 22 and the ND film 29 is performed while maintaining the film-forming regions of the near-infrared shielding film 22 and the ND film 29 on the substrate surface. In order to correct the deviation of the interference condition between the near-infrared shielding film 22 and the ND film 29 caused by changing the order and furthermore, the order of lamination being reversed, the multi-layered thin film forming the ND film 29 is laminated. By adjusting the configuration, an optical filter having substantially the same characteristics and effects as those of the second embodiment can be obtained. Here, with such a configuration, the near-infrared shielding film 22 may be formed so as to cover the entirety of the ND film 29, including the cross section, by slightly shifting the deposition region of the ND film 29 on the substrate surface. It is possible, and in some cases it is possible to obtain a third effect such as improved environmental resistance as the NDIR filter 30 or improved abrasion resistance.

As another configuration example, by adding a light shielding function in the ultraviolet wavelength region in addition to the IR shielding function of the near-infrared shielding film, the IR cut filter can be used as a UVIR cut filter.

The IR pass filter and the IR cut filter are combined with the band-pass type IR pass filter, the multi-layered antireflection film formed on the outermost layer of each functional film, the UVIR cut filter, etc. It is also possible to configure an optical filter having the two functions of

(Example 4)
An example in which the optical filter manufactured in Examples 1 to 3 is applied to an imaging device such as a video camera will be described with reference to FIG.

FIG. 6(a) shows an imaging apparatus such as a video camera, in which light rays transmitted through an imaging optical system 47 composed of aperture blades 49 and the like are passed through an optical filter disposed at an optical filter insertion position 40 to a solid-state imaging device 48. It is configured so as to obtain an appropriate image by adjusting according to the characteristics.

For example, in the configuration of FIG. 6, the optical filters having two functions of the IR pass filter and the IR cut filter produced in Examples 1 to 3 are arranged at predetermined positions in the imaging device, and the optical filters are inserted. By moving the optical filter to the position 40 where it functions as an IR pass filter or an IR cut filter, it is possible to select an appropriate filter according to the imaging situation and perform imaging. For example, using the optical filter A44 in the configuration of FIG. Either one of 42 filter areas is arranged. When the amount of incident light is sufficient for normal photography, the IR cut filter 42 is arranged at the optical filter insertion position 40 to form a color image, and conversely, when the amount of light is insufficient, the IR pass filter is used. 41 is positioned at the optical filter insertion position 40 to form a night vision image.

An image pickup device manufactured by this method removes near-infrared wavelength noise components with an IR cut filter when shooting in the daytime when the amount of incident light is high, and removes visible wavelength noise components with an IR pass filter when shooting at night when the amount of incident light is low. It becomes possible to remove it, and it is possible to improve the image quality of the photographed image.

Further, instead of the optical filter A44, an optical filter B45 having the function of the IR pass filter 41 and the NDIR filter 43 having optical characteristics obtained by combining the function of the ND filter for attenuating the amount of light in the visible wavelength region and the function of the IR cut filter. It is also possible to use Such an NDIR filter 43 has a transmission characteristic of attenuating light in the visible wavelength range and blocking light in the near-infrared wavelength range, as shown in FIG. 4(e), for example. With such a configuration, when the amount of incident light is sufficient for normal photographing, the NDIR filter 43 is arranged at the optical filter insertion position 40 to form a color image. In some cases, the IR pass filter 41 is arranged at the optical filter insertion position 40 to form a night vision image.

Furthermore, in addition to the functions of the IR pass filter 41 and the IR cut filter 42, it is also possible to use an optical filter C46 having three functions of the NDIR filter 43. In addition to the IR cut filter 41 and the IR pass filter 42, the NDIR filter 43 that attenuates the amount of light in the visible wavelength region is used. When it is placed at the insertion position 40 and the amount of incident light is sufficient for normal photographing, the IR cut filter 42 is placed at the optical filter insertion position 40 to form a color image, and conversely when the amount of light is insufficient. places an IR pass filter 41 at the optical filter insertion position 40 to form a night vision image. With such a configuration, it is possible to realize an imaging apparatus capable of achieving high image quality in various imaging situations.

Further, not only the optical device of the present embodiment, but also other optical devices have the functions of an IR pass filter and an IR cut filter as fabricated in Examples 1 to 3 on a single substrate. By using a filter, it is possible to realize an imaging apparatus capable of achieving high image quality in various shooting situations.

As described above, in the configuration of the fourth embodiment, the IR cut filter 41 and the IR pass filter 42, which are used under different shooting environments such as daytime shooting and nighttime shooting, are formed on one substrate. is individually formed as a separate filter, and compared with a device configuration in which a plurality of optical filters are provided, the number of drive mechanisms for driving the filters can be reduced, and the cost of the entire device can be reduced. can be done.

(Example 5) UVPF
A near-ultraviolet transmitting film, a near-ultraviolet shielding film, and a visible and near-ultraviolet antireflection film, which are composed of multilayer thin films, are separately arranged on both sides of a single visible and near-ultraviolet wavelength transparent substrate, as shown in FIGS. Examples in which optical filters having spectral transmission characteristics as design values were produced will be described in detail below.

The visible and near-ultraviolet transparent substrate 50 of the optical filter of Example 5 as shown in FIG. A 0.4 mm thick D263 Teco glass with transmitting spectral properties was used.

Then, after forming the visible and near-ultraviolet antireflection film 53 on one surface of the visible and near-ultraviolet transparent substrate 50 by the IAD method, the visible and near-ultraviolet transparent substrate 50 is turned over, and the other side of the visible and near-ultraviolet transparent substrate 50 is A near-ultraviolet transmitting film 51 is formed by the IAD method in a predetermined region on the surface of the substrate, and a near-ultraviolet shielding film 52 is formed by the IAD method in a region different from the region where the near-ultraviolet transmitting film 51 is formed on the same surface of the substrate. formed. The visible and near-ultraviolet antireflection film 53 is formed first because it is thinner than the near-ultraviolet transmitting film 51 and the near-ultraviolet shielding film 52, and the film stress is low. This is because the position reduces the influence of film formation errors. As described above, the optical filter 54 in the fifth embodiment has the near-ultraviolet transmissive film 51 and the near-ultraviolet shielding film 52 on one side of the visible and near-ultraviolet transparent substrate 50 as shown in FIG. A visible and near-ultraviolet antireflection film 53 is arranged on the other surface of the near-ultraviolet transparent substrate 50 .

The near-ultraviolet transmissive film 51 of Example 5 formed on the visible and near-ultraviolet transparent substrate 50, as shown in FIG. and a transmission band that transmits most of the light except for the reflection component on the back side of the substrate while suppressing the ripple of light in the wavelength range of about 350 to 377 nm from the visible wavelength to the near-ultraviolet wavelength range. have. In addition, in the wavelength region of about 380 to 395 nm sandwiched between the transmission stop band and the transmission band, there is a transmission-block transition region where the transmission continuously changes from the transmission stop band to the transmission band. Furthermore, the wavelength at which the transmittance is 50% in the transmission-blocking transition region was defined as the UV half-value wavelength, and this value was set at 382 nm. The near-ultraviolet transmission film 51 in Example 5 is composed of a 38-layer film in which La ₂ Ti ₂ O ₇ which is a high refractive index material and SiO ₂ which is a low refractive index material are alternately laminated. 2, a transmission ripple adjusting layer 55a having a transmission ripple reduction function is arranged in the first layer of the near-ultraviolet transmission film 51 directly above the visible and near-ultraviolet transparent substrate 50. As shown in FIG. Furthermore, the 38th layer, which is the outermost layer, is provided with a near-ultraviolet antireflection structure 56a composed of a single layer having an antireflection function in the transmission band of near-ultraviolet wavelengths. The transmission ripple adjustment layer 55a has the thinnest film thickness among all the film thicknesses constituting the near-ultraviolet transmission film 51, and the near-ultraviolet antireflection structure 56a has a central wavelength of the wavelength band serving as the antireflection band. It has a film thickness of about 1.0 qw of 330 to 380 nm.

As shown in FIG. 8B, the near-ultraviolet shielding film 52 of the present embodiment 5 formed on the visible and near-ultraviolet transparent substrate 50 reduces the light in the wavelength region of about 430 to 600 nm in the visible wavelength region into small ripples. While suppressing, it has a transmission band that transmits most of the light except the reflected component on the back side of the substrate and a transmission blocking band that blocks light in the wavelength range of about 350 to 400 nm from the visible wavelength range to the near-ultraviolet wavelength range. there is Also, in the wavelength region of about 400 to 430 nm sandwiched between the transmission band and the transmission stop band, there is a transmission-block transition region in which the transmission continuously changes from the transmission band to the transmission stop band. Furthermore, the wavelength at which the transmittance is 50% in the transmission-blocking transition region was defined as the UV half-value wavelength, and this value was set to 415 nm. The near-ultraviolet shielding film 52 in Example 5 is composed of a 38-layer film in which TiO ₂ as a high refractive index material and SiO ₂ as a low refractive index material are alternately laminated, as shown in FIG. As the first layer of the near-ultraviolet shielding film 52 directly above the visible and near-ultraviolet transparent substrate 50, a transmission ripple adjusting layer 55b having a transmission ripple reduction function is arranged. Furthermore, the 38th layer, which is the outermost layer, is provided with a visible antireflection structure 56b composed of a single layer having an antireflection function in the transmission band of near-ultraviolet wavelengths. The transmission ripple adjustment layer 55b has the thinnest film thickness among all the film thicknesses constituting the near-ultraviolet shielding film 52, and the visible antireflection structure 56b has the central wavelength of the wavelength range that becomes the antireflection band. It has a film thickness of about 1.0 qw from 400 to 600 nm.

The visible and near-ultraviolet antireflection film 53 of Example 5 formed on the visible and near-ultraviolet transparent substrate 50 is, as shown in FIG. 7(c) or FIG. It has an optical characteristic of having a transmission band in which most of the light in the wavelength range of about 350 to 600 nm is blocked, ie, most of the light is transmitted, except for the reflected component on the back side of the substrate. Thus, the visible and near-ultraviolet antireflection film 53 forms a transmission band at 382 nm, which is the UV half-value wavelength of the near-ultraviolet transmission film 51, and at 415 nm, which is the UV half-value wavelength of the near-ultraviolet shielding film 52. Even if the optical characteristics of the near-ultraviolet transmission film 51 and the near-ultraviolet shielding film 52 are shifted, for example, by about 10 nm to the short wavelength side or the long wavelength side due to an error or the like, the visible and near-ultraviolet antireflection film 53 can transmit at each UV half-value wavelength. You can keep your belt. Therefore, by designing the configuration as described above, even if the optical characteristics of the visible and near-ultraviolet antireflection film 53 change due to film formation errors during the formation of the visible and near-ultraviolet antireflection film 53, the visible and near-ultraviolet transparent substrate 50 can be maintained. The influence of the UV pass filter 57 or the UV cut filter 58 formed by including the UV pass filter 57 or the UV cut filter 58 on each UV half-value wavelength is extremely small, and only the error of the near-ultraviolet transmission film 51 or the near-ultraviolet shielding film 52 causes the UV pass filter 57 or the UV cut filter Since the transmission-blocking transition region of 58 is determined, the reproducibility can be further improved, and the accuracy of the optical filter 54 as a whole can be improved.

Further, the visible and near-ultraviolet antireflection film 53 in Example 5 is composed of a four-layer film in which La ₂ Ti ₂ O ₇ as a high refractive index material and SiO ₂ as a low refractive index material are alternately laminated. In particular, the fourth layer, which is the outermost layer most influencing the antireflection function, has a film thickness of about 1.0 qw at 350 to 600 nm, which is the center wavelength of the wavelength range forming the antireflection band.

Furthermore, as shown in FIG. 7B, the transmission characteristics of the transmission band produced by the single near-ultraviolet transmission film 51 formed on the visible and near-ultraviolet transparent substrate 50 are flat with little transmission ripple and substantially constant. It has a transmission characteristic of , and has a characteristic of transmitting most of the light except for the reflection component on the back side of the substrate. Similarly, the transmission characteristic of the transmission band produced by the single visible and near-ultraviolet antireflection film 53 formed on the visible and near-ultraviolet transparent substrate 50 is flat with little transmission ripple as shown in FIG. It has a constant transmission characteristic, and has a characteristic of transmitting most of the light except for the reflected component on the back side of the substrate. Strictly speaking, the transmittance of the visible and near-ultraviolet antireflection film 53 is higher than that of the near-ultraviolet transmission film 51, as shown in FIGS. 7(b) and 7(c). Although the value is slightly higher than the transmittance, it has characteristics that can be regarded as substantially the same. By synthesizing the transmission characteristics of these two functional films, which are flat with little transmission ripple and have high transmission, the transmission band of the UV pass filter 57 is obtained as shown in FIG. , the transmission ripple is small, the film is flat, and the transmission is higher than that of the near-ultraviolet transmission film 51 and the visible and near-ultraviolet antireflection film 53 . Similarly, in the blocking band of the UV pass filter 57, the transmission characteristics are determined by synthesizing the transmission characteristics produced by the two functional films. Therefore, the transmission characteristics of the UV pass filter 57 as a whole are determined by synthesizing the transmission characteristics produced by the two functional films of the near-ultraviolet transmission film 51 and the visible and near-ultraviolet antireflection film 53 .

Similarly, the transmission characteristics of the transmission band produced by the single near-ultraviolet shielding film 52 formed on the visible and near-ultraviolet transparent substrate 50 are flat and substantially constant with little transmission ripple as shown in FIG. 8(b). It has a certain transmission characteristic, and has a characteristic of transmitting most of the light except for the reflected component on the back surface side of the substrate. Similarly, the transmission characteristic of the transmission band produced by the single visible and near-ultraviolet antireflection film 53 formed on the visible and near-ultraviolet transparent substrate 50 is flat with little transmission ripple as shown in FIG. It has a constant transmission characteristic, and has a characteristic of transmitting most of the light except for the reflected component on the back side of the substrate. Strictly speaking, the transmittance of the visible and near-ultraviolet antireflection film 53 is higher than that of the near-ultraviolet shielding film 52, as shown in FIGS. Although the value is slightly higher than the transmittance, it has characteristics that can be regarded as substantially the same. By synthesizing the transmission characteristics of these two functional films, which are flat with little transmission ripple and have high transmission, the transmission band of the UV cut filter 58 is obtained as shown in FIG. , the transmittance ripple is small, the film is flat, and the transmittance is higher than that of the near-ultraviolet shielding film 52 and the visible and near-ultraviolet antireflection film 53 . Similarly, in the blocking band of the UV cut filter 58, the transmission characteristics are determined by synthesizing the transmission characteristics produced by the two functional films. Therefore, the transmission characteristics of the UV cut filter 58 as a whole are determined by synthesizing the transmission characteristics produced by the two functional films of the near-ultraviolet shielding film 52 and the visible and near-ultraviolet antireflection film 53 .

In addition, the optical sensor used for the banknote recognition sensor, etc., as in the present embodiment is very sensitive to noise components, which greatly affect the sensing accuracy. Therefore, as in the filter of this embodiment, the transmission is suppressed to 1% or less, more preferably 0.1% or less in the blocking band of the UV pass filter 57, and 80% or more, more preferably 90% or more in the transmission band. It is desirable to have a transmission characteristic of Similarly, it is desirable that the UV cut filter 58 has a transmission characteristic of 80% or more, more preferably 90% or more in the transmission band while suppressing the transmission in the stopband to 1% or less, more preferably 0.1% or less.

In the near-ultraviolet transmitting film 51, the near-ultraviolet shielding film 52, and the visible and near-ultraviolet antireflection film 53 in the present embodiment 5, La ₂ Ti ₂ O ₇ and TiO ₂ , which are high refractive index materials configured as vapor deposition films, are low. In addition to SiO ₂ as a refractive index material, Nb ₂ O ₅ , ZrO ₂ , Ta ₂ O ₅ and the like can be used as high refractive index materials, and MgF ₂ and the like can be used as low refractive index materials. In addition, it is also possible to use an intermediate refractive index material such as Al ₂ O ₃ in some layers for reasons of design and film formation. , Cr, Fe, Al, Mg, Ti, Si, Nb, Zr, Ta, In, Ag, Au, etc., and an optimum combination of materials may be selected depending on the situation.

The spectral transmission characteristics of the UV pass filter 57 manufactured as described above are approximately the design values shown in FIG. 7A, and the spectral transmission characteristics of the UV cut filter 58 are approximately the design values shown in FIG. I got the same properties. As a result, in a banknote recognition sensor or the like, the area of the UV pass filter 57 is used to block the transmission of the visible wavelength region, which becomes a noise component when UV light is emitted, and the near-ultraviolet region, which becomes a noise component when fluorescence is received. By blocking transmission of wavelengths, an optical filter capable of improving sensing accuracy can be obtained.

In addition, the near-ultraviolet transmission film 51 and the near-ultraviolet shielding film 52 are formed by forming the visible and near-ultraviolet antireflection film 53 that exhibits an antireflection effect in the transmission bands of both the near-ultraviolet transmission film 51 and the near-ultraviolet shielding film 52 . Since there is no need to construct two different types of antireflection films optimized for each of the functional films, the manufacturing process can be simplified, and the cost of the optical filter can be reduced.

As described above, it is possible to obtain the optical filter 54 having the two functions of the UV pass filter 57 and the UV cut filter 58 and capable of achieving high image quality and low cost.

Furthermore, in Example 5, the edge type UV pass filter 57 and UV cut filter 58 were produced. It is also possible to produce a UV pass filter 57 and a UV cut filter 58 of the type.

As a result, we have developed an optical filter that blocks transmission of noise components in the visible wavelength range and makes it possible to use light in the predetermined near-ultraviolet wavelength range more efficiently than ever before. Obtainable.

(Example 6) Banknote identification sensor An example in which the optical filter manufactured in Example 5 is applied to an optical sensor for a banknote identification sensor will be described with reference to Fig. 10 .

FIG. 10 is a schematic configuration diagram of a banknote identification sensor for preventing counterfeiting of banknotes. Reference numeral 60 denotes a light projecting unit; 61, a light receiving unit; 62, a UV pass filter; A measurement object 65 is an optical filter in which a UV pass filter 62 and a UV cut filter 63 are integrally constructed.

The UV light emitted from the light projecting unit 60 composed of an LED light passes through the UV pass filter 62, which is a part of the optical filter 65, thereby cutting noise components of visible light. After that, the light incident on the fluorescent paint printed on the object to be measured 64 is wavelength-converted into a visible wavelength by the fluorescence phenomenon and emitted again. reaches the light receiving portion 61 via the UV cut filter 63 .

An optical sensor such as a bill identification sensor is very sensitive to noise components when measuring light is emitted and received, and these greatly affect sensing accuracy. Therefore, the blocking band of the UV pass filter 62 must have a transmission of 1% or less, preferably 0.1% or less, while the transmission band must have a transmission of 80% or more, preferably 90% or more. Similarly, the UV cut filter 63 is required to have a transmission characteristic of 80% or more, preferably 90% or more in the transmission band while suppressing the transmission to 1% or less, preferably 0.1% or less in the stopband.

As described above, by using the optical filter manufactured in Example 5 as the optical filter 65, an optical sensor with higher precision can be obtained. Further, by using the optical filter of the present embodiment 5 not only in the configuration of the present embodiment, but also in other devices and optical sensors, high accuracy can be achieved.

10, 20. Visible and near-infrared transparent substrates 11, 21, 31 . near-infrared transmissive films 12, 22, 32; Near-infrared shielding films 13, 23, 33. Visible and near-red antireflection films 14, 24, 34. Optical filters 15a, 15b, 25a, 25b . Transmission ripple adjustment layers 16a, 26a . Near-infrared antireflection structures 16b, 26b. Visible antireflection structure 17 . IR pass filter 18 . IR cut filter 29 . ND film 30 . NDIR filter

40. Optical filter insertion position 41 . IR pass filter 42 . IR cut filter 43 . NDIR filter 44 . Optical filter A
45. Optical filter B
46. Optical filter C
47. imaging optical system 48 . Solid-state imaging device 49 . Aperture blade

50. Visible and near-ultraviolet transparent substrate 51 . Near-ultraviolet transmission film 52 . Near-ultraviolet shielding film 53 . Visible and near-ultraviolet antireflection film 54 . Optical filters 55a, 55b . Transmission ripple adjustment layers 56a, 56a . Near-ultraviolet antireflection structures 56b, 56b. Visible antireflection structure 57 . UV pass filter 58 . UV cut filter

60. Light projecting section 61 . light receiving portion 62 . UV pass filter 63 . UV cut filter 64 . object to be measured 65 . optical filter

Claims (8)

Immediately above one surface of a substrate having light transmission properties from visible wavelengths to the near-infrared wavelength region where the wavelengths are continuous with the visible wavelengths,
a near-infrared wavelength transmitting film that blocks visible wavelength light and blocks reflection of light in the near -infrared wavelength region;
a near-infrared wavelength shielding film that blocks reflection of visible wavelength light and blocks light in the near -infrared wavelength region;
At a position facing the near-infrared wavelength transmissive film and the near-infrared wavelength shielding film on the other surface of the substrate, the substrate prevents reflection of light over the visible wavelength range to the near-infrared wavelength region , A single visible and near -infrared wavelength antireflection film having a transmittance of 90% or more over the visible wavelength to the near-infrared wavelength region on the above ,
A wavelength with a transmittance of 50% in the transmission-blocking transition region of the near-infrared wavelength transmission film is defined as a first half-value wavelength,
Assuming that the wavelength at which the transmittance is 50% in the transmission-blocking transition region of the near-infrared wavelength shielding film is the second half-value wavelength,
The optical filter, wherein the first half-value wavelength and the second half-value wavelength are included in the visible wavelength to the near-infrared wavelength region. light transmission in the near-infrared wavelength region formed by the substrate and the near-infrared wavelength- transmitting film;
light transmission in the near- infrared wavelength region formed by the substrate and the visible and near-infrared wavelength antireflection film;
are substantially the same,
The substrate, the near-infrared wavelength transmission film, and the visible/ near-infrared wavelength antireflection film collectively have a light transmission characteristic of blocking visible wavelength light and transmitting near-infrared wavelength light. 2. The optical filter of claim 1 , wherein . light transmission of visible wavelengths formed by the substrate and the near-infrared wavelength shielding film;
By making the light transmission of visible wavelengths formed by the substrate and the visible and near-infrared wavelength antireflection film substantially the same,
The substrate, the near-infrared wavelength shielding film, and the visible/ near-infrared wavelength antireflection film as a whole have a light transmission characteristic of transmitting light in the visible wavelength region and blocking light in the near-infrared wavelength region. 3. Optical filter according to claim 1 or 2 , characterized in that. An ND film that attenuates transmission of light in a wavelength region including visible wavelengths is formed on at least a part of the region that overlaps the region where the near-infrared wavelength shielding film is formed on the substrate. The optical filter according to any one of claims 1 to 3 , characterized by: An optical sensor or imaging device comprising the optical filter according to any one of claims 1 to 4 . One of the region including the near-infrared wavelength transmitting film and the region including the near-infrared wavelength shielding film is driven so as to be selectively placed on the optical path according to the photographing situation. Item 6. The optical sensor or imaging device according to item 5 . The optical filter includes an ND film that attenuates transmission of light in a wavelength region including visible wavelengths in at least a part of a region that overlaps a region where the near-infrared wavelength shielding film is formed on the substrate. is formed, and one of the region including the ND film and the region including the near-infrared wavelength transmitting film is driven so as to be selectively arranged on the optical path according to the photographing situation. 6. An optical sensor or imaging device according to claim 5 . The optical filter includes an ND film that attenuates transmission of light in a wavelength region including visible wavelengths in at least a part of a region that overlaps a region where the near-infrared wavelength shielding film is formed on the substrate. is formed, and any one of a region including the near-infrared wavelength transmitting film, a region including the near-infrared wavelength shielding film, and a region including the ND film is selected according to the imaging situation. 6. The optical sensor or imaging device according to claim 5 , wherein the optical sensor or imaging device is driven so as to be arranged on the optical path.

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