JP7221617B2 - Optical filter module and optical device - Google Patents

Description

The present invention relates to optical filter modules and optical devices.

2. Description of the Related Art Optical filters that transmit only light in a predetermined wavelength range are used in special cameras for medical or agricultural use, or in near-infrared cameras. As such an optical filter, a variable-type band-pass filter is known, in which the transmission band changes depending on the position in the filter plane (Patent Document 1).

JP-A-2-132405

It has been found that a variable type filter such as that disclosed in Patent Document 1 does not have sufficient transmission blocking performance for light with a wavelength away from the transmission band. It was also found that this problem becomes conspicuous especially when the wavelength range targeted by the filter is wide.

SUMMARY OF THE INVENTION An object of the present invention is to improve the accuracy of an optical device by improving transmission blocking performance in a variable-type filter in a wavelength region other than a desired wavelength region.

In order to achieve the object of the present invention, for example, the optical filter module of the present invention has the following configuration. i.e.
A substrate and a first functional film formed on one surface of the substrate, the film thickness and transmission wavelength range of which vary depending on the position within the surface, and which transmits light in a selected wavelength region corresponding to the incident position. 1 optical filter member;
A second optical filter member that suppresses transmission of light in at least a part of a wavelength region different from the selected wavelength region, with respect to the selected wavelength region corresponding to at least one incident position of the first optical filter member. and
Does the first optical filter member suppress transmission of light having a wavelength longer than the selected wavelength region, and does the second optical filter member suppress transmission of light having a wavelength longer than the selected wavelength region? , or
The first optical filter member suppresses transmission of light with wavelengths shorter than the selected wavelength region, and the second optical filter member suppresses transmission of light with wavelengths shorter than the selected wavelength region.

In the variable type filter, by improving the transmission blocking performance in a wavelength region other than the desired wavelength region, the accuracy of the optical device can be improved.

FIG. 4 is a diagram for explaining band-pass characteristics of a variable type; Schematic cross-sectional view of a variable type filter. FIG. 10 is a schematic configuration diagram of a variable filter according to Example 3; FIG. 2 is a schematic cross-sectional view of a step-type variable filter; 1 is a schematic configuration diagram of an optical filter module according to Example 1. FIG. 4A and 4B are graphs showing spectral transmission characteristics of short-pass filters and long-pass filters according to Examples 1 and 2; FIG. 4A and 4B are graphs showing spectral transmission characteristics of the bandpass filter according to the first embodiment; FIG. FIG. 5 is a schematic configuration diagram of an optical filter module according to Example 2; FIG. 11 is a schematic configuration diagram of an optical device according to Example 4;

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. However, the scope of the present invention is not limited to the following embodiments.

An optical filter module according to one embodiment of the present invention comprises a first optical filter member and a second optical filter member. The first optical filter member has a substrate and a first functional film formed on one surface of the substrate, the film thickness and transmission wavelength range of which vary depending on the position within the surface, and selects a wavelength corresponding to the incident position. Allows light to pass through the area. Further, the second optical filter member relates to the selected wavelength region corresponding to at least one incident position of the first optical filter member, and transmits light in at least a part of the wavelength region different from the selected wavelength region. Suppress. Such a second optical filter member can suppress transmission of light having a wavelength outside the selected wavelength region when positioned on the optical path of light passing through the first optical filter member.

Thus, the first functional film has a variable type transmission characteristic. The variable type transmission characteristic refers to a characteristic in which the transmission wavelength region (transmission band) changes in the wavelength direction depending on the position within the plane. For example, as shown in FIGS. 1 and 2, the first functional film is a functional film in which the film thickness and the transmission band change along a predetermined direction, that is, the transmission wavelength region changes so as to shift in the wavelength direction. There may be.

In one embodiment, the optical filter module has a bandpass function that transmits light in a specific wavelength band (selected wavelength region) of incident light. In this case, the first optical filter member has a variable-type bandpass characteristic. The optical filter module according to this embodiment has a functional film configured such that the transmission band changes as the film thickness changes along a predetermined direction. In one embodiment, the functional film is configured such that the film thickness and transmission band are continuously varied. FIG. 2 shows a schematic diagram of a filter 3 with bandpass characteristics, in which a functional film 2 with bandpass characteristics is provided on a substrate 1 . The spectral transmittance at each light incident position 1 to 6 is shown in FIG.

The optical filter module has a function of transmitting light in a selected wavelength region, which is part of the target wavelength region, which is the target wavelength for selective light transmission by the optical filter module. According to the variable-type band-pass characteristics in which the transmission wavelength region changes along a predetermined direction, the transmission band extends along a predetermined direction from a range that includes the shortest wavelength in the target wavelength region and does not include the longest wavelength to the target wavelength region. changes to a range that includes the longest wavelength and does not include the shortest wavelength.

In one embodiment, the first optical filter member is a bandpass filter having a variable type bandpass characteristic (Example 1). For example, the first optical filter member may have a substrate and a first functional film provided on the substrate. Here, this functional film (band-pass functional film) has a film thickness and a transmission wavelength range that change along a predetermined direction, and has a wavelength longer than the selected wavelength range corresponding to the incident position and a wavelength shorter than the selected wavelength range. It is configured to suppress transmission of light. According to such a configuration, the driving section (not shown) can adjust the transmission band of the first optical filter member by moving the bandpass filter so as to control the incident position of light. In this specification, the driving section may be the driving section of the optical filter module or the driving section of the device in which the optical filter module is incorporated.

In one embodiment, the first optical filter member is a bandpass filter unit composed of a plurality of optical filters having variable type bandpass characteristics (Example 2). For example, the first optical filter member may have a first filter and a second filter. The variable-type first filter (short-pass filter) may have a substrate and a first functional film provided on the substrate. Here, this functional film (short-pass functional film) varies in film thickness and transmission wavelength region depending on the position in the plane (e.g., along a predetermined direction). is configured to suppress the transmission of Also, the variable-type second filter (long-pass filter) may have a substrate and a second functional film provided on the substrate. Here, this functional film (long-pass functional film) changes its film thickness and transmission wavelength region depending on the position in the plane (for example, along a predetermined direction), and transmits light having a wavelength shorter than the selected wavelength region corresponding to the incident position. It is configured to suppress permeation. In the band-pass filter unit, the transition region on the short wavelength side of the selected wavelength region (the region where the transmittance changes from high to low in the wavelength direction) can be formed by a long-pass filter. Also, the transition region on the long wavelength side can be formed by a short-pass filter. According to such a configuration, the drive unit adjusts the transmission band and the transmission band width of the first optical filter member by moving the short-pass filter and the long-pass filter so as to control the incident position of light. be able to.

On the other hand, the second optical filter member suppresses transmission of light with wavelengths outside the selected wavelength region when positioned on the optical path of light passing through the first optical filter member. This second optical filter member can suppress transmission of light having a wavelength that is included in the target wavelength region but is outside the selected wavelength region. For example, the second optical filter member can have a third functional film and a fourth functional film. The third functional film (short-pass functional film) suppresses transmission of light having a wavelength longer than the selected wavelength region corresponding to the incident position on the first optical filter member and included in the target wavelength region. For example, the second optical filter member has a third functional film provided on the substrate that transmits light of wavelengths shorter than the selected wavelength region and blocks transmission of light of wavelengths longer than the selected wavelength region. It may have a short-pass filter with a structure A shortpass filter may have a cutoff frequency longer than the selected wavelength region and be configured to block transmission of light with wavelengths longer than the cutoff frequency. With such a configuration, it is possible to prevent transmission of light having a wavelength longer than the selected wavelength region among the light transmitted through the first optical filter member.

The fourth functional film (long-pass functional film) suppresses transmission of light having a wavelength shorter than the selected wavelength region corresponding to the incident position on the first optical filter member and included in the target wavelength region. For example, the second optical filter member has a fourth functional film provided on the substrate that transmits light of wavelengths longer than the selected wavelength region and blocks transmission of light of wavelengths shorter than the selected wavelength region. can be a long-pass filter with a structure A longpass filter has a cutoff frequency shorter than the selected wavelength region and can be configured to block transmission of light with wavelengths shorter than the cutoff frequency. With such a configuration, it is possible to prevent transmission of light having a wavelength shorter than the selected wavelength region among the light transmitted through the first optical filter member.

In this embodiment, the third functional film can be arranged on the optical path of light passing through the first incident position of the first optical filter member. Also, the fourth functional film is arranged on the optical path of light passing through the second incident position of the first optical filter member. At this time, the selected wavelength region corresponding to the first incident position is on the shorter wavelength side than the selected wavelength region corresponding to the second incident position. As an example, when the center wavelength of the selected wavelength region is longer than the reference wavelength λ0 set within the target wavelength region, a long-pass filter (fourth functional film) can be used together. On the other hand, when the center wavelength of the selected wavelength region is shorter than the reference wavelength λ0, a short-pass filter (third functional film) can be used together. Note that when the center wavelength is near the reference wavelength λ0 (for example, when the reference wavelength λ0 is included in the selected wavelength region), either filter may be used together, the filter may not be used together, or another filter may be used. (for example, an antireflection filter) may be used together.

The drive unit can move the second optical filter member so that the third functional film is positioned on the optical path when light passes through the first incident position of the first optical filter member. . Further, the driving section moves the second optical filter member so that the fourth functional film is positioned on the optical path when the light passes through the second incident position of the first optical filter member. be able to. With such a configuration, a long-pass filter and a short-pass filter can be selectively arranged on the optical path (Example 1). On the other hand, when light passes through the first and second incident positions of the first optical filter member, the third and fourth functional films are positioned on the optical path, respectively. and the first optical filter member may be fixed (Example 3).

A short-pass filter and a long-pass filter are used for the purpose of suppressing an increase in transmittance in a wavelength region (transmission blocking region) other than the selected wavelength region. Although the first optical filter member has a bandpass function, the transmittance in the transmission blocking region corresponding to each incident position may increase, especially the transmittance at wavelengths away from the selected wavelength region. A short-pass filter can be used to block light of wavelengths near the longest wavelength in the wavelength region of interest that has passed through the first optical filter member. Also, the long-pass filter can be used for the purpose of blocking light having a wavelength near the shortest wavelength in the target wavelength region that has passed through the first optical filter member. Short-pass and long-pass filters, on the other hand, have high transmittance for selected wavelength regions.

With such a configuration, the first optical filter member extracts light in the selected wavelength region and reduces light in the transmission blocking region. The second optical filter member reduces light in a wavelength region such as near the shortest wavelength or the longest wavelength in the target wavelength region, for which it is relatively difficult for the first optical filter member to exhibit sufficient transmission blocking performance. . By using a plurality of these optical filters together, it is possible to obtain good optical characteristics as a whole optical filter module.

At least one of the third functional film and the fourth functional film is a functional film in which the film thickness and the transmission wavelength region change depending on the position in the plane, for example, the film thickness and the transmission wavelength region change along a predetermined direction. It may be a functional membrane that According to such a configuration, even when the target wavelength range is relatively long, the transmittance in the transmission stopband can be sufficiently suppressed.

The band-pass functional film, short-pass functional film, and long-pass functional film as described above can be multi-layered thin films of high refractive index thin film layers and low refractive index thin film layers. Methods are known for forming multilayer thin films having desired spectral transmission characteristics by controlling the thickness of the thin films. For example, it is known to reduce the transmittance of light of wavelength λ by alternately laminating high refractive index thin films and low refractive index thin films each having a thickness of λ/4. A desired functional film can be produced by laminating thin films of various thicknesses using such a method. Although the material of the thin film is not particularly limited, TiO ₂ , Nb ₂ O ₅ , ZrO ₂ , Ta ₂ O ₅ and the like are examples of high refractive index thin film materials. On the other hand, low refractive index thin film materials include SiO ₂ and MgF ₂ . In addition to these materials, thin film materials include metal compounds such as Ni, W, Mo, Cu, Cr, Fe, Al, Mg, Ti, Si, Nb, Zr, Ta, In, Ag, and Au. may be used.

A method for forming such a multilayer thin film is not particularly limited, and for example, a physical film forming method, a chemical film forming method, or a wet film forming method such as spin coating can be employed. From the viewpoint of improving the reproducibility or environmental resistance of the film, a process of forming a film using relatively high energy, such as a sputtering method or a vapor deposition method with some assistance, can be adopted. More specific examples include a sputtering method, an IAD (Ion Assisted Deposition) method, an ion plating method, an IBS method, or a cluster vapor deposition method. In consideration of the characteristics or productivity required for each filter, the film formation method can be appropriately selected so that the film thickness of each layer can be controlled with high accuracy and a film with high reproducibility can be obtained.

A variable-type functional film can be a film whose refractive index and physical film thickness change depending on the in-plane position. For example, it is possible to use a film whose refractive index and physical film thickness are changed continuously along a certain direction on the substrate. For example, by forming a multi-layered thin film so that the film thickness of each layer changes continuously, it is possible to produce a functional film whose film thickness and transmission wavelength region change along a predetermined direction. According to such a configuration, the center wavelength of the transmission band continuously changes according to the position on the substrate. The reproducibility and productivity of the functional film can be improved by adopting the method of continuously changing the physical film thickness.

A method for producing a thin film whose physical thickness changes continuously is not particularly limited, but a method of performing vapor deposition after tilting and fixing a substrate with respect to an evaporation source can be mentioned. For example, a thin film can be formed by vapor deposition after the substrate is fixed at a normal fixed position of a film formation jig on a vapor deposition dome with a large tilt. As another method, there is a method of forming a film in a state in which a mask is fixedly arranged so as to float from the substrate at a predetermined position closer to the evaporation source than the film forming surface of the substrate. According to such a method, it is possible to obtain a thin film in which the film thickness continuously changes in one multi-layer film forming process. Also, instead of continuously varying the thickness of each layer, as shown in FIG. A functional membrane, in which a plurality of regions are provided, can also be used. FIG. 4 shows a bandpass functional film 2 having five regions each having a uniform transmission band. type bandpass characteristics can be realized. As a method of changing the transmission band of the filter, there is a method of tilting the filter to change the incident angle of light, but using a functional film with a variable thickness makes the transmittance more constant in various transmission bands. is easy.

A bandpass filter, a shortpass filter, and a longpass filter as described above can be manufactured by providing a functional film on a substrate. For example, a short-pass filter can be produced by forming a functional film composed of multilayer thin films having short-pass characteristics on one surface of a transparent substrate. Similarly, a long-pass filter can be produced by forming a functional film composed of multilayer thin films having long-pass characteristics on one surface of a transparent substrate. A band-pass filter can also be produced by forming a functional film composed of multilayer thin films having band-pass characteristics on one surface of a transparent substrate. In these filters, an antireflection film having an antireflection function may be formed on the other surface of the transparent substrate. Furthermore, functional films that block transmission in different wavelength regions may be separately arranged on both surfaces of the substrate. With such a configuration, it is easy to fabricate a bandpass filter, a shortpass filter, and a longpass filter having a transmission stopband in a long wavelength region.

Note that the second filter member is not limited to a substrate provided with a multilayer thin film. For example, the short-pass filter or long-pass filter used as the second filter member may have a resin layer containing a pigment that absorbs light of a predetermined wavelength.

Various optical filters have a large impact on the results obtained when used in optical systems such as cameras. That is, the image quality obtained is sensitive to the amount of light in the selected wavelength region and the transmission stop wavelength region. Therefore, the average transmittance in the designed stopband of the bandpass filter, shortpass filter, and longpass filter is preferably 1% or less, more preferably 0.5% or less. On the other hand, the transmittance in the designed transmission band is desirably 80% or more on average, more preferably 90% or more on average. In addition, it is desirable that the antireflection film suppresses reflection in the target wavelength range to 1% or less on average, more preferably 0.5% or less on average.

As the substrate of the optical filter, a substrate having optical transparency in all transmission bands of the optical filter can be used. Although the material of the substrate is not particularly limited, a glass type, a resin type, an organic/inorganic hybrid type, or the like can be used. As the substrate, it is possible to select a substrate that has the strength and optical properties required for the substrate of the optical filter and can function as a base.

The target wavelength region of the optical filter module according to this embodiment is not particularly limited. For example, the target wavelength range may be a visible wavelength range such as 400-700 nm, or a near-infrared wavelength range such as 700-1200 nm. Moreover, the target wavelength range may be a visible near-infrared wavelength range such as 400 to 1200 nm, or may be a wavelength range of 1200 nm or more.

The optical filter module according to this embodiment, which has excellent optical characteristics as described above, can be provided in imaging devices such as surveillance cameras, special cameras for medical use or agriculture, or other various optical devices. A highly accurate optical device can be obtained by using the optical filter module according to the present embodiment.

Note that the first optical filter member is not limited to a bandpass filter, and may be a shortpass filter or a longpass filter, for example. As an example, the first optical filter member is a short-pass filter that suppresses transmission of light with wavelengths longer than the selected wavelength region, and the second optical filter member suppresses transmission of light with wavelengths longer than the selected wavelength region. It may be a short-pass filter that Further, the first optical filter member is a long-pass filter that suppresses transmission of light with a wavelength shorter than the selected wavelength region, and the second optical filter member is a long-pass filter that suppresses transmission of light with a wavelength shorter than the selected wavelength region. It may be a filter. Also with this configuration, the first optical filter member extracts the light in the selected wavelength region and reduces the light in the transmission blocking region, and the second optical filter member is such that the first optical filter member has sufficient transmission blocking. It is possible to reduce the light in the wavelength range where it is difficult to exhibit performance.

Hereinafter, the optical filter module according to this embodiment will be specifically described based on examples.

[Example 1]
A filter module according to an embodiment of the present invention includes a variable-type bandpass filter, a short-pass filter, and a long-pass filter, and has variable-type bandpass characteristics as a whole.

As shown in FIG. 5 , the optical filter module 10 according to Example 1 includes a bandpass filter 11 , a shortpass filter 12 and a longpass filter 13 . The optical filter module 10 has a bandpass function for the wavelength range of interest from 400 to 700 nm. That is, by moving the bandpass filter 11 so that the position at which the light that has passed through the aperture 15 is incident on the bandpass filter 11, the wavelength region (selected wavelength region) of the light that passes through the bandpass filter 11 is changed. can be changed. For the optical filter module 10, 550 nm located in the middle of the target wavelength range can be set as the reference wavelength.

The bandpass filter 11 is a variable type filter having a bandpass function for a target wavelength range of 400 to 700 nm. FIG. 7 shows an example of transmission characteristics of the bandpass filter 11. FIG. In FIG. 7, A and B indicate the transmittance of light transmitted through two different positions (A and B) on the bandpass filter 11, respectively. Thus, the transmission band of the bandpass filter 11 at position A is close to 400 nm, which is the shortest wavelength in the target wavelength region, and the transmission band of the bandpass filter 11 at position B is the longest wavelength in the target wavelength region. close to 700 nm.

The bandpass filter 11 has a substrate and high refractive index thin films and low refractive index thin films alternately laminated on the substrate. In this embodiment, on one surface of the substrate, a 30-layer film is provided in which TiO ₂ , which is a high refractive index thin film, and SiO ₂ , which is a low refractive index thin film, are alternately laminated in this order by the IAD method. . This 30-layer film has a bandpass function of transmitting light of wavelengths included in the transmission band. In addition, this 30-layer film has a variable function, and the film thickness changes continuously along a certain direction on the substrate. Also, on the other surface of the substrate, a 10-layer film in which TiO ₂ and SiO ₂ are alternately laminated in this order by the IAD method is provided. This ten-layer film has an antireflection function. In this embodiment, the 10-layer film is designed so that it exhibits a sufficient antireflection function in the target wavelength range of 400 to 700 nm even if the optical characteristics are slightly shifted due to film formation errors. there is By having such a configuration, the bandpass filter 11 selectively transmits only wavelength components within the selected wavelength range.

The short-pass filter 12 and the long-pass filter 13 are appropriately selected according to the selected wavelength region and inserted into and removed from the filter insertion position 14 . In this embodiment, multiple filters are inserted into the same filter insertion position 14 in order to keep the imaging position of the light constant. On the other hand, a plurality of filters may be inserted in different positions depending on the type or number of filters to be used. For example, if the substrates of the filters have different refractive indices, multiple filters can be inserted at different locations so that the imaging location remains constant.

FIG. 6 shows an example of transmission characteristics of the short-pass filter 12 and the long-pass filter 13. FIG. In FIG. 6, A and B indicate the transmittance of light passing through the short-pass filter 12 and the long-pass filter 13, respectively. As shown in FIG. 6, the short-pass filter 12 can be designed so that the wavelength region of about 400-570 nm is the transmission band and the wavelength region of about 600-700 nm is the transmission stop band. Further, the transition wavelength region is about 570 to 600 nm where the transmission band transitions to the transmission stop band, and the half-value wavelength at which the transmittance is 50% can be designed to be about 575 nm.

Further, the long-pass filter 13 can be designed so that the wavelength region of approximately 530 to 700 nm is the transmission band and the wavelength region of approximately 400 to 500 nm is the transmission blocking band. A transition wavelength range of about 500 to 530 nm where the transmission band transitions to the transmission stop band can be designed so that the half-value wavelength at which the transmittance is 50% is about 520 nm. In this embodiment, both the short-pass filter 12 and the long-pass filter 13 are designed so that the reference wavelength is included in the transmission band.

The short-pass filter 12 and the long-pass filter 13 each have a substrate and high-refractive-index thin films and low-refractive-index thin films alternately laminated on the substrate. In this embodiment, a 36-layer film in which TiO ₂ and SiO ₂ are alternately laminated in this order by the IAD method is provided on one surface of the substrate of the short-pass filter 12 . This 36-layer film is a short-pass functional film that transmits only light having a wavelength shorter than a predetermined cutoff wavelength. Here, the predetermined cutoff wavelength is set to be shorter than the reference wavelength. Also, on the other surface of the substrate of the short-pass filter 12, a four-layer film in which TiO ₂ and SiO ₂ are alternately laminated in this order by the IAD method is provided. In this embodiment, this four-layer film can be designed to have an antireflection function at least in the wavelength range of 380-620 nm. According to such a design, even if the optical characteristics are slightly shifted due to film formation errors, etc., good transmission in the wavelength region of 400 to 600 nm, which is the transmission band or transition region of the short-pass filter 12, can be achieved. realizable.

In this embodiment, one surface of the substrate of the long-pass filter 13 is provided with a 38-layer film in which TiO ₂ and SiO ₂ are alternately laminated in this order by the IAD method. This 38-layer film is a long-pass functional film that transmits only light with a wavelength longer than a predetermined cutoff wavelength. Here, the predetermined cutoff wavelength is set to be longer than the reference wavelength. Also, on the other surface of the substrate of the long-pass filter 13, a four-layer film in which TiO ₂ and SiO ₂ are alternately laminated in this order by the IAD method is provided. In this embodiment, this four-layer film can be designed to have an antireflection function at least in the wavelength range of 480-720 nm. According to such a design, even if the optical characteristics are slightly shifted due to film formation errors, etc., good transmission can be achieved in the wavelength region of 500 to 700 nm, which is the transmission band or transition region of the short-pass filter 12. realizable.

In this embodiment, D263 Teco glass with a thickness of 0.4 mm is used as the substrate of the band-pass filter 11, the short-pass filter 12, and the long-pass filter 13. FIG. This substrate has spectral characteristics in which most of the incident light, excluding the reflected component on the back surface side of the substrate, is transmitted in the target wavelength range of 400 to 700 nm.

The optical filter module 10 of Example 1 configured as described above is controlled as follows. That is, by moving the bandpass filter 11 with respect to the optical path, the passage position of the light on the bandpass filter 11 is controlled, and the light of the wavelength band corresponding to the position passes through the bandpass filter 11 . Thus, light in the selected wavelength region passes through the bandpass filter 11 . By moving either the short-pass filter 12 or the long-pass filter 13 to the filter insertion position 14 on the optical path according to the selected wavelength region, sufficient transmission blocking is achieved in the transmission blocking band outside the selected wavelength region. function is exhibited.

Note that the short-pass filter 12 and the long-pass filter 13 can be integrated into one filter. That is, one filter can be provided with a region functioning as a short-pass filter and a region functioning as a long-pass filter. A specific example is a turret-type filter in which a short-pass filter or a long-pass filter can be selectively placed in the optical path by driving the filter in a rotational manner.

In the example of FIG. 7, when the selected wavelength region is near the shortest wavelength of the target wavelength region (A), the band-pass filter 11 does not sufficiently prevent transmission of light near the longest wavelength. Also, in the case (B) where the selected wavelength region is around the longest wavelength, the band-pass filter 11 does not sufficiently block the transmission of light around the shortest wavelength. In general, a filter having a band-pass characteristic that transmits only light in a specific wavelength range has a structure that blocks the transmission of light in the wavelength range on the short wavelength side close to the transmission band and in the wavelength range on the long wavelength side close to the transmission band. A body is provided. However, since there is a limit to the wavelength range in which one structure can block transmission, in order to block light transmission over a longer wavelength range, it is necessary to combine multiple structures so that the stopbands are continuous. There is However, in the barrier-pull type bandpass filter 11 used in this embodiment, it is difficult to completely block light outside the selected wavelength region at all positions. In particular, in a filter using a multilayer thin film as in this example, an increase in the number of layers may cause damage due to increased film stress, deterioration in appearance quality, or deterioration in reproducibility or productivity. . Therefore, in this embodiment, different filters share the two roles of a bandpass function and a transmission reduction function of reducing light transmission in a transmission stopband away from the selected wavelength region.

In this embodiment, the short-pass filter 12 is inserted when the central wavelength of the selected wavelength region is shorter than the reference wavelength, and the long-pass filter 13 is inserted when the central wavelength of the selected wavelength region is longer than the reference wavelength. Also, if the center wavelength of the selected wavelength region is the same as the reference wavelength, either filter may be inserted. The filter to be inserted can be determined in consideration of the characteristics of a light receiving element such as an imaging element used together with the optical filter module 10 . For example, by inserting the short-pass filter 12 in this case, it is possible to improve the transmission blocking function in the vicinity of the longest wavelength of the target wavelength region, which has relatively high sensitivity and is easily affected by noise, thereby reducing noise.

In this example, the reference wavelength was set to the center wavelength of the target wavelength region. On the other hand, the reference wavelength can be selected in consideration of the sensitivity of the imaging device. Furthermore, although only one of the short-pass filter 12 and the long-pass filter 13 is inserted in this embodiment, this is not essential. For example, when the center wavelength of the selected wavelength region is near the reference wavelength, two filters may be inserted at the same time, or both filters may be removed from the optical path.

The optical filter module 10 of Example 1 manufactured as described above has a variable-type bandpass function having a relatively long target wavelength range of 400 to 700 nm. Nevertheless, the optical filter module 10 can sufficiently suppress the transmittance around 700 nm, which is the longest wavelength, even when transmitting light around 400 nm, which is the shortest wavelength in the target wavelength region. On the contrary, the optical filter module 10 can sufficiently suppress the transmittance around 400 nm, which is the shortest wavelength, even when transmitting light around 700 nm, which is the longest wavelength in the target wavelength region. Thus, an optical filter module with excellent optical characteristics can be obtained.

[Example 2]
A filter module according to an embodiment of the present invention includes a variable-type bandpass filter unit, a short-pass filter, and a long-pass filter, and has variable-type bandpass characteristics as a whole. This bandpass filter unit consists of a shortpass filter and a longpass filter.

As shown in FIG. 8, the optical filter module 20 according to the second embodiment includes a bandpass filter unit 21, a shortpass filter 22, and a longpass filter . The bandpass filter unit 21 is composed of a shortpass filter 21a and a longpass filter 21b. The optical filter module 10 has a bandpass function for the wavelength range of interest from 400 to 700 nm. For the optical filter module 20, 550 nm located in the middle of the target wavelength range can be set as the reference wavelength.

The two optical filters, the short-pass filter 21a and the long-pass filter 21b, each have variable characteristics in which the transmission wavelength band changes according to the position of the filter through which light passes. By using these two filters together, the bandpass filter unit 21 exhibits a variable type bandpass function. That is, of the two transition regions from the selected wavelength region to the transmission blocking region, the transition region on the short wavelength side is formed by the transmission-non-transmission transition region of the long-pass filter 21b, and the transition region on the long wavelength side is formed by the short-pass filter 21a. of the transparent-to-opaque transition region. With such a configuration, the bandpass filter unit 21 transmits light in the selected wavelength region. In this way, by separately adjusting the positions of the two optical filters, the short-pass filter 21a and the long-pass filter 21b, it is possible to adjust the transmitted wavelength region. With such a configuration, it is also possible to adjust the width of the transmission band.

The short-pass filter 21a has a substrate and high-refractive-index thin films and low-refractive-index thin films alternately laminated on the substrate. In this embodiment, on one surface of the substrate, a 34-layer film is provided by alternately laminating TiO ₂ , which is a high refractive index thin film, and SiO ₂ , which is a low refractive index thin film, in this order by the IAD method. . This 34-layer film is a short-pass functional film that transmits light having a wavelength shorter than the cutoff wavelength. Furthermore, the 34-layer film has a variable function, and has a structure in which the film thickness changes continuously along a certain direction on the substrate, and the cutoff wavelength changes according to the incident position. A four-layer film in which TiO ₂ and SiO ₂ are alternately laminated in this order by the IAD method is provided on the other surface of the substrate. This four-layer film is an antireflection film.

Also, the long-pass filter 21b has a substrate and a high refractive index thin film and a low refractive index thin film alternately laminated on the substrate. In this example, on one surface of the substrate, a 36-layer film was formed by alternately laminating a high refractive index thin film of TiO ₂ and a low refractive index thin film of SiO ₂ in this order by the IAD method. . This 36-layer film is a long-pass functional film that transmits light having a wavelength longer than the cutoff wavelength. Furthermore, the 36-layer film has a variable function, and has a structure in which the film thickness changes continuously along a certain direction on the substrate, and the cutoff wavelength changes according to the incident position. A four-layer film in which TiO ₂ and SiO ₂ are alternately laminated in this order by the IAD method is provided on the other surface of the substrate. This four-layer film is an antireflection film.

The configurations of the short-pass filter 22 and the long-pass filter 23 can be the same as the short-pass filter 12 and the long-pass filter 13 of the first embodiment. Also in this embodiment, both the short-pass filter 12 and the long-pass filter 13 are designed so that the reference wavelength is included in the transmission band.

In this embodiment, B270i glass with a thickness of 0.4 mm is used as the substrate of the short-pass filter 21a, the long-pass filter 21b, the short-pass filter 22, and the long-pass filter 23. FIG. This substrate has spectral characteristics in which most of the incident light, excluding the reflected component on the back surface side of the substrate, is transmitted in the target wavelength range of 400 to 700 nm.

The optical filter module 20 of Example 2 configured as described above is controlled as follows. That is, by moving the short-pass filter 21a and the long-pass filter 21b with respect to the optical path, the light passing positions on the short-pass filter 21a and the long-pass filter 21b are controlled. In this way, the short-pass filter 21 a and the long-pass filter 21 b transmit the light of the wavelength according to the passage position, so that the light of the selected wavelength region passes through the band-pass filter unit 21 . Further, as in the first embodiment, by moving the short-pass filter 22 or the long-pass filter 23 to the filter insertion position 24 on the optical path according to the selected wavelength region, sufficient transmission is achieved in the transmission stopband outside the selected wavelength region. It has a blocking function.

The optical filter module 20 of Example 2 manufactured as described above has a variable-type bandpass function having a relatively long target wavelength range of 400 to 700 nm. Nevertheless, the optical filter module 20 can sufficiently suppress the transmittance near the shortest wavelength or the longest wavelength in the target wavelength region, as in the first embodiment. Thus, an optical filter module with excellent optical characteristics can be obtained.

(Modification of Examples 1 and 2)
In Examples 1 and 2, the short-pass filters 12 and 22 and the long-pass filters 13 and 23 may be variable type optical filters. For example, the short-pass filters 12, 22 can be provided with 36 layers of functional films such that the physical film thickness varies continuously along one direction of the filter. Further, the long-pass filters 13 and 23 can be provided with 38 layers of functional films such that the physical film thickness continuously changes along one direction of the filter. Furthermore, only one of the short-pass filters 12 and 22 and the long-pass filters 13 and 23 can be of variable type.

By having such variable type short-pass filters 12, 22 or long-pass filters 13, 23, it is possible to sufficiently suppress the transmittance in the transmission stopband even when the target wavelength region is relatively long. . Therefore, it becomes easy to realize a filter module having a target wavelength range wider than the target wavelength range of 400 to 700 nm in the first and second embodiments.

For example, if the target wavelength range is long, the wavelength range of light that should be blocked by the short-pass filter 12 is also long. have a nature. On the other hand, when the variable type short-pass filter 12 is used, the incident position of light (or the transmission blocking band) to the short-pass filter 12 is determined according to the incident position (or selected wavelength region) of light to the band-pass filter 11. can be changed. Therefore, it becomes easy to use the short-pass filter 12 to suppress transmission of light outside the selected wavelength region that has passed through the band-pass filter 11 .

Furthermore, in Embodiments 1 and 2, two or more short-pass filters having different optical characteristics can be used instead of the short-pass filters 12 and 22 . Also, instead of the long-pass filters 13 and 23, two or more long-pass filters with different optical characteristics can be used. Such a configuration also facilitates suppression of transmission of light outside the selected wavelength range that has passed through the bandpass filter 11, and facilitates realization of a filter module having a wide target wavelength range.

[Example 3]
A filter module according to an embodiment of the present invention comprises a variable type bandpass filter. This band-pass filter comprises a substrate, a variable-type band-pass functional film formed on one surface of the substrate, and a short-pass functional film and a long-pass functional film formed at specific positions on the other surface of the substrate. Prepare.

The optical filter 60 according to Example 3 shown in FIG. 3 has a bandpass function for the target wavelength range of 400 to 700 nm. The optical filter 60 has four functional films, a bandpass functional film 62 , a shortpass functional film 63 , a longpass functional film 64 , and an antireflection functional film 65 , in addition to the substrate 61 .

The bandpass function film 62 is a bandpass function film having a variable function, like the 30-layer film of the bandpass filter 11 according to the first embodiment. The transmission characteristics of the bandpass functional film 62 are substantially the same as in FIG.

The short-pass functional film 63 is a short-pass functional film similar to the 36-layer film of the short-pass filter 12 according to the first embodiment. The transmission characteristic of the short-pass functional film 63 is substantially the same as A in FIG.

The long-pass functional film 64 is a long-pass functional film similar to the 38-layer film of the long-pass filter 13 according to the first embodiment. The transmission characteristics of the long-pass functional film 64 are substantially the same as B in FIG.

The antireflection film 65 is a four-layer film in which TiO ₂ and SiO ₂ are alternately laminated in this order. This four-layer film can be designed to have an antireflection function at least in the wavelength range of 380-720 nm. According to such a design, even if the optical characteristics are slightly shifted due to film forming errors or the like, good transmission in the wavelength range of 400 to 700 nm, which is the target wavelength range of the optical filter 60, can be realized.

In this embodiment, D263 Teco glass with a thickness of 0.4 mm is used as the substrate 61 . This substrate has spectral characteristics in which most of the incident light, excluding the reflected component on the back surface side of the substrate, is transmitted in the target wavelength range of 400 to 700 nm.

By moving the optical filter 60 of the third embodiment configured as described above with respect to the optical path, the incident position of the light on the bandpass functional film 62 is controlled, and the light in the selected wavelength region corresponding to the position is emitted. It passes through the bandpass functional film 62 .

On the other hand, as shown in FIG. 7A, the bandpass functional film 62 has the shortest wavelength when the selected wavelength region is near the longest wavelength of the target wavelength region, that is, when the incident position of light is on the left side of FIG. Permeation in the vicinity cannot be sufficiently suppressed. Therefore, in this embodiment, a long-pass functional film 64 is arranged at a position on the band-pass functional film 62 corresponding to the longest wavelength in the target wavelength region so as to face it with the substrate 61 interposed therebetween. Similarly, as shown in FIG. 7B, the bandpass functional film 62 has the longest wavelength when the selected wavelength region is near the shortest wavelength of the target wavelength region, that is, when the incident position of light is on the right side of FIG. Transmission in the vicinity of the wavelength cannot be sufficiently suppressed. Therefore, in this embodiment, a short-pass function film 63 is arranged at a position on the band-pass function film 62 corresponding to the shortest wavelength in the target wavelength region so as to face it with the substrate 61 interposed therebetween.

Also, in FIG. 3, an antireflection film 65 is arranged in a region sandwiched between the short-pass function film 63 and the long-pass function film 64 . At a position facing the antireflection film 65 with the substrate 61 interposed therebetween (for example, a position corresponding to the reference wavelength), the bandpass film 62 sufficiently reduces transmission near the shortest wavelength and near the longest wavelength in the target wavelength region. ing. However, the provision of the antireflection film 65 is not essential. For example, the opposite side of the bandpass functional film 62 may be entirely covered by a shortpass functional film 63 and a longpass functional film 64 enlarged from FIG.

The optical filter 60, which is the optical filter module according to Example 3 manufactured as described above, has a variable-type bandpass function having a relatively long target wavelength range of 400 to 700 nm. Nevertheless, the optical filter 60 can sufficiently suppress the transmittance near the shortest wavelength or the longest wavelength in the target wavelength region, as in the first embodiment. Thus, an optical filter module with excellent optical characteristics can be obtained.

[Example 4]
FIG. 9 shows an example in which the filter module manufactured according to Examples 1 to 3 is applied to an imaging device such as a video camera, which is one of optical devices. FIG. 9 is a schematic diagram of the imaging device 53. As shown in FIG. The imaging device 53 includes an optical filter module 50 , an imaging optical system 51 and a solid-state imaging device 52 . A light beam transmitted through an imaging optical system 51 including apertures such as aperture blades, lenses, etc. is adjusted by an optical filter module 50 to have desired optical characteristics before entering a solid-state imaging device 52 . A proper image is thus obtained. However, it is possible to incorporate the filter module manufactured according to Examples 1 to 3 into other optical devices as well as imaging devices.

As the optical filter module 50, the optical filter module 10 according to the first embodiment, the optical filter module 20 according to the second embodiment, and the optical filter 60 according to the third embodiment can be used. The method of controlling the optical filter module 50 (eg, the method of controlling the bandpass filter 11, the shortpass filter 12, and the longpass filter 13) to transmit light in selected wavelength regions has already been described.

In addition, the optical filter module 50 can also be provided with other optical filters, such as AR filters, ND filters, IR cut filters, IR pass filters, UV cut filters, UV pass filters, long pass filters, and short pass filters. .

The band-pass filter 11 of the optical filter module 10, the band-pass filter unit 21 of the optical filter module 20, and the variable pull type filters such as the optical filter 60 may change their optical characteristics. For example, optical properties can change over time or in response to environmental changes such as temperature or humidity. In particular, in the transition wavelength region from the transmission band to the transmission stopband, the transmission characteristics with respect to wavelength and the transmission characteristics with respect to position are likely to vary greatly. Therefore, in one embodiment, the relationship between the filter position and the optical characteristics is confirmed at a predetermined timing such as when the imaging device 53 is powered on, and the movement target position of the filter is corrected as necessary. Such a function is called an initialize function.

In one embodiment, the imaging device 53 moves the first optical filter member (the bandpass filter 11, the bandpass filter unit 21, and the optical filter 60) to a movement target position by a driving unit that moves the first optical filter member. You may have a correction|amendment part which correct|amends. This corrector (not shown) corrects the movement target position of the first optical filter member based on the spectral transmission characteristics of the light that has passed through the optical filter module 50 .

Specifically, the correction unit can perform initialization measurement as follows. For example, when using the optical filter module 10, the bandpass filter 11 is fixed so that the light is incident on a predetermined standard position. Then, considering the designed transmission band at the standard position, the transmitted light intensity at the center wavelength of the transmission band, which is less affected by the environment or aging, and the transmission stopband, which is far from the center wavelength and sufficiently blocks transmission and the transmitted light intensity at a wavelength of . Further, scanning determines the half-height wavelength at which the transmitted light intensity is intermediate between the transmitted light intensity in the transmission band and the transmitted light intensity in the stopband. Here, since the transmitted light intensity is affected by the sensitivity characteristics of the imaging element, the half-value wavelength may be determined in consideration of these factors. Scanning does not need to be performed in the entire target wavelength range of the band-pass filter, and it is expected that the design initial transmission band will not deviate from the transmission stopband even if it is affected by the ambient environment or changes over time. It suffices to target up to the wavelength. The band-pass filters as shown in Examples 1 to 3 have two half-value wavelengths on the short wavelength side and the long wavelength side, which can be distinguished from each other by the size of the wavelengths.

With the above processing, the transmission band (eg, represented by two half-maximum wavelengths) at the standard position can be identified. Further, such initializing measurement may be performed at a plurality of locations in addition to one location (standard location) on the bandpass filter 11 . On the other hand, the transmission band at another position may be estimated based on the determination result at the standard position. Based on the transmission band thus determined, it is possible to correct the movement position of the bandpass filter 11 for transmitting the light in the desired selected wavelength region. Similarly, the band-pass filter unit 21 (short-pass filter 21a and long-pass filter 21b) and optical filter 60 can be subjected to similar initialization measurement and movement position correction. Such an initialization function can be used not only for changes in optical characteristics but also for correcting errors in optical characteristics caused by manufacturing errors, thereby improving the optical performance of the optical device.

Such an initializing function may be performed by a correcting section of an optical device such as the imaging device 53, or may be performed by an initializing device separate from the optical device.

11 bandpass filter;12,22 shortpass filter;13,23 longpass filter;21 bandpass filter unit;62 bandpass functional film;63 shortpass functional film;64 longpass functional film

Claims (6)

formed on a substrate and one surface of the substrate, having a film thickness and a transmission wavelength region varying along a predetermined direction, transmitting light in a selected wavelength region corresponding to an incident position, and transmitting a selected wavelength corresponding to the incident position; A first functional film that suppresses transmission of light with a wavelength longer than the region , and a film thickness and a transmission wavelength region change along a predetermined direction, and transmit light with a wavelength shorter than the selected wavelength region corresponding to the incident position. an optical filter member comprising a second functional film that suppresses
a third functional film that blocks transmission of light with a wavelength longer than the selected wavelength region corresponding to the incident position;
a fourth functional film that blocks transmission of light with a wavelength shorter than the selected wavelength region corresponding to the incident position;
The third functional film is arranged on the optical path of light passing through the first incident position of the optical filter member ,
The fourth functional film is arranged on the optical path of light passing through the second incident position of the optical filter member ,
The optical filter module, wherein the selected wavelength region corresponding to the first incident position is on the shorter wavelength side than the selected wavelength region corresponding to the second incident position. a substrate and a first functional film formed on one surface of the substrate and having a film thickness and a transmission wavelength region that vary depending on the position in the surface, and transmitting light in a selected wavelength region corresponding to an incident position; a first optical filter member that suppresses transmission of light in at least a part of a wavelength region different from the selected wavelength region;
a second optical filter member that blocks transmission of light in at least a part of the wavelength region with respect to a selected wavelength region corresponding to at least one incident position of the first optical filter member;
The first optical filter member is
the first functional film whose film thickness and transmission wavelength range change along a predetermined direction and suppresses transmission of light having a wavelength longer than the selected wavelength range corresponding to the incident position;
a second functional film whose film thickness and transmission wavelength region vary along a predetermined direction and suppresses transmission of light with a wavelength shorter than the selected wavelength region corresponding to the incident position;
The second optical filter member is
a third functional film that blocks transmission of light having a wavelength longer than a selected wavelength region corresponding to the incident position on the first optical filter member;
a fourth functional film that blocks transmission of light with a wavelength shorter than the selected wavelength region corresponding to the incident position on the first optical filter member;
The third functional film is arranged on an optical path of light passing through the first incident position of the first optical filter member,
The fourth functional film is arranged on the optical path of light passing through the second incident position of the first optical filter member,
The optical filter module, wherein the selected wavelength region corresponding to the first incident position is on the shorter wavelength side than the selected wavelength region corresponding to the second incident position. moving the first optical filter member so as to control the incident position of light;
When the light passes through the first incident position of the first optical filter member, the third functional film is positioned on the optical path, and the light passes through the second incident position of the first optical filter member. moving the second optical filter member so that the fourth functional film is positioned on the optical path when passing through the position;
3. The optical filter module of claim 2, further comprising a driver configured to: At least one of the third functional film and the fourth functional film is a functional film whose thickness and transmission wavelength range change along a predetermined direction. 1. The optical filter module according to claim 1. An optical device comprising the optical filter module according to any one of claims 1 to 4. a substrate and a first functional film formed on one surface of the substrate and having a film thickness and a transmission wavelength region that vary depending on the position in the surface, and transmitting light in a selected wavelength region corresponding to an incident position; a first optical filter member that suppresses transmission of light in at least a part of a wavelength region different from the selected wavelength region; and a selected wavelength region corresponding to at least one incident position of the first optical filter member. an optical filter module comprising: a second optical filter member that blocks transmission of light in at least part of the wavelength range;
a correction unit that corrects a movement target position of the first optical filter member by a driving unit that moves the first optical filter member based on spectral transmission characteristics of light that has passed through the optical filter module. An optical device characterized by:

Images