JP2010206626A - Optical filter, and imaging system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical filter and imaging device capable of performing photographing not only at daytime during which natural light is made incident, but also under night vision such as at nighttime. <P>SOLUTION: In the imaging device 1, at least a lens 12, an optical filter 13 and an imaging element 14 are disposed in order from an external subject side along an optical axis 11, and the optical filter 13 is constituted of a crystal plate 2 and dual anti-reflection coating 3 formed on one principal surface 21 of the crystal plate 2 for preventing light beam reflection in a visible area and in an infrared area. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical filter and an imaging system that prevent reflection of light in a preset wavelength band.

  In an optical system of an electronic camera typified by a general video camera or a digital still camera, a coupling optical system, an infrared cut filter, an optical low-pass filter, a CCD (Charge Coupled Device), and a MOS from the subject side along the optical axis. Image sensors such as (Metal Oxide Semiconductor) are sequentially arranged (see, for example, Patent Document 1). Note that the imaging element referred to here has a sensitivity characteristic that responds to light having a wider wavelength band than light having a wavelength band (visible light) visible to the human eye. Therefore, in addition to visible light, it also responds to light in the infrared region and ultraviolet region.

  The human eye responds to light having a wavelength in the range of about 400 to 620 nm in a dark place and responds to light having a wavelength in the range of about 420 to 700 nm in a bright place. In contrast, for example, a CCD responds with high sensitivity to light having a wavelength in the range of 400 to 700 nm, and further responds to light having a wavelength of less than 400 nm and light having a wavelength of more than 700 nm.

  For this reason, in the imaging device described in Patent Document 1 below, an infrared cut filter is provided in addition to the CCD that is the imaging element so that infrared rays do not reach the imaging element, and the captured image is close to the human eye. Is to be obtained.

  In addition, in the conventional optical filter, an antireflection film (AR coating) that reduces the reflection of light in the visible range is provided on the main surface of the optical filter in order to improve the transmittance in the visible range that can be seen by human eyes. Applying is a general filter configuration.

JP 2000-209510 A

  By the way, in addition to general video cameras and digital still cameras, there are imaging devices used for other purposes different from normal shooting such as surveillance cameras.

  For example, in a surveillance camera, it is necessary to perform surveillance photography not only in the daytime but also in night vision. Shooting under night vision, such as at night, is performed in a state where it cannot be seen by the human eye, so a camera with a normal visible range for shooting cannot perform shooting under night vision. For this reason, currently, shooting under night vision such as night is performed using infrared rays. However, in the imaging device described in Patent Document 1, an infrared cut filter that cuts infrared rays is used. Since it is provided, it cannot be used for night vision photography. Further, in the conventional optical filter, only the antireflection film for reducing the reflection of light in the visible region is provided on the main surface, and there is no one that simultaneously reduces the reflection of light in the infrared region.

  Therefore, in order to solve the above-described problems, an object of the present invention is to provide an optical filter and an imaging device capable of photographing not only in daytime when natural light enters but also under night vision such as at night.

  In order to achieve the above object, an optical filter provided in an imaging device according to the present invention includes a transparent substrate and a dual antireflection coating that is formed on one main surface of the transparent substrate and prevents reflection of light in two wavelength bands. The two wavelength bands are a visible region and an infrared region.

  According to the optical filter of the present invention, since the dual antireflection coating that is formed on one main surface of the transparent substrate and prevents reflection of light in the visible region and the infrared region is provided, the visible region The reflectance in the desired band in the infrared region can be suppressed to substantially zero, and as a result, not only in daytime when natural light enters but also in night vision such as at night Shooting can be performed.

  In the above configuration, the dual antireflection coating may also be formed on the other main surface of the transparent substrate.

  In this case, since the dual antireflection coating is also formed on the other main surface of the transparent substrate, the visible light is compared with the case where the dual antireflection coating is formed only on one main surface of the transparent substrate. It is more preferable to suppress the reflectance in the desired band in the infrared region and the infrared region, and it is also possible to improve the transmittance in the desired band in the visible region and the infrared region. In addition, in an unnecessary band that suppresses the reflectance, the reflectance can be increased to function as a cut coat.

  Specifically, according to this configuration, when the dual antireflection coating is formed on both main surfaces of the transparent substrate, when the light enters the optical filter, one dual antireflection coating (for example, the substrate) is formed. The light passing through the dual antireflection coating formed on one main surface and passing through the one dual antireflection coating is formed on the other dual antireflection coating (for example, the other main surface of the substrate). Since the light passes through the optical filter through the dual antireflection coating, the other antireflection coating suppresses the reflectance in the desired band in the visible region and the infrared region by using the dual antireflection coating. The dual anti-reflection coating of the present invention suppresses the reflectance in the desired band of the visible region and the infrared region. It will have a multiplication effect. Further, the transmittance in the desired band in the visible region and the infrared region has a synergistic effect for the same reason as the reflectance.

  In the above configuration, the dual antireflection coating may be formed by alternately laminating a plurality of first thin films made of a high refractive index material and second thin films made of a low refractive index material.

  In the above configuration, the dual antireflection coating includes an antireflection coating for preventing light reflection in two wavelength bands and a cut coat for suppressing transmission of light in a wavelength band between the two wavelength bands. Also good.

  In the above configuration, the first thin film of the antireflection coating has a center wavelength of 450 nm or more and 550 nm or less, an optical film thickness of 2.000 or more and less than 3.000, and the reflection The second thin film of the prevention coat has a center wavelength of 450 nm or more and 550 nm or less, an optical film thickness of 0.100 or more and less than 1.000, and the cut coat has a low refractive index. It may be made of a material, the center wavelength may be 450 nm or more and 550 nm or less, and the optical film thickness may be 1.000 or more and less than 2.000.

  In this case, the reflectance in the visible region can be suppressed to substantially zero, and the reflectance in the desired band in the infrared region can be suppressed to substantially zero. Specifically, the first thin film of the antireflection coating has a center wavelength of 450 nm or more and 550 nm or less, an optical film thickness of 2.000 or more and less than 3.000, and the reflection The second thin film of the prevention coat has a center wavelength of 450 nm or more and 550 nm or less, an optical film thickness of 0.100 or more and less than 1.000, and the cut coat has a low refractive index. It is made of a material, its central wavelength is 450 nm or more and 550 nm or less, and its optical film thickness is 1.000 or more and less than 2.000. The lower limit wavelength is about 450 nm, the upper limit wavelength is about 650 nm, and the lower limit wavelength in the infrared region where the reflectance can be suppressed to substantially zero is about 800 nm, and the upper limit wavelength is about 1000 nm. It is possible to become.

In the above configuration, TiO ₂ or Nb ₂ O ₅ is used for the high refractive index material, SiO ₂ is used for the low refractive index material, and the first thin film of the antireflection coating has its physical properties. The film thickness is 97 nm or more and 180 nm or less, the second thin film of the antireflection coating has a physical film thickness of 7 nm or more and 95 nm or less, and the cut coat has a physical film thickness of 77 nm. It is above and may be 189 nm or less.

In this case, the reflectance in the visible region can be suppressed to substantially zero, and the reflectance in the desired band in the infrared region can be suppressed to substantially zero. Specifically, TiO ₂ or Nb ₂ O ₅ is used for the high refractive index material, SiO ₂ is used for the low refractive index material, and the first thin film of the antireflection coating has a physical structure. The film thickness is 97 nm or more and 180 nm or less, the second thin film of the antireflection coating has a physical film thickness of 7 nm or more and 95 nm or less, and the cut coat has a physical film thickness of 77 nm. Since it is above and is 189 nm or less, the lower limit wavelength of the visible region where the reflectance can be suppressed to substantially zero is about 450 nm, the upper limit wavelength is about 650 nm, and the infrared region where the reflectance can be suppressed to substantially zero The lower limit wavelength can be about 800 nm and the upper limit wavelength can be about 1000 nm.

  In the above configuration, the dual antireflection coating may include an adjustment coating at a position where the refractive index changes.

  In this case, since the adjustment coating is included in the dual antireflection coating, it is possible to suppress the generation of ripples, and in particular, it is possible to suppress the generation of ripples in the wavelength region where antireflection is desired. It is also possible to suppress the amount of change in the reflectance that is displaced in the distance.

  In order to achieve the above object, an imaging device according to the present invention includes, in order, at least a coupling optical system in which light is incident from the outside along the optical axis, an optical filter according to the present invention, and an imaging element. It is arranged.

  According to the imaging device of the present invention, it is possible to perform photographing in any environment such as daytime or nighttime night vision without being affected by the amount of light with a simple configuration. Further, according to the imaging device according to the present invention, at least the coupling optical system, the optical filter according to the present invention, and the imaging element are sequentially arranged from the external subject side along the optical axis. The reflectance in the visible range can be suppressed to substantially zero, and the reflectance in the desired band in the infrared region can be suppressed to substantially zero. As a result, it is possible not only in daytime when natural light enters but also in night vision such as nighttime. Even shooting is possible.

  In order to achieve the above object, an imaging device according to the present invention includes at least a coupling optical system that makes light incident from the outside along the optical axis from the outside subject side, a filter group that can switch and arrange a plurality of filters, An optical filter and an image sensor according to the present invention are arranged in order, and the filter group includes an infrared cut filter for the purpose of cutting infrared rays and a transparent filter that is not intended for the use of infrared cuts. It is selectively arranged on the optical axis.

  According to the imaging device of the present invention, it is possible to suitably perform the daytime shooting for the purpose of cutting infrared rays and the nighttime shooting for the purpose of cutting infrared rays without changing the optical path length. It becomes. Further, according to the imaging device according to the present invention, at least the coupling optical system, the filter group, the optical filter according to the present invention, and the imaging element are sequentially arranged from the outside subject side along the optical axis. In the filter group, since either one of the infrared cut filter and the transparent filter is selectively disposed on the optical axis, the reflectance in the visible region is suppressed to substantially zero, and the infrared region It is possible to suppress the reflectance in the desired band to substantially zero, and as a result, it is possible to shoot not only in the daytime when natural light enters but also under night vision such as at night. Note that the conventional antireflection coating for video is designed only in the visible range, and when shooting in the infrared range, an antireflection coating in a wider band is required. On the other hand, according to the present invention, since the dual antireflection coating for preventing reflection of light rays in the visible region and the infrared region is formed on the optical filter according to the present invention, the film of the antireflection coating An inexpensive and high-performance imaging device can be obtained without increasing the number of layers.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the optical filter and imaging device which can image | photograph not only in the daytime when natural light enters but under night visions, such as nighttime.

FIG. 1 is a schematic configuration diagram of an imaging device according to the present embodiment. FIG. 2 is a schematic diagram showing the configuration of the optical filter according to the present embodiment. FIG. 3 is a schematic configuration diagram showing the configuration of the optical filter according to the present embodiment. FIG. 4 is a graph showing the reflectance characteristics of the optical filter according to the present embodiment. FIG. 5 is a graph illustrating the reflectance characteristics of the optical filter according to the first embodiment. FIG. 6 is a graph illustrating the reflectance characteristics of the optical filter according to the second embodiment. FIG. 7 is a graph showing transmittance characteristics of an optical filter having a dual-pass filter according to the first embodiment provided on one side and an optical filter having a dual-pass filter according to another example of the first embodiment provided on both sides. FIG. FIG. 8 is a graph showing transmittance characteristics of an optical filter having a dual-pass filter according to the second embodiment provided on one side and an optical filter having a dual-pass filter according to another example of the second embodiment provided on both sides. FIG. FIG. 9 is a schematic configuration diagram of an imaging device according to another embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  As shown in FIG. 1, the imaging device 1 according to the present embodiment includes a lens 12 and an optical filter 13 that are coupled optical systems that allow light to enter at least from the outside along the optical axis 11 from the external subject side. In addition, an image sensor 14 such as a CCD or a CMOS is disposed in order.

  As shown in FIG. 2, the optical filter 13 includes a quartz plate 2 that is a transparent substrate and a dual anti-reflection coating 3 that is formed on one main surface 21 of the quartz plate 2 and prevents reflection of light rays in two wavelength bands. It consists of. Note that the two wavelength bands in the present embodiment refer to a visible region and an infrared region.

The dual antireflection coating 3 is formed by alternately laminating a plurality of first thin films 31 made of a high refractive index material and second thin films 32 made of a low refractive index material. Therefore, the odd-numbered layers counted from the one main surface 21 side of the quartz plate 2 are constituted by the first thin films 31, and the even-numbered layers are constituted by the second thin films 32. In this embodiment, TiO ₂ is used for the first thin film and SiO ₂ is used for the second thin film.

As a method of manufacturing the dual antireflection coating 3, TiO ₂ and SiO ₂ are alternately vacuum deposited on a main surface 21 of the quartz plate 2 by a known vacuum deposition apparatus (not shown), as shown in FIG. Such a dual antireflection coating 3 is formed. The film thickness adjustment of the first thin film 31 and the second thin film 32 is performed by performing a vapor deposition operation while monitoring the film thickness, and when a predetermined film thickness is reached, a shutter (not shown) provided near the vapor deposition source (not shown). (Omitted) is closed to stop the vapor deposition of the vapor deposition material (TiO ₂ , SiO ₂ ).

  As shown in FIG. 2, the dual antireflection coating 3 includes a plurality of layers defined by ordinal numbers in order from the one principal surface 21 side of the quartz plate 2, in this embodiment, one layer, two layers, three layers,... It is composed of layers. Each of these 1 layer, 2 layers, 3 layers,..., 16 layers is formed by laminating a first thin film 31 and a second thin film 32. When the optical film thickness of the laminated first thin film 31 and second thin film 32 is different, the thickness of each of the first layer, the second layer, the third layer,. In addition, the optical film thickness here is calculated | required by Numerical formula 1 mentioned below.

[Formula 1]
Nd = d × N × 4 / λ (Nd: optical film thickness, d: physical film thickness, N: refractive index, λ: center wavelength)
The dual antireflection coating 3 described above has an antireflection coating 33 that prevents reflection of light in two wavelength bands, a cut coat 34 that suppresses transmission of light in the wavelength band between the two wavelength bands, and a refractive index. An adjustment coat 35 is included at the changing position.

  Specifically, the first thin film 31 and the second thin film 32 of the antireflection coating 33 are designed as follows.

The first thin film 31 is made of TiO ₂ or Nb ₂ O ₅ which is a high refractive index material. The central wavelength of the first thin film 31 is 450 nm or more and 550 nm or less, and the optical film thickness is 2.000. It is above and is less than 3.000. The physical film thickness of the first thin film 31 is 97 nm or more and 180 nm or less.

The second thin film 32 is made of SiO ₂ which is a low refractive index material. The central wavelength of the second thin film 32 is 450 nm or more and 550 nm or less, and the optical film thickness is 0.100 or more and 1 Less than .000. The physical film thickness of the second thin film 32 is 7 nm or more and 95 nm or less.

  The cut coat 34 is a second thin film 32 that is located around the intermediate layer of the dual antireflection coating 3 and made of a low refractive index material. The center wavelength of this cut coat 34 is 450 nm or more and 550 nm or less, and its optical film thickness is 1.000 or more and less than 2.000. The physical thickness of the cut coat 34 is 77 nm or more and 189 nm or less.

  The adjustment coat 35 is positioned around the lowermost layer of the dual antireflection coating 3 and around the uppermost layer.

  With the configuration described above, the optical filter 13 according to the present embodiment can obtain reflectance characteristics as shown in FIG.

  The wavelength characteristics of the optical filter 13 according to this embodiment are actually measured, and the measurement results and configuration are shown in FIG.

In Example 1, a quartz plate 2 having a refractive index of 1.54 in the atmosphere is used as the transparent substrate. Further, as the first thin film 31, TiO ₂ having a refractive index in the atmosphere of 2.3000 is used, and as the second thin film 32, SiO ₂ having a refractive index in the atmosphere of 1.46000 is used. Is 500.00 nm.

  The dual antireflection coating 3 is composed of 16 layers, and the dual antireflection coating 3 is formed by forming the first thin film 31 and the second thin film 32 by the manufacturing method of the dual antireflection coating 3 described above. As shown in FIG. In Example 1, the incident angle of the light beam is 0 degree, that is, the light beam is vertically incident.

  Table 1 shows the composition of the dual antireflection coating 3 of the optical filter 13 and the optical film thickness of each thin film (the first thin film 31 and the second thin film 32).

  Further, in Example 1, as shown in Table 1, the dual antireflection coating 3 has 16 layers of first thin films 31 made of a high refractive index material and second thin films 32 made of a low refractive index material alternately. It is laminated. Of the 16 layers of the dual antireflection coating 3, one and two layers are configured as the adjustment coating 35, three to nine layers are configured as the antireflection coating 33, and ten layers are configured as the cut coating 34. Layers 15 to 15 are configured as an antireflection coating 33, and 16 layers are configured as an adjustment coating 35.

  As shown in FIG. 5, in the optical filter 13 according to the first embodiment, reflection of light having a wavelength from the visible range of about 400 nm to about 650 nm is suppressed (reflectance is approximately 0%), and the infrared region (particularly, The reflection of light having a wavelength from about 900 nm to about 1000 nm, which is the near-infrared region), is suppressed (reflectance of about 0%).

  Further, in the above-described embodiment and Example 1, the 16-layer dual antireflection coating 3 is described, but the number of layers of the dual antireflection coating 3 is not limited to this, and any As an example other than the 16-layer dual antireflection coating 3, an embodiment in which a 24-layer dual antireflection coating 3 is provided on the quartz plate 2 is shown below as Example 2.

In the second embodiment, a crystal plate 2 having a refractive index of 1.54 in the atmosphere is used as the transparent substrate. Further, as the first thin film 31, TiO ₂ having a refractive index in the atmosphere of 2.3000 is used, and as the second thin film 32, SiO ₂ having a refractive index in the atmosphere of 1.46000 is used. Is 500.00 nm.

  Further, the dual antireflection coating 3 is composed of 24 layers, and the first thin film 31 and the second thin film 32 are formed by the manufacturing method of the dual antireflection coating 3, and the antireflection characteristics as shown in FIG. 6 are obtained. It is done. In the second embodiment, the incident angle of the light beam is 0 degree, that is, the light beam is vertically incident.

  Table 2 shows the composition of the dual antireflection coating 3 of the optical filter 13 and the optical film thickness of each thin film (the first thin film 31 and the second thin film 32).

  Further, in Example 2, as shown in Table 2, the dual antireflection coating 3 includes 24 layers of first thin films 31 made of a high refractive index material and second thin films 32 made of a low refractive index material alternately. It is laminated. Of the 24 layers of the dual antireflection coating 3, one and two layers are configured as the adjustment coating 35, three to nine layers are configured as the antireflection coating 33, and ten layers are configured as the cut coating 34. Layers 23 to 23 are configured as an antireflection coating 33, and 24 layers are configured as an adjustment coating 35.

  As shown in FIG. 6, in the optical filter 13 according to the second embodiment, reflection of light having a wavelength from the visible range of about 450 nm to about 650 nm is suppressed (reflectance is approximately 0%), and the infrared region (particularly, The reflection of light rays having a wavelength from about 850 nm to about 1000 nm, which is the near infrared region), is suppressed (reflectance of about 0%).

  According to the optical filter 13 shown in the present embodiment and Examples 1 and 2 described above, it is formed on one main surface 21 of the quartz plate 2 and prevents reflection of light rays in two wavelength bands of the visible region and the infrared region. Since the dual anti-reflection coating 3 is provided, the reflectance in the visible region can be suppressed to substantially zero, and the reflectance in the desired band in the infrared region can be suppressed to approximately zero. As a result, daylight when natural light enters You can take pictures not only at night but also under night vision.

  The first thin film 31 of the antireflection coating 33 has a center wavelength of 450 nm or more and 550 nm or less, an optical film thickness of 2.000 or more and less than 3.000, and the antireflection coating 33. The second thin film 32 has a center wavelength of 450 nm or more and 550 nm or less, an optical film thickness of 0.100 or more and less than 1.000, and the cut coat 34 is made of a low refractive index material. Since the center wavelength is 450 nm or more and 550 nm or less and the optical film thickness is 1.000 or more and less than 2.000, the lower limit of the visible range where the reflectance can be suppressed to substantially zero. The wavelength is set to about 450 nm, the upper limit wavelength is set to about 650 nm, the lower limit wavelength in the infrared region capable of suppressing the reflectance to substantially zero is set to about 800 nm, and the upper limit wavelength is set to about 1000 nm. It is possible. Thus, according to this configuration, the reflectance in the visible region can be suppressed to substantially zero, and the reflectance in the desired band in the infrared region can be suppressed to approximately zero.

In addition, the high refractive index material, TiO ₂ is used, the low refractive index material, SiO ₂ is used, the first thin film 31 of the antireflection coating 33, the physical film thickness is not more than 97 nm 180 nm The second thin film 32 of the antireflection coating 33 has a physical film thickness of 7 nm or more and 95 nm or less, and the cut coat 34 has a physical film thickness of 77 nm or more and 189 nm or less. The lower limit wavelength in the visible range where the reflectance can be suppressed to substantially zero is about 450 nm, the upper limit wavelength is about 650 nm, and the lower limit wavelength in the infrared range where the reflectance can be suppressed to substantially zero is about 800 nm, the upper limit wavelength. Can be about 1000 nm. Thus, according to this configuration, the reflectance in the visible region can be suppressed to substantially zero, and the reflectance in the desired band in the infrared region can be suppressed to approximately zero.

  In addition, since the dual anti-reflection coating 3 includes the adjustment coating 35 at a position where the refractive index changes, it is possible to suppress the generation of ripples, and particularly suppress the generation of ripples in the wavelength region where it is desired to prevent reflection. Therefore, it is possible to suppress the amount of change in reflectance that is abruptly displaced.

  In addition, as described above, according to the imaging device 1 according to the present embodiment, shooting is performed in any environment such as daytime or nighttime night vision without being affected by the amount of light with a simple configuration. be able to. That is, it can be suitably performed without changing the optical path length in daytime shooting for the purpose of cutting infrared rays and night-time shooting for purposes such as nighttime without the purpose of cutting infrared rays.

  In addition, according to the imaging device 1 according to the present embodiment, at least the lens 12, the optical filter 13, and the imaging element 14 are arranged in this order from the external subject side along the optical axis 11, so that in the visible region The reflectance can be suppressed to substantially zero, and the reflectance in the desired band in the infrared region can be suppressed to substantially zero. As a result, it is possible to shoot not only in the daytime when natural light enters but also under night vision such as at night. . Note that the conventional antireflection coating for video is designed only in the visible range, and when shooting in the infrared range, an antireflection coating in a wider band is required. On the other hand, according to the present invention, since the dual antireflection coating for preventing reflection of light rays in the visible region and the infrared region is formed on the optical filter according to the present invention, the film of the antireflection coating An inexpensive and high-performance imaging device can be obtained without increasing the number of layers.

  In the present embodiment, the crystal plate 2 is used as the transparent substrate. However, the present invention is not limited to this, and a glass plate may be used as long as the substrate can transmit light. Further, the quartz plate 2 is not limited, and may be a single plate quartz plate, for example, a birefringent plate or a birefringent plate composed of a plurality of plates. Moreover, you may comprise a transparent substrate combining a quartz plate and a glass plate.

In the present embodiment, TiO ₂ is used for the first thin film 31. However, the present invention is not limited to this, and the first thin film 31 may be made of a high refractive index material. For example, ZrO ₂ Ta ₂ O ₂ , Nb ₂ O _5, or the like may be used. Since Nb ₂ O ₅ has substantially the same refractive index as TiO ₂ , when Nb ₂ O ₅ is used for the first thin film 31, the same effects as those of the first and second embodiments are obtained. Moreover, although SiO ₂ is used for the second thin film 32, the present invention is not limited to this, and the second thin film 32 only needs to be made of a low refractive index material. For example, MgF ₂ or the like may be used. .

  In the present embodiment, the dual antireflection coating 3 is formed on the quartz plate 2 by the vacuum deposition method. However, the present invention is not limited to this, and the dual antireflection coating 3 is formed by ion-assisted deposition or sputtering. You may form in the quartz plate 2 by other methods, such as a method.

  Further, in the present embodiment, the dual antireflection coating 3 is provided on one main surface 21 (one surface) of the crystal plate 2, but the present invention is not limited to this, and both main surfaces (one surface) of the crystal plate 2 are provided. The dual antireflection coating 3 may be provided on the main surface 21 and the other main surface 22). In this case, it is possible to prevent reflection of light rays in the two wavelength bands of the visible region and the infrared region, to suppress the reflectance in the visible region to substantially zero, and to suppress the reflectance in the desired band in the infrared region to approximately zero. Moreover, as shown in FIGS. 7 and 8, the transmittance in the desired band in the visible region and the infrared region can be improved.

  7 shows the optical filter 13 in which the dual antireflection coating 3 according to the first embodiment is provided on one main surface 21 of the crystal plate 2 and the dual antireflection coat 3 on both main surfaces (one main surface of the crystal plate 2). 21 is a diagram showing transmittance characteristics with the optical filter 13 provided on the other main surface 22). FIG. 8 shows an optical filter 13 in which the dual antireflection coating 3 according to the second embodiment is provided on one main surface 21 of the crystal plate 2 and the dual antireflection coat 3 on both main surfaces (one main surface of the crystal plate 2). 21 is a diagram showing transmittance characteristics with the optical filter 13 provided on the other main surface 22).

  As shown in FIGS. 7 and 8, when the dual antireflection coating 3 is provided on both main surfaces (one main surface 21 and the other main surface 22) of the crystal plate 2, the dual antireflection coating 3 is also dual on the other main surface 22 of the crystal plate 2. Since the antireflection coating 3 is formed, the reflectance in the desired band in the visible region and the infrared region is suppressed as compared with the case where the dual antireflection coating 3 is formed only on the one main surface 21 of the quartz plate 2. Further, it is possible to improve the transmittance in a desired band in the visible region and the infrared region. In addition, in an unnecessary band for suppressing the reflectance, the reflectance can be increased to function as a cut coat.

  Specifically, according to this configuration, when the dual antireflection coating 3 is formed on both main surfaces (one main surface 21 and the other main surface 22) of the crystal plate 2, when light enters the optical filter 13 The light passing through one dual antireflection coating 3 (for example, the dual antireflection coating 3 formed on the main surface 21 of the crystal plate 2) is passed through the one dual antireflection coating 3, and the other dual reflection. Since the anti-reflection coating 3 (for example, the dual anti-reflection coating 3 formed on the other main surface 22 of the crystal plate 2) is passed, the single dual anti-reflection coating 3 suppresses the reflectance in the desired band in the visible region and the infrared region. With respect to light, the other dual antireflection coating 3 suppresses the reflectance in a desired band in the visible region and the infrared region, and as a result, has a synergistic effect of suppressing the reflectance. It becomes door. Furthermore, the transmittance in the desired band in the visible region and the infrared region also has a synergistic effect for the same reason as the reflectance.

  Further, in the imaging device 1 according to the present embodiment, as shown in FIG. 1, at least a lens 12, an optical filter 13, and an imaging element 14 are arranged in this order from the outside subject side along the optical axis 11. However, the present invention is not limited to this, and the form shown in FIG.

  In the form shown in FIG. 9, a filter group 15 that can switch and arrange a lens 12 that is a coupling optical system that receives light from the outside at least along the optical axis 11 and a plurality of filters (see below). , An optical filter 13 that is an OLPF, and an image sensor 14 are arranged in this order.

  The filter group 15 includes an infrared cut filter 16 for the purpose of cutting infrared rays and a dummy glass 17 that is a transparent filter that does not aim at the infrared cut. Either one of the infrared cut filter 16 and the dummy glass 17 is selectively switched on the optical axis 11 by known switching means (not shown). Specifically, the infrared cut filter 16 is disposed on the optical axis 11 when natural light enters during the daytime, and the dummy glass 17 is disposed on the optical axis 11 under night vision such as at night. In addition, the infrared cut filter 16 here does not ask | require the form, if it cuts IR, such as IR cut coat and IR absorption glass.

  In addition, since the filter group 15 includes the infrared cut filter 16, the optical filter 13 that is an OLPF is not formed with an infrared cut filter, and does not emit light in two wavelength bands (visible region and infrared region). Only the dual antireflection coating 3 for preventing reflection is formed.

  As described above, according to the imaging device 1 shown in FIG. 9, it is possible to suitably perform shooting in the daytime for the purpose of cutting infrared rays and shooting under night vision such as at night without the purpose of cutting infrared rays. Further, according to the imaging device 1, at least the lens 12, the filter group 15, the optical filter 13, and the imaging element 14 are sequentially arranged from the external subject side along the optical axis 11. Since either one of the cut filter 16 and the dummy glass 17 is selectively disposed on the optical axis 11, the reflectance in the visible region is suppressed to substantially zero, and the reflectance in the desired band in the infrared region is substantially zero. Can be suppressed. As a result, according to the imaging device 1 shown in FIG. 9, it is possible to take a picture not only in the daytime when natural light enters but also in night vision such as at night.

  It should be noted that the present invention can be implemented in various other forms without departing from the spirit, gist, or main features. For this reason, the above-described embodiment is merely an example in all respects and should not be interpreted in a limited manner. The scope of the present invention is indicated by the claims, and is not restricted by the text of the specification. Further, all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.

  The present invention is suitable for an imaging device such as a camera that is used day and night, such as a surveillance camera or an in-vehicle camera.

DESCRIPTION OF SYMBOLS 1 Image pick-up device 11 Optical axis 12 Lens 13 Optical filter 14 Image pick-up element 15 Filter group 16 Infrared cut filter 17 Dummy glass 2 Crystal plate 21 One main surface 22 of a crystal plate Other main surface 3 of a crystal plate Dual antireflection coating 31 1st thin film 32 Second thin film 33 Antireflection coating 34 Cut coating 35 Adjustment coating

Claims (9)

In the optical filter provided in the imaging device,
A transparent substrate;
It is formed on one main surface of the transparent substrate, and consists of a dual antireflection coating that prevents reflection of light in two wavelength bands,
The optical filter characterized in that the two wavelength bands are a visible region and an infrared region. The optical filter according to claim 1,
The optical filter, wherein the dual antireflection coating is also formed on the other main surface of the transparent substrate. The optical filter according to claim 1 or 2,
The dual antireflection coating is an optical filter comprising a plurality of first thin films made of a high refractive index material and a plurality of second thin films made of a low refractive index material. The optical filter according to any one of claims 1 to 3,
The dual antireflection coating includes an antireflection coating for preventing reflection of light in the two wavelength bands and a cut coat for suppressing transmission of light in the wavelength band between the two wavelength bands. An optical filter. The optical filter according to claim 4.
The first thin film of the antireflection coating has a center wavelength of 450 nm or more and 550 nm or less, an optical film thickness of 2.000 or more and less than 3.000,
The second thin film of the antireflection coating has a center wavelength of 450 nm or more and 550 nm or less, an optical film thickness of 0.100 or more and less than 1.000,
The cut coat is made of a low refractive index material, has a center wavelength of 450 nm or more and 550 nm or less, and an optical film thickness of 1.000 or more and less than 2.000. filter. The optical filter according to claim 4 or 5,
For the high refractive index material, TiO ₂ or Nb ₂ O ₅ is used,
Wherein the low refractive index material, SiO ₂ is used,
The first thin film of the antireflection coating has a physical film thickness of 97 nm or more and 180 nm or less,
The second thin film of the antireflection coating has a physical film thickness of 7 nm or more and 95 nm or less,
The optical filter, wherein the cut coat has a physical film thickness of 77 nm or more and 189 nm or less. The optical filter according to any one of claims 4 to 6,
The optical filter, wherein the dual antireflection coating includes an adjustment coating at a position where the refractive index changes. In the imaging device,
A coupling optical system for entering light from the outside at least from the outside subject side along the optical axis, the optical filter according to any one of claims 1 to 7, and an imaging device being disposed in order. A characteristic imaging device. In the imaging device,
The optical filter according to any one of claims 1 to 7, wherein at least a coupling optical system that makes light incident from the outside along the optical axis, a filter group in which a plurality of filters can be switched and arranged. , The image sensor is arranged in order,
The filter group is composed of an infrared cut filter intended for infrared cut and a transparent filter not intended for infrared cut, and any one of these is selectively disposed on the optical axis. Imaging device.

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