JP2000131650A - Optical low-pass filter, solid image pickup element, color image pickup device, and camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the optical low-pass filter which has a <=0.10 MTF value by making the cycle, width, and height of a rectangular wave, and the refractive index of an atmosphere and the refractive index of a filter base material against specific wavelength light meet specific conditions. SOLUTION: The cycle of the rectangular wave is denoted as T (μm), the width as a (μm), the height as d (nm), the refractive index of the atmosphere to the light of 550 nm wavelength as n1, and the refractive index of the filter base material to the light of 550 nm wavelength as n2. Here, conditions of at least either of 0.225<=(a/T)<=0.425 and 0.3<|n1-n2|<=0.7, and Y1<=(a/T)|n1-n2|d<=Y2 are met. Here, Y1=18067(a/T)3-19350(a/T)2+7399(a/T)-868, and Y2=733(a/T)3-990(a/T)2+924(a/T)-98. Namely, a superior low-pass correcting function to light of about 550 nm wavelength can be displayed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical low-pass filter, a solid-state imaging device, a color imaging device, and a camera.

[0002]

2. Description of the Related Art In a CCD or C-MOS image sensor, an optical low-pass filter is used to limit a high spatial frequency component of subject light and remove a color light component different from light from the subject due to generation of a pseudo signal. It is necessary to perform the correction by: Here, as an optical low-pass filter, a phase grating type utilizing a diffraction phenomenon of a phase type diffraction grating (phase grating) is known (see Japanese Patent Application Laid-Open No. Sho 53-119063). Further, the MTF (MTF) which is a transfer characteristic of a phase grating type optical low-pass filter
Odulation Transfer Function
For on), the MTF value in the low spatial frequency region is important from the viewpoint of image reproducibility, and the MTF value in the high spatial frequency region is preferably small.

[0003]

FIG. 1 (1)-(2)
Are the MTF characteristics (relation between spatial frequency and MTF) of a phase grating optical low-pass filter having a rectangular wave-shaped cross section, respectively, measured with light having a wavelength in the vicinity of 550 nm, which is the wavelength region where human visibility is highest. It is a diagram showing an example of.

The MTF characteristic shown in FIG. 1A includes a cutoff frequency (a spatial frequency when the MTF value is 0).
Are present, and the cutoff frequency (f
_A rising portion (α), a smoothing portion (β), and a falling portion (γ) are continuous between _c1 ) and the cutoff frequency ( _fc2 ) on the high spatial frequency side.

In the MTF characteristic as shown in FIG. 1A, an area (S) defined by a rising portion (α), a smoothing portion (β), a falling portion (γ) and a horizontal axis (MTF = 0). ), In other words, the larger the MTF value in the smoothing section (β), the larger the pseudo signal superimposed on the image. Therefore, the M of the optical low-pass filter measured by the wavelength light near 550 nm
In the TF characteristics, it is desirable that the value of MTF in the smoothing portion (β) is as small as possible.

On the other hand, the MTF characteristics shown in FIG.
No cutoff frequency (MTFM> 0), MTF
There is a spatial frequency region [smoothing portion (β ') shown in FIG. In the MTF characteristic as shown in FIG. 1B, the MT in the smoothing portion (β ′)
The larger the value of F (the minimum value of MTF), the larger the pseudo signal superimposed on the image. Therefore, the M of the optical low-pass filter measured by the wavelength light near 550 nm
In the TF characteristic, the MTF in the smoothing portion (β ′)
Is desirably as small as possible.

The present invention has been made based on the above circumstances. An object of the present invention is to provide a phase grating type optical low-pass filter having a rectangular wave-shaped cross section,
When the MTF characteristic is measured with light having a wavelength of about 50 nm, there are two cutoff frequencies in the MTF characteristic, and in the diagram showing the MTF characteristic, the cutoff frequency (f _c1 ) on the low spatial frequency side and the high / low The value of the MTF (the maximum value of the MTF between the two cutoff frequencies) in a certain spatial frequency region (the smoothing section (β)) between the cutoff frequency ( _fc2 ) on the spatial frequency side and the cutoff frequency ( _fc2 ) is 0.10. An object of the present invention is to provide an optical low-pass filter as described below.

Another object of the present invention is to provide a phase grating type optical low-pass filter having a rectangular cross section,
When the MTF characteristic is measured with light having a wavelength of around 550 nm, there is no cut-off frequency in the MTF characteristic, and in a diagram showing the MTF characteristic, a certain spatial frequency region (the smoothing portion (β ′)) An object of the present invention is to provide an optical low-pass filter in which the value of MTF (the minimum value of MTF) is 0.10 or less.

It is another object of the present invention to provide an optical low-pass filter having a luminosity correction function. It is another object of the present invention to provide a solid-state imaging device in which a pseudo signal is hardly superimposed on an image. Another object of the present invention is to provide a color imaging device in which a pseudo signal is hardly superimposed on an image. Another object of the present invention is to provide a board camera in which a pseudo signal is hardly superimposed on an image. Another object of the present invention is to provide a digital still camera in which a pseudo signal is hardly superimposed on an image.

[0010]

As a result of extensive studies by the present inventors, a phase grating is formed so that the period, width and height of a rectangular wave having a sectional shape satisfy a specific relational expression. By configuring the optical low pass filter, the 550n measured for the optical low pass filter
In the MTF characteristic of light having a wavelength near m, the MTF in a constant spatial frequency region [the smoothing portion (β) between two cutoff frequencies or the smoothing portion (β ′) when there is no cutoff frequency). Was found to be extremely small, and the present invention was completed based on such findings.

That is, the optical low-pass filter of the present invention is a phase grating type optical low-pass filter having a rectangular cross section, wherein the period of the rectangular wave is T (μ).
m), the width of the rectangular wave is a (μm), the height of the rectangular wave is d (nm), the refractive index of the atmosphere by the wavelength light of 550 nm is n ₁ , the refractive index of the filter substrate by the light of 550 nm wavelength Is defined as n ₂ , satisfying the conditions shown in the following expressions (1) and (2) and at least one of the following expressions (3) and (4).

[0012]

(Equation 3)

The optical low-pass filter according to the present invention is a phase grating type optical low-pass filter having a rectangular cross section, wherein the period of the rectangular wave is T (μ).
m), the width of the rectangular wave is a (μm), the height of the rectangular wave is d (nm), the refractive index of the atmosphere by the wavelength light of 550 nm is n ₁ , the refractive index of the filter substrate by the light of 550 nm wavelength Is defined as n ₂ , satisfying the conditions shown in the following formulas (5) and (6) and at least one of the following formulas (7) and (8).

[0014]

(Equation 4)

The optical low-pass filter of the present invention is preferably made of an optical material that absorbs near-infrared light. In the optical low-pass filter of the present invention, it is preferable that a phase grating is formed on one surface of the transparent substrate, and a vapor-deposited film that reflects near-infrared light is provided on the other surface of the transparent substrate.

A solid-state imaging device according to the present invention is characterized in that it comprises a cover member comprising the optical low-pass filter according to the present invention. A color imaging device according to the present invention includes the optical low-pass filter according to the present invention. A board camera according to the present invention includes the optical low-pass filter according to the present invention. A digital still camera according to the present invention includes the optical low-pass filter according to the present invention.

[0017]

The conditions shown in the above equations (1) and (2),
And a rectangular-wave cross section satisfying at least one of the conditions of the above formulas (3) and (4), or the conditions shown in the above formulas (5) and (6), and the above formulas (7) and (6). When an MTF characteristic of a phase grating type optical low-pass filter having a rectangular cross section satisfying at least one of the conditions of the expression (8) is measured with light having a wavelength of around 550 nm, a constant spatial frequency region [the smoothing Part (β) or the smooth part (β ′)]
The value of F is as extremely small as 0.10 or less, a pseudo signal having a spatial frequency component in the spatial frequency region can be efficiently cut off, and a wavelength near 550 nm, which is the wavelength region where human visibility is highest, is obtained. An excellent low-pass correction function for light can be exhibited.

If there are two cut-off frequencies in the diagram showing the MTF characteristic, the value of the MTF (MTF) in a constant spatial frequency region between these cut-off frequencies ( _fc1 , _fc2 ) The maximum value of the MTF between the two cutoff frequencies) is 0.10 or less,
In the F characteristic, the rising portion (α) and the rising portion (γ) do not substantially exist, and as a result, a pseudo signal having a spatial frequency component in the spatial frequency region can be efficiently cut off.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an optical low-pass filter according to the present invention will be described. FIG. 2A is a schematic diagram showing an example of a cross-sectional shape (rectangular wave shape) of a phase grating constituting the optical low-pass filter of the present invention, and FIG.
FIG. 3 is a diagram showing an example of MTF characteristics measured at 550 nm for an optical low-pass filter having the cross-sectional shape shown in FIG.

In FIG. 2A, T is the period of the rectangular wave (unit: μm), a is the width of the rectangular wave (unit: μm), d is the height of the rectangular wave (unit: nm), and n ₁ is Refractive index of atmosphere (refractive index by wavelength light of 550 nm, usually 1.00),
n ₂ indicates the refractive index of the filter substrate (refractive index due to light having a wavelength of 550 nm).

The width a of the rectangular wave is in a range that satisfies the condition expressed by the above equation (1) or (5), that is, 0.22.
5T ~ 0.425T or 0.575T ~ 0.775T
And preferably 0.25T to 0.40T or 0.1.
60T to 0.75T.

[0022] refers to the absolute value of the difference between the difference (refractive index of the refractive index of the atmosphere (n ₁₎ the refractive index of the filter substrate and (n _2).
Hereinafter, it is also described as “Δn”. ) Is within a range satisfying the conditions shown in the above equations (2) and (6) in order to keep the MTF value in a constant spatial frequency region at 0.10 or less, that is, 0.3 to 0. .7.

The width a of the rectangular wave is 0.225T to 0.4.
In the case of 25T [when the condition shown in the above equation (1) is satisfied], the value of the height d of the rectangular wave (unit: nm)
Is a range that satisfies the condition shown in the above formula (3) and / or the above formula (4), that is, [Y1 · (a / T) ⁻¹ ·
Δn ⁻¹ ] to [Y2 · (a / T) ⁻¹ · Δn ⁻¹ ] or [Y
3 · (a / T) ⁻¹ · Δn ⁻¹ ] to [Y4 · (a / T) ^−1.
Δn ^-1 ]. Here, Y1 to Y
4 is a value represented by the following equation.

The width a of the rectangular wave is 0.575T or more.
0.775 T [The condition shown in the above equation (5) is satisfied.
The value of the height d of the rectangular wave (unit: n)
m) is represented by the above formula (7) and / or the above formula (8).
That is, a range satisfying the following condition: [Y5 · (1-a /
T)^-1.DELTA.n^-1] To [Y6 · (1-a / T)^-1・ Δ
n ^-1] Or [Y7 · (1-a / T)^-1.DELTA.n^-1] ~
[Y8 · (1-a / T)^-1.DELTA.n^-1]
It is said. Here, Y5 to Y8 are represented by the following equations.
Value.

[0025]

(Equation 5)

FIG. 3 shows X and Y (Y = X) represented by the following equations.
And Δn · d). In the figure, curve A shows Y = Y1, Y = Y5, and curve B shows Y = Y1, Y = Y5.
Curve C indicates Y = Y3, Y = Y7, curve D indicates Y = Y4, Y = Y8, and line E indicates X
= 0.225, and the straight line F indicates X = 0.425.
Further, a region indicated by oblique lines satisfies the condition of the above formula (1) and satisfies at least one of the above formulas (3) and (4), or a region of the above formula (5). This is a region that satisfies the condition and satisfies at least one of the expressions (7) and (8).
Then, the MTF value in the constant spatial frequency region can be set to 0.10 or less only in the region indicated by oblique lines in FIG.

[0027]

X = (a / T): (where 0.225 ≦ a / T ≦
0.425) X = (1-a / T): (provided that 0.575 ≦ a / T ≦
0.775)

By defining the width a and the height d of the rectangular wave in the above ranges, a constant spatial frequency range [for example,
MTF value (maximum value of MTF between two cutoff frequencies) in the fixed spatial frequency region between cutoff frequencies ( _fc1 , _fc2 ) can be set to 0.10 or less, A pseudo signal having a spatial frequency component in a frequency region can be efficiently cut off, and a wavelength region near 550 nm (for example, 550 nm) where human visibility is the highest is obtained.
An excellent low-pass correction function can be exhibited for light having a wavelength of (± 20 nm).

Further, within the range satisfying the conditions shown in the above formulas (1) and (2) and at least one of the above formulas (3) and (4), or in the above formula (5) And the width a and the height d of the rectangular wave are appropriately selected within a range that satisfies the condition shown in the above formula (6) and at least one of the above formula (7) and the above formula (8). MTF as shown in FIG.
The characteristic, that is, the value of the MTF in a certain spatial frequency region [( _fc1 ) to ( _fc2 )] can be made substantially 0. As a result, a pseudo signal having a spatial frequency component in the spatial frequency region Can be reliably shut off.

The optical low-pass filter of the present invention can be manufactured by forming a phase grating satisfying the above conditions on the surface of a transparent substrate (filter substrate) made of glass or resin. The resin constituting the transparent substrate is not particularly limited, but it is preferable to use a resin material that absorbs near-infrared light. As such a resin material (polymer), Japanese Unexamined Patent Publication No. Hei 6-118228 is used. Resin materials described in the publication can be mentioned. By using a resin material that absorbs near-infrared light, an optical low-pass filter having a visibility correction function can be manufactured.

As a method of forming a phase grating on the surface of a transparent substrate made of glass, a lift-off method, an etching method and the like can be mentioned.

As a method of forming a phase grating on the surface of a transparent substrate made of a resin, the following method can be used. A method in which a monomer composition for obtaining a resin is cast-polymerized in a mold in which a negative pattern of a phase grating is formed on a molding surface. A method in which a heating plate having a negative pattern of a phase grating formed on the surface is pressure-bonded to the surface of a transparent substrate. A method in which a photosensitive resin is applied to the surface of a transparent substrate, and the formed coating film is exposed through a photomask and then developed. A method of injection molding using a mold having a negative pattern of a phase grating formed on a molding surface. On the surface of the transparent substrate, a monomer composition for obtaining a resin was applied by spin coating, and a negative pattern of a phase grating was formed on the surface of the formed coating film of the monomer composition. A method in which the molding surface is pressed and the monomer composition is polymerized in this state. Here, by using a photosensitive composition as the monomer composition, a curing (polymerization) treatment can be performed using ultraviolet rays.

In the optical low-pass filter of the present invention, a phase grating may be formed on one surface of a transparent substrate, and a vapor deposition film for reflecting near-infrared light may be provided on the other surface of the transparent substrate. According to the optical low-pass filter having such a configuration, near-infrared light can be cut with high efficiency, and the visibility correction function can be exhibited. An example of such a deposited film is an optical multilayer film having a function of reflecting near-infrared light, and specific examples include an alternately laminated film of a silica (SiO ₂ ) layer and a titania (TiO ₂ ) layer. The thickness of each layer, the number of layers, and the like can be appropriately selected.

The optical low-pass filter of the present invention is
When disposed in the D solid-state imaging device, the optical low-pass filter of the present invention may be disposed at any position before the lens system, in the lens system, or between the lens system and the CCD in the CCD solid-state imaging device. Is also good. The optical low-pass filter of the present invention can be suitably used as a cover material of a solid-state imaging device such as a CCD solid-state imaging device. Further, the optical low-pass filter of the present invention can be mounted on an imaging system such as a color imaging device, a board camera, and a digital still camera.

[0035]

Hereinafter, embodiments of the present invention will be described.
The present invention is not limited to these examples. In the following examples, “parts” means “parts by mass”.

<Example 1> (1) Preparation of monomer composition: 10 parts of a specific phosphoric acid group-containing monomer represented by the following structural formula [1] and a compound represented by the following structural formula [2] 10 parts of a specific phosphoric acid group-containing monomer to be
58.5 parts of methyl methacrylate, 20 parts of diethylene glycol dimethacrylate, and 1.5 parts of α-methylstyrene were mixed well to prepare a mixed monomer. 14 parts of copper benzoic anhydride (mixed monomer 10
0 parts by weight of 2.9 parts of copper metal) and 6
The mixture was sufficiently dissolved by stirring and mixing at 0 ° C. to obtain a monomer composition in which anhydrous copper benzoate was dissolved in the mixed monomer.

[0037]

Embedded image

[0038]

Embedded image

(2) Production of an optical low-pass filter (cast polymerization): After adding 2.0 parts of t-butyl peroxypivalate to the monomer composition prepared in the above (1), The monomer composition is charged into a mold in which a mold plate in which a negative pattern of a phase grating is formed on the glass surface by an etching method and a flat glass mold plate are arranged to face each other, and the mixture is heated at 45 ° C. for 16 hours at 60 ° C. for 8 hours and 90.degree. C. for 3 hours to perform cast polymerization, thereby forming a crosslinked copolymer containing copper ions, and having a period (T) of 200 .mu.m and a width (a) of 150 .mu.m.
A phase grating type optical low-pass filter (thickness: 1 mm) having a rectangular wave-shaped cross section (0.75 T) and height (d) of 550 nm was manufactured. When a spectral transmittance curve of this optical low-pass filter was measured using a spectrophotometer, it was confirmed that the optical low-pass filter had an excellent function of absorbing near-infrared light (700 to 1000 nm). The refractive index (n ₂ ) of the optical low-pass filter at a wavelength of 550 nm was 1.51.

(3) Evaluation of optical low-pass filter (measurement of MTF characteristics): The optical low-pass filter of the present invention obtained as described above was incorporated into an MTF measuring device (manufactured by Image Science), and the optical The MTF characteristic of the low-pass filter was measured by using light having a wavelength of 550 nm. Here, the air-equivalent distance between the optical low-pass filter and the image plane was set to 3 mm. Fig. 4 shows the results.
Shown in As shown in FIG. 4, the value of the MTF at a spatial frequency of 30 to 90 (lines / mm) was 0.

Example 2 Example 2 was the same as Example 1 except that the monomer composition was charged into a mold in which a mold plate on which a different negative pattern was formed and a flat glass mold plate were opposed to each other. Similarly, the period (T) is 200 μm,
Width (a) 50 μm (0.25T), height (d) 550n
An optical low-pass filter (thickness: 1 mm) of a phase grating type having a rectangular wave-shaped cross section of m was manufactured. The MTF characteristics of the optical low-pass filter of the present invention obtained in this manner were measured with light having a wavelength of 550 nm in the same manner as in Example 1.
Characteristics [M at a spatial frequency of 30 to 90 (lines / mm)
MTF characteristic in which the value of TF becomes 0] was obtained.

Example 3 Example 3 was the same as Example 1 except that the monomer composition was charged into a mold in which a mold plate on which a different negative pattern was formed and a flat glass mold plate were opposed to each other. Similarly, the period (T) is 200 μm,
Width (a) 60μm (0.30T), height (d) 400n
An optical low-pass filter (thickness: 1 mm) of a phase grating type having a rectangular wave-shaped cross section of m was manufactured. The MTF characteristics of the thus obtained optical low-pass filter of the present invention were measured in the same manner as in Example 1 by using light having a wavelength of 550 nm. FIG. 5 shows the results. As shown in FIG. 5, the MTF value at a spatial frequency of 36 to 85 (lines / mm) (the smoothing portion (β ′)) was 0.01.

<Comparative Example 1> The same procedure as in Example 1 was carried out except that the monomer composition was charged into a mold in which a mold plate on which a different negative pattern was formed and a flat glass mold plate were opposed to each other. Similarly, the period (T) is 200 μm,
Width (a) 80 μm (0.40 T), height (d) 550 n
An optical low-pass filter (thickness: 1 mm) of a phase grating type having a rectangular wave-shaped cross section of m was manufactured. With respect to the optical low-pass filter for comparison obtained in this manner, the MTF characteristic by 550 nm wavelength light was measured in the same manner as in Example 1. FIG. 6 shows the results. As shown in FIG. 6, in this MTF characteristic, a cutoff frequency [30 (lines / mm)] on the low spatial frequency side and a cutoff frequency [90 (lines / mm)] on the high spatial frequency side are obtained. Indicates the MTF in the smooth portion (48 to 73 lines / mm) in which a rising portion, a smooth portion, and a falling portion are continuous.
Was as large as 0.60.

<Embodiment 4> Etching on the surface of a glass plate
By performing the processing, the period (T) is 360 μm and the width is 360 μm.
(A) 240 μm (0.67 T), height (d) 340 n
Phase grating type optical roper having rectangular wave-shaped cross section of m
A filter (thickness 0.55 mm) was manufactured. This light
Low-pass filter to 550nm wavelength light
Refractive index (n _Two) Was 1.51. Like this
Optical low-pass filter of the present invention obtained by
In the same manner as in the first embodiment,
The MTF characteristics were measured. FIG. 7 shows the results. Shown in FIG.
Thus, a spatial frequency of 74 to 144 (lines / mm) [the
The value of MTF in the smoothing portion (β ′)] was 0.05.
Was.

<Embodiment 5> Etching on the surface of a glass plate
By processing, the period (T) is 200 μm and the width is 200 μm.
(A) 150 μm (0.75 T), height (d) 650 n
Phase grating type optical roper having rectangular wave-shaped cross section of m
A filter (thickness 0.55 mm) was manufactured. This light
Low-pass filter to 550nm wavelength light
Refractive index (n _Two) Was 1.51. Like this
Optical low-pass filter of the present invention obtained by
In the same manner as in the first embodiment,
The MTF characteristics were measured. FIG. 8 shows the results. Shown in FIG.
As described above, the spatial frequency of 29 to 91 (lines / mm) [the flat
The value of MTF in the smooth part (β ′)] was 0.10.
Was.

Table 1 summarizes the conditions and results of the above Examples 1 to 5 and Comparative Example 1.

[0047]

[Table 1]

[0048]

According to the optical low-pass filter according to claim 1 or 2, when the MTF characteristic is measured by using light having a wavelength near 550 nm, a constant spatial frequency region [the smooth portion (β) or the smooth portion (β) is obtained. ')] In M
The value of TF is extremely small at 0.10 or less. Therefore, according to the optical low-pass filter according to the first and second aspects, the pseudo signal having the spatial frequency component in the spatial frequency region can be efficiently cut off, and the wavelength region where the human visibility is highest is obtained. An excellent low-pass correction function can be exhibited for light having a wavelength around 550 nm.

According to the optical low-pass filter according to the third and fourth aspects, the visibility correction function can be further exhibited. According to the solid-state imaging device of the present invention, it is difficult to superimpose the obtained pseudo signal on an image. According to the color imaging apparatus of the present invention, it is difficult to superimpose the obtained pseudo signal on the image. According to the board camera and the digital still camera of the present invention, it is difficult to superimpose the obtained pseudo signal on the image.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of MTF characteristics of a phase grating type optical low-pass filter having a rectangular wave-shaped cross section, measured with light having a wavelength near 550 nm.

FIG. 2A is a schematic diagram showing a cross-sectional shape of a phase grating constituting an optical low-pass filter of the present invention;
(2) shows the MTF measured at 550 nm of the optical low-pass filter having the cross-sectional shape shown in (1).
It is a diagram showing an example of a characteristic.

FIG. 3 is a graph showing a relationship between X and Y (Y = X ・ Δn ・ d).

FIG. 4 is a diagram showing MTF characteristics measured at 550 nm for the optical low-pass filter according to Example 1.

FIG. 5 is a diagram showing MTF characteristics of an optical low-pass filter according to Example 3 measured at 550 nm.

FIG. 6 is a diagram showing MTF characteristics of an optical low-pass filter according to Comparative Example 1 measured at 550 nm.

FIG. 7 is a diagram showing MTF characteristics of an optical low-pass filter according to Example 4 measured at 550 nm.

FIG. 8 is a diagram showing MTF characteristics of an optical low-pass filter according to Example 5 measured at 550 nm.

Claims (8)

[Claims] 1. A phase grating type optical low-pass filter having a rectangular wave-shaped cross section, wherein the period of the rectangular wave is T (μm) and the width of the rectangular wave is a
(Μm), the height of the rectangular wave is d (nm), 550 nm
When the refractive index of the atmosphere due to the wavelength light is n ₁ , and the refractive index of the filter substrate due to the light having the wavelength of 550 nm is n ₂ ,
An optical low-pass filter which satisfies the conditions shown in the following expressions (1) and (2) and at least one of the following expressions (3) and (4). (Equation 1) 2. A phase grating type optical low-pass filter having a rectangular wave-shaped cross section, wherein the period of the rectangular wave is T (μm) and the width of the rectangular wave is a
(Μm), the height of the rectangular wave is d (nm), 550 nm
When the refractive index of the atmosphere due to the wavelength light is n ₁ , and the refractive index of the filter substrate due to the light having the wavelength of 550 nm is n ₂ ,
An optical low-pass filter which satisfies the conditions shown in the following expressions (5) and (6) and at least one of the following expressions (7) and (8). (Equation 2) 3. The optical low-pass filter according to claim 1, comprising an optical material absorbing near-infrared light. 4. A phase grating is formed on one surface of the transparent substrate,
The optical low-pass filter according to claim 1, wherein a vapor deposition film that reflects near-infrared light is provided on the other surface of the transparent substrate. 5. A solid-state imaging device comprising a cover member comprising the optical low-pass filter according to claim 1. 6. A color imaging apparatus comprising the optical low-pass filter according to claim 1. 7. A board camera comprising the optical low-pass filter according to any one of claims 1 to 4. 8. A digital still camera comprising the optical low-pass filter according to claim 1.