JP2000329933A - Multilayered film filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a multilayered film filter that the width of the inhibition range can be changed without changing the film material. SOLUTION: The multilayered film filter is produced by laminating two or more kinds of substances having different refractive indices. In this method, a high refractive index material H and a low refractive index material L are laminated for the design wavelength λ in such a manner that the film includes a portion where a film structure of (L1H2L3H4L5H6) laminated in this order is continuously repeated. In the aforementioned structure, L1 is a low refractive index layer consisting of L and having the optical film thickness nLd1 satisfying 0.2×λ<=nLd1<=0.3×λ, H2 is a high refractive index layer consisting of H and having the optical film thickness nHd2 satisfying 0.025×λ<=nHd2<=0.05×λ, L3 is a low refractive index layer consisting of L and having the optical film thickness nLd3 satisfying 0.25×λ<=nLd3<=0.05×λ, H4 is a high refractive index layer consisting of H and having the optical film thickness nHd4 satisfying 0.2×λ<=nHd4<=0.3×λ, L5 is a low refractive index layer consisting of L and having the optical film thickness nLd5 satisfying 0.025×λ<=nLd5<=0.05×λ, and H6 is a high refractive index layer consisting of H and having the optical film thickness nHd6 satisfying 0.025×λ<=nHd6<=0.05×λ.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer filter having an optical property of transmitting light of a specific wavelength and not transmitting light of a specific wavelength.

[0002]

2. Description of the Related Art Optical systems such as cameras, microscopes, and endoscopes transmit specific light for the purpose of extracting light of a specific wavelength or cutting light of an optically harmful wavelength. An optical filter having a property of not transmitting specific light is used. As one example, an infrared cut filter is used in an optical system to cut off infrared light which is insensitive to human eyes but has high sensitivity to a semiconductor imaging device. in this case,
When the wavelength to transmit and the wavelength to block transmission are close,
When the transmittance of the wavelength to be blocked is suppressed to a very low level, a filter using a dye or a pigment cannot provide sufficient optical characteristics. Therefore, a so-called multilayer filter in which two or more substances having different refractive indexes are laminated in a multilayer. Are used in the optical system.

[0003] In general, a multilayer filter has an optical film thickness of 1/4 of the design wavelength λ as a basic film thickness, a high-refractive-index material and a low-refractive-index material of this basic film thickness are laminated, and the optical characteristics are further adjusted. The structure is such that an adjustment layer is added. Of these,
JP-A-6-109921 discloses that the optical film thickness of a high refractive index material constituting a portion excluding an adjustment layer is 0.1 to 0.1 mm in order to prevent peeling and cracking of a film after film formation from a substrate. 0.2
λ, the optical film thickness of the low refractive index substance is set to 0.3 to 0.5λ.

[0004]

However, in a multilayer film having an optical thickness of １ ／ of the design wavelength λ, the refractive index of the film material, the refractive index of the high refractive index material, the refractive index of the low refractive index material, The difference in rates determines the bandwidth of the stopband approximately. This stop band appears around the design wavelength λ. The larger the difference between the refractive indices of the basic high refractive index material and the low refractive index material, the larger the bandwidth of the stop band.

[0005] High refractive index material and the refractive index of the low refractive index material each n _H, When n _L, in general, the ratio to the design wavelength λ of the total width about the central wavelength of the stopband is given approximately by the number 1 It is known.

[0006]

(Equation 1)

That is, to change the bandwidth of the stop band,
Basically, it is necessary to change the difference between the refractive indices of the high refractive index substance and the low refractive index substance, that is, to change the material of the film. But,
In general, the material of the film is determined not only by the refractive index but also by considering the strength, durability, stability, and productivity of the film. ing.

In addition to the stop band appearing at the design wavelength λ,
Even when the design wavelength is λ / 3, a stop band is formed secondarily. This is called a third-order stop band or the like. For this reason,
For example, when high transmittance is required in the entire visible region by cutting infrared rays, there is also a problem that a secondary blocking region covers the visible region and good characteristics cannot be obtained. The problem with the third-order stop band is that the optical film thickness of the high-refractive-index material is 0.1 to 0.2λ and the optical film thickness of the low-refractive-index material is 0.3 to 0.5λ. This appears even when the position of the secondary blocking zone is changed by changing the film thickness of the period.

In view of the above problems, the present invention provides an optical system in which the width of the stop band can be changed without changing the film material, or the stop band does not appear in the wavelength range where high transmittance is required. It is an object of the present invention to provide an effective multilayer filter.

[0010]

In order to achieve the above object, the invention of claim 1 is a multilayer filter in which two or more materials having different refractive indices are laminated, wherein a high refractive index material is H. When the low-refractive-index substance is L and the design wavelength is λ, the optical film thickness n _L d _{1 of L} is 0.2 × λ ≦ n _L.
d ₁ ≦ 0.3 optical thickness _n H _{d 2} composed of a low refractive index layer L1H of × lambda is _{0.025 × λ ≦ n H d 2} ≦ 0.05 × λ
The optical film thickness n _L d ₃ made of the low refractive index layer H2L of 0.
025 × λ ≦ n _L d ₃ ≦ 0.05 × λ Low refractive index layer L3
Optical film thickness _n H _{d 4} is 0.2 × λ ≦ _n H _{d 4} consisting of H
Optical film thickness n composed of low refractive index layer H4L of ≦ 0.3 × λ
Optical film thickness _n H _{d 6 where L} d ₅ is made of a low refractive index layer L5H of _{0.025 × λ ≦ n L d 5} ≦ 0.05 × λ 0.02
5 × consists _{λ ≦ n H d 6 ≦ 0.05} × low refractive index layer of lambda H6, and having a portion which film structure arranged in this order is repeated several times in succession the (L1H2L3H4L5H6).

That is, in such a multilayer filter, a multilayer filter having two or more sets obtained by stacking at least one set on L1 to H6 is formed as one set. Things.
In this multilayer filter, the layers may be sequentially stacked from the substrate side, or may be sequentially stacked from the side in contact with air. Here, n _H is the refractive index of the high refractive index material, n _L is the refractive index of the low refractive index material, d is the thickness of each substance.

In addition to the above-mentioned repeating layer, an adjusting layer for adjusting optical characteristics may be provided, but the adjusting layer may not be provided. In addition, a substance other than H and L used repeatedly may be used for the adjustment layer.

In the above film configuration, a low refractive index layer having a thickness (0.1 × λ ≦ ndL ₁ ≦ 0.15 × λ) that is half the thickness of L1 is defined as L1 ′ and (L1′H2L3H4L5H6L
1 '). When the configuration having L1 'is used, the periodic structure between the low-refractive-index layers L1' can be expressed in a more symmetrical manner. In particular, when H2 = H6 and L3 = L5, the periodic structure becomes symmetric. However, it is not necessary that H2 = H6 or L3 = L5.

The high refractive index substance H used in the present invention includes:
TiO ₂ , Ta ₂ O ₅ , Nb ₂ O ₅ , ZrO ₂ , HfO
₂ , Y ₂ O ₃ , Al ₂ O ₃ , WO ₃ , MoO ₃ , and oxides and fluorides such as SiO ₂ and MgF ₂ are used as the low-refractive-index substance L from the viewpoint of productivity and the like. However, these are not limited.

In the present invention described above, the conventional high-refractive-index layer made of the high-refractive-index material H having a thickness of λ / 4 or near the same is provided;
0.02 between the low refractive index layer made of the low refractive index material L
Two layers each having a very thin film thickness of 5 to 0.05λ are sandwiched. This is because when considering the system (L1H2L3H4L5H6), for example, L1 and (H2L3H4L5H)
6), the layer H4 is surrounded on both sides by layers H2L3 and L5H6 having an average refractive index lower than that of H4. Also, (H2L
If the entire group of 3H4L5H6) is considered as one layer, it can be said that it is a layer equivalent to a refractive index slightly lower than H4. This makes it possible to arbitrarily reduce the difference between the apparent refractive indices of the high-refractive-index substance and the low-refractive-index substance, and arbitrarily adjust the bandwidth of the stop band. Further, by adjusting the thicknesses of H2L3 and L5H6 at this time, it is possible to eliminate a secondary stop band formed at a wavelength of λ / 3.

[0016]

(Embodiment 1) In this embodiment, a 73-layer infrared cut filter is provided on the surface of a glass lens having a refractive index of 1.52 as a substrate. For film formation, put a glass lens in a vacuum chamber and put 1 × 1
0 ^-4 was evacuated to ^Pa, it was carried out by summing 73 layer deposition by electron beam evaporation on the surface of the lens.

In this film formation, TiO ₂ is used as the high refractive index substance H (refractive index n _H ), and SiO ₂ is used as the low refractive index substance L (refractive index n _L ). Determined as the following numerical values, and n _L d = 0.2 for the L1 layer
_{5 × λ, n H d =} 0.034 × λ as H2 layer, _n H d = 0.034 × λ as H3-layer, _n H d as L4 layer =
0.25 × λ, n _L d = 0.034 × λ as the L5 layer,
The optical film thickness comprising _n H d = 0.034 × λ as H6 layers deposited by repeating 12 times, then finally was formed L = 0.125 × λ as the adjustment layer. The design wavelength λ at this time
Is 1100 nm.

The spectral reflectance characteristics of the infrared cut filter manufactured as described above at 400 to 2,000 nm of the vertically incident light were measured. FIG. 1 shows the measurement results.
As shown in FIG. 1, this filter is an infrared cut filter that blocks transmission of a wavelength centered at 1400 nm, and has a transmittance of 80% or more in the entire wavelength range from the visible range to a wavelength of 1000 nm, and a transmittance of 500 to 1000 nm. Good characteristics of 90% or more could be obtained.

Although the refractive indexes of TiO ₂ and SiO ₂ are set to 2.3 and 1.46, respectively, in this embodiment, the width of the blocking region in the infrared region is set so that the refractive index of SiO ₂ is 1 .46, the refractive index of TiO ₂ is 2.1.
It turns out that it is considerable. Further, when a high refractive index material having a refractive index of 2.1 and a low refractive index material having a refractive index of 1.46 are repeatedly formed 12 times each at λ / 4, a stop band appearing at 460 to 500 nm is formed. And a high transmittance could be obtained over the entire visible range.

Comparative Example 1 In this comparative example, a high refractive index material H was formed on a substrate similar to that of the first embodiment.
O ₂ is SiO ₂ as the low-refractive-index substance L, and the optical film thickness of n _L d = 0.25 × λ as the L1 layer and n _H d = 0.25 × λ as the H2 layer is 12 from the substrate side. The film was repeatedly formed twice, and finally, as an adjustment layer, n _L d = 0.125 × λ was formed as an L25 layer made of a low refractive index material. The design wavelength λ at this time is 1400 nm.

FIG. 2 shows the results of measuring the spectral characteristics of the infrared cut filter manufactured in this manner at 400 to 2,000 nm of the vertically incident light. This is 1400n
This is an infrared cut filter that blocks transmission of wavelengths centered at m. Compared with the first embodiment, the infrared cut filter has a wider blocking region in the infrared region, and has a wavelength of 460 to 500.
It can be seen that almost no light is transmitted in nm. From comparison with Comparative Example 1, it is understood that the multilayer filter of Embodiment 1 has excellent performance.

Embodiments 2 to 8 In Embodiments 2 to 8, the film thickness of the film of Embodiment 1 is changed to that shown in Table 1. In Table 1, for example, the optical film thickness n _L d = 0.25 × λ made of the low-refractive-index substance L formed as the first layer on the substrate side is represented as 0.25 _L. The same is true for

FIGS. 3 to 9 show the results of measuring the spectral reflectance characteristics of the infrared cut filters according to Embodiments 2 to 8 at 400 to 2000 nm of the vertically incident light. FIG. 3 shows the second embodiment, FIG. 4 shows the third embodiment, FIG. 4 shows the third embodiment, FIG. 5 shows the fourth embodiment, and FIG. 6 shows the fifth embodiment.
FIG. 7 corresponds to the sixth embodiment, FIG. 8 corresponds to the seventh embodiment, and FIG. 9 corresponds to the eighth embodiment.

As shown in FIGS. 3 to 9, each embodiment is an infrared cut filter capable of blocking transmission of a wavelength centered at 1400 nm. Therefore, as in the first embodiment, it is possible to obtain a high transmittance in the entire visible region.

(Embodiment 9) In this embodiment, the design wavelength λ, which was the design wavelength 1100 nm in the first embodiment, is changed to 800 nm, and the design wavelength
The number of repetitions was set to 20 in order to further reduce the transmittance in the stop region centered at 1050 nm, specifically, to reduce the transmittance in the stop region in Embodiment 1 from 0.1% to 0.01%. . The first layer on the substrate side is an intermediate refractive index material (Al ₂ O ₃ ) having a thickness of λ / 8 and a refractive index of 1.6.
And Table 1 shows the film design values. By adding the intermediate refractive index layer, it was possible to reduce the transmittance ripple (wavelength of the transmittance) particularly in the transmission band in the wavelength range of 800 nm to 500 nm.

That is, in this embodiment, (0.1
25L 0.031H 0.0345L 0.25H
(0.0345L 0.031H 0.125L) is repeated 20 times, in which only the first layer 0.125L in contact with the substrate is changed from a low refractive index material to an intermediate refractive index material. It is.

FIG. 10 shows the results of measuring the spectral reflectance characteristics of the infrared cut filter manufactured as described above at 400 to 1300 nm of the vertically incident light. This is 10
An infrared cut filter that can block transmission of wavelengths centered on 00 to 1050 nm. Therefore, in this embodiment, as in the first embodiment, 80% over the entire visible range.
As described above, it is possible to obtain a high transmittance of 90% or more at 500 to 700 nm.

In each of the embodiments of the present invention, the high refractive index material or the low refractive index material having an optical thickness nd of 0.05 × λ or less has the same thickness. Within the range of the optical film thickness described in the claims,
It is not necessary that they have the same thickness.

[0029]

[Table 1]

[0030]

As described above, according to the first aspect of the invention, it is possible to arbitrarily reduce the difference between the apparent refractive indices of the high-refractive index substance and the low-refractive index substance. Can be adjusted arbitrarily. Further, by optimizing the film thickness, it is possible to eliminate a secondary stop band formed at a wavelength of λ / 3 or the like.

[Brief description of the drawings]

FIG. 1 is a spectral reflectance characteristic diagram of a multilayer filter according to a first embodiment.

FIG. 2 is a spectral reflectance characteristic diagram of a multilayer filter of Comparative Example 1.

FIG. 3 is a spectral reflectance characteristic diagram of the multilayer filter according to the second embodiment.

FIG. 4 is a spectral reflectance characteristic diagram of a multilayer filter according to a third embodiment.

FIG. 5 is a spectral reflectance characteristic diagram of a multilayer filter according to a fourth embodiment.

FIG. 6 is a spectral reflectance characteristic diagram of the multilayer filter according to the fifth embodiment.

FIG. 7 is a spectral reflectance characteristic diagram of a multilayer filter according to a sixth embodiment.

FIG. 8 is a spectral reflectance characteristic diagram of the multilayer filter according to the seventh embodiment.

FIG. 9 is a spectral reflectance characteristic diagram of the multilayer filter according to the eighth embodiment.

FIG. 10 is a spectral reflectance characteristic diagram of the multilayer filter according to the ninth embodiment.

Claims (1)

[Claims] 1. A multilayer filter comprising two or more kinds of materials having different refractive indices, wherein a high refractive index material is H, a low refractive index material is L, and a design wavelength is λ. Optical film thickness n _L d ₁ is 0.2 × λ ≦ n _L d ₁
≦ 0.3 optical film thickness _n H _{d 2} composed of a low refractive index layer L1 H of × lambda is 0.025 × λ ≦ _{n H}
The optical film thickness n _L d ₃ of the low refractive index layer H 2 L with d ₂ ≦ 0.05 × λ is 0.025 × λ ≦ n _L
d ₃ ≦ 0.05 × optical thickness made of a low refractive index layer L3 H of lambda _n H _{d 4} is 0.2 × λ ≦ _n H _{d 4}
≦ 0.3 × optical thickness _n L _{d 5} composed of a low refractive index layer H4 L of lambda is 0.025 × λ ≦ _{n L}
d ₅ ≦ 0.05 optical thickness _n H _{d 6} composed of a low refractive index layer L5 H of × lambda is 0.025 × λ ≦ _{n H}
A multilayer filter comprising a low refractive index layer H6 of d ₆ ≦ 0.05 × λ, and having a portion in which a film configuration arranged in the order of (L1H2L3H4L5H6) is continuously repeated a plurality of times.