JP5888124B2 - Multilayer filter and method for manufacturing multilayer filter - Google Patents

Description

  The present invention relates to a multilayer filter used for optical communication, an optical device, and the like, and a method for manufacturing the multilayer filter.

  Conventionally, in order to selectively transmit light in a predetermined wavelength range, a dielectric thin film layer made of a high refractive index material and a thin film layer made of a dielectric thin film layer made of a low refractive index material alternately A multilayer filter formed so as to selectively transmit light in a desired wavelength region by laminating is known. As such a multilayer filter, a low-refractive index film made of SiO2 and a high-refractive index film made of a-Si (amorphous silicon) are alternately laminated on a substrate, so that a wavelength in the visible range and an infrared range are set. A multilayer filter capable of separating wavelengths is known (see Patent Document 1).

JP 2001-066424 A

  Since the multilayer filter disclosed in Patent Document 1 simply aims to separate light having wavelengths in the visible region and infrared region, it is possible to obtain desired optical characteristics while suppressing the number of films to be stacked. However, when it is intended to selectively transmit only a specific wavelength in the infrared wavelength range, the number of films formed on the substrate in order to obtain the desired optical characteristics increases, which is costly. Become. In addition, the problem that film cracking is likely to occur due to an increase in internal stress due to the increase in the number of films, and the desired optical characteristics by using many Si (silicon) films that have strong absorption characteristics in the near-infrared wavelength range. There is a problem that it is difficult to obtain.

  In view of the problems of the prior art, the present invention is a multilayer filter that can extract light of a specific infrared wavelength with a simple configuration at low cost while using Si as a high refractive index film, and An object of the present invention is to provide a method for manufacturing a multilayer filter.

In order to solve the above problems, the present invention is characterized by having the following configuration.
(1) The multilayer filter of the present invention is a multilayer filter formed by laminating thin films having different refractive indexes on a transparent substrate, the first thin film layer made of Si formed on the transparent substrate, and the first filter A second thin film layer formed on the thin film layer and having a refractive index lower than that of the first thin film layer; and a refraction lower than the refractive index of the second thin film layer formed on the second thin film layer. A third thin film layer having a refractive index and the same refractive index as the second thin film layer formed on the third thin film layer, or the refractive index of the first thin film layer and the refractive index of the third thin film layer A fourth thin film layer having an intermediate refractive index in between,
The first thin film to the fourth thin film are used as one stack, and a predetermined number of the stacks are stacked on the substrate.
(2) The multilayer filter of (1) transmits light within a wavelength range of 900 nm to 1200 nm when light including a near-infrared region is incident on the multilayer filter at 45 °. It is characterized by forming each said thin film so that the light of a wavelength range may be reflected.
(3) In the multilayer filter according to (1) or (2), the second thin film layer and the fourth thin film layer are made of a material selected from Ta2O5, Nb2O5, TiO2, and ZrO2.
(4) The multilayer filter according to any one of (1) to (3), wherein the third thin film layer is made of a material of SiO 2 or MgF 2.
(5) In the method of manufacturing a multilayer filter in which thin films having different refractive indexes are laminated on a transparent substrate, a first step of forming a first thin film layer made of Si with a predetermined thickness on the transparent substrate; A second step of forming a second thin film layer having a refractive index lower than a refractive index of the first thin film layer on the first thin film layer formed by the first step with a predetermined film thickness; A third step of forming a third thin film layer having a refractive index lower than the refractive index of the second thin film on the second thin film layer formed by the second step with a predetermined thickness; The third thin film layer formed in three steps has the same refractive index as that of the second thin film layer, or is intermediate between the refractive index of the first thin film layer and the refractive index of the third thin film layer. A fourth step of forming a fourth thin film layer having a refractive index with a predetermined film thickness; , As the first step to the first film layer to 1 stack the fourth thin film layer is formed by the fourth step, characterized in that a predetermined number of stacked said stack on the substrate.
(6) In the method of manufacturing a multilayer filter according to (5), the second thin film layer and the fourth thin film layer are made of a material selected from Ta2O5, Nb2O5, TiO2, and ZrO2, and the third thin film layer is made of SiO2. , Or MgF2 material.

  According to the present invention, while using Si as a high refractive index film, light having a wavelength in a specific infrared region can be extracted at a low cost with a simple configuration.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram schematically showing the configuration of the multilayer filter of the present embodiment.

  The multilayer filter 100 shown in the figure has an optical characteristic of selectively transmitting light having a wavelength in the near infrared region, and particularly has an optical characteristic of transmitting light having a wavelength in the near infrared region of about 900 nm to 1200 nm. It is an edge filter formed to have.

  It should be noted that when light is made incident from a non-perpendicular angle with respect to a predetermined optical filter, a difference always appears between the transmission / reflectance curves of p-polarized light and s-polarized light. Therefore, in the case where light is obliquely incident on the optical filter and only light in a specific wavelength range is transmitted, it is desired in consideration of the transmittance / reflectance of both the p-polarized component and the s-polarized component. The multilayer film must be designed so as to obtain optical characteristics. In particular, the multilayer filter of the present embodiment transmits light having a wavelength in the above-described range in consideration of transmission of light of p-polarized component and s-polarized component with respect to 45 ° obliquely incident light. It has a characteristic of sufficiently limiting the transmission of the light.

The multilayer filter 100 of the present embodiment shown in the figure includes a first thin film layer 2 formed on a transparent substrate 1, a second thin film layer 3 formed on the first thin film layer 2, and a second thin film layer 3. And the fourth thin film layer 5 formed on the third thin film layer. The first thin film layer 2 to the fourth thin film layer 5 are formed on the substrate 1 as one stack S. A plurality of stacks S (S ₁ , S ₂ ... S _n ) are stacked.

  The transparent substrate 1 is preferably made of a material that easily transmits light having a near infrared wavelength. As such a material, most glass for optical use corresponds, and quartz glass, magnesium fluoride, calcium fluoride, etc. are mentioned to others. In addition, the transparent substrate 1 is preferably a flat plate shape, but is not limited thereto, and the film configuration of the present embodiment may be formed using an optical member having a predetermined shape as a substrate to form a multilayer filter. Is possible.

  The film material used for forming the first thin film layer 2 is Si having a high refractive index (silicon having a refractive index of about 3 to 4). The film thickness of the first thin film layer 2 made of such a Si thin film is such that the transmittance of light in the near infrared region in the wavelength range of 900 nm to 1200 nm is light in other wavelength regions as the optical characteristics of the target multilayer filter. The film thickness is determined so as to be larger than the above. Such a film thickness (optical film thickness) is desirably ½λ or less with respect to the target design wavelength λ and has a physical film thickness.

  The film material used for forming the second thin film layer 3 is a metal oxide having an intermediate refractive index that is a refractive index between the refractive index of the first thin film layer 2 and the refractive index of the third thin film layer 4 described later. The material of a thing is mentioned. Examples of materials having such an intermediate refractive index include Ta2O5 (refractive index 2.18), Nb2O5 (refractive index 2.32), TiO2 (refractive index 2.31), ZrO2 (refractive index 1.97), etc., but Ta2O5 should be used. Is particularly preferred. The film thickness of the second thin film layer 3 made of such a metal oxide thin film is (1 / 8λ to 3 / 4λ) with respect to the target design wavelength λ.

  Examples of the film material used for forming the third thin film layer 4 include a metal oxide material having a refractive index lower than that of the second thin film layer 3. Examples of such a low refractive index material include SiO2 (refractive index 1.46), MgF2 (refractive index 1.37), and it is particularly preferable to use SiO2. The film thickness (optical film thickness) of the third thin film layer 4 made of such a metal oxide thin film is set to 1 / 8λ to 3 / 4λ with respect to the target design wavelength λ.

  The film material used to form the fourth thin film layer 5 is a metal oxide having an intermediate refractive index that is a refractive index between the refractive index of the first thin film layer 2 and the refractive index of the third thin film layer 4. Any material may be used, and the same material as that of the second thin film layer 3 may be used. In addition, although it may be the same material used for the 2nd thin film layer 3, or a different material, it is especially preferable to use Ta2O5. The film thickness of the fourth thin film layer 5 made of such a metal oxide thin film is (1 / 8λ to 3 / 4λ) with respect to the target design wavelength λ.

  The first thin film layer 2 to the fourth thin film layer 5 are sequentially formed on the transparent substrate 101 using a known coating technique such as a vacuum deposition method. When using the vacuum deposition method, the transparent substrate 1 is placed in a vacuum deposition machine, and the material for forming the first thin film layer 2 (Si) is used as a deposition source to perform vacuum deposition until a desired film thickness is obtained. Next, the evaporation source is changed to a material for forming the second thin film layer 3 (for example, Ta2O5), and vacuum evaporation is performed until a desired film thickness (optical film thickness) is obtained in the same manner. Such thin film layers are sequentially formed, and the first thin film layer 2 to the fourth thin film layer 5 are sequentially formed on the transparent substrate 1 with a desired film thickness. The coating technique may be another method, and a known coating technique such as a sputtering method or an ion plating method can be used.

  In the present embodiment, the first thin film layer 2, the second thin film layer 3, the third thin film layer 4, and the fourth thin film layer 5 sequentially formed on the transparent substrate 1 in this way are formed into a single layer structure. Call it. In the present embodiment, in order to produce a multilayer filter, at least one or more such stacks S formed on the transparent substrate 1 are formed. In addition, by forming a multilayer filter by stacking a plurality of such stacks on a transparent substrate, it is possible to transmit only light in a desired wavelength range more selectively, but as the number of stacks increases, As a result, the maximum transmittance decreases. For this reason, the number of stacks is selected based on the relationship between the allowable transmittance in a wavelength region other than the wavelength region desired to be transmitted and the transmittance required for the design wavelength. In this embodiment, the number of stacks is preferably about 2 to 10, and more preferably 4 to 8.

  Moreover, the film thickness (optical film thickness) of each thin film layer may be the same for each stack, or may be different. In order to obtain more desired optical characteristics, optical simulation is performed using a predetermined calculation formula, and the film thickness of the thin film layer can be determined for each stack.

  Next, preferred examples of the present invention and comparative examples will be described below, but the present invention is not limited to the examples.

<Example 1>
A multilayer filter was designed using the following conditions.

"the purpose"
Edge filter that selectively transmits light with a wavelength of 1000nm to 1080nm (target transmittance 70% or more)
"conditions"
Transparent substrate: Glass (refractive index 1.51)
Medium: 1.64
Design wavelength λ ₀ : 1000 nm
Incident angle: 45 °
Film materials used: Si (refractive index 3.90), Ta2O5 (refractive index 2.18), SiO2 (1.46)
Total: 28 layers (7 stacks)
Table 1 shows the material and film thickness of each thin film layer constituting the multilayer filter. Note that the thin film layer No. 1 is the first layer formed on the transparent substrate, and the outermost layer is the layer No. 28.

この条件によって設計される多層膜フィルタについて入射角45°としたときの分光透過率特性（シュミレーション値）を図２に、ｓ偏光に注目した分光透過率特性（シュミレーション値）を図３に、ｐ偏光に注目した分光透過率特性（シュミレーション値）を図４にそれぞれ示す。

The spectral transmittance characteristic (simulation value) when the incident angle is 45 ° for the multilayer filter designed under these conditions is shown in FIG. 2, and the spectral transmittance characteristic (simulation value) focusing on s-polarized light is shown in FIG. FIG. 4 shows spectral transmittance characteristics (simulation values) focusing on polarized light.

<Comparative Example 1>
The conditions were the same as in Example 1 except that only SiO2 and Ta2O5 were used and the number of films was 29. Table 2 shows the material and film thickness of each thin film layer constituting the multilayer filter in the comparative example.

この条件によって設計される多層膜フィルタについて入射角45°としたときの分光透過率特性（シュミレーション値）を図２に、ｓ偏光に注目した分光透過率特性（シュミレーション値）を図３に、ｐ偏光に注目した分光透過率特性（シュミレーション値）を図４にそれぞれ示す。

The spectral transmittance characteristic (simulation value) when the incident angle is 45 ° for the multilayer filter designed under these conditions is shown in FIG. 2, and the spectral transmittance characteristic (simulation value) focusing on s-polarized light is shown in FIG. FIG. 4 shows spectral transmittance characteristics (simulation values) focusing on polarized light.

<Result>
The multilayer filter of Example 1 can selectively transmit only 70% or more of light in a specific wavelength range with respect to light incident at 45 °.

It is the schematic diagram which showed the structure of the multilayer filter in this embodiment. It is the figure which showed the spectral transmittance (simulation value) of the multilayer filter of Example 1 and Comparative Example 1. It is the figure which showed the spectral transmittance (simulation value) which paid its attention to the s polarization | polarized-light of the multilayer filter of Example 1 and Comparative Example 1. FIG. It is the figure which showed the spectral transmittance (simulation value) which paid its attention to p polarization | polarized-light of the multilayer filter of Example 1 and Comparative Example 1. FIG.

DESCRIPTION OF SYMBOLS 1 Transparent substrate 2 1st thin film layer 3 2nd thin film layer 4 3rd thin film layer 5 4th thin film layer 100 Multilayer film filter

Claims (6)

In a multilayer filter formed by laminating thin films having different refractive indexes on a transparent substrate, a first thin film layer made of Si formed on the transparent substrate, and the first thin film formed on the first thin film layer A second thin film layer having a refractive index lower than the refractive index of the layer; a third thin film layer formed on the second thin film layer and having a refractive index lower than that of the second thin film layer; A fourth thin film formed on three thin film layers and having the same refractive index as that of the second thin film layer or having an intermediate refractive index between the refractive index of the first thin film layer and the refractive index of the third thin film layer; And having a layer
A multilayer filter comprising the first thin film to the fourth thin film as one stack, and a predetermined number of the stacks stacked on the substrate. The multilayer filter according to claim 1 transmits light in a wavelength range of 900 nm to 1200 nm when light including a near-infrared region is incident on the multilayer filter at 45 °, and transmits light in other wavelength ranges. A multilayer filter formed by forming each layer thin film so as to reflect light. 3. The multilayer filter according to claim 1, wherein the second thin film layer and the fourth thin film layer are made of a material selected from Ta2O5, Nb2O5, TiO2, and ZrO2. 4. The multilayer filter according to claim 1, wherein the third thin film layer is made of a material of SiO 2 or MgF 2. In the method for producing a multilayer filter in which thin films having different refractive indexes are laminated on a transparent substrate,
A first step of forming a first thin film layer made of Si with a predetermined thickness on the transparent substrate;
A second step of forming a second thin film layer having a refractive index lower than the refractive index of the first thin film layer on the first thin film layer formed by the first step with a predetermined thickness;
A third step of forming a third thin film layer having a refractive index lower than the refractive index of the second thin film on the second thin film layer formed by the second step with a predetermined thickness;
The third thin film layer formed by the third step has the same refractive index as the second thin film layer, or between the refractive index of the first thin film layer and the refractive index of the third thin film layer. A fourth step of forming a fourth thin film layer having an intermediate refractive index with a predetermined film thickness;
Have
A manufacturing method of a multilayer filter, wherein the first thin film layer to the fourth thin film layer formed by the first step to the fourth step are used as one stack, and a predetermined number of the stacks are stacked on the substrate. . 6. The method of manufacturing a multilayer filter according to claim 5, wherein the second thin film layer and the fourth thin film layer are made of a material selected from Ta2O5, Nb2O5, TiO2, and ZrO2, and the third thin film layer is made of SiO2 or MgF2. A method for producing a multilayer filter, characterized by being formed from a material of

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