JPH0553011A - Optical filter made of multilayered film - Google Patents

Abstract

PURPOSE:To decrease the number of thin films constituting blocking layers for blocking light of the wavelength, the transmission of which is required to be blocked. CONSTITUTION:The surface of a substrate 1 is roughened 2 and the layers 3 which are constituted by superposing low-refractive index thin films L and high-refractive index thin films H and allow the transmission of the light of the desired wavelength region is provided on the rough surface 2 of the substrate 1. The blocking layers 4 which are constituted by superposing the low-refractive index thin films L and the high-refractive index thin films H and block the noise components exclusive of the desired wavelength region are provided on the other surface of the substrate 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer optical filter used for various purposes such as an air-fuel ratio meter, a gas analyzer and the like.

[0002]

2. Description of the Related Art Among the multilayer optical filters used in the air-fuel ratio meter and gas analyzer, for example, the multilayer optical filter shown in FIG. 6 is known.

In FIG. 6, reference numeral 21 is an infrared transparent substrate such as silicon (Si), quartz or the like, both surfaces of which are mirror-polished. Then, for example, describing a bandpass filter, a bandpass layer 22 (hereinafter referred to as a BP layer) that transmits a predetermined wavelength band of infrared rays to one surface of the substrate 21.
However, in order to remove noise components other than the transmission band on the other surface, a short long cut layer 23 (hereinafter referred to as an SLC layer) that cuts a short wavelength band and a long wavelength band of infrared rays is, for example, a high refractive index material. Germanium as (G
A high refractive index thin film H made of e) and a low refractive index thin film L made of silicon monoxide (SiO) as a low refractive index material are formed in multiple layers. Then, the BP layer 22 and the SLC layer 23
Each of them is composed of a thin film formed by alternately vacuum-depositing germanium and silicon monoxide, and it is necessary to form the SLC layer 23 thicker than the BP layer 22. When the incident light transmitted from the BP layer 22 through the substrate 21 is incident on the SLC layer 23, the multilayer optical filter S
The LC layer 23 cuts a short wavelength band and a long wavelength band of infrared rays and transmits a predetermined wavelength band of infrared rays.

The multilayer optical filter has been shown to transmit a predetermined wavelength band, but for example, it cuts light in a wavelength range shorter than a desired wavelength such as 6μ and outputs light in a longer wavelength range. There is also a multilayer optical filter that transmits light (long wavelength transmission filter). In this case, both surfaces are configured to transmit light in the long wavelength range.

[0005]

As described above, in the case of the bandpass filter, the multilayer optical filter is such that the substrate 21 is provided with the BP layer 22 on one side and the SLC layer 23 on the other side. Further, both the BP layer 22 and the SLC layer 23 are formed by stacking thin films formed by alternately vacuum-depositing germanium and silicon monoxide to form a multilayer structure. Moreover, the BP layer 22 is relatively thin, in other words, the number of thin films of germanium and silicon monoxide may be relatively small. However, the SLC layer 23 is a thin film of germanium and silicon monoxide. It is necessary to make the number much larger than the BP layer 22 to make it thicker. Therefore, although the formation of the BP layer 22 is relatively easy, the SLC layer 23 has a problem that the time required for the formation thereof becomes long, the time and effort required for vapor deposition increase, and the cost increases. And SLC
Since the number of layers is large and the residual stress of the layers 23 is large, the adhesion strength of each layer is reduced and the durability is deteriorated.

The present invention is to solve the above-mentioned problems, and for example, a thin film forming a block layer for blocking light having a wavelength required to prevent transmission, such as the SLC layer. The purpose is to reduce the number of.

[0007]

A multilayer optical filter according to the present invention is a pass layer that transmits light in a desired wavelength band and is formed by alternately stacking high refractive index thin films and low refractive index thin films. And, a blocking layer that blocks the transmission of light in a wavelength band other than the desired wavelength band, in a multilayer optical filter provided on the substrate, the surface of the substrate, most of the light in the desired wavelength band. It is characterized in that it has a roughened surface that allows transmission and scattering of light in a wavelength band shorter than that.

The roughening of the surface of the substrate is performed on one or both sides. The wavelength range for transmitting the pass layer may be a specific wavelength band or a wavelength range longer than the specific wavelength.

The present inventor has conducted various studies to solve the above problems. As a result, the spectral characteristics of infrared rays and near infrared rays of sample A in which the surface of the silicon plate forming the substrate is a mirror surface and samples B, C, and D in which the state of the rough surface is different are measured, and in the infrared region. 250cm ^-1 , 500cm ^-1 ,
The transmittances (%) of 1000 μm ⁻¹ , 2000 cm ⁻¹ and 3000 cm ⁻¹ respectively and 2 μm and 1.5 μm in the near infrared region were obtained. The results are shown in Table 1 below.

[0010]

[Table 1]

In Table 1, R _a is the center line average roughness, RMS is the root mean square roughness, and R _max is the maximum height, respectively. The smaller these values are, the more the surface condition of the silicon substrate is a mirror surface. The closer to polishing, the larger the surface, the rougher the surface. Therefore, the surface roughness of the sample C is larger than that of the sample B, and the sample C is larger than the sample B.
Has a higher surface roughness. The numbers in parentheses are the transmittance (%) of each of Samples B to D with respect to Sample A.

As is clear from Table 1, Sample A transmits almost all infrared rays and near infrared rays. On the other hand, the transmittance of infrared rays in sample B is maintained at the same level as sample A or slightly lower than that of sample A, but the transmittance of near infrared rays in a shorter wavelength band than infrared rays is It can be seen that the value drops considerably more than A. Further, the transmittances of the samples C and D tend to be almost the same as the transmittance of the sample A, but the decrease in the infrared transmittance also becomes large.

FIG. 4 shows the spectrum of the samples A to D in the infrared region, and FIG. 5 shows the spectrum of the samples A to D in the near infrared region. 4 to 5, the tendency of each transmittance of Samples A to D in which the transmittance in the short wavelength region decreases when the surface of the substrate becomes a rough surface can be understood more easily and clearly. The present invention has been completed by obtaining the results shown in Table 1 and FIGS.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the multilayer optical filter of the present invention will be described with reference to FIG. 1 by taking a bandpass filter as an example.

In FIG. 1, reference numeral 1 is a substrate made of silicon (Si), one surface of which is roughened. The rough surface 2 is formed by sandblasting or buffing the surface of the substrate 1, and can be formed by any means. Reference numeral 3 is a bandpass layer formed on the rough surface 2 of the substrate 1 for transmitting infrared rays in a desired wavelength band.
This is formed by alternately vacuum-depositing a low refractive index thin film L made of silicon monoxide as a low refractive index material and a high refractive index thin film H made of germanium as a high refractive index material. Reference numeral 4 denotes a blocking layer that cuts a short wavelength band and a long wavelength band of infrared rays in order to remove noise components other than the transmission band, which is formed on the other surface of the substrate 1. Similar to the bandpass layer 3, the blocking layer 4 is formed by alternately vacuum depositing a low refractive index thin film L and a high refractive index thin film H.

This multilayer optical filter is constructed as described above, and in the incident light 5 incident on the substrate 1 from the bandpass layer 3 in the schematic diagram of the spectrum shown in FIG. The rough surface 2 scatters the light b in the wavelength band shorter than the infrared light a in the desired wavelength band transmitted through the bandpass layer 3 to generate scattered light 5a (see FIG. 1).
Then, in the incident light 5 transmitted through the substrate 1, the blocking layer 4 blocks transmission of the light b in the shorter wavelength band and the light c in the longer wavelength band than the infrared light a in the desired wavelength band, and the desired light is obtained. The infrared ray a in the wavelength band of is transmitted. In this way, the light b in the wavelength band shorter than the infrared light a in the desired wavelength band of the incident light 5 is scattered as the scattered light 5a in advance on the rough surface 2 of the substrate 1, and then the incident light 5
Is incident on the blocking layer 4, it is possible to reduce the number of layers of the low refractive index thin film L and the high refractive index thin film H constituting the blocking layer 4 corresponding to the scattered light 5a scattered on the rough surface 4. It is possible. Therefore, the cost required to form the blocking layer 4 can be reduced, and
It is possible to increase the adhesive force of each layer and improve the durability.

Although the substrate 1 is made of Si in the first embodiment, the substrate 1 is made of, for example, SiO ₂ or A.
It is possible to use l ₂ O ₃ , quartz, or any other optical substrate, and use high and low refractive index materials for forming the bandpass layer 3 and the blocking layer 4 as well. Is possible. The surface of the substrate 1 on which the bandpass layer 3 is provided is the rough surface 4, but the surface of the substrate 1 on which the blocking layer 4 is provided can be the rough surface 4.
The scattering of light in this case is also the same. Further, the multilayer optical filter of the first embodiment transmits only infrared rays in a desired wavelength band, but cuts light in a wavelength range shorter than a desired wavelength such as 6 μ, and the like. It is also possible to apply it to a multilayer optical filter that transmits light in the long wavelength region of.

FIG. 3 shows a second embodiment in which rough surfaces 4a and 4b are formed on both surfaces of the substrate 1. The other structure is the same as that of the first embodiment, and therefore the same reference numerals are given. And
In this embodiment, the rough surfaces 4a and 4b on both sides of the substrate 1 are
Since light in a wavelength range shorter than a desired wavelength range is scattered, it is possible to further reduce the number of layers of the low refractive index thin film L and the high refractive index thin film H forming the blocking layer 4.

[0019]

As described above, the multilayer optical filter of the present invention makes the surface of the substrate a rough surface, scatters light in a wavelength range shorter than a desired wavelength range, and blocks its transmission, In addition, the light having a wavelength other than the desired wavelength range is blocked by the blocking layer, and the light having the desired wavelength range is transmitted. Therefore, it is necessary to form the blocking layer because it is possible to reduce the number of layers of the high-refractive-index thin film and the low-refractive-index thin film that form the blocking layer in response to the scattered light scattered on the rough surface of the substrate. It is possible to shorten the time and reduce the cost. Further, as the number of the blocking layers is reduced, the stresses of the blocking layers are reduced and the adhesive force of each layer is increased, so that the durability of the filter can be improved.

[Brief description of drawings]

FIG. 1 is an enlarged front view with a part of the first embodiment omitted.

FIG. 2 is a schematic diagram of a spectrum of the first embodiment.

FIG. 3 is an enlarged front view with a part of the second embodiment omitted.

FIG. 4 is a spectrum diagram in the infrared region of a substrate with a roughened surface.

FIG. 5 is a spectral spectrum diagram in the near infrared region of a substrate having a roughened surface.

FIG. 6 is an enlarged front view in which a part of a conventional example is omitted.

[Explanation of symbols]

1: substrate, 2: rough surface, 3: bandpass layer, 4: blocking layer.

Claims (1)

[Claims] 1. A layer for transmitting light in a desired wavelength range, comprising a high refractive index thin film and a low refractive index thin film alternately stacked to form a multilayer, and light in a wavelength range other than the desired wavelength range. The blocking layer for blocking the transmission of, in the multilayer optical filter provided on the substrate made of an optical material, the surface of the substrate, most of the light of the desired wavelength range is transmitted, shorter wavelength range than it A multilayer optical filter characterized by having a roughened surface capable of scattering the light of.