JPH10153705A - Dichroic mirror - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dichroic mirror, which functions as an almost total reflection mirror in a reflected wavelength band region, suppresses transmissivity in a transmitted wavelength band region, and functions as a half mirror having a flat spactal transmission characteristic. SOLUTION: A transmissivity adjustment film 14, which is constituted of a 3-layers film structure: a TiO2 film 12 consisting essentially of TiO2 having the high refractive index, a SiO2 film 13 having the low refractive index and the TiO2 film 12 consisting essentially of TiO2 having the high refractive index, is applied on the surface of an optical glass substrate 11 of BK 7. A multilayer film 15, which is constituted of a 13-layer film structure in which the TiO2 film 12 consisting essentially of TiO2 having the high refractive index and a SiO2 film 13 having the low refractive index are alternately laminated, is applied thereon. The transmissivity adjustment film 14 is a 3-layers transmission film structure, in which the transmissivity in the transmitted wavelength band region is possible to be suppressed to the extent of 90 to 50% due to the optical film thickness of each high refractive index film. If the film thickness is <=1/50 of the designed center wavelength of the multilayer film 15, the effect of suppression is little. If the film thickness is >=1/8, some type of the basic structure raises transmissivity. Further, flatness in the transmitted wavelength band region and a restrained wavelength region are controlled by the film thickness of the low refractive index film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a camera, a copying machine,
The present invention relates to a dichroic mirror used for an optical machine such as a printer.

[0002]

2. Description of the Related Art Conventionally, a dichroic mirror that reflects light in a specific wavelength range and transmits light in another wavelength range has been designed by using dielectric materials of a high refractive index film and a low refractive index film as a design center wavelength λ. /
The optical film of No. 4 is composed of multilayer films alternately stacked.

The simplest film configuration of such a multilayer film is as follows:
When the substrate is G, the high refractive index film is H, and the low refractive index film is L, G
+ H + L + H + L... H + L + H, and the basic configuration includes a type 1 (L / 2, H, L / 2) M and a type 2 (H / 2, L, H / 2) M. Type 1 is used when the long wavelength side of the reflection wavelength region is a high transmission wavelength band, and type 2 is used when the short wavelength side of the reflection wavelength region is a high transmission wavelength band.

FIG. 5 shows a usage form of this conventional dichroic mirror. A dichroic mirror 2 of a basic structure type 1 having a 12-layer film structure is provided on one surface of a transparent substrate 1 and a two-layer film is formed on the other surface. A half mirror 3 having a configuration is provided.

FIG. 6 shows a characteristic diagram of the transmittance of the dichroic mirror. A is a transmittance characteristic of the dichroic mirror 2, B is a transmittance characteristic of the half mirror 3, and C is a combination of the dichroic mirror 2 and the half mirror 3. It is a transmittance characteristic.

[0006]

However, in the above-mentioned prior art, in order to obtain a high transmittance in the transmission wavelength band, there are various techniques for reducing the ripple in the transmission wavelength band accompanying an increase in the number of stacked multilayer films. However, there is a problem that it is difficult to significantly suppress the transmittance of the transmission wavelength band.

For this reason, when the multi-layer dichroic mirror 2 and the half mirror 3 are used in combination with other surfaces as in the above-described conventional example, the number of transmission or reflection surfaces becomes two or more, and the ghost However, there arises a problem of high cost due to a decrease in optical characteristics and a complicated optical system.

An object of the present invention is to solve the above-mentioned problems,
It is an object of the present invention to provide a dichroic mirror that functions as a substantially total reflection mirror in a reflection wavelength band and suppresses transmittance in a transmission wavelength band and functions as a half mirror having flat spectral transmission characteristics.

[0009]

In order to achieve the above object, a dichroic mirror according to the present invention uses a transmittance adjusting film formed on the surface of a transparent substrate to transmit a light having a design center wavelength of λ / 4. And a multi-layered film in which dielectric materials of a high-refractive-index film and a low-refractive-index film having an optical film thickness are alternately laminated.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the embodiments shown in FIGS. FIG. 1 is a schematic sectional view showing a dichroic mirror. In this dichroic mirror, a TiO ₂ film 12 composed mainly of TiO ₂ having a high refractive index is formed on the surface of an optical glass substrate 11 of BK 7.
And a low refractive index SiO ₂ film 13 and a high refractive index TiO ₂
Is coated with a transmittance adjusting film 14 having a three-layer structure of a TiO ₂ film 12 containing TiO ₂ as a main component, and a high refractive index TiO ₂ film is formed thereon.
₂ as main component, TiO ₂ film 12 and SiO ₂ film 1 with low refractive index
3 is covered with a multilayer film 15 having a 13-layer film configuration in which 3 are alternately stacked.

The transmittance adjusting film 14 has a three-layered transmittance film configuration, and the transmittance in the transmission wavelength band can be suppressed to about 90% to 50% by the optical thickness of each high refractive index film. Assuming that the thickness of the multilayer film 15 is designed at λ, the suppression effect is small when the thickness of the high refractive index film is λ / 50 or less.
If it is 8 or more, the transmittance is increased depending on the type of the basic horizontal structure. Further, the flatness of the transmission wavelength band and the suppression wavelength band can be controlled by the thickness of the low refractive index film.

In the first embodiment, B
Put an optical glass substrate 11 of K7, to to 300 ° C. The surface temperature of the substrate 11, the degree of vacuum after vacuum heat evacuated to 1 × 10 ^-3 Pa or less pressure, mainly composed of TiO ₂ Ti
O ₂ film 12 is 44 nm, SiO ₂ film 13 is 220 nm,
A transmittance adjusting film 14 having a three-layer structure in which a TiO ₂ film 12 mainly composed of TiO ₂ is formed to a thickness of 44 nm is formed. Further, a low refractive index SiO ₂ film 13 is formed thereon.
And a TiO ₂ film 12 containing TiO ₂ having a high refractive index as a main component
With a design center wavelength λ of 880 nm, a film thickness of λ / 4 is alternately laminated at an incident angle of 38 °, and a 13-layer final layer is formed of a low refractive index SiO ₂ film 13 with a film thickness of λ / 8. Then, a multilayer film 15 having a 13-layer structure is formed, and a dichroic mirror having a total of 16 layers is formed, and then taken out from the vacuum evaporation apparatus.

FIG. 2 is a characteristic diagram showing the spectral transmittance of the dichroic mirror of this embodiment at an incident angle of 38 degrees.
As can be seen from FIG. 2, the dichroic mirror reflects substantially totally at a wavelength of 880 nm, and has a wavelength of 400
Between m and 700 nm, a flat spectral transmission characteristic with a transmittance of 80% is obtained.

In the second embodiment, BK7
Put the optical glass substrate 11, to to 300 ° C. The surface temperature of the substrate 11, the degree of vacuum after vacuum heat evacuated to 1 × 10 ^-3 Pa or less pressure, TiO ₂ mainly composed of TiO ₂
The film 12 has a thickness of 67 nm, the SiO ₂ film 13 has a thickness of 205 nm,
A TiO ₂ film 12 containing O ₂ as a main component is formed at a thickness of 67 nm, a transmittance adjusting film 14 having a three-layer structure is formed, and a low-refractive-index SiO ₂ film 13 and a high-refractive-index SiO ₂ film 13 are formed thereon. stacking a TiO ₂ film 12 of TiO ₂ rate was mainly composed of the designed center wavelength lambda alternately thickness of lambda / 4 at an incident angle of 38 degrees 880 nm, the final layer the low refractive index of the 13-layer SiO ₂ The film 13 is formed to have a film thickness of λ / 8, a multilayer film 15 having a 13-layer structure is formed, and a dichroic mirror having a total of 16 layers is formed and then taken out from the vacuum evaporation apparatus.

FIG. 3 is a characteristic diagram showing the spectral transmittance of the dichroic mirror of this embodiment at an incident angle of 38 degrees.
As can be seen from FIG. 3, the dichroic mirror of the present embodiment is substantially totally reflected at a wavelength of 880 nm, and a flat spectral transmission characteristic with a transmittance of 70% is obtained in the visible light range between 400 nm and 700 nm.

In the third embodiment, BK7
Put the optical glass substrate 11, to to 300 ° C. The surface temperature of the substrate 11, the degree of vacuum after vacuum heat evacuated to 1 × 10 ^-3 Pa or less pressure, TiO ₂ mainly composed of TiO ₂
The film 12 30 nm, a SiO ₂ film 13 was deposited transmittance adjusting film 14 made of two-layer structure was deposited 440 nm, TiO ₂ film mainly containing TiO ₂ of high refractive index thereon 1
2 and low refractive index SiO ₂ film 13
A thickness of λ / 4 is alternately stacked at 40 nm, and a TiO ₂ film having a high refractive index is formed to a thickness of λ / 8 as a final layer of 11 layers, thereby forming a multilayer film 15 having an 11-layer structure. 13 layers in total
After forming the dichroic mirror of the layer film, it is taken out from the vacuum evaporation apparatus.

FIG. 4 is a characteristic diagram showing the spectral transmittance of the dichroic mirror of this embodiment at an incident angle of 0 degree. As can be seen from this figure, the dichroic mirror of this embodiment is substantially totally reflected at a wavelength of 440 nm, and has a wavelength of 5 in the visible light range.
It has a flat spectral transmission characteristic with a transmittance of 80% between 20 nm and 700 nm.

[0018]

As described above, the dichroic mirror according to the present invention functions as a substantially total reflection mirror in the reflection wavelength band, suppresses the transmittance in the transmission wavelength band, and functions as a half mirror having flat spectral transmission characteristics. Mirrors can be realized, greatly contributing to higher performance and simplification of various optical machines.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a film configuration of a dichroic mirror.

FIG. 2 is a transmittance characteristic diagram of the dichroic mirror of the first embodiment.

FIG. 3 is a transmittance characteristic diagram of a dichroic mirror according to a second embodiment.

FIG. 4 is a transmittance characteristic diagram of a dichroic mirror according to a third embodiment.

FIG. 5 is a sectional view of a conventional dichroic mirror.

FIG. 6 is a transmittance characteristic diagram of a conventional dichroic mirror.

[Explanation of symbols]

Reference Signs List 11 substrate 12 TiO ₂ film 13 SiO ₂ film 14 transmittance adjusting film 15 multilayer film

Claims (5)

[Claims] 1. A dielectric material for a high refractive index film and a low refractive index film having an optical thickness of λ / 4 of a design center wavelength λ via a transmittance adjusting film formed on the surface of a transparent substrate. A dichroic mirror comprising a multilayer film in which are alternately stacked. 2. The dichroic mirror according to claim 1, wherein the transmittance adjusting film is made of a dielectric material of a high refractive index film and a low refractive index film. 3. The optical film thickness of the high refractive index film of the transmittance adjusting film is λ / 50 with respect to the design center wavelength λ of the multilayer film.
The dichroic mirror according to claim 2, wherein the range is λ / 8. 4. The method according to claim 1, wherein the dielectric material is MgF ₂ , SiO ₂ ,
The dichroic mirror according to claim 1, wherein the dichroic mirror is made of Al ₂ O ₃ , ZrO ₂ , TiO ₂ , Ta ₂ O ₅ , or a mixture thereof. 5. An optical instrument comprising the dichroic mirror according to claim 1.