JP2001337210A - Optical reflection mirror - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve such problems that a conventional optical reflection mirror generates polarized light when non-polarized incident light enters oblique to the mirror and that use of a filter to control the polarized light to natural light is required and this decreases the intensity of the reflected light. SOLUTION: The optical reflection mirror is obtained by successively laminating on a substrate, from the substrate side, a metal film having enough thickness not to transmit light as a first layer and a transparent dielectric film as a second layer. The metal film is specified to have <=1.5 refractive index and >=6.0 extinction coefficient at the wavelength of the incident light. The refractive index of the dielectric film at the wavelength of the incident light is specified to >=1.30 and <=1.65, and the optical film thickness is specified to >=0.20 λ and <=0.38 λ, wherein λ is the wavelength of the incident light.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to optical communication, sensors to which optical technology is applied, liquid crystal display elements, optical measuring devices, and the like.
The present invention relates to an optical reflecting mirror made of metal widely used in the optical technology field.

[0002]

2. Description of the Related Art Conventionally, optical reflecting mirrors include an Al reflecting mirror and an A reflecting mirror.
A device utilizing a high reflectance of a metal, such as a g reflector, is often used. These optical reflecting mirrors are required to have clarity of the reflected image, and therefore are required to have optical smoothness.
However, it is difficult to process metal optically smoothly,
A metal film is formed on glass, which is easy to obtain optical smoothness, and this is used as a reflector.

It is known that these metal reflectors, especially Al reflectors, have poor oxidation resistance. In order to improve the durability, overcoating is performed on a metal film. In particular, in the case of an Al reflecting mirror, it is known that oxidation resistance is improved by using a magnesium fluoride film as an overcoat.

Further, in order to improve the reflectance of a metal reflector, there is also a reflector called an enhanced reflection mirror in which a transparent dielectric film having a low refractive index and a transparent dielectric film having a high refractive index are laminated on a metal film. I do. Further, there is a metal reflecting mirror having a light transmittance called a metal semi-transparent mirror (half mirror). This has a light transmissivity provided by forming a thin metal film on a light transmissive substrate, and has both light reflectivity and light transmissivity.

[0005]

However, with a conventionally known optical reflecting mirror, even when unpolarized light is incident,
At oblique incidence, reflected light is polarized. When the angle (incident angle) between the incident light and the normal line of the incident substrate surface is close to 0 ° and close to normal incidence, the p-polarized light reflectance and the s-polarized light reflectance are close to each other, but the incident angle is large. As the ratio increases, the ratio between the p-polarized light reflectance and the s-polarized light reflectance increases. That is, it is known that the ratio between the p-polarized light reflectance and the s-polarized light reflectance depends on the incident angle.

As described above, in an optical system in which light is obliquely incident on a reflecting mirror, outgoing light is polarized even if the incident light is in a non-polarized state. Therefore, when it is desired to extract unpolarized light as an output, the polarization component having a high reflection intensity is reduced by some means so as to be substantially the same as the polarization component having a low reflection intensity, and the s-polarization intensity and the p-polarization intensity are reduced. The ratio had to be adjusted to 1: 1. Specifically, there is a method using a polarizing filter. However, when the reflected light is made to be in a non-polarized state by such a method, there is a problem that a decrease in light intensity cannot be avoided.

According to the present invention, in order to solve such a problem, even when light is obliquely incident (when the angle between the incident light and the normal to the substrate surface is larger than 0 °), reflected light is not generated. An object of the present invention is to provide a metal reflecting mirror that maintains a polarization state.

[0008]

The optical reflecting mirror of the present invention comprises:
This is a reflecting mirror in which a metal film having a thickness sufficient to prevent light from passing through is formed as a first layer and a transparent dielectric film is formed as a second layer on the substrate in order from the substrate side. Here, the refractive index of the metal film at the wavelength of incident light is 2.0
Hereinafter, the extinction coefficient is set to 6.0 or more. In addition, the refractive index of the dielectric film at an incident light wavelength is 1.30 or more and 1.65 or less, and the optical film thickness is 0.20 when the incident light wavelength is λ.
It is set to λ to 0.38λ. Further, the refractive index of the dielectric film at the wavelength of incident light is more preferably 1.30 or more and 1.46 or less.

As the metal film, Al or an alloy containing Al as a main component, Ag or an alloy containing Ag as a main component,
Either Cu or an alloy containing Cu as a main component, Au or an alloy containing Au as a main component can be used.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments. In order to find a film configuration for achieving the object of the present invention, a simulation was first performed using a method called a matrix method. This method is described in H.
A. This is described in detail in "Optical Thin Film" by Macleod (Nikkan Kogyo Shimbun).

According to this simulation, the present inventors provide a laminated structure of the metal film 14 and the transparent dielectric film 16 on the substrate 12 as shown in FIG. 1 so that even when the incident light 30 is obliquely incident, It has been found that the optical reflecting mirror 10 that does not generate polarized light can be realized.

An example of manufacturing a reflecting mirror based on the simulation results will be described below. Summarizing the results, it can be seen that a material having an extinction coefficient (imaginary part of the complex refractive index) k as large as 6.0 or more is preferable for increasing the reflectance as the metal film. In addition, k is about 20 or less in a normal metal. The refractive index (the real part of the complex refractive index) n is 2.
A material as small as 0 or less is preferable. The normal metal n is about 0.2 or more. Examples of the metal material satisfying such characteristics include Al, Ag, and Au shown in the examples, Cu, and the like. In addition to a single element metal such as these, these metals are mainly used. Alloys can also be used.

The transparent dielectric film has a refractive index of 1.30 or more and 1.6 at the wavelength of incident light.
5 or less, and when the incident light wavelength is λ, the optical film thickness is 0.5.
It is necessary to be 20λ or more and 0.38λ or less. further,
The refractive index of the dielectric film at an incident light wavelength is more preferably 1.30 or more and 1.46 or less. Examples of the transparent dielectric film satisfying such characteristics include magnesium fluoride, silicon dioxide, aluminum oxide, calcium fluoride, aluminum fluoride, yttrium fluoride, ytterbium fluoride, silicon monoxide, etc. Can be used. In particular, when fluorides such as magnesium fluoride and calcium fluoride are formed on a metal film,
This is preferable because the surface of the metal film is not oxidized.

There is no particular limitation on the material of the substrate. However, in order to obtain a reflection image, optical smoothness is necessary, so that an optically smooth substrate is important.

The method for forming the metal film and the transparent dielectric film of the present invention is not particularly limited, and a vacuum deposition film formation method, a sputtering film formation method, a sol-gel film formation method, a chemical vapor deposition method ( CVD), a vacuum deposition film forming method using plasma called ion plating, or the like can be used. Note that A
When the adhesion to the substrate is insufficient in the u film, etc.,
If necessary, for example, a Cr film or the like may be used as an intermediate layer between the substrate and the metal film, and the film configuration is not necessarily limited to two layers.

Example 1 A quartz glass substrate having a size of 30 mm long × 30 mm wide × 10 mm thick was placed in a vacuum evaporation apparatus, and the quartz glass substrate was heated to 150 ° C. by a substrate heater installed in the apparatus. In the state, an Al film (n = 1.88 at an incident light wavelength λ = 1550 nm, k = 1)
2.96) was formed to a thickness of 200 nm.
Thereafter, a magnesium fluoride (MgF ₂ ) film is
54 nm (optical thickness = 0.2 when λ = 1550 nm)
2λ) to form an optical reflecting mirror.

The vacuum evaporation was performed by an electron beam evaporation method, and the film was formed while rotating the glass plate while setting the distance from the evaporation crucible to the glass plate to 100 cm. The ultimate vacuum before the start of vapor deposition was 0.00
Evacuation was performed up to 3 Pa. Both the Al layer and the MgF ₂ layer were deposited without introducing a gas.

As shown in FIG. 1, the obtained optical reflecting mirror 1
At 0, incident light 30 having a wavelength of 1550 nm was incident from the coating surface side, and the s-polarized light reflectance and p-polarized light reflectance of the outgoing light 32 were measured. The measurement was performed by changing the incident angle 22 (the angle formed by the normal 20 of the surface of the substrate 12 and the incident light 30) between 5 and 75 degrees. FIG. 2 shows the measurement results.

It is understood that the s-polarized light reflectance and the p-polarized light reflectance are almost equal in the range of the incident angle from 5 degrees to 75 degrees. Also at 75 degrees incidence, the s-polarized light reflectance is 95.9% and the p-polarized light reflectance is 95.4%, which is almost a non-polarized state, and the natural light reflectance is 95.7% (= (95.9 + 95. 4) / 2), the reflectance is high, indicating that the mirror has a sufficient function.

Example 2 In the same manner as in Example 1, an Ag film having a thickness of 200 nm (n = 1.58 at λ = 1550 nm, k = 0.10) was formed on an optically smooth soda lime glass plate.
75), a SiO ₂ film (λ = 155) having a thickness of 267.7 nm
In the case of 0 nm, the optical film thickness = 0.25λ) was sequentially formed by a vacuum evaporation method.

FIG. 3 shows the measurement results of the s-polarized light reflectance and the p-polarized light reflectance as in Example 1. Incident angle from 5 degrees to 75
It can be seen that the s-polarized light reflectance and the p-polarized light reflectance are almost equal in the range of degrees. Even at 75 degrees incidence, s-polarized light reflectance = 9
6.4%, p-polarized light reflectance = 98.0%, almost non-polarized state, natural light reflectance = 97.2% (= (96.4 + 9)
It can be seen that the reflectance is high (8.0) / 2), and that it has a sufficient function as a reflector.

Example 3 In the same manner as in Example 1, an Au film having a thickness of 200 nm (n = 0.41 at λ = 1200 nm, k = 7.5) was formed on an optically smooth soda lime glass plate.
2), an Al ₂ O ₃ film having a film thickness of 264.8 nm (λ = 1200
In the case of nm, the optical film thickness = 0.36λ) was sequentially formed by a vacuum evaporation method.

FIG. 4 shows the measurement results of the s-polarized light reflectance and the p-polarized light reflectance when the wavelength of the incident light was 1200 nm and the other conditions were the same as in Example 1. Incident angle from 5 degrees to 75
It can be seen that the s-polarized light reflectance and the p-polarized light reflectance are almost equal in the range of degrees. Even at 75 degrees incidence, s-polarized light reflectance = 9
5.9%, p-polarized light reflectance = 96.7%, almost non-polarized state, natural light reflectance = 96.3% (= (95.9 + 9)
It can be seen that the reflectance is high at 6.7) / 2), and that it has a sufficient function as a reflector.

Comparative Example 1 In the same manner as in Example 1, only an Al film having a thickness of 200 nm was formed on an optically smooth soda lime glass plate by a vacuum evaporation method. FIG. 5 shows the measurement results of the s-polarized light reflectance and the p-polarized light reflectance as in Example 1.
Shown in As the angle of incidence increases from 5 degrees to 75 degrees,
It can be seen that the difference between the s-polarized light reflectance and the p-polarized light reflectance increases. For 75 degree incidence, s-polarized light reflectance = 98.9%, p
The polarized light reflectance is 85.5%, which is a polarized state. To make this into a non-polarized state (ie, s-polarized light intensity: p-polarized light intensity = 1: 1) with a filter, the s-polarized light reflection intensity must be at least 85.5%. It turns out that it is necessary to reduce it to 5%. Therefore, the natural light reflectance when adjusted to obtain a non-polarized state is 85.5% at the maximum, which indicates that a sufficient function as a reflector cannot be exhibited.

Comparative Example 2 In the same manner as in Example 1, a 200 nm thick Ni film (λ = 1550 nm, n = 3.18, k = 4.4) was formed on an optically smooth soda lime glass plate.
8), and then an MgF ₂ film (optical thickness = 0.22λ in the case of λ = 1550 nm) was sequentially formed to produce a reflecting mirror.
FIG. 6 shows the measurement results of the s-polarized light reflectance and the p-polarized light reflectance as in Example 1. It can be seen that the reflectivity is very low at about 40% to about 60% when the incident angle is in the range of 5 ° to 75 °, which is a level that cannot be used as a reflecting mirror.

Comparative Example 3 An Al film (film thickness: 1) was formed on an optically smooth soda lime glass plate in the same manner as in Example 1.
50 nm) and then a 172.2 nm-thick MgF ₂ film (optical thickness = 0.15λ in the case of λ = 1550 nm) to form a reflecting mirror. FIG. 7 shows the measurement results of the s-polarized light reflectance and the p-polarized light reflectance as in Example 1. When the incident angle is 65 degrees, the ratio of the p-polarized light reflectance / s-polarized light reflectance is about 0.957, indicating that polarized light is generated.

Comparative Example 4 An Au film (thickness: 200) was formed on an optically smooth soda lime glass plate by sputtering.
nm), and then an Si ₃ N ₄ film having a thickness of 208.1 nm (in the case of an incident light wavelength λ = 1200 nm, the optical thickness = 0.33).
λ) were sequentially laminated to form a reflecting mirror.

FIG. 8 shows the measurement results of the s-polarized light reflectance and the p-polarized light reflectance when the incident light wavelength was 1200 nm and the other conditions were the same as in Example 1. Incident angle from 5 degrees to 60
As the angle increases, the difference between the s-polarized light reflectance and the p-polarized light reflectance increases. When the incident angle is 60 degrees or more, the difference between the s-polarized light reflectance and the p-polarized light reflectance decreases as the incident angle increases. I understand.

In the case of 55 degree incidence, s-polarized light reflectance = 8
The polarization state is 5.7% and the p-polarized light reflectance is 83.5%. To make this into a non-polarized state (that is, s-polarized light intensity: p-polarized light intensity = 1: 1) with a filter, s-polarized light is used. It can be seen that the reflection intensity needs to be reduced to at least 83.5%. Therefore, the natural light reflectance when adjusted so as to obtain a non-polarized state is 83.5% at the maximum.
Therefore, a sufficient reflectance cannot be realized as a reflecting mirror.

[0030]

The optical reflecting mirror of the present invention does not produce polarized light for obliquely incident light. Therefore, there is no need to consider the influence of polarized light when using the optical reflecting mirror of the present invention, and the optical design can be made very simple. Also,
Since the reflected light is unpolarized, it is not necessary to use a filter for adjusting the polarized light to natural light.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a structure of an optical reflecting mirror according to the present invention.

FIG. 2 is a diagram illustrating reflection characteristics of the optical reflecting mirror of the first embodiment.

FIG. 3 is a diagram illustrating reflection characteristics of an optical reflecting mirror according to a second embodiment.

FIG. 4 is a diagram illustrating reflection characteristics of an optical reflecting mirror according to a third embodiment.

FIG. 5 is a diagram showing reflection characteristics of the optical reflecting mirror of Comparative Example 1.

FIG. 6 is a diagram showing reflection characteristics of the optical reflecting mirror of Comparative Example 2.

FIG. 7 is a diagram showing the reflection characteristics of the optical reflecting mirror of Comparative Example 3.

FIG. 8 is a diagram showing reflection characteristics of the optical reflecting mirror of Comparative Example 4.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Optical reflecting mirror 12 Substrate 14 Metal film 16 Transparent dielectric film 20 Normal to substrate surface 22 Incident angle 30 Incident light 32 Emitted light

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shinji Kawamoto 3-5-11 Doshomachi, Chuo-ku, Osaka-shi, Osaka Inside Nippon Sheet Glass Co., Ltd. (72) Isao Muraguchi 3-chome, Doshucho, Chuo-ku, Osaka-shi, Osaka No.5-11 Nippon Sheet Glass Co., Ltd. F-term (reference) 2H042 DA02 DA04 DA05 DA07 DA12 DA18 DB00 DC02 DE00 DE04 DE09

Claims (3)

[Claims] 1. An optical device comprising: a metal film having a thickness sufficient to prevent light from passing through at least as a first layer and a transparent dielectric film as a second layer on a substrate in order from the substrate side. In the reflecting mirror, the refractive index of the metal film at an incident light wavelength is 2.0 or less, the extinction coefficient is 6.0 or more, and the refractive index of the dielectric film at an incident light wavelength is 1.30 or more. An optical reflector, wherein the optical thickness is not more than 65 and the optical film thickness is not less than 0.20 times and not more than 0.38 times the wavelength of the incident light. 2. The optical reflecting mirror according to claim 1, wherein a refractive index of said dielectric film at an incident light wavelength is from 1.30 to 1.46. 3. The method according to claim 1, wherein the metal film is made of Al or an alloy mainly containing Al, Ag or an alloy mainly containing Ag, Cu or an alloy mainly containing Cu, Au or an alloy mainly containing Au. The optical reflecting mirror according to claim 1, wherein: