JPH11305035A - Multilayer film filter free of temperature dependence and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the practical multilayer film filter whose characteristics do not depend upon temperature without using a substrate which has a large coefficient of expansion. SOLUTION: On a transparent substrate 1, a multilayer film is vapor- deposited. In this case, the transparent substrate 1 in use does not have a large coefficient for thermal expansion and is free of the peeling of the multilayer film 2 and its breakage, when cooled down to a room temperature after being raised in temperature at the vapor-deposition of the multi-layered film 2. After the transparent substrate 1 and multilayer film 2 are cooled, a transparent adhesive 3 is applied over the multilayer film 2, and a body 4 is adhered. The coefficient of thermal expansion of the body 4 in use is larger than that of the transparent substrate 1 and if characteristics of the multilayer filter vary with temperature, the body 4 thermally expands or contracts large to hold constant the product of the mean refractive index and thickness of the multilayer film 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical multilayer filter used for optical communication and the like, and more particularly to a multilayer filter whose wavelength characteristic does not depend on temperature and a method of manufacturing the same.

[0002]

2. Description of the Related Art With the recent development of high-speed communication networks, research and development for practical use of optical communication have been actively conducted. In such optical communication, it is necessary to transmit a large amount of signals at high speed, and as one of the methods, a wavelength division multiplexing method is considered to be promising. In wavelength division multiplexing, attempts have been made to increase the amount of information transmitted at a time by storing as many signals having different carrier wavelengths as possible in a narrow band.

Therefore, the wavelengths of different channels having different carrier wavelengths are very close to each other, and are used in optical communication networks to correctly transmit and receive signals of these channels having wavelengths that are close to each other. The performance of the optical multilayer filter becomes a problem. In particular, when the wavelengths of different channels are close to each other, it is necessary that the characteristics of the multilayer filter with respect to the wavelength be stable, and a slight change in the wavelength characteristics degrades the quality of optical signal transmission / reception. I will.

On the other hand, a multilayer filter is conventionally formed on a transparent substrate heated by an electron beam evaporation method or the like. However, such a multilayer film has a low packing density of a film and adsorbs moisture in the multilayer film. The change in wavelength characteristics due to the change in ambient humidity was large. On the other hand, in recent years, a multilayer film with a high packing density can be formed by a film forming process using ions or plasma such as an ion assisted vapor deposition method, an ion plating method, and a sputtering method. It is now negligible. However, with respect to a temperature change, the refractive index and the physical thickness of each layer constituting the multilayer film change with temperature, so that the average optical thickness (the average refractive index and the physical thickness of the multilayer film) Product) and the wavelength characteristic changes.
In general, the refractive index of a film tends to increase as the temperature rises, and the physical film thickness also increases due to thermal expansion. Therefore, the average optical film thickness of the multilayer film increases with the temperature rise, and the wavelength characteristics also increase. It tends to shift to the wavelength side.

To solve this problem, a technique of using a substrate having a large expansion coefficient to expand a multilayer film two-dimensionally by thermal expansion of the substrate, causing volume distortion in the film, and reducing a wavelength shift is a special feature. It is disclosed in Japanese Unexamined Patent Publication No. Hei 7-198935.

[0006]

According to the above-mentioned prior art, Japanese Patent Application Laid-Open No. 7-198935, in order to make the wavelength shift of the multilayer filter close to zero, it depends on the material of the multilayer film. The expansion coefficient is approximately 107 to 121 (×
10 ⁻⁷ / ° C.).
However, when a multilayer film is actually formed directly on a substrate having such a large expansion coefficient, the multilayer film peels off from the substrate,
It was found that the substrate was damaged or deformed and was not practical. The cause is considered as follows.

In a film forming process using ions or plasma, the temperature of the substrate increases during the film formation due to the influence of radiant heat. Therefore, in the case of a substrate having a large expansion coefficient, a multilayer film is formed with the substrate greatly expanded. . After the film is formed, the substrate shrinks greatly when the temperature is returned to room temperature, so that the multilayer film receives a strong compressive stress from the substrate. Furthermore, in the film formation process using ions or plasma, the film packing density is high, so that the multilayer film is potentially multi-layered. The membrane has a compressive internal stress. As described above, both the internal compressive stress of the film itself and the compressive stress received from the substrate are applied to the multilayer film. It is considered that the substrate may be damaged or deformed even if it comes into close contact with the substrate.

An object of the present invention is to solve the above-mentioned problems and to provide a practical multilayer film filter whose characteristics do not depend on temperature without using a substrate having a large expansion coefficient, and a method of manufacturing the same.

[0009]

A multilayer filter according to the present invention comprises: a transparent substrate having a multilayer film formed on at least one side;
Adhered to at least the surface of the multilayer film, or the periphery thereof,
An object having a thermal expansion coefficient larger than that of the multilayer film and the transparent substrate, and a change in average optical film thickness of the multilayer film caused by a change in temperature is caused by a change in volume caused by a change in temperature of the object. This offsets the deformation of the multilayer film, thereby keeping the wavelength characteristics of the multilayer film approximately unchanged.

[0010] In the method for manufacturing a multilayer filter according to the present invention, a multilayer film is formed on at least one surface of a transparent substrate, and an object having a larger thermal expansion coefficient than the multilayer film and the transparent substrate is formed on at least the surface of the multilayer film. Or adhered to the surroundings, the change in the average optical film thickness of the multilayer film caused by a temperature change is offset by the deformation of the multilayer film due to a change in volume caused by a temperature change of the object, The wavelength characteristic of the multilayer film is kept approximately unchanged.

According to the present invention, since the coefficient of thermal expansion of the substrate on which the multilayer film is formed is not increased, even if the temperature increased during the formation of the multilayer film decreases after the formation, the multilayer film may be peeled off or the substrate may be damaged. Does not occur. In addition, changes in the characteristics of the multilayer filter due to temperature changes are compensated by attaching an object having a large thermal expansion coefficient to the surface of the multilayer film or to the surface of the multilayer film and the back side of the substrate with an adhesive. The temperature does not rise extremely at the time of sticking, and there is no defect such as breakage during the production of the multilayer filter.

The object to be attached to the multilayer filter is
If the temperature rises, mechanically pull the multilayer film,
Reduce the physical thickness of the multilayer and keep the optical thickness of the multilayer constant. Similarly, when the temperature drops, the object shrinks more than the multilayer film or the substrate, increasing the physical thickness of the multilayer film and again keeping the optical thickness of the multilayer film constant.

In this connection, the term "around the multilayer film" means not the surface of the multilayer film but the side edge thereof.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION A multilayer filter according to the present invention comprises a transparent substrate having a multilayer film formed on at least one side, and a multilayer film and a transparent substrate adhered to at least the surface or periphery of the multilayer film. An object having a large coefficient of thermal expansion, and a change in the average optical film thickness (product of the average refractive index and the physical film thickness) of the multilayer film caused by a temperature change is caused by a change in the temperature of the object. The deformation of the multilayer film due to the resulting change in volume is offset by the deformation, and the wavelength characteristic of the multilayer film is kept approximately unchanged.

Here, the average refractive index means the following. That is, the multilayer film is formed by stacking films having different refractive indexes in any number of layers. With such a configuration, light having a characteristic wavelength of incident light is transmitted. This is the function of the multilayer film as a bandpass filter. At this time, the transmitted light passes through the layers of the films having different refractive indices so that the multilayer film has a certain refractive index. Feels like a substance. Therefore, the transmitted light propagates through the multilayer film at the same optical distance as when passing through a specific refractive index and is output. The average refractive index is obtained by dividing the physical distance of the transmitted light by the optical distance that the transmitted light felt when the transmitted light passed through the multilayer film. The average optical distance or the optical thickness is the total optical distance felt from the time when light is incident to the time when light is emitted. Here, the term “average” does not mean that the optical distance of each layer of the multilayer film is always kept constant, but that if the total is kept constant, the wavelength characteristics do not change. Based on

When the multilayer film expands with an increase in temperature to increase the physical film thickness and increase the average refractive index, when the multilayer film is bonded to the substrate on which the multilayer film is formed or the surface of the multilayer film or the periphery thereof, The expanded object also expands at the same time. Since the coefficient of thermal expansion of the object is larger than that of the multilayer film or the substrate, the expansion amount is large, and the object is expanded by pulling the multilayer film or the substrate. Here, since the multilayer film is pulled by the object, the multilayer film is mechanically stretched. Due to this mechanical stretching effect, the physical thickness of the multilayer film is reduced, and the product of the average refractive index and the physical film thickness of the multilayer film changed by the temperature rise, that is, the change of the average optical film thickness. Cancel out and remain approximately unchanged. Since the wavelength characteristic of the multilayer film is basically determined by the average optical film thickness, if this is kept unchanged by the temperature, the wavelength characteristic of the multilayer film is also kept unchanged.

When the temperature decreases, the multilayer film shrinks, and the physical film thickness decreases accordingly. However, objects adhered to or around the multilayer film shrink more than the multilayer film, causing the multilayer film to shrink further. As a result, the physical film thickness of the multilayer film increases, and as a result, the product of the average refractive index of the multilayer film and the physical film thickness approximates to the temperature change as in the case of the temperature rise. Will be kept unchanged.

FIG. 1 is a view for explaining a method of manufacturing the multilayer filter of the first embodiment, and FIG. 2 is a view for explaining the multilayer filter manufactured in the first embodiment. is there. FIG. 3 is a diagram illustrating a wavelength transmission characteristic of the multilayer filter of the first embodiment.

A method for manufacturing the multilayer filter of the present embodiment will be described with reference to FIG. FIG. 1A shows that
This is a transparent substrate 1. In the present embodiment, as the transparent substrate 1,
A flat plate made of optical glass having a coefficient of thermal expansion α of 79 (× 10 ⁻⁷ / ° C.) and made of S-TIM25 (trade name, manufactured by OHARA CORPORATION) was used. First, a multilayer film 2 is formed on the surface of the transparent substrate 1 by an ion plating method (not shown). The multilayer film 2 of the present embodiment is made of a dielectric material of SiO ₂ and Ta ₂ O _5.
Are alternately laminated, and functions as a bandpass filter that transmits only a specific wavelength as shown in FIG. The coefficient of thermal expansion α of the film is 5 for the SiO ₂ film.
６6 (× 10 ⁻⁷ / ° C.), 70 to 90 for Ta ₂ O ₅ film
(× 10 ⁻⁷ / ° C.). The temperature of the transparent substrate 1 during the formation of the multilayer film was raised to about 200 to 250 ° C. due to the radiation heat of the plasma. No breakage or deformation of the substrate occurred. As a comparative example, S-FPL52 (trade name, manufactured by OHARA CORPORATION,
When α = 124 × 10 ⁻⁷ / ° C.) or S-PHM52 (trade name, manufactured by Ohara Corporation, α = 101 × 10 ⁻⁷ / ° C.), the temperature of the transparent substrate 1 after forming the multilayer film is reduced. When the temperature was returned to room temperature, peeling of the film, breakage and deformation of the substrate occurred, which was not practical.

Next, as shown in FIG.
In a 0 nm band (refer to a wavelength band of about 1530 nm to about 1565 nm), an appropriate amount of a transparent adhesive 3 is applied to the surface of the multilayer film 2 formed on the transparent substrate 1.
Then, the object 4 having a larger coefficient of thermal expansion than the multilayer film 2 is adhered to the object 4 while taking care not to allow air to enter therebetween. In the present embodiment, the transparent adhesive 3 is a thermosetting epoxy-based adhesive, trade name EPO-TEK353ND (EPOXY
TECHNOLOGY, INC.) And a flat plate made of optical glass having a thermal expansion coefficient α of 142 (× 10 ⁻⁷ / ° C.) S-FPL53 (manufactured by OHARA) was used as the object 4. After bonding the object 4 to the transparent substrate 1, the adhesive is cured by leaving the object 4 at a high temperature of 100 ° C. for 30 minutes. At this time, since the thermal expansion coefficient of the object 4 is larger than that of the transparent substrate 1 and the multilayer film 2, the temperature of the
Shrinks more than the multilayer film 2, the physical thickness of the multilayer film 2 slightly increases, and as shown in FIG. 3, the wavelength characteristic shifts slightly (about 0.3 nm) to the longer wavelength side. The wavelength shift amount is a value determined by the curing temperature of the adhesive and the thermal expansion coefficient of the object 4, the multilayer film 2, and the transparent substrate 1. Therefore, in this embodiment, the wavelength shift amount of the multilayer film is determined in advance in consideration of the wavelength shift amount. The characteristics are made shorter than the desired wavelength characteristics. The curing temperature of the adhesive is set to 80 to 15
By changing the temperature within the temperature range of 0 ° C., the wavelength shift amount can be adjusted without changing the object 4, the multilayer film 2, and the transparent substrate 1, and the wavelength characteristic of the multilayer film after bonding can be adjusted to a desired value. Can be adjusted.

FIG. 2 shows the multilayer filter of the present embodiment manufactured by the above steps. In the present embodiment, an object 4 having a larger coefficient of thermal expansion than the multilayer film 2 is adhered to the surface of the multilayer film 2, and the multilayer film 2 has a higher thermal expansion coefficient.
The average refractive index of the multilayer film 2 increases and the physical film thickness increases, so that the average optical film thickness increases. The configuration is such that changes in film thickness are offset.

The multilayer film (band pass) of the present embodiment is actually
FIG. 4 shows the result of measuring the temperature change of the transmission center wavelength of the filter. As a comparative example, FIG. 4 also shows the results of a similar measurement performed on a conventional multilayer filter in which the object 4 having a large thermal expansion coefficient is not adhered to the surface. As shown in FIG. 4, the multilayer filter of the present embodiment has a sufficiently small wavelength shift due to temperature as compared with the conventional multilayer filter, and has a temperature of 0 to 80 ° C.
In the temperature range of about 0.024 nm. Here, the temperature change of the wavelength shift changes quadratically, which is caused by the temperature coefficient of the refractive index of SiO ₂ or Ta ₂ O ₅ constituting the multilayer film 2 or the S-FPL 53 which is the object 4. It is presumed that the thermal expansion coefficient of the optical glass gradually increases due to the temperature rise. In the present embodiment, 0 to 80
In the temperature range of ° C., the transmission center wavelength, that is, the temperature at which the optical film thickness (the product of the average refractive index and the physical film thickness) of the multilayer film becomes minimum is almost at the center of the temperature range. The temperature dependency is the smallest.

In the first embodiment, a multilayer filter having a small temperature dependence of the wavelength characteristic was obtained even if the configuration was changed as follows. -Transparent substrate 1 is trade name S-BSL7 (manufactured by OHARA, α =
72 × 10 ⁻⁷ / ° C.). TiO ₂ (α = 70 to 90 × 10 ⁻⁷ / ° C.) or N instead of Ta ₂ O ₅ which is a dielectric material constituting the multilayer film 2
When b ₂ O ₅ (α = 70 to 90 × 10 ⁻⁷ / ° C.) is used. SiO ₂ , Ta ₂ O as a dielectric constituting the multilayer film 2
_When other dielectrics (such as Al ₂ O ₃ ) are used in addition to ₅ . -When the multilayer film 2 is composed of a dielectric and a metal (Ag or the like). When the wavelength characteristic of the multilayer film 2 is a long wave pass filter that transmits the long wavelength side, a short wave pass filter that transmits the short wavelength side, or the like. Here, when a long wave pass filter or a short wave pass filter is formed, it can be formed by alternately laminating a suitable material with the same thickness as a multilayer film. On the other hand, when a bandpass filter is formed, a thick portion serving as a spacer is periodically inserted at predetermined intervals between the stacked films. As described above, although the band-pass filter and the short-pass filter and the long-pass filter are different in the configuration of the multilayer film, the band-pass filter is a thin film layer attached to the substrate by an intermolecular force and has a large thermal expansion coefficient. The temperature independence due to the configuration in which 4 is attached with an adhesive is similarly obtained. Other physical film forming methods using ion or plasma such as ion assisted vapor deposition or sputtering (P
VD). -As the transparent adhesive 3, other thermosetting epoxy adhesives (trade name: Stycast 1264 (manufactured by Grace Japan) or acrylates (trade name: Aron Alpha # 10)
1 (manufactured by Toa Gosei Co., Ltd.)) and other adhesives. -The object 4 is S-FPL51 (trade name, manufactured by OHARA, α
= 133 × 10 ⁻⁷ / ° C.), S-FPL52 (Ohara, α = 124 × 10 ⁻⁷ / ° C.), S-PHM52 (Ohara, α = 101 × 10 ⁻⁷ / ° C.), FCD100 ( H
OYA, α = 142 × 10 ⁻⁷ / ° C.), FCD1 (H
OYA, α = 133 × 10 ⁻⁷ / ° C), FCD10
(Made by HOYA, α = 101 × 10 ⁻⁷ / ° C.). FIG. 5 is a diagram illustrating a multilayer filter according to the second embodiment.

In the present embodiment, similarly to the first embodiment, SiO ₂ and Ta ₂₀ are formed on the surface of a transparent substrate 11 made of optical glass having a trade name of S-TIM25 (manufactured by OHARA CORPORATION).
Multilayer film 1 which is a bandpass filter made of a dielectric material of ₅
2 is formed. Further, as in the first embodiment, a flat plate made of optical glass having a trade name of S-FPL53 (manufactured by OHARA CORPORATION) is used as the object 14, but in this embodiment, an opaque adhesive 15 is used to transmit light. Object 14 except area
Is adhered to the surface of the multilayer film 12. Therefore, since light enters and exits from the transmission region, the opaque adhesive 15 does not hinder the transmission of light. The opaque adhesive 15 is a thermosetting epoxy adhesive.
Stycast 2057 (trade name, manufactured by Grace Japan) was used.

Also in the present embodiment, a multilayer filter having a small temperature dependence of the wavelength characteristic as in the first embodiment was obtained. In the second embodiment, the opaque adhesive 1
Even if the object 14 is adhered to the surface of the multilayer film 12 except for the light transmission region using a metal solder made of a Pb-Sn eutectic alloy instead of the multilayer film filter 5, the temperature dependence of the wavelength characteristic is small. was gotten. In order to improve the adhesion of the metal solder, a metal film (such as Cr) may be formed on the surface of the multilayer film 12 except for the light transmission region.

Of course, the adhesive is not necessarily opaque, and a transparent adhesive may be used. FIG. 6 is a diagram illustrating a multilayer filter according to the third embodiment.

In this embodiment, similarly to the first embodiment, SiO ₂ and Ta ₂ O are formed on the surface of a transparent substrate 21 made of optical glass having the trade name of S-TIM25 (manufactured by OHARA).
Multilayer film 2 which is a bandpass filter made of a dielectric material of ₅
2 is formed. In the present embodiment, the object 26 is made of SUS, which is a metal having a coefficient of thermal expansion α of 187 (× 10 ⁻⁷ / ° C.).
304, and has an opening 27 at the center for transmitting light. Therefore, since light enters and exits through the opening 27, the transmission of light is not hindered by the metal object 26. The object 26 is made of a thermosetting epoxy adhesive 23 (trade name: EPO-TEK353N).
D) is used to adhere to the surface of the multilayer film 22.

The multilayer film (band pass) of the present embodiment is actually
FIG. 7 shows the result of measuring the temperature change of the transmission center wavelength of the filter. As a comparative example, an object 26 having a large thermal expansion coefficient
FIG. 7 also shows the results of a similar measurement performed on a conventional multilayer filter having no surface-adhered surface. As shown in FIG. 7, the multilayer filter of the present embodiment has a sufficiently small wavelength shift due to temperature as compared with the conventional multilayer filter, and has a temperature of 0 to 70 ° C.
Was in the temperature range of about 0.027 nm.

Further, the object 26 is made of SU which can be easily laser-welded.
Since the object 5 is made of S304 (JIS standard), the object 5 can be fixed to another structure made of SUS304 or the like by laser welding.

In the third embodiment, as the object 26
SUS403 (α = 104 × 10^-7/ ° C)
A multilayer filter with small temperature dependence of long characteristics can be obtained.
Was. A5052 (JIS standard; α =
230 × 10^-7/ ° C), the transparent substrate 21
The product name is BPM51 (manufactured by OHARA, α = 52 × 10
^-7/ ° C) when using optical glass, temperature dependence of wavelength characteristics
A multi-layer filter with low properties was obtained.

FIG. 8 shows a multilayer filter according to a fourth embodiment.
FIG. Also in the present embodiment, the third actual
As in the embodiment, the trade name is S-TIM25 (manufactured by OHARA)
S on the surface of the cylindrical transparent substrate 31 made of optical glass
iO_TwoAnd Ta _TwoO_FiveBandpass fill made of dielectric material
A multilayer film 32 is formed. In addition, SUS30
The object 37 consisting of 4 has a hollow cylindrical shape,
It has an opening 38 for transmitting light. Therefore,
Since light enters and exits through the opening 38, it is made of metal.
The light transmission is not hindered by the object 37. Book
In the embodiment, the periphery of the multilayer film 32 and the transparent substrate 31 (the multilayer
The side surfaces of the film 32 and the transparent substrate 31;
Not the side edge) is the inner surface of the object 37
The thermosetting epoxy adhesive 33 (trade name EPO-
(TEK353ND). This embodiment
In the case of the state, the object 37 expands with an increase in temperature,
It expands in the radial direction of the cylinder. Therefore, other fruits
As in the embodiment, the multilayer film 32 and the transparent substrate 31 are elongated.
And the physical thickness of the multilayer film 32 is reduced.
This serves to keep the optical film thickness approximately constant.
When the temperature decreases, the object 37 becomes cylindrical.
Since it contracts in the radial direction, the multilayer film 32 and the transparent substrate 31
Is compressed, the physical thickness of the multilayer film 32 increases, and the average
To cancel the change in optical film thickness due to the decrease in the refractive index of
Work on.

Also in this embodiment, a multilayer filter having a small temperature dependence of the wavelength characteristic as in the third embodiment was obtained. Further, in the present embodiment, as the temperature rises,
The expansion of the object 37 having a large thermal expansion coefficient causes the multilayer film 32 to expand.
And the transparent substrate 31 is pulled from the surroundings to form the multilayer film 3.
2 is configured to cancel the change in the optical film thickness. Therefore, the transparent substrate 31 does not warp as compared with the case where an object having a large thermal expansion coefficient is adhered to the surface of the multilayer film 32, and therefore the surface of the multilayer film 32 does not warp.

FIG. 9 is a view for explaining a multilayer filter according to the fifth embodiment. In the present embodiment, similarly to the first embodiment, SiO ₂ and T are formed on the surface of a transparent substrate 41 made of optical glass having a trade name of S-TIM25 (manufactured by OHARA CORPORATION).
It is formed a multilayer film 42 is a band-pass filter composed of a dielectric of a ₂ O _5.

In the present embodiment, there are two flat bodies 44 of the trade name S-FPL53, one of which is the surface of the multilayer film 42 and the other is the surface of the transparent substrate 41 on which the multilayer film 42 is formed. Glued to the opposite side. As in the first embodiment, a transparent adhesive that is a thermosetting epoxy adhesive (trade name: EPO-TEK353ND) is used as the adhesive 43.

Also in the present embodiment, a multilayer filter having a small temperature dependence of the wavelength characteristic as in the first embodiment can be obtained. Further, in the present embodiment, as the temperature rises,
The expansion of the object 44 having a large thermal expansion coefficient causes the multilayer film 42 to expand.
In addition, the transparent substrate 41 is evenly pulled from both sides to cancel the change in the optical film thickness of the multilayer film 42. Therefore, the transparent substrate 41 does not warp as compared with the case where the object 44 having a large thermal expansion coefficient is adhered only to the surface of the multilayer film 42, and therefore, the surface of the multilayer film 42 does not warp.

In each of the above embodiments, the thickness of the multilayer film is about 0.6 μm, and the thickness of the substrate and the object is on the order of about 1 mm. FIG. 10 is a diagram showing a configuration example of a multilayer filter having a multi-cavity structure.

The multilayer film 52 is made of a dielectric material of SiO._Two, T
a_TwoO_FiveAre alternately stacked, as shown in FIG.
Functions as a bandpass filter that transmits only specific wavelengths
It works. It should be noted that the multilayer film 52 of this configuration example is a capacitor.
The bitness (hollow) layer is SiO _TwoConsisting of a cavity
A four-cavity bandpass filter with four layers
is there. In the present invention, the thermal expansion coefficient
Large objects with small temperature dependency
Configure a bandpass filter.

FIG. 11 is a diagram showing a change in transmission band characteristics depending on the number of cavity layers. As shown in the figure, since the top of the light transmission band becomes closer to a rectangular shape as the number of cavity layers is larger, the light transmission band is expanded,
There is an effect that the wavelength adjustment of the filter is facilitated. In addition, since the bottom of the transmission band (the effect of blocking light having a wavelength shifted from the transmission band) is improved, the performance as a filter is also improved.

In FIG. 10, the multilayer film 52 may be a one-cavity band-pass filter having only one cavity layer. A one-cavity band-pass filter is similar to a solid etalon. However, a solid etalon is a glass plate formed by polishing a cavity layer, and thus has a limit of at least about 2000 nm in thickness at the minimum. Since the cavity layer is a thin film, the thickness can be up to about 50 to 700 nm.

FIG. 12 is a diagram showing a change in transmission characteristics due to a change in cavity thickness in a multilayer film filter having a single cavity structure. As shown in the figure,
If the thickness of the cavity layer is small, a filter having a wide half-value width and moderate characteristics can be obtained. A bandpass filter having a cavity layer having a thickness of about 50 to 700 nm is too thin, so that it can no longer be held by a film alone and needs to be formed on a transparent substrate.

If the thickness of the transparent substrate on which the multilayer film is formed is too large, a change in the average optical film thickness of the multilayer film caused by a temperature change is accompanied by a temperature change of an object having a large thermal expansion coefficient. The resulting change in volume undesirably prevents the effect of being offset by deformation of the multilayer film formed on the substrate. On the other hand, if the thickness of the transparent substrate is too small, it is not preferable because the holding of the substrate becomes difficult or the substrate warps due to the internal stress of the multilayer film itself. The thickness of the transparent substrate needs to be 0.1 mm or more and 2 mm or less, and 0.5 mm or more,
More preferably, it is 1.5 mm or less.

[0042]

As described above, according to the present invention,
A transparent substrate having a multilayer film formed on at least one side, and an object having a larger thermal expansion coefficient than the multilayer film and the transparent substrate adhered to at least the surface or the periphery of the multilayer film, which is caused by a temperature change. The change in the average optical film thickness (the product of the average refractive index and the physical film thickness) of the multilayer film is caused by the deformation of the multilayer film due to the change in volume caused by the temperature change of the object. The present invention provides a practical multilayer filter and a method for manufacturing the multilayer filter, wherein the characteristics do not depend on the temperature without using a substrate having a large expansion coefficient because the wavelength characteristics of the multilayer film are kept substantially unchanged. Can do things.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a method for manufacturing a multilayer filter according to a first embodiment.

FIG. 2 is a diagram illustrating a multilayer filter manufactured in the first embodiment.

FIG. 3 is a diagram illustrating a wavelength transmission characteristic of the multilayer filter of the first embodiment.

FIG. 4 is a diagram showing a result of actually measuring a temperature change of a transmission center wavelength of a multilayer film (bandpass) filter of the present embodiment.

FIG. 5 is a diagram illustrating a multilayer filter according to a second embodiment.

FIG. 6 is a diagram illustrating a multilayer filter according to a third embodiment.

FIG. 7 is a diagram showing a result of actually measuring a temperature change of a transmission center wavelength of the multilayer film (bandpass) filter of the present embodiment.

FIG. 8 is a diagram illustrating a multilayer filter according to a fourth embodiment.

FIG. 9 is a diagram illustrating a multilayer filter according to a fifth embodiment.

FIG. 10 is a diagram illustrating a configuration example of a multilayer filter having a multi-cavity structure.

FIG. 11 is a diagram showing a change in transmission band characteristics depending on the number of cavity layers.

FIG. 12 is a diagram showing a change in transmission characteristics due to a change in cavity thickness in a multilayer filter having a single cavity configuration.

[Explanation of symbols]

 1, 11, 21, 31, 41 Transparent substrate 2, 12, 22, 32, 42, 52 Multilayer film 3, 15, 23, 33, 43 Adhesive 4, 14, 26, 37, 44 Object 27, 38 Opening

Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI C23C 14/08 C23C 14/08 N (72) Inventor Hiroaki Matsuda 2-1-1 Kita-Ichijo-Nishi, Chuo-ku, Sapporo, Hokkaido Fujitsu Hokkaido Digital Technology Co., Ltd. Within the company (72) Inventor Hideki Noda 4-1-1, Kamidadanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Inside Fujitsu Limited (72) Inventor Nobuhiro Fukushima 4-1-1, Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Fujitsu Stock In company

Claims (19)

[Claims] 1. A transparent substrate having a multilayer film formed on at least one side thereof, and at least a surface of or a periphery of the multilayer film adhered to the transparent substrate.
An object having a thermal expansion coefficient larger than that of the multilayer film and the transparent substrate, wherein a change in average optical film thickness of the multilayer film caused by a temperature change causes a change in volume caused by a temperature change of the object. The multi-layer filter is characterized in that the multi-layer filter is offset by the deformation of the multi-layer film, and the wavelength characteristics of the multi-layer film are kept approximately unchanged. 2. The method according to claim 1, wherein the object is bonded to both surfaces of the multilayer film and a surface of the transparent substrate opposite to a surface on which the multilayer film is formed. The multilayer filter according to any one of the preceding claims. 3. The multilayer filter according to claim 1, wherein the multilayer film is a band-pass filter including a multilayer film containing at least two types of dielectrics. 4. The method according to claim 1, wherein said dielectric is at least TiO ₂ , TaO.
₅ , one or more materials selected from Nb ₂ O ₅ and Si
Multilayer filter according to claim 3, characterized in that it consists of O _2. 5. The multilayer filter according to claim 1, wherein the object is adhered to at least a surface or a periphery of the multilayer film by a transparent adhesive. 6. The multilayer filter according to claim 5, wherein the transparent adhesive is a thermosetting epoxy adhesive. 7. The multilayer filter according to claim 1, wherein the material of the transparent substrate is optical glass. 8. The multilayer filter according to claim 7, wherein a coefficient of thermal expansion of the optical glass as a material of the transparent substrate is in a range of 50 to 80 (× 10 ⁻⁷ / ° C.). 9. The multilayer filter according to claim 1, wherein the material of the object is optical glass. 10. The multilayer filter according to claim 9, wherein the optical glass as the material of the object has a coefficient of thermal expansion in a range of 100 to 150 (× 10 ⁻⁷ / ° C.). 11. The multilayer according to claim 1, wherein the object is adhered to the surface or the periphery of the multilayer film except for a light transmitting area by an opaque adhesive or a metal material. Membrane filter. 12. The object is made of an opaque material,
The multilayer filter according to claim 1, further comprising an opening through which light is transmitted. 13. The multilayer filter according to claim 12, wherein the material of the object is a metal. 14. The multilayer filter according to claim 13, wherein a thermal expansion coefficient of the metal as the material of the object is in a range of 100 to 240 (× 10 ⁻⁷ / ° C.). 15. A multilayer film is formed on at least one surface of a transparent substrate, and the multilayer film and an object having a larger coefficient of thermal expansion than the transparent substrate are adhered to at least the surface or the periphery of the multilayer film. The resulting change in the average optical film thickness of the multilayer film is offset by the deformation of the multilayer film due to a change in volume caused by a change in the temperature of the object, and the wavelength characteristic of the multilayer film is approximately A method for producing a multilayer filter, characterized in that it is kept unchanged. 16. The method for manufacturing a multilayer filter according to claim 15, wherein the method for forming the multilayer film is a physical film formation method (PVD) using ions or plasma. 17. The method according to claim 17, wherein the object is heat-cured with a thermosetting epoxy-based adhesive at a temperature in the range of 80.degree. C. to 150.degree. The method for manufacturing a multilayer filter according to claim 16. 18. The wavelength characteristic of the multilayer film is set to a wavelength shorter than a desired wavelength characteristic in advance in consideration of an amount by which the wavelength characteristic of the multilayer film shifts to a long wavelength after the adhesive is thermally cured and bonded. The method for manufacturing a multilayer filter according to claim 17, wherein the filter is formed. 19. The multilayer filter according to claim 18, wherein the wavelength characteristic of the multilayer film after bonding is adjusted to a desired value by changing a temperature at which the epoxy adhesive is thermally cured. Production method.