JP4331547B2 - Optical filter and optical apparatus - Google Patents

Description

  The present invention relates to an optical filter and an optical apparatus.

A fluorescence microscope, an optical instrument used for observing biological samples, etc., analyzes the structure and properties of a sample by observing the fluorescence emitted by the sample when excitation light is applied to a sample such as a stained cell. Can do.
For recent genome analysis, for example, there is a need to observe fluorescence having a peak wavelength at 526 nm with excitation light having a wavelength of 502 nm. In this case, since the excitation light and the fluorescence wavelength are close to each other, an optical filter that cuts the excitation light in the stop band and transmits the light of the fluorescence observation wavelength in the transmission band in order to efficiently detect the fluorescence is sensitive and accurate in fluorescence measurement. It is used as a very important key part.

This optical filter is required to have a sharp rise in spectral characteristics at the boundary between the transmission band and the stop band and to transmit almost 100% of light in the transmission band. Furthermore, in the transmission band, it is desirable that there is no periodic fluctuation (ripple) of the transmittance with respect to the increase or decrease of the wavelength.
Thus, the minus filter, which is an optical filter that blocks light of a predetermined wavelength band and transmits light of other wavelengths, has a high refractive index layer and a low refractive index on the substrate as shown in FIG. It is made of a multilayer film in which rate layers are alternately stacked. Here, the horizontal axis represents the optical film thickness, and the vertical axis represents the refractive index of the film. Further, FIG. 5B shows the relationship between the wavelength of light transmitted through the film and the transmittance in this film configuration as spectral characteristics.

  In this optical filter, the rise of the boundary between the transmission band and the stop band can be made steeper as the number of layers is increased. However, there is a problem that the ripple in the transmission band increases as the number of layers increases. Further, as shown in FIG. 6A, it is possible to design a film that reduces the ripple by changing the optical film thickness of each layer, but it is difficult to completely eliminate the ripple as shown in FIG. 6B. It is. Furthermore, in this case, since the film thicknesses of the respective layers of the multilayer film are all different, there is a problem that controllability during actual film formation is very poor and it is extremely difficult to obtain stable optical characteristics. It was.

On the other hand, as shown in FIG. 7A, when the refractive index of the film is periodically and continuously changed in the film thickness direction and the refractive index distribution is changed to a shape called a wavelet (wave packet), FIG. As shown in b), ripples in the transmission band can be eliminated in principle (for example, see Non-Patent Document 1).
However, it is very difficult to continuously change the refractive index of the film during actual film formation. Therefore, for example, as shown in FIG. 8, various types of approximations obtained by dividing a continuous refractive index distribution in a staircase shape have been proposed (see, for example, Patent Document 1, Non-Patent Document 2, and Non-Patent Document 3). .)
Japanese Patent No. 3290629 (FIG. 1) WHSouthwell, Using Apodization Function to Reduce Sidelobes in Rugate Filters, Appl.Opt., 1989, Vol.28 PGVery, JADobrowolski, WJWild, and RLBurton, Synthesis of high rejection filters with the Fourier transform method, APPLIED OPTICS, 15 July (1989), Vol.28, No.14, p2867-2874 HAND BOOK OF OPTICS, Second Edition, Vol.1, Fundamentals, Techniques, and Design, OPTICAL SOCIETY OF AMERICA, McGRAW-Hill, 1995, p42.50

However, in the above-described conventional optical filter, the refractive index distribution is divided into steps, and the film is formed. However, if the difference in refractive index between the high refractive index film and the low refractive index film is constant, a constant width is obtained. It is only a minus filter having a stop band, and a filter characteristic having a wide stop band or a plurality of stop bands cannot be obtained.
The present invention has been made in view of the above circumstances, and an optical filter having a wide stop band and a plurality of stop bands even if the refractive index difference between the high refractive index film and the low refractive index film is constant, And it aims at providing an optical instrument.

The present invention employs the following means in order to solve the above problems.
The optical filter according to the present invention is an optical filter composed of a substrate and a thin film formed on the substrate, wherein the thin film has a relatively low refractive index layer and a relatively low refractive index layer. High refractive index layers are alternately stacked from the substrate side, and the first stacked portion in which the refractive index of the high refractive index layer gradually increases toward the substrate; and A second laminated part adjacent to the laminated part, wherein the refractive index of the high refractive index layer is substantially the same as the highest refractive index of the high refractive index layers constituting the first laminated part, and the second laminated part And a third laminated portion in which the refractive index of the high refractive index layer gradually decreases from the second laminated portion side, and the first laminated portion, the second laminated portion toward the substrate laminated portion, repeating the third stack pattern arranged in the order of the lamination of more than two times in the thickness direction at one surface of the substrate Is arranged, characterized in that each stacking patterns have different thicknesses from each other.

When transmitting light, the filter characteristics of blocking light corresponding to the stop band in the vicinity of a predetermined wavelength and transmitting light in the transmission band corresponding to the other wavelengths is that of the high refractive index layer and the low refractive index layer. By changing the film thickness, the center wavelength of the stop band changes.
According to this invention, it is possible to obtain a filter characteristic in which the stop bands of the respective laminated patterns are combined by repeating the laminated patterns having the same refractive index distribution and different film thicknesses twice or more. Therefore, by selecting a different value for the thickness of each laminated pattern, it is possible to make the stop band wider or to have a filter characteristic having a plurality of stop bands.

The optical filter according to the present invention is the optical filter, wherein at least one of the first to third stacked portions has a refractive index of the high refractive index layer via the low refractive index layer. It is preferable that a high refractive index varying layer portion set lower than other high refractive index layers on both sides adjacent to each other is inserted.
According to the present invention, ripples in the transmission band can be effectively suppressed.

The optical filter according to the present invention is an optical filter composed of a substrate and a thin film formed on the substrate, wherein the thin film has a relatively low refractive index layer and a relatively low refractive index layer. High refractive index layers are alternately stacked from the substrate side, and the first stacked portion in which the refractive index of the low refractive index layer gradually decreases toward the substrate; and A second laminated portion adjacent to the laminated portion and having the refractive index of the low refractive index layer substantially the same as the lowest refractive index of the low refractive index layers constituting the first laminated portion; and the second laminated layer And a third laminated portion in which the refractive index of the low refractive index layer gradually increases from the second laminated portion side, and the first laminated portion, the second laminated portion toward the substrate laminated portion, repeating the third stack pattern arranged in the order of the lamination of more than two times in the thickness direction at one surface of the substrate Is arranged, characterized in that each stacking patterns have different thicknesses.

  According to the present invention, by repeating a laminated pattern having the same refractive index distribution and different film thicknesses twice or more, the filter characteristics can be made to be a stop band obtained by combining the stop bands of the respective laminated patterns. Therefore, by selecting a different value for the thickness of each laminated pattern, it is possible to make the stop band wider or to have a filter characteristic having a plurality of stop bands.

When the design wavelength is λ / n (n is an integer) with respect to the center wavelength (λ) of the wavelength band that blocks transmission in each laminated pattern, the high refractive index layer and the low refractive index in each laminated pattern The optical film thickness of the layer is preferably set to approximately n / 4 times the design wavelength.
According to this invention, since the optical film thickness is approximately n / 4 times the design wavelength of each laminated pattern, the film thickness controllability at the time of actual film formation is improved, and stable optical characteristics can be obtained.

An optical apparatus according to the present invention includes the optical filter according to the present invention.
According to the present invention, even when the blocking wavelength band is wide or when the transmitted wavelength is between a plurality of blocking wavelengths, the optical filter having a wide blocking band or a plurality of blocking bands can reduce the wavelength of the transmission band. Can transmit efficiently and have filter performance with excellent spectral characteristics

According to the optical filter of the present invention, since the laminated pattern having the same refractive index distribution is repeated twice or more and each laminated pattern has a different film thickness, the filter characteristics are matched with the stop band of each laminated pattern. Since the band can be set, a desired filter characteristic having a wide stop band or a plurality of stop bands can be obtained with a film configuration that can be easily controlled during film formation.
Moreover, according to the optical apparatus of the present invention, since the optical filter according to the present invention is provided, the selection performance of desired incident light can be improved.

Next, a first embodiment of the present invention will be described with reference to FIGS.
A fluorescence microscope (optical apparatus) 10 shown in FIG. 1 according to the present embodiment includes an excitation filter 11, a dichroic mirror 12, an absorption filter (optical filter) 13, an eyepiece lens 14, and an objective lens 15.

The excitation filter 11 is disposed on the optical path of the light source 16 so as to selectively transmit only a specific wavelength of the light generated from the light source 16 as excitation light.
The dichroic mirror 12 is a semi-transmission mirror, and changes the light path of the light transmitted through the excitation filter 11 so as to irradiate the sample 17 such as a living cell, for example. Is set so as to transmit the fluorescence generated from the light to the observation side.
The eyepiece 14 and the objective lens 15 are arranged so as to be adjusted so that the fluorescence can be observed.

The absorption filter 13 includes a glass substrate 18, a thin film 19 formed on the substrate 18, and an incident medium 18 ′ provided on the thin film 19, and selectively transmits only the fluorescence. The incident medium 18 ′ is made of a member having the same refractive index as that of the substrate 18, for example, a glass plate.
As shown in FIG. 2A, the thin film 19 is formed of a first laminated pattern 20 having a similar refractive index distribution and a second laminated pattern 21 in order toward the substrate 18.
The first laminated pattern 20 is configured by alternately laminating a low refractive index layer 22 having a relatively low refractive index and a high refractive index layer 23 having a relatively high refractive index. The first stacked portion 30 in which the refractive index gradually decreases toward the substrate 18 and the refractive index of the high refractive index layer 23 gradually increases toward the substrate 18 is adjacent to the first stacked portion 30 and has a low refractive index. The refractive index of the refractive index layer 22 is substantially the same as the lowest refractive index of the first laminated portion 30 and the refractive index of the high refractive index layer 23 is the high refractive index layer 23 constituting the first laminated portion 30. A second laminated portion 31 that is substantially the same as the highest refractive index, and adjacent to the second laminated portion 31, the refractive index of the low refractive index layer 22 gradually increases from the second laminated portion 31, and the high refractive index. A third laminated portion 32 in which the refractive index of the refractive index layer 23 gradually decreases from the second laminated portion 31 side; It is provided.
Similarly to the laminated pattern 20, the second laminated pattern 21 has the same refractive index distribution as the second laminated portion 31 and the fourth laminated portion 33 having the same refractive index distribution as that of the first laminated portion 30. A fifth stacked portion 34 and a sixth stacked portion 35 having the same refractive index distribution as the third stacked portion 32 are provided.
The low refractive index layer 22 is mainly composed of silicon oxide, and the high refractive index layer 23 is mainly composed of niobium oxide.
In this embodiment, the refractive index of the substrate 18 is 1.8, the refractive index of the high refractive index layer 23 is changed from 1.9 to 2.2, and the refractive index of the low refractive index layer 22 is 1.4 to 1. It is changed to .75.

Further, the thin film 19 has a high refractive index varying layer portion 36 in which the refractive index of the high refractive index layer 23 is set lower than the other high refractive index layers 23 on both sides adjacent to each other through the low refractive index layer 22. The boundary between the first and third stacked portions 30 and 32 and the second stacked portion 31, and the fourth and sixth stacked portions 33 and 35 and the fifth stacked portion 34. One layer is inserted at each boundary.
In the present embodiment, the refractive index of the high refractive index varying layer portion 36 is set to 2.1 with respect to the refractive index 2.2 of the high refractive index layer 23 in the second stacked portion 31.
In the first and second laminated patterns 20 and 21, the center wavelengths of the wavelength bands that prevent transmission in each pattern are λ ₁ and λ ₂ , and the design wavelengths are λ ₁ / n and λ ₂ / m (n and m are (Integer), for example, n = m = 1, and the optical film thickness of the high refractive index layer 23 and the low refractive index layer 22 of each laminated pattern is set to 1/4 times the design wavelength.
In this embodiment, since λ ₁ is set to 600 nm and λ ₂ is set to 720 nm, the optical film thicknesses are 150 nm and 180 nm, respectively.
In addition to the above-described configuration, the simulation is performed assuming that the total number of layers is 89, the substrate having a refractive index of 1.8 is also present on the incident medium 18 ′ side of the thin film 19, and there is no refractive index dispersion of each layer. Is shown in FIG.

Next, an observation method using the fluorescence microscope 10 according to the present embodiment will be described.
The light emitted from the light source 16 passes through the excitation filter 11 and is projected onto the dichroic mirror 12 as excitation light having a specific wavelength.
The excitation light has its optical path bent by the dichroic mirror 12, condensed by the objective lens 15, and applied to the specimen 17. At this time, fluorescence is generated from the specimen 17 by this irradiation. This fluorescence is converted into parallel light through the objective lens 15 and reaches the dichroic mirror 12, passes through this, and reaches the absorption filter 13.

The fluorescence that reaches the absorption filter 13 is incident from the first stacked unit 30, passes through the second to sixth stacked units 31 to 35, and is emitted from the substrate 18 side to the outside again.
Excitation light having a wavelength other than fluorescence is also mixed and incident on the absorption filter 13. However, since the thin film 19 has the first laminated pattern 20 and the second laminated pattern 21 described above, the absorption filter 13 externally transmits light in the stop band 38 that is a wavelength band to which excitation light and the like belong. The light in the transmission band 39, which is the wavelength band to which the fluorescence belongs, is transmitted while being prevented from being emitted to the light.
Thus, the fluorescence emitted from the absorption filter 13 passes through the eyepiece 14 and is collected to reach the observation side.

  According to this absorption filter 13, for example, as shown in FIG. 2B, the stop band 38 can be widened by arranging a plurality of laminated patterns having the same refractive index distribution and different film thicknesses. In addition, since the first laminated pattern 20 and the second laminated pattern 21 are different in film thickness and have the same refractive index distribution in each laminated pattern, the film configuration is easy to control during film formation, and optical The stability of characteristics can be improved.

Next, a second embodiment according to the present invention will be described with reference to FIG. In the following description, the same reference numerals are given to the components described in the above embodiment, and the description thereof is omitted.
The second embodiment is different from the first embodiment in that the center wavelength λ _{1 of} the first laminated pattern 20 is 480 nm and the film thickness is 120 nm.
Similarly to the above, it is assumed that the total number of layers is 89, the substrate having a refractive index of 1.8 is also present on the incident medium 18 ′ side of the thin film 40, and the simulation result is shown in FIG. Shown in (b).

  According to the absorption filter and the fluorescence microscope according to this embodiment, for example, as shown in FIG. 3B, the stop band 38 </ b> A by the first stacked pattern 20 and the stop band 38 </ b> B by the second stacked pattern 21 are formed. It is possible to separate and obtain a filter characteristic having a transmission region in between.

Next, a third embodiment according to the present invention will be described with reference to FIG. In the following description, the same reference numerals are given to the components described in the above embodiment, and the description thereof is omitted.
The third embodiment is different from the first embodiment in that the thin film 41 according to the third embodiment is refracted by the low refractive index layer 22 constituting the first laminated pattern 20 and the second laminated pattern 21. The rate is constant at the same value as the refractive index of the substrate 18.

That is, the thin film 41 is formed such that the refractive index of the low refractive index layer 22 constituting the first to sixth stacked portions 30 to 35 is the same value as the refractive index on the substrate 18 side.
In this embodiment, the refractive index of the substrate 18 is 1.5, the refractive index of the high refractive index layer 23 is changed from 1.55 to 2.4, and the refractive index of the low refractive index layer 22 is 1.5. Is a constant value.
In addition to the above configuration, the total number of layers is 93, the substrate having a refractive index of 1.5 is also present on the incident medium 18 ′ side of the thin film 41, and there is no refractive index dispersion of each layer. Shown in 4 (b).

  Also with the absorption filter and the fluorescence microscope according to the present embodiment, as shown in FIG. 4B, for example, the stop band and the second stacked pattern of the first stacked pattern 20 are the same as in the first embodiment described above. A filter characteristic combining 21 stop bands can be obtained.

In the above embodiment, n = m = 1, the design wavelength is the same as the center wavelength of each laminated pattern, and the optical film thicknesses of the high refractive index layer 23 and the low refractive index layer 22 are ¼ times the design wavelength. However, even if n = m = 2 and the optical film thickness of the high refractive index layer 23 and the low refractive index layer 22 is set to ½ times the design wavelength, a thin film is formed in exactly the same manner. An absorption filter having excellent spectral characteristics can be obtained.
Furthermore, the design wavelength is set to 600 / n (n is an integer) nm with respect to the center wavelength of 600 nm, and the optical film thicknesses of the high refractive index layer 23 and the low refractive index layer 21 are set to n / 4 times the design wavelength. Even if a thin film is formed, an absorption filter having similar spectral characteristics can be obtained.

The technical scope of the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.
For example, the laminated pattern is repeated twice, but the present invention is not limited to this and may be repeated three or more times. By doing in this way, it can be set as the filter characteristic which has a wider stop band, and it can be set as the filter characteristic which has more transmission bands.
Further, the center wavelengths (λ ₁ , λ ₂ ) are not limited to 480, 600, and 720 nm, and by changing the values of λ ₁ and λ ₂ appropriately according to the wavelength of excitation light and the wavelength of fluorescence to be detected, the desired optical Characteristics can be obtained.

It is a figure which shows the outline | summary of the fluorescence microscope of 1st Embodiment which concerns on this invention. It is a graph which shows the film | membrane structure and spectral characteristic of the absorption filter in 1st Embodiment based on this invention. It is a graph which shows the film | membrane structure and spectral characteristic of the absorption filter in 2nd Embodiment which concern on this invention. It is a graph which shows the film | membrane structure and spectral characteristic of the absorption filter in 3rd Embodiment based on this invention. It is a graph which shows the film | membrane structure and spectral characteristic of the conventional absorption filter. It is a graph which shows the film | membrane structure and spectral characteristic of the conventional absorption filter. It is a graph which shows the film | membrane structure and spectral characteristic of the conventional absorption filter described in the nonpatent literature 1. It is a graph which shows the film | membrane structure and spectral characteristic of the conventional absorption filter.

Explanation of symbols

10 Fluorescence microscope (optical equipment)
13 Absorption filter (optical filter)
18 Substrate 19, 40, 41 Thin film 20 First laminated pattern 21 Second laminated pattern 22 Low refractive index layer 23 High refractive index layer 30 First laminated part 31 Second laminated part 32 Third laminated part 36 High Refractive index variation layer

Claims (5)

An optical filter comprising a substrate and a thin film formed on the substrate,
The thin film is configured by alternately laminating a low refractive index layer having a relatively low refractive index and a high refractive index layer having a relatively high refractive index from the substrate side,
A first stacked portion in which a refractive index of the high refractive index layer gradually increases toward the substrate;
A second laminated part adjacent to the first laminated part, wherein the refractive index of the high refractive index layer is substantially the same as the highest refractive index of the high refractive index layers constituting the first laminated part;
A third laminated portion adjacent to the second laminated portion and having a refractive index of the high refractive index layer that gradually decreases from the second laminated portion side;
A laminated pattern arranged in the order of the first laminated portion, the second laminated portion, and the third laminated portion toward the substrate is repeatedly arranged in the film thickness direction twice or more on one surface of the substrate , An optical filter, wherein each laminated pattern has a different film thickness.   At least one of the first to third stacked portions has a refractive index of the high refractive index layer set lower than other high refractive index layers on both sides adjacent to each other through the low refractive index layer. The optical filter according to claim 1, wherein a high refractive index varying layer portion is inserted. An optical filter comprising a substrate and a thin film formed on the substrate,
The thin film is configured by alternately laminating a low refractive index layer having a relatively low refractive index and a high refractive index layer having a relatively high refractive index from the substrate side,
A first laminated portion in which the refractive index of the low refractive index layer gradually decreases toward the substrate;
A second laminated part adjacent to the first laminated part, wherein the refractive index of the low refractive index layer is substantially the same as the lowest refractive index of the low refractive index layers constituting the first laminated part;
A third stacked portion adjacent to the second stacked portion and having a refractive index of the low refractive index layer that gradually increases from the second stacked portion side;
A laminated pattern arranged in the order of the first laminated portion, the second laminated portion, and the third laminated portion toward the substrate is repeatedly arranged in the film thickness direction twice or more on one surface of the substrate , An optical filter, wherein each laminated pattern has a different film thickness. When the design wavelength is λ / n (n is an integer) with respect to the center wavelength (λ) of the wavelength band for preventing transmission in each of the laminated patterns,
4. The optical film thickness of the high refractive index layer and the low refractive index layer in each of the laminated patterns is set to approximately n / 4 times the design wavelength. 5. Optical filter as described in one.   An optical apparatus comprising the optical filter according to claim 1.

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