JP2016218144A - Spectral filter and spectroscopic measurement device - Google Patents

Abstract

Position accuracy in superposition of a long pass filter and a short pass filter is reduced. Good transmission performance is ensured at any position in one direction where the film thickness changes. A long-pass filter LP, a short-pass filter SP, and a band-pass filter BP of the spectral filter 10 each monotonically increase in film thickness as it goes in one direction, and each cutoff wavelength monotonously as the film thickness increases. Overlapping is performed so that the one direction coincides with each other. The film thickness gradient GL of the long pass filter LP is larger than the film thickness gradient GB of the band pass filter BP. At each position in the one direction, the cutoff wavelength WL of the long pass filter LP is shorter than the cutoff wavelength WB1 on the short wavelength side of the band pass filter BP, and the cutoff wavelength WS of the short pass filter SP is on the long wavelength side of the band pass filter BP. By being longer than the cutoff wavelength WB2, light in the wavelength region between the cutoff wavelength WB1 and the cutoff wavelength WB2 is transmitted. [Selection] Figure 1

Description

  The present invention relates to a spectral filter whose transmission wavelength continuously changes in one direction, and a spectroscopic measurement device including the spectral filter.

  An example of a conventional spectral filter is disclosed in Patent Document 1, for example. The spectral filter of Patent Document 1 is configured using a first interference filter and a second interference filter. The first interference filter is a filter (long-pass filter) that transmits light in a wavelength range longer than the cutoff wavelength WL, with the cutoff wavelength WL increasing monotonously along one direction. The second interference filter is a filter (short-pass filter) that transmits light in a wavelength range shorter than the cutoff wavelength WS, with the cutoff wavelength WS increasing monotonously along one direction. In this way, the interference filter whose cutoff wavelength monotonously changes along one direction can be formed of a so-called wedge-shaped interference filter whose film thickness continuously increases along one direction. In Patent Literature 1, the first and second interference filters have the same film thickness gradient.

  The first interference filter and the second interference filter are configured such that the monotonically increasing direction of the cutoff wavelength WL matches the monotonically increasing direction of the cutoff wavelength WS, and the cutoff wavelength WL of the first interference filter is the second The interference filters are overlapped so as to be shorter than the cutoff wavelength WS at the corresponding position. In this configuration, the cutoff characteristic on the short wavelength side and the cutoff characteristic on the long wavelength side with respect to the peak wavelength of the spectral transmittance at each position in the one direction can be set by separate interference filters. Thereby, it is possible to easily obtain a spectral characteristic superior to that obtained with a single interference filter.

Japanese Patent Laid-Open No. 2-132405 (refer to claims, actions, examples, FIGS. 1 to 3)

  However, as in Patent Document 1, when a spectral filter is configured with two layers of a first interference filter and a second interference filter, a positional shift (particularly a film thickness that changes when the two layers are overlapped). When the direction misalignment occurs, the transmission wavelength width defined by the cutoff wavelength WL and the cutoff wavelength WS changes greatly. For example, when the cutoff wavelength WL of the first interference filter and the cutoff wavelength WS of the second interference filter approach each other due to the positional deviation between the two layers, the transmission wavelength width becomes narrower, and conversely, the cutoff wavelength WL and the cutoff wavelength WS As the distance increases, the transmission wavelength width increases. In order to suppress such fluctuations in the transmission wavelength width, it is necessary to superimpose the two layers with high positional accuracy, but such superposition with high positional accuracy is actually difficult. Therefore, it is desirable to configure the spectral filter so that the allowable range of positional deviation can be expanded, that is, the positional accuracy of superposition can be relaxed.

  Further, the material of the film constituting the interference filter always has so-called wavelength dispersion in which the refractive index changes depending on the wavelength. That is, the refractive index of the film material increases as the wavelength decreases, and conversely decreases as the wavelength increases. In particular, the high refractive index material has a large chromatic dispersion in the visible light wavelength range (a large change in refractive index with respect to a change in wavelength). Due to the influence of such wavelength dispersion, the ratio of the change in the cut-off wavelength with respect to the change in the film thickness (the shift amount of the cut-off wavelength) differs among the plurality of interference filters having different film types. For this reason, if a plurality of interference filters are overlapped with the same film thickness gradient, it is possible to secure good transmission performance at a certain position in one direction where the film thickness changes, but at a different position. Then, there are cases where good transmission performance cannot be ensured.

  The present invention has been made to solve the above-described problems, and its purpose is to reduce the positional accuracy when the long-pass filter and the short-pass filter are superposed and to reduce the film thickness in one direction. An object of the present invention is to provide a spectral filter that can ensure good transmission performance at any position, and a spectroscopic measurement device including the spectral filter.

In the spectral filter according to one aspect of the present invention, the film thickness monotonously increases in one direction, transmits light in a wavelength region longer than the cutoff wavelength WL, and the cutoff wavelength WL increases as the film thickness increases. Is a long pass filter whose length is monotonously increased, and the film thickness monotonously increases in one direction, transmits light in a wavelength region shorter than the cutoff wavelength WS, and the cutoff wavelength WS monotonously increases as the film thickness increases. And a short-pass filter that becomes longer, the film thickness monotonously increases in one direction, and transmits light in a wavelength region between the cutoff wavelength WB ₁ on the short wavelength side and the cutoff wavelength WB ₂ on the long wavelength side. , as the film thickness increases, and a band-pass filter the cut-off wavelength WB ₁ and the cutoff wavelength WB ₂ is monotonically increased, and the long-pass filter, said sheet The band pass filter and the band pass filter are overlapped so that the one direction in which the film thickness monotonously increases coincides with each other, and the film thickness gradient of the long pass filter is larger than the film thickness gradient of the band pass filter. The cut-off wavelength WL is shorter than the cut-off wavelength WB _{1 and the} cut-off wavelength WS is longer than the cut-off wavelength WB ₂ at each position in the one direction, so that the cut-off wavelength WB ₁ and the cut-off wavelength WB Transmits light in the wavelength range between ₂ .

The difference between the cutoff wavelength WB ₁ and the cutoff wavelength WL is preferably 13 nm or more and 42 nm or less at all positions where visible light is transmitted in the one direction.

The long pass filter and the band pass filter are multilayer films in which a layer made of a first refractive index material and at least one layer made of at least one second refractive index material having a higher refractive index than the first refractive index material are laminated. When the main refractive index material is a material having at least one of the number of layers and the total film thickness among the at least one second refractive index material, in the long pass filter, the main refraction The refractive index of the refractive index material at a wavelength of 380 nm is nL ₃₈₀ , the refractive index of the main refractive index material at a wavelength of 780 nm is nL _780, and the thickness of the transmission part that transmits light of wavelength 780 nm is dL _780. The film thickness of the transmission part that transmits light of 380 nm is dL _380, and in the bandpass filter, the refractive index at the wavelength of 380 nm of the main refractive index material is set. NB ₃₈₀ , the refractive index of the main refractive index material at a wavelength of 780 nm is nB ₇₈₀ , the thickness of the transmission part that transmits light of wavelength 780 nm is dB _780, and the transmission part of light of wavelength 380 nm is transmitted. When the film thickness is dB ₃₈₀ , it is desirable to satisfy the following conditional expression. That is,
0.98 <{(dL ₇₈₀ / dL ₃₈₀ ) / (dB ₇₈₀ / dB ₃₈₀ )} × [(nL ₇₈₀ / nL ₃₈₀ ) / {(nB ₇₈₀ / nB ₃₈₀ ) ^0.4 }] <1.17
It is.

  The band pass filter and the short pass filter may be formed on the front and back surfaces of the same substrate, respectively, and the long pass filter may be formed on a separate substrate.

  The band-pass filter, the short-pass filter, and the long-pass filter may be formed on different substrates.

  Each said board | substrate may be bonded together through the adhesive agent.

  A spectroscopic measurement apparatus according to another aspect of the present invention includes a spectral filter having the above-described configuration and a light receiving element that receives light transmitted through the spectral filter, and the light receiving element is disposed in the one direction of the spectral filter. Are arranged side by side.

According to the above configuration, by using a band pass filter in addition to the long pass filter and the short pass filter, the cutoff wavelength WL is made shorter than the cutoff wavelength WB ₁ and the cutoff wavelength WS is made longer than the cutoff wavelength WB _2. Thus, it is possible to realize a configuration that transmits light in a wavelength region between the cutoff wavelength WB ₁ and the cutoff wavelength WB ₂ . In such a configuration, even if a slight positional deviation occurs between the long pass filter and the short pass filter, the transmission performance of the spectral filter can be obtained by the transmission performance of the band pass filter. Therefore, it is not necessary to require high positional accuracy for the superposition of the long pass filter and the short pass filter, and the positional accuracy can be relaxed and the allowable range of positional deviation between the long pass filter and the short pass filter can be widened. .

In addition, by setting the film thickness gradient of the long pass filter to be larger than the film thickness gradient of the band pass filter, the long pass filter is shifted to the amount of shift of the cutoff wavelength WB ₁ of the band pass filter at each position where the film thickness changes. The shift amount of the cutoff wavelength WL of the filter can be made closer. This makes it possible to make the cutoff wavelength WL shorter than the cutoff wavelength WB ₁ at any position in one direction where the film thickness changes. As a result, at each position of the one direction, shorter cutoff wavelength WL than cutoff wavelength WB _1, by longer than the cutoff wavelength WS is cutoff wavelength WB _2, between the cut-off wavelength WB ₁ and cutoff wavelength WB ₂ It is possible to realize a configuration that transmits light in the wavelength range, and it is possible to ensure good transmission performance at any position in the one direction.

It is sectional drawing which shows the schematic structure of the spectrometer which concerns on one Embodiment of this invention. It is sectional drawing which shows the other structure of the said spectrometer. It is a graph which shows the spectral characteristic of each filter when a spectral filter is comprised by two layers, a short pass filter and a long pass filter, and position shift does not arise with the said short pass filter and the said long pass filter. It is a graph which shows the spectral characteristic of each filter when the position shift has arisen with the said short pass filter and the said long pass filter. It is a graph which shows the total spectral characteristic of the said short pass filter and the said long pass filter. It is a graph which shows the spectral characteristic of each filter when a spectral filter is comprised by three layers, a short pass filter, a long pass filter, and a band pass filter. It is a graph which shows typically the ideal spectral characteristic of each said filter. It is a graph which shows the change of the spectral characteristics at the time of changing the refractive index of a high refractive index material in a general reflective film. In the long pass filter, it is a graph showing the change of the spectral characteristics accompanying the change of the refractive index of the high refractive index material. In the short pass filter, it is a graph showing a change in spectral characteristics accompanying a change in the refractive index of a high refractive index material. It is a graph which shows the relationship between the wavelength and refractive index in niobium oxide. It is a graph which shows the relationship between the wavelength and refractive index in a silicon oxide. It is a graph which shows transition of the total film thickness in a long pass filter and a short pass filter with the same film thickness gradient. It is a graph which shows an example of the spectral characteristic of the spectral filter comprised by superimposing the said long pass filter and the said short pass filter. It is a graph which shows an example of the relationship between a film thickness ratio and a cut-off wavelength in three types of filters constituting a spectral filter. It is a graph which shows dispersion | distribution of two types of high refractive index materials. It is a graph which shows the other example of the relationship between film thickness ratio and cut-off wavelength in the above-mentioned three kinds of filters. It is a graph which shows the spectral characteristic of the said spectral filter in each position of one direction where a film thickness changes. It is a graph which shows an example of the spectral characteristic of three types of filters when a long pass filter has shifted with respect to a band pass filter. It is a graph which shows the other example of the spectral characteristic of three types of filters when a long pass filter has shifted position with respect to a band pass filter. It is explanatory drawing which plotted on the coordinate plane the actual design value of M corresponding to a dispersion | distribution ratio, and E corresponding to a gradient ratio. It is a graph which shows the spectral characteristics in the transmission position of wavelength 380nm in the spectral filter of Example 1. FIG. It is a graph which shows the spectral characteristics in the transmission position of wavelength 580nm in the spectral filter of Example 1. FIG. It is a graph which shows the spectral characteristics in the transmission position of wavelength 780nm in the spectral filter of Example 1. FIG. It is a graph which shows the spectral characteristic in the transmission position of wavelength 380nm in the spectral filter of Example 2. FIG. It is a graph which shows the spectral characteristics in the transmission position of wavelength 580nm in the spectral filter of Example 2. FIG. It is a graph which shows the spectral characteristics in the transmission position of wavelength 780nm in the spectral filter of Example 2. FIG. It is a graph which shows the spectral characteristics in the transmission position of wavelength 380nm in the spectral filter of Example 3. FIG. It is a graph which shows the spectral characteristics in the transmission position of wavelength 580nm in the spectral filter of Example 3. FIG. It is a graph which shows the spectral characteristics in the transmission position of wavelength 780nm in the spectral filter of Example 3. It is a graph which shows the spectral characteristics in the transmission position of wavelength 380nm in the spectral filter of Example 4. FIG. It is a graph which shows the spectral characteristics in the transmission position of wavelength 580nm in the spectral filter of Example 4. FIG. It is a graph which shows the spectral characteristics in the transmission position of wavelength 780nm in the spectral filter of Example 4. It is a graph which shows the spectral characteristics in the transmission position of wavelength 380nm in the spectral filter of Example 5. FIG. It is a graph which shows the spectral characteristics in the transmission position of wavelength 580nm in the spectral filter of Example 5. FIG. It is a graph which shows the spectral characteristics in the transmission position of wavelength 780nm in the spectral filter of Example 5. FIG. 6 is a graph showing spectral characteristics at a transmission position with a wavelength of 380 nm in the spectral filter of Comparative Example 1; 6 is a graph showing spectral characteristics at a transmission position with a wavelength of 580 nm in the spectral filter of Comparative Example 1; 7 is a graph showing spectral characteristics at a transmission position with a wavelength of 780 nm in the spectral filter of Comparative Example 1; It is a graph which shows the spectral characteristic in the transmission position of wavelength 380nm in the spectral filter of the comparative example 2. It is a graph which shows the spectral characteristic in the transmission position of wavelength 580nm in the spectral filter of the comparative example 2. It is a graph which shows the spectral characteristics in the transmission position of wavelength 780nm in the spectral filter of the comparative example 2. In Examples 1-5 and Comparative Examples 1-2, it is explanatory drawing which plotted on the coordinate plane the value of M equivalent to a dispersion | distribution ratio, and E corresponding to a gradient ratio.

  An embodiment of the present invention will be described below with reference to the drawings. In addition, in this specification, when a numerical range is described as ab, the value of the lower limit a and the upper limit b shall be included in the numerical range. The present invention is not limited to the following contents. In the following description, the half width refers to the full width at half maximum.

(Configuration of spectrometer)
FIG. 1 is a cross-sectional view illustrating a schematic configuration of a spectrometer 1 according to the present embodiment. The spectrometer 1 includes a spectral filter 10 and a light receiving unit 20. The spectral filter 10 is a linear variable filter (LVF) whose transmission wavelength continuously changes in one direction, and includes a band pass filter BP, a short pass filter SP, and a long pass filter LP.

  The band pass filter BP and the short pass filter SP are respectively formed on the front and back of the same substrate 11, and the long pass filter LP is formed on the surface of another substrate 12. The substrates 11 and 12 are made of a transparent substrate such as glass. The substrate 12 is located between the substrate 11 and the light receiving unit 20, and the band pass filter BP and the long pass filter LP are located in the outermost layer of the spectral filter 10, respectively.

  By using the substrates 11 and 12, the band-pass filter BP, the short-pass filter SP, and the long-pass filter LP can be overlaid and positioned as shown in FIG. The substrates 11 and 12 are bonded together with an adhesive 31, and the relative positional relationship between the substrates 11 and 12 (the relative positional relationship between the filters) is thereby fixed. The substrates 11 and 12 may be supported by a support member (not shown) so as to be in non-contact with each other through an air layer.

  The long pass filter LP has a film thickness gradient GL in which the film thickness monotonously increases in one direction. The film thickness gradient GL corresponds to | tan α | when the angle between the surface of the substrate 12 and the outermost surface of the long pass filter LP is α (°). The long pass filter LP includes a layer made of a first refractive index material (low refractive index material) and a layer made of at least one second refractive index material (high refractive index material) having a higher refractive index than the first refractive index material. Are transmitted, light in a wavelength region longer than the cutoff wavelength WL is transmitted, and transmission of other light is blocked. The cut-off wavelength WL is a wavelength (cutoff wavelength) when the transmittance is 50%, and monotonically increases (shifts to the longer wavelength side) as the film thickness increases in the one direction.

  The short pass filter SP has a film thickness gradient GS in which the film thickness monotonously increases in one direction. The film thickness gradient GS corresponds to | tan β | when the angle formed by the surface of the substrate 11 and the outermost surface of the short pass filter SP is β (°). The short pass filter SP includes a layer made of a first refractive index material (low refractive index material) and at least one second refractive index material (high refractive index material) having a refractive index higher than that of the first refractive index material. It is composed of a multilayer film in which layers are laminated, transmits light in a wavelength range shorter than the cutoff wavelength WS, and blocks transmission of other light. The cut-off wavelength WS is a wavelength (cutoff wavelength) when the transmittance is 50%, and monotonously increases (shifts to the longer wavelength side) as the film thickness increases.

The bandpass filter BP has a film thickness gradient GB in which the film thickness monotonously increases in one direction. The film thickness gradient GB corresponds to | tan γ | when the angle between the surface of the substrate 11 and the outermost surface of the bandpass filter BP is γ (°). The film thickness gradient GB of the band pass filter BP is almost the same as the film thickness gradient GS of the short pass filter SP, but may be different. The bandpass filter BP includes a layer made of a first refractive index material (low refractive index material) and at least one second refractive index material (high refractive index material) having a refractive index higher than that of the first refractive index material. It is composed of a multi-layered film, and transmits light in the wavelength range between the short wavelength side cutoff wavelength WB ₁ and the long wavelength side cutoff wavelength WB ₂ , while blocking the transmission of other light To do. The above cut-off wavelengths WB ₁ and WB ₂ are wavelengths (cutoff wavelengths) when the transmittance is 50%, and monotonically increases (shifts to the longer wavelength side) as the film thickness increases.

  As shown in the figure, the long-pass filter LP, the short-pass filter SP, and the band-pass filter BP are overlapped so that the one direction in which the film thickness monotonously increases coincides with each other. Further, the film thickness gradient GL of the long pass filter LP is larger than the film thickness gradient GB of the band pass filter BP. Details of the reason will be described later.

Since each cutoff wavelength (WL, WS, WB ₁ , WB ₂ ) shifts to the longer wavelength side as the film thickness increases, the transmission wavelength region between the cutoff wavelength WB ₁ and the cutoff wavelength WB ₂ is also As the film thickness increases, it shifts to the longer wavelength side. This means that the wavelength (transmission wavelength region) of the light transmitted through the spectral filter 10 continuously changes in the one direction in which the film thickness increases.

  The light receiving unit 20 includes a plurality of light receiving elements 21 and a support substrate 22 that supports each light receiving element 21. Each light receiving element 21 is a sensor that receives light transmitted through the spectral filter 10, and is arranged side by side on the support substrate 22 along the one direction in which the film thickness of the long pass filter LP of the spectral filter 10 increases monotonously. Has been. In the spectral filter 10, since the transmission wavelength continuously changes in the one direction, the light receiving element 21 among the plurality of light receiving elements 21 arranged along the one direction is detected. Thus, the wavelength (wavelength range) of the light incident on the spectral filter 10 can be detected.

  In FIG. 1, the positional relationship between the band pass filter BP and the short pass filter SP relative to the substrate 11 may be reversed. That is, the band pass filter BP may be positioned on the light receiving unit 20 side with respect to the substrate 11 and the short pass filter SP may be positioned on the opposite side of the light receiving unit 20.

  Further, the positional relationship between the substrate 11 and the substrate 12 may be reversed. That is, the substrate 11 may be located between the substrate 12 and the light receiving unit 20. However, when the substrates 11 and 12 are bonded with the adhesive 31 in such a positional relationship, the characteristics may change when the films formed on the substrates 11 and 12 are bonded to each other with the adhesive 31. The substrates 11 and 12 are bonded together so that the long-pass filter LP on 12 is the outermost layer of the spectral filter 10 (the long-pass filter LP is positioned on the opposite side of the substrate 11 from the substrate 12). Is desirable.

  FIG. 2 is a cross-sectional view showing another configuration of the spectrometer 1. In the spectral filter 10 of the spectrometer 1, the band pass filter BP, the short pass filter SP, and the long pass filter LP may be formed on different substrates 11, 12, and 13, respectively. Even with such a configuration, the band-pass filter BP, the short-pass filter SP, and the long-pass filter LP can be overlaid. The substrates 11 and 12 are bonded together via an adhesive 31, and the substrates 12 and 13 are bonded together via an adhesive 32. In addition, each board | substrate 11-13 may be supported by the supporting member (not shown) so that an air layer may interpose and it may become non-contact. Moreover, the arrangement | positioning order of each board | substrate 11-13 is not limited to the order shown in FIG. 2, For example, you may arrange | position in order of the board | substrate 11, the board | substrate 12, and the board | substrate 13 from the light-receiving part 20 side.

(About overlay position accuracy)
In the present embodiment, the spectral filter 10 is configured using three layers of a long pass filter LP, a short pass filter SP, and a band pass filter BP, thereby reducing the positional accuracy of the superposition of the long pass filter LP and the short pass filter SP. can do. Hereinafter, this point will be described first.

  FIG. 3 shows the spectral characteristics of each filter when the spectral filter is composed of two layers of a short pass filter SP and a long pass filter LP, and no positional deviation occurs between the short pass filter SP and the long pass filter LP. The spectral characteristics at the film thickness position where light having a wavelength of around 600 nm is transmitted are shown. When the short-pass filter SP and the long-pass filter LP are overlapped with each other without causing a positional shift, the transmittance near the wavelength of 600 nm is caused by the spectral characteristics of the short-pass filter SP and the long-pass filter LP as shown in FIG. The peak is formed.

  In the above-described spectral filter having a length of 6 mm and covering the visible range (transmitting light in the entire wavelength range of visible light in the range of 6 mm in length), the short path having the spectral characteristics shown in FIG. When a relative positional deviation of, for example, 0.1 mm occurs in one direction in which the film thickness changes between the filter SP and the long pass filter LP, as shown in FIG. 4, one of the short pass filter SP and the long pass filter LP Is deviated relative to the other spectral characteristic.

  FIG. 5 shows the total spectral characteristics of the short pass filter SP and the long pass filter LP. As shown in the figure, when there is no positional deviation between the short pass filter SP and the long pass filter LP and when there is a positional deviation of 0.1 mm, the wavelength at which the transmittance is peak, and the transmittance at which the peak is transmitted. It turns out that it fluctuates itself. That is, in the two-layer configuration of the short pass filter SP and the long pass filter LP, it is understood that a slight positional deviation between these two layers greatly affects the characteristics of the entire spectral filter, and the positional deviation between the two layers is hardly allowed.

FIG. 6 is a spectral characteristic of each filter when the spectral filter is composed of three layers of a short pass filter SP, a long pass filter LP, and a band pass filter BP, and at a film thickness position that transmits light in the vicinity of a wavelength of 600 nm. The spectral characteristics of are shown. As shown in the figure, in the spectral filter having a three-layer structure, the cutoff wavelength WL of the long pass filter LP is made shorter than the cutoff wavelength WB ₁ on the short wavelength side of the band pass filter BP, and the cutoff wavelength WS of the short pass filter SP. Is made longer than the cutoff wavelength WB ₂ on the long wavelength side of the bandpass filter BP, so that light in the wavelength region between the cutoff wavelength WB ₁ and the cutoff wavelength WB ₂ is transmitted and the other light is blocked. Characteristic can be brought out. In other words, in this configuration, the transmission characteristics of the spectral filter are substantially determined by the transmission characteristics of the bandpass filter BP, so the difference (wavelength difference) between the cutoff wavelength WL of the longpass filter LP and the cutoff wavelength WS of the shortpass filter SP is set. It is possible to ensure a wider area than the above-described two-layered spectral filter.

  Even if the cutoff wavelengths WL and WS fluctuate (shift) due to misalignment when the long pass filter LP and the short pass filter SP are superposed, the cutoff wavelengths WL and WS are changed. Can hardly overlap the transmission wavelength region of the bandpass filter BP, and the transmission characteristics (= transmission characteristics of the spectral characteristics) of the bandpass filter BP can be ensured. Therefore, it is not necessary to require a high positional accuracy for the superposition of the long pass filter LP and the short pass filter SP. The positional accuracy is relaxed, and an allowable range of positional deviation between the long pass filter LP and the short pass filter SP is increased. It can be expanded.

(About setting the film thickness gradient)
FIG. 7 schematically shows ideal spectral characteristics of each filter in a three-layer spectral filter. In order to obtain a desired transmission characteristic at each position in one direction where the film thickness changes, the relationship between the cutoff wavelengths of the bandpass filter BP, the shortpass filter SP, and the longpass filter LP (the wavelength difference between the cutoff wavelengths) is as described above. Ideally, it is almost constant at each position in one direction. That is, in any of the band-pass filter BP, the short-pass filter SP, and the long-pass filter LP, the cutoff wavelength monotonously changes (shifts) as the film thickness (position) changes. Is ideally the same among the three filters.

  However, in actuality, since the film material has wavelength dispersion, the shift amount of the cut-off wavelength with respect to the change in film thickness differs among the bandpass filter BP, the shortpass filter SP, and the longpass filter LP. For this reason, when the above three types of filters are overlapped with the same film thickness gradient, even if a good transmission performance can be ensured at a certain position where the film thickness changes, In the position, it may be impossible to ensure good transmission performance. Therefore, in this embodiment, by varying the film thickness gradient of at least two types of filters, the desired transmission characteristics can be obtained at any position in one direction in which the film thickness changes while being affected by the chromatic dispersion. It has been realized. Hereinafter, this point will be described in detail.

  FIG. 8 shows a general reflective film composed of a multilayer film of a high refractive index material and a low refractive index material, and the refractive index nH of the high refractive index material is changed to 2.30, 2.38, and 2.46. The change of the spectral characteristics in the case of As shown in the figure, it is known that the reflection wavelength region A of the reflective film becomes wider when the refractive index nH of the high refractive index material becomes higher and becomes narrower when the refractive index nH becomes lower.

  Considering such a change in spectral characteristics in the reflective film by applying it to a long-pass filter LP and a short-pass filter SP formed of a multilayer film of a high refractive index material and a low refractive index material, the following is obtained. That is, the spectral characteristics (especially the spectral characteristics in the wavelength range where the transmittance suddenly increases from 0%) in the reflection wavelength range A of the reflective film are the spectral characteristics (especially the transmittance is from 0%) of the long pass filter LP. The spectral characteristics on the short wavelength side of the reflected wavelength range A (especially the spectral characteristics in the wavelength range where the transmittance sharply drops to 0%) correspond to the sharply increasing spectral characteristics in the vicinity of the cutoff wavelength WL. This corresponds to the spectral characteristics of the filter SP (particularly, the spectral characteristics in the vicinity of the cut-off wavelength WS where the transmittance rapidly decreases to 0%). Therefore, in the long pass filter LP, as shown in FIG. 9, when the refractive index nH of the high refractive index material increases, the cutoff wavelength WL shifts to the long wavelength side, and in the short pass filter SP, as shown in FIG. When the refractive index nH of the high refractive index material increases, the cutoff wavelength WS shifts to the short wavelength side. On the other hand, when the refractive index nH of the high refractive index material is lowered, the cutoff wavelength WL is shifted to the short wavelength side in the long pass filter LP, and the cutoff wavelength WS is shifted to the long wavelength side in the short pass filter SP.

FIG. 11 shows the relationship between the wavelength and refractive index of niobium oxide (Nb ₂ O ₅ ), which is a kind of high refractive index material, and FIG. 12 shows silicon oxide (SiO _2), which is a kind of low refractive index material. ) Shows the relationship between the wavelength and the refractive index. The material constituting the film always has chromatic dispersion, and the refractive index increases as the wavelength becomes shorter. It can be seen that such a tendency appears more remarkably in the high refractive index material than in the low refractive index material. That is, the wavelength dispersion of the low refractive index material is negligibly small compared to the wavelength dispersion of the high refractive index material.

  FIG. 13 shows the transition of the total film thickness in the long pass filter LP and the short pass filter SP having a film thickness gradient. In the figure, for both the long pass filter LP and the short pass filter SP, the total film thickness at the position where the transmittance peak exists at the wavelength of 600 nm (600 nm peak position) is used as the reference (total film thickness 1). The ratio of the total film thickness at other positions is shown. As shown in FIG. 13, a long-pass filter LP and a short-pass filter SP having the same film thickness gradient, that is, a long-pass filter LP and a short-pass filter SP whose total film thickness is changed in the same ratio in one direction are superposed on each other. As shown in FIG. 14, in the wavelength region shorter than a certain reference (wavelength 600 nm) (for example, around 380 nm wavelength), due to the influence of wavelength dispersion of the high refractive index material described above (with a refractive index nH) As a result, the cutoff wavelength WL of the long pass filter LP is shifted to the long wavelength side, and the cutoff wavelength WS of the short pass filter SP is shifted to the short wavelength side. As a result, the full width at half maximum of the transmittance near the wavelength of 380 nm is narrowed. On the other hand, in the wavelength range longer than a certain reference (wavelength 600 nm) (for example, near 780 nm wavelength), the cutoff wavelength of the long pass filter LP is affected by the wavelength dispersion of the high refractive index material (by decreasing the refractive index nH). WL shifts to the short wavelength side, and the cutoff wavelength WS of the short pass filter SP shifts to the long wavelength side. As a result, the full width at half maximum of the transmittance near the wavelength of 780 nm is widened.

  Thus, when the shift of the cut-off wavelength is considered based on the 600 nm peak position, the ratio of the cut-off wavelength change to the change in film thickness (the cut-off wavelength shift amount) is longer than that of the short-pass filter SP as shown in FIG. It can be said that the filter LP is smaller (the cutoff wavelength WL has a smaller shift amount than the cutoff wavelength WS with respect to the change in film thickness from the 600 nm peak position).

  FIG. 15 shows this in relation to the film thickness ratio and the cutoff wavelength. Note that the film thickness ratio on the horizontal axis in FIG. 15 is a reference position (for example, a position where the cutoff wavelength is 350 nm for the long pass filter LP, a position where the cutoff wavelength is 380 nm for the band pass filter BP, and a cutoff position for the short pass filter SP. The film thickness at the position where the wavelength is 410 nm is assumed to be a film thickness ratio 1, and the ratio of the film thickness at each position to the film thickness at the reference position is shown. The cut-off wavelength on the vertical axis is the wavelength when the transmittance is 50%, but for the band-pass filter BP, the cut-off wavelength on the short wavelength side is shown. In FIG. 15, it is assumed that the film thickness gradients of the long pass filter LP, the band pass filter BP, and the short pass filter SP are the same.

  As shown in the figure, the ratio of the change in the cut-off wavelength (the shift amount of the cut-off wavelength) relative to the film thickness ratio (change in the film thickness) corresponds to the slope of the graph shown by the straight line in FIG. Therefore, in the long pass filter LP, the ratio of change in the cutoff wavelength with respect to the change in film thickness (straight line) is smaller than in other filters. As shown in FIG. 15, it is known that the bandpass filter BP is similar to the shortpass filter SP in how the cutoff wavelength changes with respect to the change in film thickness. For this reason, it can be said that the ratio of the change in the cutoff wavelength with respect to the change in the film thickness is smaller in the long pass filter LP than in the band pass filter BP and the short pass filter SP.

  FIG. 16 shows the dispersion of the two types of high refractive index materials A and B, respectively. In the figure, it is shown that the high refractive index material A has a larger dispersion than the high refractive index material B (the change in refractive index with respect to the change in wavelength is large). When the change in the cutoff wavelength with respect to the change in film thickness shown in FIG. 15 is a change in the case of using the high refractive index material A having a larger dispersion, the case of using the high refractive index material B having a smaller dispersion. The change of the cutoff wavelength with respect to the change of the film thickness is as shown in FIG. That is, as shown in FIG. 15 and FIG. 17, the ratio of the change in the cutoff wavelength with respect to the change in the film thickness varies depending on the dispersion of the high refractive index material. The ratio of the change in the cut-off wavelength with respect to the change is small (in FIG. 15, the slope of the straight line in each graph is smaller than in FIG. 17). However, even when a high refractive index material with smaller dispersion is used, the ratio of the change in the cutoff wavelength to the change in the film thickness is smaller in the long pass filter LP than in the band pass filter BP and the short pass filter SP. It is the same as the case of.

  Thus, since the ratio of the change in the cutoff wavelength with respect to the change in the film thickness is different at least between the band pass filter BP and the long pass filter LP, the filters are overlapped with the film thickness gradients of these filters being substantially the same. When combined, good transmission performance may not be ensured at a position in one direction where the film thickness changes. For example, in Comparative Example 2, which will be described later, in the transmission band of wavelength 380 nm (particularly at the position where the transmittance peak of the bandpass filter BP is 380 nm), the wavelength shift amount with respect to the change in film thickness is longer than the bandpass filter BP. Therefore, the transmission wavelength range of the bandpass filter BP is closer to the shorter wavelength side than the cutoff wavelength WL of the longpass filter LP (see FIG. 40). In this case, the light passing through the band pass filter BP is blocked from being transmitted by the long pass filter LP, and good transmission performance cannot be ensured.

Therefore, in the present embodiment, the film thickness gradient GL of the long pass filter LP is made larger than the film thickness gradient GB of the band pass filter BP. In this way, the shift amounts from the reference of the cutoff wavelengths WB ₁ and WL can be made closer to each other at each position in one direction where the film thickness changes. For example, at the position where the film thickness ratio of the band pass filter BP is 3, the cutoff wavelength WL is shifted by the shift amount at the position where the film thickness ratio of the long pass filter LP is larger than 3, so that the cutoff wavelengths WB ₁ and WL are The shift amounts can be made closer to each other. Further, even when the film thickness ratio of the bandpass filter BP is other than 3, it can be considered in the same manner as described above. In the long pass filter LP, the film thickness ratio is shifted at a position larger than the film thickness ratio of the bandpass filter BP. By shifting the cutoff wavelength WL by an amount, the shift amounts of the cutoff wavelengths WB ₁ and WL can be made closer to each other.

Therefore, at any position of the one direction, the cut-off wavelength WL substantially the same amount to shift the cutoff wavelength WB _1, shorter than the cutoff wavelength WB ₁ the cut-off wavelength WL, that is, cut off the cut-off wavelength WL wavelength WB ₁ It is possible to position it on the shorter wavelength side. As a result, at any position of the one direction, shorter cutoff wavelength WL than cutoff wavelength WB _1, by longer than the cutoff wavelength WS is cutoff wavelength WB _2, between the cut-off wavelength WB ₁ and cutoff wavelength WB ₂ It is possible to realize a configuration that transmits light in the wavelength range. That is, as shown in FIG. 18, it is possible to ensure good transmission performance at any position in the one direction that transmits visible light. In addition, the length of the said one direction in a spectral filter can be set arbitrarily, for example, can be 6-20 mm in length.

  As shown in FIGS. 15 and 17, the short-pass filter SP and the band-pass filter BP have almost the same ratio of change in cutoff wavelength (straight line) with respect to the change in film thickness. The film thickness gradient GS of the SP and the film thickness gradient GB of the bandpass filter BP may be the same, but the film thickness gradient GS and the film thickness gradient GB are increased by an amount corresponding to the difference in the inclination of each straight line. The cut-off wavelength shift amount may be equalized at each position in one direction where the film thickness changes between the short pass filter SP and the band pass filter BP with a difference.

(Preferable range of wavelength difference between cutoff wavelength WB ₁ and cutoff wavelength WL)
In the spectral filter 10 of the present embodiment, the wavelength difference between the cutoff wavelength WB ₁ and the cutoff wavelength WL (at all positions where visible light (for example, light having a wavelength of 380 to 780 nm) is transmitted in one direction in which the film thickness changes) In the following, it is desirable that it is also described as ΔW) in the range of 13 nm to 42 nm.

By allowing ΔW to be 13 nm or more, the allowable range of the positional deviation in the one direction of the long pass filter LP can be surely expanded. That is, as shown in FIG. 19, when the cutoff wavelength WL overlaps the cutoff wavelength WB ₁ of a certain transmission band due to the positional deviation of the long pass filter LP, the transmission wavelength range (the cutoff wavelength WB ₁ and the cutoff wavelength WB of the band pass filter BP). The wavelength range between ₂ and ₂ becomes narrow, and good transmission characteristics cannot be secured. By ensuring 13 nm or more as ΔW, the allowable range of the positional deviation in the above-mentioned one direction of the long pass filter LP is widened. Therefore, even if some positional deviation occurs, it is possible to reliably ensure good transmission performance. Become.

  Further, when ΔW is 42 nm or less, light transmission leakage due to the positional deviation of the long pass filter LP can be reliably reduced. That is, as shown in FIG. 20, due to the positional deviation of the long pass filter LP in the one direction, the cutoff wavelength WL of the long pass filter LP becomes the stop band of the band pass filter BP (wavelength range for blocking light transmission; In the example, when positioned on the shorter wavelength side than around 540 to 590 nm, light on the shorter wavelength side than the stopband of the bandpass filter BP is transmitted without being blocked by the longpass filter LP, and light transmission leakage Will occur. For this reason, the transmission leakage can be reliably reduced by setting ΔW to 42 nm or less.

  In addition, it is possible to reduce the transmission leakage by widening the stop band of the band pass filter BP. However, the design to widen the stop band increases the number of layers of the band pass filter BP. Design is likely to be difficult. In this regard, by setting ΔW to 42 nm or less as described above, the transmission leakage can be eliminated without increasing the number of layers of the bandpass filter BP, and the design of the bandpass filter BP is facilitated. .

  From the viewpoint of obtaining the above effect more reliably, a desirable range of ΔW is 20 nm or more and 30 nm or less.

(Specific conditions for keeping ΔW within a desired range)
Next, specific conditions for realizing the above-described range of ΔW in the spectral filter 10 of the present embodiment will be examined.

  As described above, the long pass filter LP and the band pass filter BP of the spectral filter 10 are composed of a layer made of the first refractive index material and at least one second refractive index material having a refractive index higher than that of the first refractive index material. It is comprised with the multilayer film which laminated | stacked the layer. Here, among at least one second refractive index material, a material in which at least one of the number of layers and the total film thickness is maximum is defined as a main refractive index material. When there is only one kind of second refractive index material, the second refractive index material becomes the main refractive index material. In addition, when the second refractive index material having the maximum number of layers and the second refractive index material having the maximum total film thickness are different, any second refractive index material can be used as the main refractive index material. .

In the long pass filter LP, the refractive index of the main refractive index material at a wavelength of 380 nm is nL ₃₈₀ , the refractive index of the main refractive index material at a wavelength of 780 nm is nL _780, and the film thickness of the transmission part that transmits light of wavelength 780 nm is set. , DL ₇₈₀ (nm), and the thickness of the transmission part that transmits light with a wavelength of 380 nm is dL ₃₈₀ (nm).

Further, in the band pass filter BP, the refractive index of the main refractive index material at a wavelength of 380 nm is nB ₃₈₀ , the refractive index of the main refractive index material at a wavelength of 780 nm is nB _780, and a transmission portion that transmits light having a wavelength of 780 nm is used. The film thickness is dB ₇₈₀ (nm), and the film thickness of the transmission part that transmits light with a wavelength of 380 nm is dB ₃₈₀ (nm).

It is desirable that the spectral filter 10 satisfies the following conditional expression (1). That is,
0.98 <{(dL ₇₈₀ / dL ₃₈₀ ) / (dB ₇₈₀ / dB ₃₈₀ )} × [(nL ₇₈₀ / nL ₃₈₀ ) / {(nB ₇₈₀ / nB ₃₈₀ ) ^0.4 }] <1.17 ( 1)
It is.

In conditional expression (1),
(DL ₇₈₀ / dL ₃₈₀ ) / (dB ₇₈₀ / dB ₃₈₀ ) = E
(NL ₇₈₀ / nL ₃₈₀ ) / {(nB ₇₈₀ / nB ₃₈₀ ) ^0.4 } = M
E × M = F
Then, the conditional expression (1) can be simplified as the following conditional expression (1 ′).
0.98 ≦ F ≦ 1.17 (1 ′)

Further, it is more desirable for the spectral filter 10 to satisfy the following conditional expression (2). That is,
1.03 <{(dL ₇₈₀ / dL ₃₈₀ ) / (dB ₇₈₀ / dB ₃₈₀ )} × [(nL ₇₈₀ / nL ₃₈₀ ) / {(nB ₇₈₀ / nB ₃₈₀ ) ^0.4 }] <1.1 ( 2)
It is.

Conditional expression (2) can be simplified as conditional expression (2 ′) below, following conditional expression (2 ′).
1.03 ≦ F ≦ 1.1 (2 ′)

Here, E indicates the ratio of the film thickness gradient GL of the long pass filter LP to the film thickness gradient GB of the band pass filter BP (hereinafter also referred to as gradient ratio). The value of E increases as dL ₇₈₀ / dL ₃₈₀ becomes larger than dB ₇₈₀ / dB ₃₈₀ , that is, as the film thickness gradient GL becomes larger than the film thickness gradient GB.

Further, M represents the ratio between the dispersion of the main refractive index material applied to the long pass filter LP and the dispersion of the main refractive index material applied to the band pass filter BP (hereinafter also referred to as dispersion ratio). Yes. In the equation of M, the dispersion (nB ₇₈₀ / nB ₃₈₀ ) of the main refractive index material of the bandpass filter BP is raised to the power of 0.4 because the above E is used as the variable y in the xy orthogonal coordinate system. When each point of the design value represented by the coordinates (M, E) is plotted with the above M corresponding to the variable x, each point is arranged almost linearly on the coordinate plane, This is because the constants corresponding to the upper and lower limits of the conditional expression (1) or (2) can be easily obtained. In the equation of M, the power part may be other than 0.4, but in this case, since the points corresponding to the plurality of spectral filters are arranged in a curved line, it is difficult to specify the regression equation. There is a possibility. Therefore, it is desirable that the power of the expression of M is 0.4.

When the dispersion of the main refractive index material of the long pass filter LP is small, the ratio of the change in the cutoff wavelength with respect to the change in the film thickness in the long pass filter LP is relatively large as shown in FIG. For this reason, even if the gradient ratio (GL / GB) is not increased so much, the shift amount from the reference of the cutoff wavelength at each transmission position (film thickness position) is substantially equalized between the long pass filter LP and the band pass filter BP. It becomes possible. When the dispersion of the main refractive index material of the long pass filter LP is small, the value of (nL ₇₈₀ / nL ₃₈₀ ) is large (because the denominator nL ₃₈₀ is small), so the above dispersion ratio tends to be large. Become. Therefore, when the dispersion ratio is large, it can be said that the difference (ΔW) between the cutoff wavelengths Wb ₁ and WL can be kept within a predetermined range at each position in one direction where the film thickness changes by decreasing the gradient ratio.

On the contrary, when the dispersion of the main refractive index material of the long pass filter LP is large, the ratio of the change in the cutoff wavelength with respect to the change in the film thickness in the long pass filter LP becomes relatively small as shown in FIG. For this reason, in order to make the long-pass filter LP and the band-pass filter BP have the same shift amount from the cutoff wavelength reference at each transmission position, it is necessary to increase the gradient ratio (GL / GB). When the dispersion of the main refractive index material of the long pass filter LP is large, the value of (nL ₇₈₀ / nL ₃₈₀ ) is small (because the denominator nL ₃₈₀ is large), and thus the above dispersion ratio tends to be small. Become. Therefore, when the dispersion ratio is small, it can be said that the gradient ratio needs to be increased in order to keep the difference (ΔW) between the cutoff wavelengths Wb ₁ and WL at each position in one direction where the film thickness changes within a predetermined range. .

  From the above, it can be said that in order to keep ΔW within a predetermined range at each position in one direction where the film thickness changes, the gradient ratio and the dispersion ratio need only be in an inversely proportional relationship.

  FIG. 21 is a plot of actual design values of M corresponding to the dispersion ratio and E corresponding to the gradient ratio on the coordinate plane (the coordinates of each point indicating the design value are (M, E)). In the group A in the figure, ΔW is as large as about 35 to 42 nm in the light transmission part (380 nm transmission band) with a wavelength of 380 nm, and as small as about 13 to 17 nm in the light transmission part (780 nm transmission band) with a wavelength of 780 nm. A set of such design values is shown. Group B shows a set of design values such that ΔW is as small as about 13 to 17 nm in the 380 nm transmission band and as large as about 35 to 42 nm in the 780 nm transmission band. If the design value of the A group, the design value of the B group, or the design value between the A group and the B group is adopted, ΔW is in the range of 13 nm or more and 42 nm or less, and the long pass filter LP is misaligned. Even if it occurs, the transmission performance described above can be secured.

  As described above, when M and E are in an inversely proportional relationship, the regression equation p indicating the upper limit of the A group and the regression equation s indicating the lower limit of the B group can be approximated by y = a / x, respectively. In this case, F, which is the product of M and E, corresponds to the constant a of the regression equation. When the regression equation p and the regression equation s were obtained from FIG. 21, y = 1.17 / x was obtained as the regression equation p, and y = 0.98 / x was obtained as the regression equation s. Therefore, if the value of F, which is the product of M and E, is larger than 0.98 and smaller than 1.17 (if conditional expression (1) or (1 ′) is satisfied), the film thickness changes. It can be said that at any position in the direction, the above-mentioned effect can be obtained by realizing ΔW of 13 nm or more and 42 nm or less.

  Further, the group C in FIG. 21 is a set of design values in which ΔW is about 20 to 30 nm in both the 380 nm transmission band and the 780 nm transmission band. By adopting the design value of group C, it is possible to reliably block the light in the stopband of the bandpass filter BP with the longpass filter LP while reliably extending the allowable range of positional deviation of the longpass filter LP. From FIG. 21, the regression equation q indicating the upper limit of the C group and the regression equation r indicating the lower limit of the C group were obtained, and y = 1.1 / x was obtained as the regression equation q, and y = 1 as the regression equation r. 0.03 / x was obtained. Therefore, if the value of F is larger than 1.03 and smaller than 1.1 (if conditional expression (2) or (2 ′) is satisfied), ΔW is set as ΔW at any position in one direction where the film thickness changes. It can be said that the above-described effects can be obtained by realizing 20 nm or more and 30 nm or less.

(Example)
Next, a description will be given of the results of designing a plurality of three-layered spectral filters using the long-pass filter LP, the short-pass filter SP, and the band-pass filter BP and examining the characteristics of each spectral filter. In addition, let a representative thing be the Examples 1-5 and Comparative Examples 1-2 among the some spectral filter designed.

Here, the high refractive index material H1 made of Nb ₂ O ₅ and the high refractive index materials H2 to H4 in which the dispersion of the high refractive index material H1 is changed are considered as the high refractive index materials. Further, a low refractive index material L1 made of SiO ₂ is considered as a low refractive index material. Table 1 shows dispersion data (refractive index for each wavelength) of the high refractive index materials H1 to H4, and Table 2 shows dispersion data of the low refractive index material L1.

  Further, any one of LP1 to LP5 is considered as the long pass filter LP, any one of SP1 to SP5 is considered as the short pass filter SP, and any one of BP1 to BP5 is considered as the band pass filter BP. LP1 to LP5 are configured by laminating one or more layers selected from high refractive index materials H1 to H4 and a layer made of low refractive index material L1. Tables 3 to 7 show reference layer configurations of LP1 to LP5 at a transmission position with a wavelength of 380 nm, respectively. The film thickness of each layer at the transmission position of each wavelength is set based on the above reference layer configuration so that a desired film thickness gradient GL is obtained. For example, when the total film thickness at the transmission position of the wavelength 380 nm when the desired film thickness gradient GL of LP1 is obtained is 1942.5 nm, the total film thickness of each layer shown in Table 3 is 1696.78 nm. The film thickness of each layer at the transmission position with a wavelength of 380 nm is set to a value obtained by multiplying each film thickness shown in Table 3 by a coefficient (1942.5 / 16696.78). The film thickness of each layer at the transmission position of other wavelengths is also set by the same method as described above.

  SP1 to SP5 are configured by laminating one or more layers selected from high refractive index materials H1 to H4 and a layer made of low refractive index material L1. Tables 8 to 12 show the reference layer configurations of SP1 to SP5 at the transmission position with a wavelength of 380 nm, respectively. The film thickness of each layer at the transmission position of each wavelength is set by the same method as in the case of LP1 to LP5 based on the above reference layer configuration so as to obtain a desired film thickness gradient GS.

  The BP1 to BP5 are configured by laminating one or more layers selected from the high refractive index materials H1 to H4 and a layer made of the low refractive index material L1. Tables 13 to 17 show reference layer configurations of BP1 to BP5 at the transmission position with a wavelength of 380 nm, respectively. The film thickness of each layer at the transmission position of each wavelength is set by the same method as in the case of LP1 to LP5 based on the above reference layer configuration so as to obtain a desired film thickness gradient GB.

  In the following table, the layer number is the number of the layer when counted in order from the substrate side, and the film thickness indicates the physical film thickness.

  The layer configuration of LP5 shown in Table 7 is such that only the second layer of LP1 shown in Table 3 is replaced with the high refractive index material H1 with the high refractive index material H3. The layer structure of SP5 shown in Table 12 is such that the high refractive index material H1 is replaced with the high refractive index material H3 only in the first layer of SP1 shown in Table 8. Further, the layer configuration of BP5 shown in Table 17 is obtained by replacing the high refractive index material H1 with the high refractive index material H3 only in the first layer of BP1 shown in Table 13.

  Hereinafter, the spectral filters of Examples 1 to 5 and Comparative Examples 1 to 2 will be further described. In the following description, wavelength 1 refers to wavelength 380 nm, wavelength 3 refers to wavelength 580 nm, and wavelength 5 refers to wavelength 780 nm.

Example 1
In the first embodiment, the cutoff wavelength WB ₁ on the short wavelength side of the bandpass filter BP, the cutoff wavelength WL of the long pass filter LP, and the cutoff wavelength WS of the short pass filter SP at the transmission positions of wavelength 1, wavelength 3, and wavelength 5 are as follows. The spectral filter was designed by adjusting the film thickness gradient of each layer of BP1, LP1, and SP1 so as to have the values shown in Table 18, respectively. In the spectral filter of Example 1, the spectral characteristics at the transmission positions of wavelength 1, wavelength 3, and wavelength 5 are shown in FIGS. For reference, Table 18 also shows the cutoff wavelength WB ₂ on the long wavelength side at each transmission position of the bandpass filter BP (the same applies to the following tables).

Example 2
In the second embodiment, the cutoff wavelength WB ₁ on the short wavelength side of the band-pass filter BP, the cutoff wavelength WL of the long-pass filter LP, and the cutoff wavelength WS of the short-pass filter SP at the transmission positions of wavelength 1, wavelength 3, and wavelength 5 are as follows. The spectral filters were designed by adjusting the film thickness gradients of the BP2, LP2, and SP1 layers so that the values shown in Table 19 were obtained. In the spectral filter of Example 2, the spectral characteristics at the transmission positions of wavelength 1, wavelength 3, and wavelength 5 are shown in FIGS.

Example 3
In the third embodiment, the cutoff wavelength WB ₁ on the short wavelength side of the bandpass filter BP, the cutoff wavelength WL of the long pass filter LP, and the cutoff wavelength WS of the short pass filter SP at the transmission positions of wavelength 1, wavelength 3, and wavelength 5 are as follows. The spectral filter was designed by adjusting the film thickness gradient of each layer of BP2, LP4, and SP1 so as to have the values shown in Table 20, respectively. In the spectral filter of Example 3, the spectral characteristics at the transmission positions of wavelength 1, wavelength 3, and wavelength 5 are shown in FIGS.

Example 4
In the fourth embodiment, the cutoff wavelength WB ₁ on the short wavelength side of the bandpass filter BP, the cutoff wavelength WL of the long pass filter LP, and the cutoff wavelength WS of the short pass filter SP at the transmission positions of wavelength 1, wavelength 3, and wavelength 5 are as follows. The spectral filter was designed by adjusting the film thickness gradient of each layer of BP3, LP2, and SP1 so as to have the values shown in Table 21, respectively. In the spectral filter of Example 4, the spectral characteristics at the transmission positions of wavelength 1, wavelength 3, and wavelength 5 are shown in FIGS.

Example 5
In the fifth embodiment, the cutoff wavelength WB ₁ on the short wavelength side of the band pass filter BP, the cutoff wavelength WL of the long pass filter LP, and the cutoff wavelength WS of the short pass filter SP at the transmission positions of wavelength 1, wavelength 3, and wavelength 5 are as follows. The spectral filters were designed by adjusting the film thickness gradients of the BP5, LP5, and SP5 layers so that the values shown in Table 22 were obtained. In the spectral filter of Example 5, the spectral characteristics at the transmission positions of wavelength 1, wavelength 3, and wavelength 5 are shown in FIGS. In BP5, LP5, and SP5 of Example 5, among the plurality of high-refractive index materials H1 and H3, the high-refractive index material H1 having a large number of layers and a total film thickness is the main refractive index material.

<< Comparative Example 1 >>
In Comparative Example 1, the cutoff wavelength WB ₁ on the short wavelength side of the band-pass filter BP, the cutoff wavelength WL of the long-pass filter LP, and the cutoff wavelength WS of the short-pass filter SP at the transmission positions of wavelength 1, wavelength 3, and wavelength 5 are The spectral filters were designed by adjusting the film thickness gradients of the BP1, LP1, and SP1 layers so that the values shown in Table 23 were obtained. In the spectral filter of Comparative Example 1, spectral characteristics at the transmission positions of wavelength 1, wavelength 3, and wavelength 5 are shown in FIGS.

<< Comparative Example 2 >>
In Comparative Example 2, the cutoff wavelength WB ₁ on the short wavelength side of the band pass filter BP, the cutoff wavelength WL of the long pass filter LP, and the cutoff wavelength WS of the short pass filter SP at the transmission positions of wavelength 1, wavelength 3, and wavelength 5 are The spectral filters were designed by adjusting the film thickness gradients of the BP1, LP1, and SP1 layers so that the values shown in Table 24 were obtained. In the spectral filter of Comparative Example 2, spectral characteristics at the transmission positions of wavelength 1, wavelength 3, and wavelength 5 are shown in FIGS.

Table 25 collectively shows the values of the parameters in the spectral filters of Examples 1 to 5 and Comparative Examples 1 and 2. As for the short pass filter SP, the refractive index at a wavelength of 380 nm of the main refractive index material is nS ₃₈₀ , the refractive index at a wavelength of 780 nm of the main refractive index material is nS _780, and a transmission part that transmits light at a wavelength of 780 nm. The film thickness of the transmission part was dS ₇₈₀ (nm), and the film thickness of the transmission part that transmits light with a wavelength of 380 nm was dS ₃₈₀ (nm).

From Table 25, in Comparative Example 1, the value of E is 1, and the film thickness gradient GL of the long pass filter is equal to the film thickness gradient GB of the band pass filter BP. In this case, since the difference (ΔW) between the cutoff wavelengths WB ₁ and WL is too wide at 119.2 nm at the transmission position of the wavelength 5, as shown in FIG. 39, it can be completely blocked by the stop band of the bandpass filter BP. No light (for example, light around a wavelength of 650 to 660 nm) is transmitted through the long pass filter LP.

In Comparative Example 2, the value of E is smaller than 1, and the film thickness gradient GL is smaller than the film thickness gradient GB. In this case, since ΔW is −8.8 nm and the cutoff wavelength Wl is on the longer wavelength side than the cutoff wavelength WB ₁ , the light transmitted through the bandpass filter BP is blocked by the longpass filter LP as shown in FIG. As a result, it is impossible to ensure the transmission characteristics of wavelength 1 (380 nm).

On the other hand, in Examples 1 to 5, the values of E are all larger than 1, and the film thickness gradient GL is larger than the film thickness gradient GB. As a result, the cutoff wavelength WL is shorter than the cutoff wavelength WB ₁ and the cutoff wavelength WS is longer than the cutoff wavelength WB ₂ at the transmission positions of the wavelength 1, wavelength 3, and wavelength 5, respectively. It has a characteristic of transmitting light in a wavelength region between the cutoff wavelength WB ₁ and the cutoff wavelength WB ₂ . From this, it can be easily estimated that good transmission performance can be secured at any position in one direction where the film thickness changes (at any wavelength transmission position).

  FIG. 43 plots the values of M and E in Examples 1 to 5 and Comparative Examples 1 and 2 on a coordinate plane. Each of the points in Examples 1 to 5 (coordinates are (M, E)) is between the regression equation p (y = 1.17 / x) and the regression equation s (y = 0.98 / x). It can be seen that the characteristic that can secure 13 nm or more and 42 nm or less is obtained as ΔW. In particular, Examples 1 and 5 are located between the regression equation q (y = 1.1 / x) and the regression equation r (y = 1.03 / x), and ΔW is 20 nm or more as described above. It turns out that the characteristic which can ensure 30 nm or less is acquired. Since Comparative Examples 1 and 2 are not located between the regression equation p and the regression equation s, a desired range (13 nm or more and 42 nm or less) is set as ΔW at any position in one direction where the film thickness changes. It is clear that cannot be secured.

  The present invention can be used for an LVF whose transmission wavelength continuously changes in one direction, and a spectroscopic measurement apparatus including the LVF.

DESCRIPTION OF SYMBOLS 1 Spectrometer 10 Spectral filter 11 Substrate 12 Substrate 13 Substrate 21 Light receiving element 31 Adhesive 32 Adhesive LP Long pass filter SP Short pass filter BP Band pass filter

Claims (7)

A long pass filter in which the film thickness monotonously increases in one direction, transmits light in a wavelength region longer than the cutoff wavelength WL, and the cutoff wavelength WL monotonously increases as the film thickness increases;
A short pass filter in which the film thickness monotonously increases in one direction, transmits light in a wavelength region shorter than the cut-off wavelength WS, and the cut-off wavelength WS monotonously increases as the film thickness increases;
The film thickness monotonously increases in one direction, transmits light in the wavelength region between the short wavelength side cutoff wavelength WB ₁ and the long wavelength side cutoff wavelength WB _2, and as the film thickness increases. A band pass filter in which the cut-off wavelength WB ₁ and the cut-off wavelength WB ₂ are monotonously increased,
The long pass filter, the short pass filter, and the band pass filter are overlapped so that the one direction in which the film thickness monotonously increases coincides with each other,
The film thickness gradient of the long pass filter is larger than the film thickness gradient of the band pass filter,
At each position in the one direction, the cutoff wavelength WL is shorter than the cutoff wavelength WB ₁ , and the cutoff wavelength WS is longer than the cutoff wavelength WB ₂ , whereby the cutoff wavelength WB ₁ and the cutoff wavelength WB ₂ are A spectral filter characterized by transmitting light in the wavelength region between. 2. The spectral filter according to claim ₁ , wherein a difference between the cutoff wavelength WB ₁ and the cutoff wavelength WL is 13 nm or more and 42 nm or less at all positions where visible light is transmitted in the one direction. The long pass filter and the band pass filter are multilayer films in which a layer made of a first refractive index material and at least one layer made of at least one second refractive index material having a higher refractive index than the first refractive index material are laminated. Configured,
Among the at least one second refractive index material, when the material having at least one of the number of layers and the total film thickness is the main refractive index material,
In the long pass filter,
The refractive index at a wavelength of 380 nm of the main refractive index material is nL ₃₈₀ ,
The refractive index at a wavelength of 780 nm of the main refractive index material is nL ₇₈₀ ,
The film thickness of the transmissive portion for transmitting the wavelength 780nm light, and dL _780,
The film thickness of the transmission part that transmits light with a wavelength of 380 nm is dL ₃₈₀ ,
In the bandpass filter,
The refractive index at a wavelength of 380 nm of the main refractive index material is nB ₃₈₀ ,
The refractive index at a wavelength of 780 nm of the main refractive index material is nB ₇₈₀ ,
The thickness of the transmission part that transmits light having a wavelength of 780 nm is dB ₇₈₀ ,
When the thickness of the transmission part that transmits light with a wavelength of 380 nm is dB ₃₈₀ ,
The spectral filter according to claim 2, wherein the following conditional expression is satisfied:
0.98 <{(dL ₇₈₀ / dL ₃₈₀ ) / (dB ₇₈₀ / dB ₃₈₀ )} × [(nL ₇₈₀ / nL ₃₈₀ ) / {(nB ₇₈₀ / nB ₃₈₀ ) ^0.4 }] <1.17
It is. The band pass filter and the short pass filter are respectively formed on the front and back of the same substrate,
The spectral filter according to claim 1, wherein the long pass filter is formed on another substrate.   The spectral filter according to claim 1, wherein the band-pass filter, the short-pass filter, and the long-pass filter are formed on different substrates.   6. The spectral filter according to claim 4, wherein each of the substrates is bonded with an adhesive. The spectral filter according to any one of claims 1 to 6,
A light receiving element for receiving the light transmitted through the spectral filter,
The spectroscopic measurement apparatus, wherein the light receiving elements are arranged side by side along the one direction of the spectral filter.

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