JPS6227361B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a dichroic film having an appropriate half-width and good reflective properties. Dichroic films usually consist of alternating layers of high refractive index and low refractive index layers. Conventionally, in the structure of a dichroic film, the basic film thickness of the high refractive index layer H and the low refractive index layer L is 3:1 (hereinafter H:L=3:
Conventionally, a film with a basic film thickness of H:L=3:1 is often used. In this configuration, the half-width of the three-color separation optical system, especially the blue-reflecting dichroic film, cannot be sufficiently secured, and in order to improve the efficiency of the blue channel, it is necessary to widen this half-width. According to this request,
In the patent application No. 52-71896, H:L=3:1 configuration,
A method of widening the half-width by mixing H:L=1:1 configurations is shown. With this method, it is possible to expand the half-width, but in order to remove ripples in the transmission band, it is necessary to provide a suppression layer in the intermediate layer with a thickness sufficient to remove ripples, and the deposition procedure is complicated. Therefore, it requires skill to manufacture. SUMMARY OF THE INVENTION An object of the present invention is to provide a dichroic film that has an appropriate half-width, excellent reflective properties, and is easy to manufacture. In the dichroic film according to the present invention, we focused on the fact that the half-width increases in a film with a basic film thickness of H:L=1:3.
This is an effective combination of a 3:1 configuration and an H:L=1:3 configuration. With this configuration, it is possible to obtain a dichroic film that has an appropriate half-width, has little change in reflection characteristics depending on the angle of incident light, and is easy to manufacture. The present invention will be described in detail below with reference to the drawings. Figure 1 shows the basic film thickness configurations of H:L=3:1 (solid line) and H:L=1:3 (dashed line), assuming that there is no dispersion in the high refractive index layer. This is a diagram showing a transmittance characteristic curve for an incident angle of 0 degrees, with transmittance T plotted on the vertical axis and wavelength λ plotted on the horizontal axis. 1st
Table 1 shows data corresponding to the solid line 11 and broken line 12 shown in the figure. As shown in FIG. 1, if there is no dispersion in the high refractive index layer, the half widths are the same in all configurations, but in reality, since high refractive index substances have dispersion, the half widths are not equal.

[Table] Figures 2 and 3 are diagrams showing the characteristics of high refractive index materials when dispersion is considered. Figure 2 shows H:L=3:
1, and FIG. 3 shows the case of H:L=1:3. The film structure corresponding to the transmittance characteristic curves in FIGS. 2 and 3 is the same as the structure shown in Table 1, but the difference is that the refractive index n _H of the high refractive index layer is n _H =2.07+
11/λ-318 (where λ is the wavelength, the unit is nm). In FIGS. 2 and 3, solid lines 21 and 31 represent the characteristics when the angle of incidence of the incident light is 0 degrees, and broken lines 22 and 32 represent the characteristics when the angle of incidence is 0 degrees.
The characteristics for the case of 44.6° are shown. As is clear from Figures 2 and 3, the characteristics of H:L = 3:1 are H:L
Compared to the characteristic of =1:3, the half-width is clearly narrower at an incident angle of 0 degrees, and if the reflection peak is moved to the same wavelength at an incident angle of 43.6 degrees and compared, this tendency becomes even more remarkable. That is, the configuration with H:L=1:3 has a wider half-width than the configuration with H:L=3:1, and the configuration with H:L=1:3 is preferable regarding the half-width. On the other hand, when the incident angle is 43.6 degrees compared to 0 degrees, the amount of shift of the characteristic curve toward the shorter wavelength is H:L
=3:1 configuration is smaller than H:L=1:3 configuration. Therefore, the configuration of H:L=3:1 is better in terms of the angular dependence of the incident light flux. FIG. 4 shows the transmittance characteristic curve of the dichroic film according to the present invention, where the solid line shows the characteristics when the incident angle of the light beam is 0 degrees and the broken line shows the characteristics when the incident angle of the light beam is 44.6 degrees. Table 2 shows the data of the film structure corresponding to the characteristic curve shown in FIG. However _{, n H =} 2.07
+11/λ-318 (λ is wavelength, unit is nm), and the reference wavelength is λ ₀ =484 nm. As shown in Table 2, the film structure of the present invention includes a mixture of 3/4λ ₀ and 1/4λ ₀ as a high refractive index basic layer, and a low refractive index base layer.

【table】

The basic layer of [Table] also has a configuration in which 3/4λ ₀ and 1/4λ ₀ are mixed. That is, by making at least one basic layer of the low refractive index layer have a thickness of 3/4λ ₀ , the half-width is expanded, and by using a large amount of 3/4λ ₀ in the high refractive index film thickness, the incident luminous flux is By effectively mixing both film configurations as shown in Figure 4, a dichroic film with a sufficiently wide half-width and excellent angle dependence can be created. be done. In addition, in the film structure according to the present invention, ripples can be effectively removed using conventional ripple suppression methods, and the first layer, second layer, and final layer from the substrate side are used for ripple removal. The adjustment layer is changed from the basic membrane layer. In this way, when the layer on the substrate side and the layer on the medium side are used as adjustment layers, the deposition technique is much simpler than when the adjustment layer is included in the intermediate layer, and it can be easily deposited in terms of manufacturing. . The thickness of the ripple suppressing layer is not limited to the values shown in Table 2, but may vary slightly without any practical problems.The thickness of the first layer is _d1 , and the thickness of the second layer is _d2 ,
If the thickness of the 12th layer is d ₁₂ , d ₁ , d ₂ , d ₁₂ are
2.5・λ ₀ /4<d ₁ <3.5・λ ₀ /4, 0.5・λ ₀ /4<d
Ripples can be effectively removed if ₂ <1.5·λ ₀ /4 and 0.5·λ ₀ /4<d ₁₂ <1.9·λ ₀ /4. Further, the most suitable high refractive index layer is a layer having a refractive index of 2.0 to 2.5, and the low refractive index layer is a layer having a refractive index of 1.35 to 1.50. As described above, in the dichroic film according to the present invention, layers of λ ₀ /4 and 3/4λ ₀ are used as the basic layer of the high refractive index layer, and layers of λ ₀ /4 and 3/4λ ₀ are used as the low refractive index layer. By effectively mixing each of them, a sufficient half-width can be obtained, there is little movement of the reflectance characteristic curve depending on the incident angle, and manufacturing is easy.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the transmittance characteristics of dichroic films with basic configurations of H:L = 3:1 and H:L = 1:3, assuming that there is no dispersion in the high refractive index layer. Figure 2 shows that when the high refractive index layer has dispersion,
A diagram showing an example of the transmittance characteristics of a dichroic film having a basic configuration of H:L=3:1. FIG. FIG. 4 is a diagram showing an example of the transmittance characteristics of the dichroic film according to the present invention. T...Transmittance, λ...Wavelength.

Claims (1)

[Claims] 1 High refractive index layers and low refractive index layers are arranged alternately
It is composed of 12 layers, and if the reference wavelength is λ ₀ , the optical thickness of the basic layer of the low refractive index layer is λ ₀ /4 and 3.
The basic layer of the high refractive index layer has a mixture of _{λ 0 /} 4 and 3λ ₀ /4, and the first, third, fifth, and The 7th layer is a high refractive index layer with a basic thickness of 3λ ₀ /4; the 9th and 11th layers are high refractive index layers with a basic thickness of λ ₀ /4; 6. The 8th and 12th layers are λ
A dichroic film characterized in that the tenth layer is a low refractive index layer having a basic thickness of _{3λ 0} /4.