JPS63218902A - Optical fiber decreased in ripple - Google Patents

Abstract

PURPOSE:To obtain an optical filter which has fewer ripples and permits easy prepn. by using specific film configuration. CONSTITUTION:The number of the total layers is assumed to be N layers, then the odd layers counted from a substrate are dielectric material layers (TiO2 layers) having a high refractive index and the even layers are dielectric material layers (SiO2 layers) having a low refractive index. The alternate multi- layered films are formed by shifting the optical film thicknesses of the 1st layer, 3rd layer, (N-2)th layer and N-th layer which are the dielectric material layers having the high refractive index by about the same degrees from 1/3 of a design reference wavelength lambda0, and setting the optical film thicknesses of the other dielectric material layers having the refractive index at lambda0/3 and the optical film thicknesses of the dielectric material layers having the low refractive index at lambda0/6. The optical fiber having the fewer ripples in transmission band is thereby obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical filter used in optical devices and the like.

BACKGROUND OF THE INVENTION Optical multilayer films such as color separation filters are used in three-color separation prisms for three-panel cameras. For example, a red reflective filter, a blue reflective filter, etc. fall under this category.

A three-color separation prism is an optical component that uses a blue reflection filter to reflect the blue light that enters the prism, and then reflects the red light from the remaining light to separate it into blue, red, and green light.

Therefore, the reflection characteristics and transmission characteristics have an important influence on the color characteristics, and if the optical characteristics of the blue-red reflective filter are poor, the green characteristics will also be adversely affected.

Conventionally, these blue reflection filters and red reflection filters have been realized using dielectric multilayer films. A dielectric multilayer film can be realized by alternately depositing a high refractive index material and a low refractive index material using a vacuum deposition method.

Tλ0□, 5i02, etc. have been mainly used as vapor deposition substances. An example of a red reflection filter is shown in FIG. Regarding the film structure, the odd numbered layers counting from the substrate are T-02 and the even numbered layers are 5IO2. The optical thickness of each layer is λ based on the design wavelength.

Then, λ. /4, and the incident angle is θ=13°.

Problems to be Solved by the Invention Problems that arise when such an optical multilayer film (optical filter) is used in a color separation optical system such as a three-color separation prism will be explained.

In FIG. 9, large ripples occur in the transmission region below λ=580 nm. This is a red reflective filter,
This has an important effect when extracting green light using a blue reflective filter. That is, although red light can be sufficiently separated by this filter, since there is a ripple in the transmission band (green wavelength band), this optical characteristic directly affects the optical characteristic of green color. This film configuration is for the case where the optical film thickness of the high refractive index material H and the low refractive index material is 1=1, but it is also the same when H:L=3:1, which removes ripples in the transmission band. I couldn't do that.

The present invention has been made in view of this point, and an object of the present invention is to provide a color separation filter with less ripples in the transmission band.

Means to solve problems The technical means of the present invention to solve the above problems is as follows.

Assuming that the total number of layers is N, the odd-numbered layers counting from the substrate are dielectric material layers with a high refractive index, the even-numbered layers are dielectric material layers with a low refractive index, and the first layer is a dielectric material layer with a high refractive index. layer, third layer, Nth layer
- The optical thickness of the second layer and the Nth layer is set to the design reference wavelength λ. The optical thickness of the dielectric material layer with a high refractive index other than the above is λ. The optical thickness of the dielectric material layer with power refractive index is λ. /6 and an alternating multilayer film.

Function The present invention provides an optical filter with few ripples in the transmission band by using the above-mentioned thin film system.

Example The total number of layers is 19, and the odd-numbered layers counting from the substrate are TiO2 layers of a high refractive index material, and the even-numbered layers are SIO layers of a low refractive index material.
Figure 1 shows the transmittance characteristics of a two-layer red reflective filter.

The design standard wavelength is λ. = esonm, and the incident angle is 1
3°, Ti02(7) refractive index nu = 2.3o,
The refractive index of 5in2 is nL: 1.46. The refractive index of the substrate is ng=1.61.

The vertical axis is transmittance (unit: h), the horizontal axis is wavelength (unit: nm)
It is.

The structure of this membrane is shown in Figure 2. It can be seen that the ripples in the first layer, third layer, and green light region are significantly reduced.

Although some ripples occur in the blue region, the tricolor separation prism first separates the light in the blue light region using a blue reflection filter, so there is no particular problem even if the ripples occur.

FIG. 3 shows the transmittance characteristics when the refractive index of the substrate is ng=+1.51 and FIG. 4 shows the transmittance characteristics when ng=1.80.

It can be seen that good spectral characteristics with few ripples in the green light region have been achieved. This film configuration is very useful because it can achieve good transmittance characteristics even if the refractive index of the substrate changes.

FIG. 6 shows the transmittance characteristics when the total number of layers is B layers. The optical thickness of the first, third, eleventh, and thirteenth layers is 2.18X'', and there are even layers.The forming material is Ti.
O2 (nH=2.30), SiO□ (nL==1.
46) is used. The design wavelength is λo” 680 nm, the incident angle is θ = 13°, and the refractive index of the substrate is ng = 1.6.
It is 1.

Similarly, when the number of layers is 13, ripples in the transmission band can be significantly reduced.

FIG. 6 shows the transmittance characteristics when the total number of layers is 26. As in the case of the 19 layers in FIG. 1 and the 13 layers in FIG. 4, ripples are significantly improved.

Therefore, even if the number of layers changes, the optical thicknesses of the first layer, the third layer, the N-2 layer, and the N-th layer can be set to 2.00.

Generally, if the number of layers changes, the reflectance and rise characteristics of the reflection band will change. As the number of layers increases, the reflectance increases and the rise becomes steeper. Therefore, the number of layers may be determined depending on desired characteristics. Furthermore, the width of the reflection band varies depending on the refractive index ratio of the material used. As the refractive index ratio 11 increases, the width of the reflection band also increases. Another high refractive index material is zro2.

Examples of low refractive index materials include ZrTiO4, ZnS, and MgF. The present invention can realize a color separation filter that is useful even with these materials and has reduced ripples.

If the angle of incidence is θ = 0 in Figure 7, then θ = 300 in Figure 8.
The case is shown below. The number of layers is 19, and T is used as a high refractive index material.
iO2 and 5102 are used as the low refractive index material.

It can be seen that the membrane configuration of the present invention is useful even at different angles.

Generally, the reflection band region (red light in this example) shifts depending on the size of the design wavelength.

As the trench angle increases, the reflection band shifts toward shorter wavelengths. Therefore, the film forming material and the number of layers per design wavelength are determined according to the desired reflection band width 9 reflection area and the incident angle, and the first layer,
The optical thickness of the high refractive index material of the third layer, the N-2 layer, and the N-th layer is 2. By shifting from OX-gλ0, good film characteristics with reduced ripples can be achieved.

This film structure is used in optical heads of rewritable optical disk devices, which are attracting attention as future large-capacity memories.
Also useful for wavelength separation filters. That is, the wavelength λ
. Transmits light of 7801 m in wavelength, 830 nm in wavelength λ0
It is a filter that reflects light.

In optical heads, λ. There is a demand for high efficiency and high stability in the light transmittance of Ki7801m, and the film structure of the optical multilayer film with reduced ripples of the present invention is very useful.

If this film configuration is used, the optical λ0 of the high refractive index material The film thickness is 2.0OXH, and the first layer is shifted from this.

This can be achieved by combining a total of three optical thicknesses: the optical thicknesses of the third layer, H-2 layer, and Nth layer, and 1.00 X-1i of the low λ0 refractive index material.

This is very useful when setting the film thickness during actual thin film formation, and the difficulty in setting the film thickness can be reduced to within a dog's width.

Effects of the Invention As described above, by using the film structure of the present invention, ripples can be significantly reduced and an optical filter that is easy to manufacture can be realized.

[Brief explanation of the drawing]

FIG. 1 is a transmittance characteristic diagram of an optical filter according to an embodiment of the present invention, FIG. 2 is a horizontal view of the same filter, and FIG. 3 is a transmittance characteristic diagram when the refractive index of the substrate is ngl, 61.
Figure 4 is a transmittance characteristic diagram when ng=1.80, Figure 5 is a transmittance characteristic diagram when the number of film layers is 13, Figure 6 is a transmittance characteristic diagram when the number of film layers is 25, and Figure 7 is a transmittance characteristic diagram when the number of film layers is 13. is a transmittance characteristic diagram when the incident angle is θ = 0, Fig. 8 is a transmittance characteristic diagram when θ = 30, and Fig. 9 is a transmittance characteristic diagram when the incident angle is θ = 0.
The figure is a transmittance characteristic diagram of a conventional optical filter. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure WAVELENCrTH (fL=r=) Figure 2: jr, Figure 3 Reno'AVELENcrTHtam) Figure 4 WAVELENC7TH (a<) Figure 5 WAVELENeTHmn-) Figure 6 WAVELENGTH (fL slope p; Figure 17 WAVELEN (rTH (= cm) Fig. 8 WAVELENCrTH(?LfrL) Fig. 9

Claims (1)

[Claims] It is equipped with a substrate, a dielectric multilayer film formed on the substrate, and a substrate bonded thereon.If the total number of layers is N, odd-numbered layers counting from the substrate are dielectric material layers with a high refractive index. The even-numbered layers are dielectric layers with a low refractive index, and the optical thicknesses of the first layer, the third layer, the N-2 layer, and the N-th layer are dielectric layers with a high refractive index. Shift the same amount from 1/3 of the design standard wavelength λ_0, set the optical thickness of the dielectric material layer with a high refractive index other than the above to λ_0/3, and set the optical thickness of the dielectric material layer with a low refractive index to λ
A filter with reduced ripple of _0/6.