JPS5831307A - Interference filter - Google Patents

Abstract

PURPOSE:To obtain an interference filter undergoing a small change in the central wavelength due to a temp. change by suitably combining a substance undergoing a plus change in the refractive index due to a temp. change with a substance undergoing a minus change in the refractive index due to a temp. change to form a multilayer film. CONSTITUTION:A multilayered film is formed by suitably combining at least 1 layer of a film forming substance undergoing a plus change in the refractive index due to a temp. change such as ZnS, SiO2, ZnSe or Ge with at least 1 layer of a film forming substance undergoing a minus change in the refractive index due to a temp. change such as PbTe, PbSe, CaF2, BaF2, LaF3 or MgF2. For example, a band-path filter is manufactured by forming a multilayered film consisting of alternate PbTe and ZnS layers 1-3, 5-7 and a spacer layer 4 made of ZnS having a low rate of change in the refractive index due to a temp. change on a substrate (sapphire) 8. The filter has reduced dependency of the central wavelength position on temp.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical interference filter. More specifically, the present invention relates to an interference filter whose center wavelength changes little with temperature changes.

Conventional optical interference filters consist of a substrate made of silicon, germanium, quartz, sapphire, or glass, and multiple materials with different refractive indexes such as Kf germanium silicon oxide (and 0) and zinc sulfide deposited on one side of the substrate. It consisted of a multilayer film formed by

However, it is known that the transmittance of such conventional optical interference filters, center wavelength, and band half width Fi vary depending on the temperature.

Such temperature dependence of the spectral characteristics of the interference filter significantly impairs wavelength selectivity and causes a large measurement difference, which is a fatal drawback especially when used for precision measurement.

The optical interference filter disclosed in Japanese Utility Model Application Publication No. 55-105II05 focuses on the temperature dependence of transmittance in conventional interference filters, and compensates for the change by using the spectral characteristics of a single layer film. There is.

Looking even more closely, in the technique disclosed in Utility Model Application Publication No. 5S-IOS No. 05, the thickness of the single layer film is adjusted, and the center wavelength of the multilayer film under low temperature conditions and that of the single layer film are adjusted. Match the center wavelength under high temperature conditions by #t.
This further eliminates the temperature dependence of transmittance.

However, the proposed technology still does not solve the problem of center wavelength shift and band half-width change due to temperature changes. It can be seen that the change is compensated for, but on the other hand, the transmittance is sacrificed to compensate for this change in transmittance.

At present, the center wavelength shift due to temperature g and /
There is no known optical element chain filter that solves the problem of change in the half-width of the fourth wave.

Further, among the transmittance change, shift in center wavelength, and change in band half-width due to temperature change, the shift in center wavelength is particularly noticeable.

An object of the present invention is to provide an interference filter in which the temperature dependence of the center wavelength position is reduced.

The above object of the present invention can be achieved by constructing a multilayer film by appropriately combining materials whose refractive index changes with temperature are positive and negative.

Temperature changes in the spectral characteristics of an interference filter are caused by changes in the film thickness and refractive index of the filter's constituent films, but it is generally difficult to suppress such phenomena.

However, while the film thickness increases in proportion to the temperature, the refractive index either increases or decreases as the temperature increases, depending on the material that makes up the film. By utilizing this, it becomes possible to improve the above-mentioned drawbacks of conventional interference filters.

Mu51Sto is an example of a substance whose refractive index changes positively with temperature.
, MuS・, G・, etc. are known, while PbT・, PbS・, MgF are known as substances whose refractive index changes with temperature negatively.
2, CaF2, BaF2, LaF3, etc. are known.

(9) As the filter substrate, conventionally known materials such as silicon, rumanium, quartz, glass, etc. are used.

By changing the film structure and KI of the filter (by appropriately selecting and combining materials), it is possible to reduce the temperature change in the spectral characteristics of the filter in the used wavelength range.

EXAMPLES The present invention will be explained in more detail with reference to Examples below. However, these Examples are merely illustrative and do not limit the invention in any way.

Example 1 In this example, h3 is used as a material with a positive temperature change in refractive index.
On the other hand, a Δ-and-pass filter using PbT as a negative O substance is illustrated.

The -1RK, ΔnPΔ filter has at least seven spacer layers, and this has a great influence on the temperature dependence of the bandpass filter's spectral characteristics.

Comparing the temperature change rates of the refractive index of hS and PlsT, we find that kSO is smaller than that of PIeT.
Therefore, the lIIλ layer has a small temperature change rate of refractive index.
It is composed of □ hSK. This K makes it possible to reduce the temperature change in the center wavelength of the Δnd Δspace filter.

The film structure of this example Q is 1PbT@ as shown in FIG.
G & S C) Cross m
It also consists of a multilayer film and a substrate (+fire) fabric. The thickness of each of these deposited films is set to λo/2, with the center wavelength of the Pandos filter being λ0, and the optical film thickness of only the spacer layer 4 (C refractive index x thickness mnd) being λo/2. Layers 1 to 3 and S to 7 were made to have λO4.

The temperature change in the spectral characteristics of a filter having a film structure such as ζO is shown in 11I, and the relationship between the temperature and the rate of change in the center wavelength of this filter is shown in 11I.

On the other hand, the ninth comparison shows SDA l1WK! lll
Since it has 1III, it is a Δn filter, that is, alternating layers 1 to 4 and 6 to 9 of PbT, which has a negative temperature change in refractive index, and zIaS, which has a positive temperature change, and Pb, which has a large temperature change rate in its refractive index.
FIG. 5 shows temperature changes in the spectral characteristics of a 7-ilter consisting of a single-layer spacer made of T. and a substrate 10.

As is clear from the comparison between No. Jll and No. 5 IEI, it can be seen that the bandpass filter having the film structure of the present invention exhibits a much smaller temperature change rate of the center wavelength than the filter of the comparative example.

(9) As is clear from the temperature change in the spectral characteristics of the interference filter of the present invention, the temperature of the filter is
It can be seen that the transmittance hardly changes even with the change, and the change in the output value O is also small.

Therefore, it can be understood that the interference filter of the present invention, which has a relatively low density, has extremely excellent spectral properties. An example in which a substance other than MuS having a small rate of temperature change in the refractive index of the O layer is used is shown below.

In the example fO membrane structure, only the spacer layer 4 is 5o
The detailed membrane structure of KJD is shown in Figure sI6)'
? A) It is the same as in Example 1 except that the spacer layer 4 is made of 0. A filter with such a membrane structure is also used in Example 1.
The temperature dependence of the spectral characteristics was similar to that of the spectral characteristics.

In the above embodiments, 7
Although a four-type interference filter has been described, more complex bandpass filters having one or more spacer layers are equally applicable.

Thus, according to the present invention, it is possible to reduce the temperature change in the center wavelength due to the temperature change of the interference filter. Therefore, by using the interference filter of the present invention, it is possible to significantly improve the accuracy of various optical measuring instruments.

[Brief explanation of drawings]

Figure 1M is a schematic diagram showing the composition of the bandpass filter 011111 of the present invention)1 Figure 1 is a diagram showing temperature changes in the spectral characteristics of a filter having the film configuration shown in Figure 1IEIK.
Figure 4 is a schematic diagram showing the film structure of a filter as a comparative example of the present invention. S 581 is a graph showing the relationship between the temperature and the rate of change of the center wavelength of a filter having the front film structure shown in FIG. 4. FIG. 6 is a schematic diagram showing the film structure of another embodiment of the present invention. It is a diagram. Horse 1 Figure 6 Figure Horse 3 Filter 1 Temperature (°C) Horse 5 Figure Filter 1 Temperature (°C)

Claims (1)

[Claims] (!) Spectral characteristics having a multilayer film including at least a layer of a film material whose temperature change in refractive index is positive and a layer of a film material whose concentration change in refractive index is negative. An interference filter that reduces temperature changes. (2) The number of substances whose refractive index changes with temperature is positive is 7!
1IIS. and 0, ZmS@ and G.
An interference filter according to claim (1). (3) The substance whose refractive index changes with temperature is negative is PbTl.
Pb5s, CaF2.88F2, LaF3 and MgF
2. Claim No. (1)
Interference filter as described in section. (4) Claim m1 (1
) to (3), a sat interference filter.