JPH0395502A - Filter for flame sensor - Google Patents

Abstract

PURPOSE:To obtain an inexpensive filter for the flame sensor which has high sensitivity and immune from malfunction by providing wide-band filters which have specific structural formulas and differ in cutoff wavelength range on both surfaces of a quartz substrate and using Ge as a material with a high refractive index. CONSTITUTION:On the top surface of the quartz substrate (1) of the 4.3mu monochromatic filter for the flame sensor, the wide-band interference filter (2) has the structural formula I and the 2.3 - 4mum cutoff wavelength range is formed. (In the formula, H and L are the optical path lengths of a high-refractive-index material and a low-refractive-index material corresponding to 1/4 wavelength (lambda) respectively.) Similarly, the wide-band interference filter (3) which has the structural formula II and a 1.5 - 2.3mum cutoff wavelength range is formed on the reverse surface of the substrate similarly and Ge is used as the high- refractive-index materials of the wide-band interference filters (2) and (3). Consequently, the high-SN-ratio filter for the flame sensor which cuts off a noise input and transmits a signal input excellently can be obtained at low cost.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a monochromatic filter that transmits only infrared rays having a center wavelength of 4.3μ, and more specifically, to a monochromatic filter that is used in combination with a heat ray sensor as a flame sensor. Regarding a 3μ monochromatic filter.

(Prior art) In a flame sensor, the wavelength 4. 3t
It is necessary to have good sensitivity to infrared rays with a center wavelength at 1, and to eliminate malfunctions due to noise input.

Therefore, in combination with a heat ray sensor, it is necessary to use a filter that has the function of transmitting as much of the wavelength range around 4.3μ in the flame emission spectrum as possible, and blocking all other wavelength ranges.

Those with these functions are 4.3μ for flame sensors.
A monochromatic filter is used.

Conventionally, 4.3μ monochromatic filters for flame sensors have used substrates made of infrared transmitting materials such as Si%Ge or Ai203, which have low absorption in the infrared region. Filters are known, such as Si. High refractive index material such as Ge and Si
A material in which low refractive index materials such as n, ZnS, etc. are alternately laminated is used.

However, although this 7-abbrelow type interference filter can realize a transmission band having a sharp peak at the center wavelength, it does not have a broadband cutoff band at other than the center wavelength.

Therefore, in order to have blocking properties for wavelengths other than the center wavelength, at least two types of broadband filters, one for blocking shorter wavelengths and the other for blocking longer wavelengths, should be used as a smooth filter in the non-interference layer. It must be stacked with two layers separated.

All of these are fabricated by processing several lO layers on a hard and brittle optical substrate using a highly accurate multilayer thin film technology, and are easily damaged and expensive.

(Problems to be Solved by the Invention) 3 To explain the present invention using figures, FIG. 1 is a sectional view of a 4.3μ monochromatic filter for a flame sensor according to the present invention, in which 1 is a quartz substrate, 2 and 3 are is a broadband interference filter made of alternating layers of high and low refractive index materials.

As is clear from FIG. 1, the flame sensor 4 of the present invention
．． The 3μ monochromatic filter has the following structural formula on the top surface of the quartz substrate.
I] Quartz substrate/[H + L 1] ' H r , λ
+'=2973Cnm)...CI) A broadband interference filter 2 is formed by alternately laminating high and low refractive index materials, and the lower surface of the quartz substrate 1 has the following structural formula (
1) Quartz substrate/c H! L 2 P, λ2 color l931
A broadband interference filter 3 is formed by alternately laminating high and low refractive index materials as shown in (1).

In structural formula [1], (1), HI and L. represent the optical path length of 1/4 wavelength 01) of the high refractive index material and the low refractive index material of the broadband filter 2, respectively, and H2 and L represent the 1/4 wavelength of the high refractive index material and the low refractive index material of the broadband filter 3, respectively. The present invention has an optical path length of 4 wavelengths (λ2) as a 4.3μ monochromatic filter for flame sensors, which has excellent noise input blocking properties and signal input transparency, and is the result of repeated research in an effort to obtain further workability and productivity. For flame sensors, it has excellent noise input blocking performance and signal input transparency by providing a quartz substrate and one broadband filter with a different cutoff band on both sides, and has good processability and productivity, which has great industrial benefits. 4.
The purpose of the present invention is to provide a 3μ monochromatic filter.

(Means for Solving the Problems) The present invention provides two broadband filters with different cutoff bands by alternately laminating high and low refractive index materials on a quartz substrate and both surfaces thereof,
It is characterized in that Ge is used as the high refractive index material.

The 4.3μ monochromatic filter for flame sensors according to the present invention has excellent noise input blocking properties and signal input transparency, so when used in combination with a heat ray sensor, a flame sensor with high sensitivity and no malfunction can be achieved. can do.

(effect) 4 represent

Here, the optical path length is defined as the product of film thickness and refractive index.

It is difficult to monitor the film thickness or refractive index during the deposition of high and low refractive index materials, and it is common to monitor the optical path length.
An interference filter is formed by alternately laminating low refractive index materials.

In addition, by increasing the values of λ1 and λ2 shown here, the cutoff band of the broadband interference filter can be designed to move to the longer wavelength side, and conversely, by decreasing the values, the cutoff band can be designed to the shorter wavelength side. The optimum value can be selected for the cutoff band.

Wideband interference filters 2 and 3 used in the present invention
Ge is used as the high refractive index material.

This is because Ge itself blocks signals of 1.7 μm or less due to its absorption characteristics.

The low refractive index material is not particularly limited, but Si
The method of forming the high and low refractive index materials alternately laminated as the broadband interference filters 2 and 3, which may include O%Si02, ZnS, etc., is not particularly limited in the present invention. For example, it can be formed by vacuum evaporation, sputtering, or the like.

The quartz substrate 1 needs to be transparent at a wavelength of 4.3 μm and absorb infrared wavelengths of 5 μm or more.

It is better to make the thickness of the quartz substrate l thinner in order to improve permeability. Conversely, in order to absorb infrared wavelengths of 5μ or more, the thickness needs to be O lμ or more.

Therefore, the preferred thickness of the quartz substrate l varies depending on the type, but is preferably 0.1 to 1 mm.

Broadband filters are provided on both sides of the quartz substrate, for example, by quartz substrate/filter 2/filter 3 on one side of the quartz substrate.
If two interference filters are stacked on top of each other in this configuration, they will no longer function as filters at all.

When two different interference filters are stacked, it is necessary to use a non-interference layer, which can block light with a wavelength of 75 to 2.3 microns using quartz.

High refractive index material (H+): Ge and low refractive index material (L+)
): Nine layers are alternately laminated on the surface of quartz glass by vacuum evaporation method while monitoring to obtain a predetermined film thickness so that the optical path length of SiO is λ1/4 in each case, and a broadband interference filter 2 is formed.
was shaped.

Further, on the other surface of the quartz glass opposite to the shaped broadband interference filter 2, a high refractive index material (H2), 2 Ge, and a low refractive index material (L2): Si○ have optical path lengths of λ2/
4, eight layers were alternately laminated on the surface of quartz glass by vacuum evaporation while monitoring to obtain a predetermined film thickness, thereby forming the broadband interference filter 3.

Example 2 The quartz substrate 1 has a thickness of 0. Example 2 uses 3 mm quartz glass and provides broadband interference filters 2 and 3 in the same manner as Example 1.

Here, the thickness is 0.3 mm and 0.3 mm. Figure 4 shows the spectral transmittance of 5 mm quartz glass.

This results in a complicated structure.

Therefore, when there are two interference filters, it is important to provide them on both sides of the quartz substrate.

(Example) Example 1 The quartz substrate 1 has a thickness of Q. A 5 mm thick quartz glass was used, and Ge was used as the high refractive index material and SiO was used as the low refractive index material of the broadband interference filters 2 and 3 attached to both sides. The structures of the broadband interference filters 2 and 3 are determined by the following structural formulas (1) and [II].

Quartz substrate 7 [H, L+]'Hl, λ+ = 2973 [nm
)・(1) Quartz substrate // [H 2 T- 2 ]
' , λ2=l931[nm]...''(1) (However, H
, L are 1. of high refractive index material and low refractive index material, respectively. /4 represents the optical path length of wavelength (λ). ) Figures 2 and 3 show spectral transmittances based on simulations.

In this way, the broadband interference filter 2 transmits light with a wavelength of 2.3 to 4μ, and the broadband interference filter 3 transmits light with a wavelength of 1,8μ. are shown in FIGS. 5 and 6.

Furthermore, using the flame of a gas lighter as the signal S and the light source of a fluorescent lamp as the noise N, let the output ratio of the heat ray sensor before and after inserting the filter be S and N, and consider these as the spectral efficiency of the filter.
Furthermore, the ratio was taken as the S/N ratio.

Table 1 shows the results using commercially available 4.3μ monochromatic filters as Examples 1 and 2 and Comparative Example 1 as filters.

Table 1 (Effects of the Invention) As explained above, according to the present invention, the infrared monochromatic filter of the present invention has a quartz substrate and two different cutoff bands on both sides thereof.
A filter consisting of two wideband filters with excellent noise isolation and signal gain is a cheaper filter, and an infrared monochromatic filter with a high S/N ratio is used for flame sensors with high sensitivity and no malfunction. This is what we provide.

[Brief explanation of drawings]

Figure 1 shows the configuration (cross-sectional view) of a 4.3μ monochromatic filter for flame sensors, Figure 2 shows the simulated spectral transmittance of broadband interference filter 2, Figure 3 shows the simulated spectral transmittance of broadband interference filter 3, and Figure 3 shows the simulated spectral transmittance of broadband interference filter 3. Figure 4 shows thickness O-
3mm and 0. Spectral transmittance of 5 mm quartz glass,
FIG. 5 shows the spectral transmittance of the monochromatic filter for a flame sensor obtained in Example 1, and FIG. 6 shows the spectral transmittance of the monochromatic filter for a flame sensor obtained in Example 2.

Claims (1)

[Claims] (1) In a flame sensor filter with a broadband interference filter with different cutoff bands made by alternately laminating high and low refractive index materials on both sides of a quartz substrate with a thickness of 0.1 to 1 mm, one side of the quartz substrate The broadband interference filter attached to the other side is shown by the following structural formula [I], and the cutoff band wavelength range is 2.3 to 4μ, and the broadband interference filter attached to the other side is shown by the following structural formula [II]. The cutoff wavelength range is 1.5 to 2.3μ.
A filter for a flame sensor, further comprising using germanium as a high refractive index material for these two broadband interference filters. [Structural formula] Quartz substrate //[H_1L_1]^4H_1, λ_1≒2
973 [nm]...[I] Quartz substrate //[H_2L_2
]^4, λ_2≒1931 [nm]...[II] However, H
, L are the quarter wavelengths of the high refractive index material and the low refractive index material, respectively (
λ) represents the optical path length.