TECHNICAL FIELD

This disclosure relates to a NDIR gas sensor, an optical device, and an optical filter for a NDIR gas sensor.

BACKGROUND

A non-dispersive infrared (NDIR) gas concentration measuring device has been known as a gas concentration measuring device for measuring the concentration of a gas to be measured in the atmosphere. Different kinds of gas absorb infrared light at different wavelengths, and a non-dispersive infrared absorption gas concentration measuring device utilizes this principle and measures the concentration of a gas by detecting its absorption amount. Examples of the gas concentration measuring device utilizing this principle include a device which is obtained by combining a filter (a transmission member) that transmits infrared light limited to a wavelength at which a gas to be measured has absorption characteristics and an infrared light receiving device, and is configured to measure the concentration of the gas to be measured by measuring the absorption amount of infrared light absorbed by the gas. JP H09-33431 A (PTL 1) describes a carbon dioxide concentration measuring device utilizing this principle.

CITATION LIST

Patent Literature

PTL 1: JP H09-33431 A

SUMMARY

However, an optimum combination of an infrared light source, an infrared light emitting and receiving device and an optical filter for each gas to be detected has not been studied. In particular, the specifications of the optical filter have not been optimized so far.

It could thus be helpful to provide a NDIR gas sensor with high accuracy even using a simplified optical filter, an optical device, and an optical filter for a NDIR gas sensor.

The primary features of this disclosure are as described below.

One aspect of the NDIR gas sensor of the present disclosure includes:

an optical filter having a substrate and a multilayer film having a plurality of layers with different refractive indexes formed on at least one side of the substrate; and

an infrared light emitting and receiving device having a semiconductor layer of a first conductive type, an active layer, and a semiconductor layer of a second conductive type; where

the multilayer film has a structure in which a first layer and a second layer are alternately stacked, the first layer has a refractive index of 1.2 or more and 2.5 or less in a wavelength range of 6 μm to 10 μm, and the second layer has a refractive index of 3.2 or more and 4.3 or less in a wavelength range of 6 μm to 10 μm;

the active layer contains InAsySb1-y(0.1≤y≤0.2); and

the optical filter includes a wavelength range having an average transmittance of 70% or more with a width of 50 nm or more in a wavelength range of 6 μm to 10 μm, and has a maximum transmittance of 10% or more in a wavelength range of 12.5 μm to 20 μm and an average transmittance of 5% or more and 60% or less in a wavelength range of 12.5 μm to 20 μm.

Another aspect of the NDIR gas sensor of the present disclosure includes:

an optical filter having a substrate and a multilayer film having a plurality of layers with different refractive indexes formed on at least one side of the substrate; and

an infrared light emitting and receiving device having a semiconductor layer of a first conductive type, an active layer, and a semiconductor layer of a second conductive type; where

the multilayer film has a structure in which a first layer and a second layer are alternately stacked, the first layer contains at least one selected from the group consisting of TiO2and ZnS, and the second layer contains at least one selected from the group consisting of Si and Ge;

the active layer contains InAsySb1-y(0.1≤y≤0.2); and

the optical filter includes a wavelength range having an average transmittance of 70% or more with a width of 50 nm or more in a wavelength range of 6 μm to 10 μm, and has a maximum transmittance of 10% or more in a wavelength range of 12.5 μm to 20 μm and an average transmittance of 5% or more and 60% or less in a wavelength range of 12.5 μm to 20 μm.

One aspect of the optical device of the present disclosure includes:

an optical filter having a substrate and a multilayer film having a plurality of layers with different refractive indexes formed on at least one side of the substrate; and

an infrared light emitting and receiving device having a semiconductor layer of a first conductive type, an active layer, and a semiconductor layer of a second conductive type; where

the multilayer film has a structure in which a first layer and a second layer are alternately stacked, the first layer has a refractive index of 1.2 or more and 2.5 or less in a wavelength range of 6 μm to 10 μm, and the second layer has a refractive index of 3.2 or more and 4.3 or less in a wavelength range of 6 μm to 10 μm;

the active layer contains InAsySb1-y(0.1≤y≤0.2); and

the optical filter includes a wavelength range having an average transmittance of 70% or more with a width of 50 nm or more in a wavelength range of 6 μm to 10 μm, and has a maximum transmittance of 10% or more in a wavelength range of 12.5 μm to 20 μm and an average transmittance of 5% or more and 60% or less in a wavelength range of 12.5 μm to 20 μm.

Another aspect of the optical device of the present disclosure includes:

an optical filter having a substrate and a multilayer film having a plurality of layers with different refractive indexes formed on at least one side of the substrate; and

an infrared light emitting and receiving device having a semiconductor layer of a first conductive type, an active layer, and a semiconductor layer of a second conductive type; where

the multilayer film has a structure in which a first layer and a second layer are alternately stacked, the first layer contains at least one selected from the group consisting of TiO2and ZnS, and the second layer contains at least one selected from the group consisting of Si and Ge;

the active layer contains InAsySb1-y(0.1≤y≤0.2); and

the optical filter includes a wavelength range having an average transmittance of 70% or more with a width of 50 nm or more in a wavelength range of 6 μm to 10 μm, and has a maximum transmittance of 10% or more in a wavelength range of 12.5 μm to 20 μm and an average transmittance of 5% or more and 60% or less in a wavelength range of 12.5 μm to 20 μm.

One aspect of the optical filter for a NDIR gas sensor of the present disclosure is an optical filter for a NDIR gas sensor having a substrate and a multilayer film having a plurality of layers with different refractive indexes formed on at least one side of the substrate, where

the multilayer film has a structure in which a first layer and a second layer are alternately stacked, the first layer has a refractive index of 1.2 or more and 2.5 or less in a wavelength range of 6 μm to 10 μm, and the second layer has a refractive index of 3.2 or more and 4.3 or less in a wavelength range of 6 μm to 10 μm; and

the optical filter includes a wavelength range having an average transmittance of 70% or more with a width of 50 nm or more in a wavelength range of 6 μm to 10 μm, and has a maximum transmittance of 10% or more in a wavelength range of 12.5 μm to 20 μm and an average transmittance of 5% or more and 60% or less in a wavelength range of 12.5 μm to 20 μm.

Another aspect of the optical filter for a NDIR gas sensor of the present disclosure is an optical filter for a NDIR gas sensor having a substrate and a multilayer film having a plurality of layers with different refractive indexes formed on at least one side of the substrate, where

the multilayer film has a structure in which a first layer and a second layer are alternately stacked, the first layer contains at least one selected from the group consisting of TiO2and ZnS, and the second layer contains at least one selected from the group consisting of Si and Ge; and

the optical filter includes a wavelength range having an average transmittance of 70% or more with a width of 50 nm or more in a wavelength range of 6 μm to 10 μm, and has a maximum transmittance of 10% or more in a wavelength range of 12.5 μm to 20 μm and an average transmittance of 5% or more and 60% or less in a wavelength range of 12.5 μm to 20 μm.

Note that the above summary does not enumerate all the necessary features of the present disclosure. In addition, a subcombination of these features is also included in the present disclosure.

According to the present disclosure, it is possible to provide a NDIR gas sensor with high accuracy even using a simplified optical filter, an optical device, and an optical filter for a NDIR gas sensor.

