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The IR region is defined as that from 0.7 to 1,000um, and is usually divided into 3 sections, which are near infrared (0.7 to 2.5um), mid infrared (2.5 to 25um) and far infrared (25um to 1,000um). Objects at normal temperature (around 300K) emit in the IR around 10um wavelength, which requires the use of mainly multi-layer interference filters for their detection. They are used for the following reasons;
1) There are several substrate materials which have high refractive index and are transparent;
2) Light division by absorption can only be used as supplementary since mid IR is much wider region comparing to visible region.
 Feature
This is a filter which controls IR light by interference effects made by multi layered thin film coating on IR optical substrate, such as Quartz, Sapphire, Silicon, Germanium. We select an optical substrate, which is closest to the required optical specification.
Applications
Those filters are used for measurement, controlling machine, equipment and other optics utilizing IR light such as;
1) IR gas analysis; the filter is for detecting mainly CO2, CO, HC, NO x, SO x, O3 gas density, is used for flame sensor, organic sensor, exhaust gas sensor, etc.;
2) IR water analysis; the filter is for detecting H2O absorption to measure moisture;
3) IR radiometric thermometer, which is used for thermograph, thermometer, etc.;
4) IR thickness analysis, which is used for a measurement of film thickness detecting HC absorption region contained in polymer;
5) Order sorting filter for diffraction grating;
6) Human detector; the filter is used for human detection sensor such as automatic door, security alarm sensor, etc. |
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The main IR filters are categorized as under;
[Features]
It is designed to pass only limited IR region. Though it will have transmission on both sides of the target wavelength, such transmission can be cut off with other filters if it is necessary. We sort filters from type "0" to type "3" depending on the size of half value width based on CWL. The larger number corresponds to the type with a greater half value width. Their basic optical characteristics are shown below. These can be customized in case your required spec is not sufficiently satisfied.
[Typical Spectral Characteristics]
Fig.1 IR-BPF-0 type (Si substrate)
Fig.2 IR-BPF-1 type (Si substrate)
Fig.3 IR-BPF-2 type (Sapphire substrate)
Fig.4 IR-BPF-3 type (Sapphire substrate)
Table.1 Characteristic Standard
| Type |
IR-BPF-0 type |
IR-BPF-1 type |
IR-BPF-2 type |
IR-BPF-3 type |
Available
wavelength
range [um]
|
Maxi-
mum
Trans-
mittance
[%]
|
Appro-
ximate
ratio of
half width
to center
wave-
length
[%]
|
Maxi-
mum
Trans-
mittance
[%]
|
Appro-
ximate
ratio of
half width
to center
wave-
length
[%]
|
Maxi-
mum
Trans-
mittance
[%]
|
Appro-
ximate
ratio of
half width
to center
wave-
length
[%]
|
Maxi-
mum
Trans-
mittance
[%]
|
Appro-
ximate
ratio of
half width
to center
wave-
length
[%]
|
| 1.7-1.79 |
- |
- |
>/=40 |
2.9 |
>/=50 |
6.0 |
- |
- |
| 1.8-1.99 |
- |
- |
>/=60 |
3.4 |
>/=50 |
7.0 |
- |
- |
| 2.0-2.49 |
- |
- |
>/=70 |
4.0 |
>/=70 |
8.0 |
>/=70 |
16.0 |
| 2.5-4.99 |
>/=60 |
2.0 |
>/=70 |
4.0 |
>/=70 |
8.0 |
>/=70 |
16.0 |
| 5.0-5.5 |
>/=60 |
2.0 |
>/=70 |
4.0 |
>/=70 |
8.0 |
>/=70 |
16.0 |
Allowable
range of
center
wavelength [%] |
+0.35
-0.35 |
+0.5
-0.5 |
+0.5
-0.5 |
+0.5
-0.5 |
Standard
dimensions
Diameter
[mm] |
10 15 20 25 30 |
[Features]
It is designed to pass the longer wavelength while cutting shorter wavelengths off sharply at the certain specified wavelength.
[Typical Spectral Characteristics (at normal incidence)]
Fig.5 IR-LWPF(Ge substrate)
Fig.6 IR-LWPF(Si substrate)
Fig.7 BSE(Si substrate)
Fig.8 BSE(Si substrate)
[Features]
It is designed to pass the shorter wavelength while cutting off sharply at the certain specified wavelength to block longer wavelength. Also, it can create a broad band BPF in combination with Long pass filter. Their basic optical characteristics are shown below. These can be customized if your required spec is not sufficiently satisfied.
[Typical Spectral Characteristics (at normal incidence)]
Fig. 9 IR-SWPF＋LWPF(Ge substrate)
Fig.10 IR-SWPF(Sapphire substrate)
Table.2 Specification
|
Substrate material
|
Standard dimensions
|
IR-LＷPF
IR-SWPF |
Conventional optical
grade glass,
Quartz,
Sapphire,
Silicon,
Germanium |
15,20,25,30(mm)
4 inches |
| BSE |
Si |
4 inches |
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