The filters exploit the interference effect of reflected light generated at the interface of a thin film to transmit desired wavelength regions. Compared with absorptive colored glass filter and gelatin filters, etc., interference filters have extremely good contrast with very narrow or sharply defined transmission bands.
Applicable to colorimeters, flame spectrometers, monochrometer, laser, optical communication, optical data storage, etc.
Effect of angle of incidence
When a filter is tilted with respect to the optical axis of the incident light, its transmission band shifts toward the shorter wavelength. At angles of incidence larger than 20 degrees, the transmission band splits into two separate peaks, because the P-component (parallel to the plane of incidence) and the S-component (perpendicular to the plane of incidence) are shifted by different amounts.
The MIF type or DIF type should be used for operation for long periods up to 50deg C. It can also be used up to 80deg C for short periods. The interference filter may suffer deterioration such as change of filter characteristics depending on the operating environmental conditions. When ordering, inform us of the environmental conditions.
When you place an order, please state the required CWL, Half value width and filter size. Out of band blocking should also be specified. This can be achieved by the combination of multi-layer cut filter and color glass. So, please designate the cut off region matching to your needs corresponding to sensor sensitivity.
Specifications of an interference filter
Tmax : Maximum transmittance
Lambda 0 : Center wavelength
Lambda 0 = (Lambda 1+Lambda 2)/2
Delta 1/2 = Lambda 2-Lambda 1 : Half-width
A standard product
Metal-dielection interference filters : MIF=S/W type
All-dielectric interference filters : DIF-A/B/C type, DIF-BPF-1/2/3/4/5 type
Plasma ion coat band-pass filter : PIF-BPF type
Infrared interference filter : IR-BPF 0/1/2/3/4 type
Cut regions of all-dielectric interference filters and plasma ion coat band-pass filters
An interference filter is made up of a combination of several filters as shown in the figure below. Normally, a standard cut region is used unless specified otherwise. The cut region is generally determined according to the sensitivity region of the sensor. It is possible to further widen the cut region, but this reduces transmittance slightly due to loss caused by the cut filter.