Definition:
Wide bandpass filters are optical filters designed to transmit a wide range of wavelengths while blocking out unwanted wavelengths. These filters are designed by combining a long pass filter and a short pass filter which can be positioned anywhere to create a bandpass filter of any width.
Design and Manufacture:
At Vortex we can manufacture any custom wide bandpass filter between 300nm to 6000 nm. Click on the relevant wavelength range below for more information about our capabilities, applications and case study examples of our previous work.
Our wide bandpass filters are deposited using sputter deposition technology which has a process energy 3 times higher than conventional thermal evaporation. This means they are highly durable in challenging environments and more stable with temperature change. More information about this can be found below.
More information about our capabilities can be found through the links below

Visible 300 - 700nm Wide Band Pass Filters

Near Infrared 700 - 2500nm Wide Band Pass Filters

Mid Infrared 2500 - 6000 nm Wide Band Pass Filters
Spluttering Vs Evaporation
Traditional Thermal Evaporation
- Voids in coating.
- Poor environmental performance.
- High shift with temperature change.

Open structure of traditionally evaporated coatings with gaps and voids.

Sputter Deposition
- Voids eliminated.
- Excellent environmental performance.
- Extremely low temperature shift.

Densely packed sputtered coating with no gaps
or voids.

Coating Durability
We carry out the following MIL-C-48497A tests on samples from every coating run to ensure all coatings are durable and will stand the test of time.
Adhesion Test:
The adhesion test is a guide as to how well the coating is bonded to the substrate. The test involves pressing ‘Scotch’ tape against the coating and then pulling it off, it should stay firmly attached and show no signs of removal.
Humidity Resistance Test:
The humidity resistance test assesses the performance of the coating in an atmosphere of 95% relative humidity for a 24 hour period. There should be no change in optical performance or physical integrity.
Mild Abrasion Test:
The mild abrasion test evaluates the resistance of the coating to surface wear. The filter is subjected to a dry rubbing cloth for 50 strokes. After a clean with acetone, there should be no evidence of marking visible when viewed with the naked eye.
Severe Abrasion Test:
The severe abrasion test is similar to the mild abrasion test but involves more aggressive abrasion conditions to simulate harsher wear scenarios. The coating is subjected to 10 strokes of abrasion with the Mil Spec abrader which is impregnated with grit. This test is particularly important for filters used in rugged environments or applications with high mechanical stress.
Cleanability Test:
The cleanability test ensures the filter can be cleaned with standard laboratory solvents such as propan-2-ol (IPA) and acetone. The coating should survive 10 minutes immersion in each solvent.
Water Solubility Test:
The filter is immersed in water for 24 hours and it should comfortably survive this with no signs of damage or delamination.
Wide Bandpass Filter Key terms explained.
Peak Transmission:
This is the point where the filter reaches its highest transmittance percentage.
Half Power Point:
This is sometimes referred to as the 50% point. It is the point at which the transmission is half of the peak transmission (If Peak transmission was 80% the half power point would be at 40% transmission).
Bandwidth or Full Width Half Maximum (FWHM):
This is the width of the filter in nm or µm between the two 50% (of peak) transmission points. It is calculated by subtracting half power point A from half power point B, see diagram below.
Centre Wavelength:
This is the ‘centre axis’ of the filter in nm or µm, it is calculated by adding together the two half maximum points together and dividing them by two. See diagram below.
Transmission Band:
This is the wider range at which a high level of transmission is required. Normally a wavelength range where transmission must be above a certain level of transmission.
Blocking Range:
This is where the filter needs to have a low transmittance percentage to prevent the detector from picking up any unintended signals. It should always cover the full range of the detector’s sensitivity plus a small amount of safety margin.
Cut on Wavelength:
This refers to the first wavelength at which a filter starts to transmit light it is often specified as the 5% transmission point. In some specifications it can be the 1% or 10% transmission point.
Cut off Wavelength:
This is at the opposite end of the passband and refers to the wavelength at which a filter stops transmitting light usually the 5% transmission point, sometimes the 1 or 10% point. The diagram below shows ‘cot-on’ and ‘cut-off’ at the 5% level.
Slope of a filter Left Hand side:
The left-hand slope is calculated as follows, (ʎ 80% of Peak T in nm-ʎ 5% of Peak T in nm)*100/ʎ 5% of Peak T in nm, see the diagram below.
Slope of a filter Right Hand side:
The right-hand slope is calculated as follows, (ʎ 5% of Peak T in nm-ʎ 80% of Peak T in nm)*100/ʎ 80% of Peak T in nm, see the diagram below.
Wide Bandpass Filter Terms Explained Graph
