Beamsplitters and dichroic filters selectively transmit and reflect light into 2 separate channels inside optical systems (see fig 1 below). Beam combiners work in the opposite way (see Fig 2), they transmit and reflect 2 separate incoming light beams into one single beam. Both have a tendency to work at 45° but not exclusively. There are many variations of these filters and the more common ones are outlined below the diagrams.


Plate Beamsplitters and Beam-Combiners:
Typically consist of a thin, flat piece of glass, Silicon or Sapphire with a partially reflective coating on one side. They are typically used at a specific angle of incidence (often 45 degrees).
Cube Beamsplitters and Beam-Combiners:
Made by cementing two right-angle prisms together, with a partially reflective coating on the hypotenuse face and AR coatings on the 4 other faces. Preferred for their compact form and ability to handle higher power. Vortex has in house assembly capability to deliver the whole optics package.
Polarising Beamsplitters and Beam-Combiners:
Split light based on polarisation, reflecting one polarisation state while transmitting the other. They are often used in applications requiring polarisation management, such as laser systems and microscopy.
Dichroic Filters:
Often either a long pass filter reflecting the short waves and transmitting the long waves, or a short pass filter transmitting the shorter wavelengths and blocking the longer wavelengths. These coatings are the basis for almost all beamsplitters and combiners.
Design and Manufacture:
At Vortex we can design and manufacture any custom beamsplitters, beam-combiners, and dichroic filters between 300 nm to 6000 nm. Click on the relevant wavelength range below for more information about our capabilities, applications and case studies of our previous work.
All of our beamsplitters, beam-combiners, and dichroic filters are deposited using sputter deposition technology which typically has a process energy 1000x higher than thermal evaporation. This means that all our coatings are highly durable in tough environments and very 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 Beamsplitters, Beam-Combiners and Dichroic Filters

Near and Mid Infrared 700–6000nm Beamsplitters, Beam-Combiners and Dichroic 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.
Key terms explained
Peak or Minimum Transmission:
This is the point or range where the filter must have transmission above a specified level.
Transmission Band Range:
The range at which peak transmission performance is required. This can be a short as one single wavelength or as wide as 1000’s of nanometres.
Passband Average Transmission:
This can be defined as the average transmission, in the passband, between the two points where transmission exceeds 80% of the peak value.
Blocking Range:
This is where the filter needs to have a low transmittance percentage to prevent the detector from picking up any signals from stray light.
Cut on Wavelength:
This refers to the wavelength at which a filter starts to transmit light. This can be specified at any percentage but is often between 1 and 10%. The diagram below shows it at 5%.
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.
Ripple:
This normally refers to the allowed variation between maximum and minimum in the pass band of a filter. For example, ripple variation to be< +/-5% form the passband average.
Angle of Incidence:
The angle at which light will interact with the beamsplitter or beam-combiner coating. (usually 45⁰)
Terms Explained Graph
