Size of light from broadcast beam splitter

The size of light after a beam splitter is generally preserved, but plate and cube designs can introduce slight beam shifts or divergence depending on the splitter type and angle of incidence.

Beam Splitter Types and Light Size

Cube Beam Splitters: These are made from two right-angle prisms cemented together, often with a partially reflective coating on the hypotenuse surface. The transmitted and reflected beams maintain the original beam diameter, but a small lateral displacement can occur due to the refractive index of the prisms and the thickness of the adhesive layer. Cube splitters are commonly used in interferometers and laser systems where maintaining beam profile is important.

Plate Beam Splitters: These consist of a thin glass plate with a reflective coating on one surface. When light passes through at a 45° angle, the transmitted and reflected beams can experience a beam shift proportional to the plate thickness and refractive index. For a typical glass substrate (n ≈ 1.

5) at 45° incidence, the lateral shift can be approximated using geometric optics formulas. The beam diameter itself is largely unchanged, but the beam path is slightly offset. Pellicle Beam Splitters: These are extremely thin membranes that minimize beam displacement and preserve the original beam size and wavefront.

They are ideal for high-precision applications where even small shifts or interference effects must be avoided.

Factors Affecting Beam Size

Splitting Ratio: Non-polarizing splitters divide light by intensity, while polarizing splitters separate beams by polarization. The splitting ratio does not significantly alter the beam diameter but affects the optical power in each output beam. Angle of Incidence: Deviations from the design angle can introduce slight divergence or astigmatism in the output beams.

Coatings and Substrate: Anti-reflection coatings reduce unwanted reflections, helping maintain beam quality. Thick substrates or high-index materials can slightly alter the beam path.

Practical Implications

For broadcast or laser applications, the output beam size is nearly identical to the input beam, especially with cube or pellicle splitters. Plate splitters may require alignment adjustments to compensate for lateral beam shifts. In high-precision optical systems, pellicle splitters are preferred to avoid any beam distortion.

In summary, while the beam diameter is largely preserved after a beam splitter, the exact output position and minor shifts depend on the splitter type, substrate thickness, and angle of incidence. Cube and pellicle splitters are best for maintaining beam size, whereas plate splitters may introduce small lateral displacements.