Beam splitters divide incident light into transmitted and reflected beams according to a specified splitting ratio, commonly 50/50, but ratios can vary and be adjustable depending on the type and design.

Standard Splitting Ratios

Beam splitters are designed to split light into two beams with a defined Reflection/Transmission (R/T) ratio. The most common ratio is 50/50, where half of the incident light is reflected and half is transmitted, often used in laboratory interferometers and optical experiments . Other standard ratios include 30/70, 70/30, or 10/90, depending on the application and the desired distribution of optical power .

Types of Beam Splitters and Ratio Control

• Cube Beam Splitters: Constructed from two right-angle prisms cemented together, with a coated hypotenuse surface. The coating determines the splitting ratio, which is usually fixed but can be designed for specific wavelengths .
• Plate Beam Splitters: Thin glass plates with a partially reflective coating. The splitting ratio is determined by the coating thickness and material, typically optimized for a 45° angle of incidence .
• Polarizing Beam Splitters: Use birefringent materials to separate light into orthogonal polarization states. The splitting ratio depends on polarization rather than intensity, often producing nearly 100% transmission for one polarization and 100% reflection for the orthogonal polarization .
• Variable Beam Splitters: Allow continuous adjustment of the splitting ratio. This can be achieved using a rotating disk with gradient coatings or a rotatable half-wave plate combined with a polarizing beam splitter, enabling precise control of the transmitted and reflected power according to Malus' law .
• Fiber-Optic Splitters: Include Fused Biconical Taper (FBT) and Planar Lightwave Circuit (PLC) splitters. The splitting ratio can be designed or adjusted during fabrication, with PLC splitters offering highly accurate and uniform ratios across multiple outputs .

Factors Affecting Splitting Ratios

• Wavelength Dependence: Coatings are optimized for specific wavelengths; a 50/50 splitter at green light may not maintain the same ratio in infrared or ultraviolet .
• Polarization: Reflection and transmission differ for s- and p-polarized light, affecting the effective splitting ratio in non-polarizing splitters .
• Angle of Incidence: Deviations from the design angle can alter the ratio, especially in plate splitters .

Summary

Beam splitters can have fixed or adjustable splitting ratios, commonly 50/50, but also 30/70, 70/30, or other custom ratios. The ratio depends on the type of splitter, coating, wavelength, polarization, and angle of incidence. Advanced designs, such as variable or fiber-optic splitters, allow precise control of the light distribution for specialized optical applications .