The optical glass surface is coated with one or more layers of thin film. When a beam of light is projected onto the coated glass, it is divided into two or more beams through reflection and refraction. This coated glass is called a beam splitter.
Polarizing prism is a kind of device often used in the polarized light path, which mainly plays the role of polarization splitting. It is widely used in laser systems, optical communication devices, optical measuring instruments, display instruments and other consumer industries.
The existing glass polarizing beam splitter prism is composed of a pair of right-angle prisms. The slope of one right-angle prism is coated with polarizing beam splitter film, and the slope of the other right-angle prism is a polishing surface. The slope of the two prisms is glued, and the four right-angle prisms are coated with antireflective film to reduce the reflection loss of light when passing through the prism. When the natural light is incident, the two beams of linearly polarized light with high degree of polarization are emitted, Tp: Ts>1000: l, and these two beams of polarized light are perpendicular to each other. However, in many system applications, higher extinction ratio is required. At this time, the existing glass polarizing prism cannot meet the requirements.
The beam splitter is mainly used to divide the incident beam into transmitted and reflected beams with a certain intensity ratio. There are two types of beam splitters: fixed beam splitter and variable beam splitter. The variable beam splitting ratio beam splitting mirror can be divided into step and continuous transient.
The beam splitter is always used obliquely. It can easily separate the incident light into reflected light and transmitted light. If the reflected light and the transmitted light have different spectral components, or have different colors, this beam splitter is usually called a dichroic mirror. If a beam of light is divided into two beams of light with the same spectral composition, that is, in a certain wavelength region, such as the visible light region, it has the same transmittance and reflectivity ratio for each wavelength, so the reflected light and transmitted light are neutral, and this beam splitter is called a neutral beam splitter. Neutral beam splitters with a transmission and reflection ratio of 50/50 are commonly used.
The commonly used neutral beam splitter has two structures, one is to coat the film on a transparent flat plate, the other is to coat the film on a 45 ° angle prism slope, and then glue a prism of the same shape to form a glued cube. Because of the inevitable astigmatism, flat beam splitters are usually used in medium and low level optical devices. For optical systems with high performance requirements, prism beam splitter can be used. The advantages of glued cube beam splitter (also called beam splitter) are that it is easy to install and adjust in the instrument, and because the film is not exposed to the air, it is not easy to be damaged and corroded, so the mechanical and chemical stability requirements of the film material are low. However, it is also obvious that the deflection effect of glued cube beam splitter is large.
Thin films or film combinations with almost constant reflectivity in a certain wavelength range can play the role of neutral beam splitting. Commonly used are metal beam splitter and dielectric beam splitter.
