Polarizer, also known as polarizing filter, is an optical element that controls the polarization state of light waves. By filtering out light with a specific polarization direction or generating a beam with specific polarization characteristics, polarizers play an important role in optical imaging, photography, polarization analysis, and many scientific and industrial applications.
1.Basic principles of polarizers
Light is a transverse wave, containing vibrations of electric and magnetic fields perpendicular to the propagation direction. In natural light, the vibration direction of light waves is randomly distributed. Polarizers control the polarization state of light waves by selectively allowing light with a specific vibration direction to pass (such as linearly polarized light).
Linearly polarized light: The vibration direction of the light wave is fixed on a plane.
Circularly polarized light: The electric field vector rotates in a circle in the propagation direction.
Elliptically polarized light: The electric field vector rotates in an elliptical shape.
The function of a polarizer is to convert natural light into linearly polarized light or other light with a specified polarization form.
2.Classification of polarizers
Based on the principle and method of achieving polarization, polarizers can be divided into the following categories:
2.1 Linear polarizers
Linear polarizers only allow light vibrating in a specific direction to pass through, blocking vibrations in other directions.
Absorption polarizers: polarization is achieved by absorbing light waves with unwanted polarization directions. For example, polarizers (Polaroid Film), commonly used in photography and display screens.
Reflective polarizers: polarization is achieved by using the reflection principle, commonly seen in beam splitters.
Birefringent polarizers: birefringent materials (such as polarizing beam splitters) are used to split a light beam into two beams of light with different polarization directions.
2.2 Circular polarizers
Circular polarizers are composed of a linear polarizer and a quarter-wave plate, and are used to convert linear polarized light into circular polarized light or vice versa. They are often used in photography to reduce reflection interference.
2.3 Polarizing beam splitters (PBS)
Polarizing beam splitters split incident light into two beams of light with orthogonal polarization directions, and are widely used in optical measurement and laser systems.
2.4 Tunable polarizers
Optical components that change the polarization direction by rotation or electrical control, such as liquid crystal polarizers, which are used in optical communications and display technology.
3.Polarizer parameters
Polarizer performance is usually measured by the following parameters:
Polarization Efficiency
Indicates the ability of a polarizer to produce polarized light, defined as:
are the light intensities in the parallel and perpendicular directions respectively. The higher the degree of polarization, the better the performance of the polarizer.
Transmission
The efficiency of a polarizer in allowing light of a specific polarization direction to pass through.
Extinction Ratio
Indicates the polarization purity of the transmitted light, which is the ratio of parallel light intensity to perpendicular light intensity (such as 10^4:1. A high cutoff ratio is suitable for high-precision polarization measurement.
Spectral Range
Refers to the working performance of a polarizer in different wavelength ranges, such as visible light (400-700nm) or infrared band.
4.Application of polarizer
4.1. Photography and imaging
Reducing interference from reflected light: Polarizers can effectively reduce reflected light from surfaces such as water and glass, and improve image quality.
Enhancing contrast and color: By adjusting the direction of polarized light, scene contrast and color saturation can be enhanced.
4.2. Optical measurement and analysis
Stress detection: In glass or plastic products, polarizers can be used to observe polarization changes caused by internal stress.
Polarization microscope: Used to analyze the optical anisotropy of materials, such as in mineralogy and biological research.
4.3. Laser and optical communication
Laser polarization control: In laser systems, polarizers are used to stabilize or control the polarization state of lasers.
Fiber optic communication: Improve the efficiency and stability of fiber optic transmission through polarization control.
4.4. Display technology
Liquid crystal display (LCD): Use the characteristics of polarizers to control the brightness and darkness of pixels to achieve high-definition display.
5.Precautions and optimization
Angle dependence: The polarization effect of polarizers is closely related to the angle of incident light, and the incident angle should be kept vertical as much as possible.
Spectral matching: Different types of polarizers are suitable for different wavelengths, and the appropriate spectral range should be selected according to application requirements.
Environmental adaptability: In high temperature, high humidity or high radiation environments, polarizer materials with strong weather resistance should be selected.
As a core device for controlling the polarization characteristics of light, polarizers play an important role in various fields of optical technology. By correctly selecting and using polarizers, the performance of the optical system can be effectively improved to meet diverse application requirements.
