What are Polarizing Beam Splitters (PBS)?
A PBS is an optical device that splits a beam of light into two separate beams with orthogonal (perpendicular) polarizations. In simpler terms, it takes unpolarized light and divides it into two components: one with vertical polarization and the other with horizontal polarization.
How Does a PBS Work?
There are a few different ways to construct a PBS, but the most common methods involve:
- Dielectric Coatings: Thin layers of carefully chosen dielectric materials are deposited onto a transparent substrate (often glass). These coatings are designed to transmit light with one polarization (typically p-polarization, parallel to the plane of incidence) and reflect light with the orthogonal polarization (s-polarization, perpendicular to the plane of incidence).
- Wire Grid Polarizers: A grid of microscopic wires is embedded within the substrate. This grid acts as a polarizer, reflecting light with one polarization while transmitting light with the other.
Key Specifications of PBS
- Extinction Ratio: This measures how effectively the PBS separates the two polarizations. It's the ratio of the transmitted power of the desired polarization to the transmitted power of the unwanted polarization. Higher extinction ratios indicate better polarization separation.
- Transmission: The percentage of light transmitted for the desired polarization.
- Reflection: The percentage of light reflected for the unwanted polarization.
- Wavelength Range: The range of wavelengths over which the PBS operates effectively.
- Angle of Incidence: The angle at which the light beam strikes the PBS. This can affect the performance of the device.
Types of PBS
- Plate Beamsplitters: These are thin, flat plates with the polarizing coating on one side. They are simple and cost-effective but can be sensitive to the angle of incidence.
- Cube Beamsplitters: Two right-angle prisms are cemented together with the polarizing coating at the interface. They are more robust and less sensitive to the angle of incidence than plate beamsplitters.
Applications of PBS
PBSs are used in a wide variety of optical applications, including:
- Optical Isolation: To prevent reflected light from damaging a laser source or interfering with other optical components.
- Polarization Analysis: To measure the polarization state of light.
- Fiber Optics: To combine or separate signals with different polarizations in fiber optic communication systems.
- Interferometry: To create and analyze interference patterns between beams with different polarizations.
- Microscopy: To enhance contrast and image quality in microscopy techniques.
Typical Specification
| Application | F#1.5 ~ F#2.8 LCOS Engine System |
| Material | SF57HHT, H-ZF52A, SF2, etc. |
| Dimensions | 2mm ~ 50mm |
| Angle Accuracy | ±3’ |
| Environmental Stability | MIL – STD 810E 507.3 Procedures Ⅲ |
| Spectrum (440nm - 660nm) | Tp(0°) : 90% Tp (±16°) : 75% |