Choosing the Right Polarizer — PBS vs TFP Simply Explained
Polarizers are fundamental building blocks in laser systems. The choice between a Polarizing Beamsplitter Cube (PBS) and a Thin-Film Polarizer (TFP) Plate significantly affects system performance. Although both components separate s and p polarization states, their behavior conditions differs dramatically. This guide explains these differences in a practical, application-driven way.
What Is a Polarizing Beamsplitter (PBS) Cube?
An Alien Photonics PBS cube is built from two precision right-angle prisms that are either cemented (glued) or optically contacted. The hypotenuse interface contains a dielectric coating engineered so that:
- p-polarized light is transmitted along the incoming beam direction
- s-polarized light is reflected at 90-degree angle (perpendicular to incoming beam) This makes PBS cubes simple, intuitive components used in R&D lasers, educational systems, fiber-coupled modules, micromachining, OEM assemblies and even some quantum applications
PBS Cube construction – Glued vs Optical Contact
Alien Photonics PBS cubes are produced in two ways, depending on budget and application requirements.
Glued PBS cubes – low-cost option
While glued PBS cubes are the most economical solution, but some limitations must be considered. First, cement(glue) limits laser induced damage threshold (LIDT). These cubes should be used in low (or medium) power applications only. Another important factor is glue degradation, which limits shelf-life, storage conditions and thermal stability.
Optical contact PBS cubes for high energy applications
Optically contacted PBS cubes eliminate cement entirely. This allows PBS cubes to be used in high energy applications. Generally, the surface quality of prisms and the overall performance (extinction ratio, LIDT, thermal stability) of the polarizing beamsplitter is better than standard glued cube.
Single-Wavelength vs Broadband PBS Cubes
PBS cubes can be designed to perform either for single wavelength (standard or high power) or multi-wavelength and broadband range.
PBS Cubes for specific wavelengths
Alien Photonics offers High Power PBS and Low-Medium Power PBS depending on the laser. Our PBS cubes are suitable for Nd:YAG, Yb:YAG, Ti:Sapphire, Diode, Argon and many other lasers. By focusing on a single wavelength, it is possible to achieve high reflection (Rs>99.7% or even higher) and good extinction ratio (e.g. Tp:Ts 1000:1 or even higher).
PBS Cubes for multi-wavelength and broadband spectra
If one wavelength is not enough – Alien Photonics broadband PBS cubes can cover several wavelengths or wide spectral ranges, e.g. 450-650, 650-900, 900-1200,1200-1600 nm. However, like in all broadband optics, the wide coverage has its costs – the reflection and extinction ratio is lower than PBS cube for single wavelength.
What Is a Thin Film Polarizer (TFP) Plate?
A Thin Film Polarizer (TFP) is a plate with a polarizing dielectric-coating on it. Alien Photonics offers Brewster-type and 45-deg-type polarizers. Both types work very similarly, with the main function of polarization separation by transmitting and reflecting polarization. Unlike PBS, a TFP is not cemented and not optically contacted — the clear aperture is in an air-dielectric interface, which dramatically increases:
- Damage threshold and tolerance to peak power
- Thermal stability
- Ultrafast compatibility This is why TFP polarizers dominate femtosecond, picosecond and high-power fiber laser systems.
TFP plate – Brewster’s type
A Brewster thin-film polarizer plate is designed to work at Brewster’s angle (angle depends on refractive index of substrate material). This angle not only allows us to avoid backside coating but also helps to achieve good extinction ratios (e.g. Tp:Ts 3000:1 or similar).
TFP plate – 45-deg-type or custom angle
Thin film polarizers working at other angles (e.g. 45 deg., 22.5 deg or others), can be designed to reflect s or even reflect p. While extinction ratios are high (Tp:Ts 1:1000 or similar), but they are typically lower than Brewster’s-type TFP.
PBS Cube vs TFP Plate — Polarizers Comparison Table
| Feature | PBS Cube (Glued) | PBS Cube (Contact) | TFP Plate (Brewster’s) | TFP Plate (Custom) |
|---|---|---|---|---|
| Budget-friendliness | 5 | 3 | 2 | 2 |
| Extinction ratio | 2 | 3 | 5 | 4 |
| Ease of handling | 4 | 5 | 3 | 3 |
| LIDT | 1 | 4 | 5 | 5 |
| Thermal stability | 1 | 3 | 5 | 5 |
| Low GDD | 1 | 2 | 5 | 4 |
Summary
PBS cubes and TFP plates perform the same function, but they behave completely differently under real laser conditions. Glued PBS cubes are alignment-friendly, and ideal for low–mid power systems, while optical contact option is also good for higher power lasers. Thin-Film Polarizers, on the other hand, require additional alignment effort, but feature better extinction ratio, higher damage threshold, and low GDD - the right choice for modern ultrafast and high-power laser systems.
Still not sure which one to choose ? Contact us for consultation!