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Polarization Beam Combining

Author: the photonics expert Dr. Rüdiger Paschotta (RP)

Definition: a technique for combining two polarized laser beams

Categories: article belongs to category general optics general optics, article belongs to category methods methods

DOI: 10.61835/tmc Cite the article: BibTex plain text HTML Link to this page LinkedIn

Polarization beam combining (or polarization coupling) is a technique for combining (superimposing) two linearly polarized laser beams.

Incoherent Polarization Combining

The simpler variant is incoherent combining. For example, the output beams of two broad area laser diodes, one being vertically polarized and the other one horizontally polarized, can be sent onto a thin-film polarizer such that one of the beams is reflected, the other one transmitted, and both beams then propagate in the same direction. As a result, one obtains an unpolarized beam having the combined optical power of the input beams (neglecting some parasitic losses) and the same beam quality. Accordingly, the brightness is nearly doubled.

This technique is often used e.g. for end pumping of a solid-state laser with an increased power. It works only if the laser crystal can similarly well absorb pump radiation with both polarization directions. This is the case e.g. for Nd:YAG, but not for Nd:YVO₄.

Incoherent polarization beam combining can not be considered as a method for power scaling, as it is not repeatable: it requires polarized input beams and leads to an unpolarized output beam.

Coherent Polarization Combining

If two mutually coherent beams are polarization combined, it is possible to obtain a linear polarization state for the output. Assuming equal input powers for the two ports, the output polarization will be rotated by 45° with respect to the polarization direction of any of the input beams. The method is one variant of coherent beam combining.

Due to the linear output polarization, coherent polarization combining can be repeated many times. It is thus a technique suitable for power scaling.

More to Learn

Encyclopedia articles:

Suppliers

The RP Photonics Buyer's Guide contains 18 suppliers for polarization beam combining optics. Among them:

Artifex Engineering

Polarizing beamsplitter cubes combine the “s” and “p” polarization components of a light beam. These two polarization components are reflected (“s”) and transmitted (“p”) respectively.

Edmund Optics

Edmund Optics offers a wide range of dichroic, crystalline, and wire grid polarizers which can also be used for polarization beam combining.

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