difference between waverotators and wavesplitters?

[Nii]

Some sellers have circular "waverotators" and some sell square "waveplates". What's the difference between the two, other than the difference of shape?

[kecked]

https://www.rp-photonics.com/waveplates.html

describes the different kinds of plates. Rotator I think they mean a 1/2 wavelength polarization plate which rotates the polarization 90 degrees. That's what you want in our case so that the didoes stripes line up after a PBS cube. before the correction optics. remember the way the pbs cube works is to select the s or the p polarization but not both. This lets you add the diodes together and keep the stripe rather than a cross. The cross is still used in some cases with single mode diodes to fill in the beam pattern rather than use cylinder optics to expand the beam to a square shape.

A typical setup up is to knife edge two diodes and combine with a waveplate so you get twice the power in each strip but the thickness of the knifed pair is half as thick as it would be if you just knife edged the four diodes.

Oh and then there is the faraday rotator that is used to make sure back reflections don't blow your diode up. Only used in really high power systems. This changes the rotation of the polarization of any back reflections so they can't get back through the optic to the chain before it. This effectively traps the back reflection.

Hope that was clear.

[Nii]

So waverotators and square waveplates from your nearest laser parts seller are basically the same? Thanks.

[mixedgas]

There are half-wave and quarter-wave plates. Quarter wave plates are very, very, common as cheap surplus, but are nearly useless* in laser show use, as they create circular or elliptical polarization. You thus want half wave plates for combining diodes... Outline Shape does not matter much, once x-ray oriented, coated, and cut, a waveplate is a waveplate, is a waveplate.
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*certain types of stereoscopic 3D laser displays use left and right circular polarization, but this is not common any more. One can place several quarter plates in series and derive the whole Poincare sphere of polarization orientations, but that again is not practical for laser shows.
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Steve