A plate of birefringent crystal or polymer cut so that light polarized along its fast and slow axes picks up a set phase difference. A half-wave plate rotates linear polarization by twice the angle between the input and its axis; a quarter-wave plate converts linear to circular and back. Zero-order plates are less sensitive to wavelength and temperature than multi-order ones, and a half-wave plate plus polarizer makes a standard variable attenuator.
Rotate the half-wave plate before the cube to set the power, never adjust it with the pump current or the mode changes.
Also heard as
- wave plate
- retarder
Related terms
Optical isolator
A one-way valve for light that passes a beam forward and blocks reflections from returning to the laser.
Pockels cell
An electro-optic crystal that changes a beam's polarization when high voltage is applied, used as a fast optical switch.
PM fiber
Polarization-maintaining fiber: fiber with built-in stress that keeps linearly polarized light in its launch orientation.
Periscope
A pair of stacked mirrors that changes a laser beam's height above the table, and optionally rotates its polarization.