| Electro-optic retarder | An applied electric field changes a crystal’s refractive indices, altering the phase delay between orthogonal polarization components. | Voltage or electric field | Adjustable retardance; can convert linear, circular, and elliptical states when correctly aligned. | Can support fast modulation; performance depends on crystal, wavelength, drive voltage, and optical alignment. |
| Electro-optic polarization rotator | An electric-field-induced change in birefringence or coupled optical modes rotates or transforms the polarization state. | Voltage or electric field | Controlled rotation or switching between polarization states. | Response and required drive depend on the material and device geometry; polarization alignment is important. |
| Fiber-squeezer polarization modulator | Transverse pressure on optical fiber induces stress birefringence, changing the relative phase of guided polarization components. | Mechanical force, often driven electrically | Variable retardance and polarization-state control. | Convenient for fiber systems; response, stability, and insertion loss depend on the actuator and fiber arrangement. |
| Liquid-crystal variable retarder | An electric field reorients liquid-crystal molecules, changing the effective birefringence and optical retardance. | Electrical drive | Variable phase delay between polarization components. | Often useful for low-power state control; response is generally slower than fast electro-optic crystal modulation and can be temperature-sensitive. |
| Magneto-optic Faraday rotator | A magnetic field produces the Faraday effect, rotating the plane of polarization as light passes through a magneto-optic material. | Magnetic field or current-driven coil | Polarization rotation; the Faraday effect is non-reciprocal. | Useful where non-reciprocal rotation is needed; modulation speed and range depend on material and magnetic-field design. |
| Photoelastic modulator | A resonantly driven optical element experiences periodic stress-induced birefringence, producing time-varying retardance. | Mechanical resonant drive | Periodic polarization modulation, commonly used for measurement and spectroscopy. | Typically operates at a design-dependent resonant frequency rather than providing arbitrary modulation frequencies. |
| Rotating wave plate | Rotation of a birefringent plate changes its orientation relative to the input polarization and therefore changes the output state. | Motorized mechanical rotation | Periodic or selectable polarization-state transformation. | Optically straightforward, but mechanical inertia and moving parts limit modulation speed and long-term robustness. |
| MEMS-actuated polarization controller | Microelectromechanical actuators bend, press, or reposition optical elements or fiber to change birefringence or polarization coupling. | Electrical actuator drive | Selectable or adjustable polarization transformation, depending on the design. | Compact integration is possible; range, repeatability, and response are design-specific. |
| Thermo-optic polarization controller | Heating changes refractive index and optical phase in a birefringent or integrated waveguide structure. | Heater current or temperature | Thermally tuned retardance or polarization-mode coupling. | Can suit compact, steady-state adjustment; thermal response and power consumption should be considered. |
| Acousto-optic polarization modulator | An acoustic wave creates a moving refractive-index grating; in suitable anisotropic configurations, diffraction and polarization coupling alter the output state. | Radio-frequency acoustic drive | Configuration-dependent polarization conversion, often accompanied by diffraction or beam deflection. | The effect depends strongly on crystal orientation, acoustic frequency, wavelength, and optical geometry. |