A Route to Ultra‐Fast Amplitude‐Only Spatial Light Modulation using Phase‐Change Materials

Abstract A phase‐change material based, thin‐film, amplitude‐only spatial light modulator is presented. The modulator operates in reflection and modulates the amplitude of light incident on its surface with no effect on optical phase when the phase‐change material is switched between its amorphous and crystalline states. This is achieved using a thin‐film device with an embedded, switchable, GeTe phase‐change layer. Test modulation patterns are written to the device using laser scans, and the amplitude and phase response measured, using optical spectroscopy and off‐axis digital holography. Experimental results reveal reflected intensity to be modulated by up to 38%, with an averaged phase difference of less than ≈π/50. Since phase‐change materials such as GeTe can be switched on sub‐microsecond timescales, this approach maps out a route for ultra‐fast amplitude spatial light modulators with widespread applications in fields such as wavefront shaping, communications, sensing, and imaging.