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.