Integrated electroholographic photorefractive gratings with sustained longevity by LED illumination

A method for creating photorefractive electroholographic gratings with sustained operational longevity is presented and demonstrated. The method circumvents the thermal decay and erasure during readout characteristic of photorefractive devices by augmenting the device with a built-in mechanism that writes and periodically and/or continuously refreshes the space-charge gratings which are the core elements of such devices. The mechanism was demonstrated in a slab waveguide constructed in a KLTN:Cu crystal. The space-charge grating was created by illuminating the slab waveguide through a binary grating mask deposited on top of the surface of the crystal by incoherent illumination from a LED. The electroholographic performance manifested by the grating was similar to that of gratings constructed by interfering beams. This makes electroholography to be the basis for a viable technology for performing wavelength selective switching and electrical wavelength tuning at the device level, and enables their assembly in integrated photonic circuits.