Optical characterization at wavelengths of 632.8 nm and 1549 nm of policryps switchable diffraction gratings

Optical characterization at the wavelengths of 632.8 nm and 1549 nm of an electrically switchable POLICRYPS grating sample is reported. The sample consists of a 10 mum thick cell made of ITO coated glass filled with a mixture of 30% nematic liquid crystal 5CB and pre-polymer NOA61. ne grating with a period of 1.34 mum was written by laser curing at wavelength of 351 nm. A self-aligning setup both for visible and for infrared was used for the characterization. At the Bragg angle the grating starts to be switched off by applying an electric field of 2.5 V/mum and complete switching occurs at about 5 V/mum both at visible and at infrared. The grating shows a switching time of about 4 ms for both wavelengths. A FWHM of about 7degrees was measured at 1549 nm, corresponding to an optical bandwidth of about Deltalambda = 266 nm.