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

Abstract:

Optical characterization at the wavelengths of 632.8nm and 1549nm of an electrically switchable POLICRYPS grating sample is reported. The sample consists of a 10 μm thick cell made of ITO coated glass filled with a mixture of 30% nematic liquid crystal 5CB and pre-polymer NOA61, The grating with a period of 1.34 μm 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 2.5V/μm and complete switching occurs at about 5V/μm both at visible and at infrared. The grating shows a switching time of about 4ms for both wavelengths. A FWHM of about 7° was measured at 1549nm, corresponding to an optical bandwidth of about Δλ. = 266nm.