Efficient Holographic Polymer Dispersed Liquid Crystal Bragg Grating Performance Of Parametric Studies

Holographic polymer dispersed liquid crystal (HPDLC) is a novel kind of photoelectronic information materials, and has many perfect characters including rapid response, high diffraction efficiency and easy manufacture. HPDLC devices are potentially useful for panel display, optical communication, holographic display, information storage and integrated optics, especially for making optical switching because the diffraction efficiency is able to be modulated by electric field. Focusing on the subject of fabricating good performance HPDLC volume Bragg Grating, we have done three parts of work as below:1. The optical performance of HPDLC devices'is largely affected by the gap thickness, convenient and accurate measurement on cell gap is highly desirable in HPDLC based devices. By using focused incident light beam, instead of collimated one, the spectral modulations could be largely enhanced. In this paper, we report a spectral interferometric method for air gap measurement with a focused light beam from a single white light LED. By means of angular integration on multiple-beam F-P interference, the transmittance spectra of the air etalon can be accurately simulated as function of cell gap and other subsidiary parameters.2. The integrated system of making HPDLC optical switching and real-time measurement was established. The affect of different curing time on diffraction and transmittance during the process of making HPDLC are all studied.3. Experimentally, in order to get better performance on electro-optical switching, the Bragg gratings with diffraction efficiency as high as 98% we made was re-fabricated in a new way. In addition, threshold voltage of the grating was reduced to 0.13 V/μm. Response times of the up and down slopes were measured to be 230ms and 80 ms respectively. In the end, alignment of liquid crystal molecules was investigated through optically polarized microscope.