New Measuring Method For Bragg Mismatch

Along with the development of science and technology, great changes have taken place in people’s life. The society is now in a rapid development of information era. More and more information need to deal with in our daily life, so advanced storage technology should to meet the various needs of the society. Holographic technology is rising in the last century 60’s, it is a holographic storage technology and its main principle is to use the light interference and diffraction to record and reappear all the information of subjects. After just a few years of development, the technology is mature. Holographic storage has a large capacity, fast reading and writing speed, high transmission rate, etc. In order to make better development, finding out the right record material is the first problem to be solved, after unremitting exploration and discovery the researchers find photopolymer is the ideal holographic material, it not only has high sensitivity, high diffraction efficiency but also has the advantages of low cost, easy to make, now it become the focus in the holographic storage research recent years.Light to the photopolymer in the process of recording, photosensitizer absorbs a photon energy and then energy transfer with light initiator, active seeds and free radicals will be produced, then the active seeds and free radicals can trigger monomer polymerization. Coherent beam can come into being interference fringes, bright light zone will have a lot of active seeds and free radicals, but in the dark area, there may be little or no active seeds and free radicals, the concentration of polymer is difficient in the bright and dark zoon, and this lead to material deformation. Information, due to the polymerization process and the deformation of the material,will be changed. Then the photopolymer will have Bragg-mismatch, so Bragg-mismatch can not be ignored in the research of photopolymer. It is not only affected the direction of the original reference beam light diffraction efficiency, but also increasing the noise ratio.Traditional measuring method is using galvanometer scanning system to find the max diffraction efficiency of reconstruction light, then compared it with the original reference beam incident Angle, calculate the Bragg mismatch, but this method has some disadvantages, for example, repeatedly adjust the galvanometer deflection Angle is needed to change the representation of light incident Angle and measuring the corresponding diffraction efficiency, it need longer measuring time and the grating may be destruction, the reproduce light incident Angle change minimum completely decided by the resolution of the galvanometer. Aiming at the disadvantages of that method, we put forward a new kind of measuring method, the method combine Fourier transform lens and liner CCD. The main principle is to use Fourier transform properties of the Fourier lens, parallel light can be converted into different spatial frequencies plane wave at the focus of Fourier transform lens, plane wave of different frequency equals different incident Angle, then different linear CCD pixel record the diffraction efficiency of incident light which have different incident Angle. We can compare different maximum strength pixel of reference beam survey sheet and reappear light survey sheet, then calculate the angle between the pixels, so the Bragg-mismatch could be measured.