Anew method for the preparation of stratified light-sensitive film is developed, and the stratified gratings (SG's) are recorded in the film. The sensitive layers on both sides of a dichromated cellulose triacetate film are produced simultaneously through chemical reaction and not with the conventional coating technique. Compared with SG's in other materials made with coating techniques, double-layer SG's in the film have, to my knowledge, the highest experimental diffraction efficiency (~54%) in addition to their having a simple recording optical system. The diffraction efficiency and the periodic Bragg selectivity of the SH in the film is given. Based on the SG's of the film, several beam splitters with 2, 3, 4, or 7 fan-outs and higher than 80% total diffraction efficiencies are realized experimentally. The advantages of this method as compared with others, such as the method based on volume holographic beam splitters, are explained.

Dichromated cellulose triacetate (DCCTA), a new, to our knowledge, holographic recording film, is presented. The material has some special properties, such as good environmental stability, a stronger real-time effect, strong relief modulation, a stratified sensitivity without the use of any coating technique, a light weight, flexibility, easy fabrication in a large area, and more. By the systematic study of the physicochemical changes of the microstructure of DCCTA in photochemical reaction processes with an electron paramagnetic resonance spectrometer, an infrared spectrometer, an UV spectrophotometer, and interferometric microscopy, we found that, as a dichromated light-sensitive system, DCCTA has a novel imaging mechanism: Light irradiation causes not only the formation of the cross links between Cr(3+) and molecular chains but also the decomposition of the main molecular chains of the film. In the real-time imaging process of DCCTA holograms the former plays a dominant role after the holograms are postprocessed; however, the latter is more important in the imaging process, and the holograms exhibit a positive etching property, which differs completely from that of other well-known dichromated materials, such as dichromated gelatin and dichromated poly(vinyl) alcohol.

A new method for the preparation of stratified light-sensitive film is developed and the stratified gratings are recorded in the film. The real-time splitting behaviour concerning angular sensitivity and diffraction properties as a function of the normalized buffer-layer thickness in this stratified holographic optical gratings have been analyzed. It is found that by optimizing the combination of modulation of grating, spatial frequency and the total thickness of grating, the changeable number of output beams can be obtained. . INTRODUCTIONRecently the stratified grating ( S G ) has received an increase in interest and attention due to its high diffraction efficiency and its distinct diffraction properties .The stratified volume holographic optical elements comprisea proposed class of novel diffraction structures in which multiple layers of a thin holographic material are interleaved with optically homogeneous buffer layers. In addition, the relation between the diffraction efficiency and the incident angle of the readout beam has a strict periodic selectivity. The stratified gratings used as beam splitters can be easily realized with simple recording setups and high diffraction efficiencies. Although the beam splitters can be made by several methods, each of them has its shortcomings. One of the authors of the paper reported a new method for making stratified light sensitive films and double -layer stratified gratings were fabricated with the confact-printing method with partial coherent light . In the fabrication , cellulose triacetate (CTA)film is used as the substrate .Without the use of any coating , the sensitive layers of the film are produced simultaneously on both sides of the film. The refractive indexes of the sensitive layers are approximately equal to that of the buffer, so the diffraction efficiency of the resultant stratified gratings may be increased to some extent. Based on the new stratified gratings of the film, several beam splitters with 2, 3, 4 and 7 fan-outs and higher than 80% total diffraction efficiencies are realized. In this paper. the real-time splitting behaviour concerning angular sensitivity and diffraction properties as a function of the normalized buffer-layer thickness in the new stratified holographic optical gratings hase been further analyzed. It is found that by optimizing the combination of modulation of grating, spatial frequency and the total thickness of grating, the changeable number of output beams can be obtained. 2. ANGULAR SENSITIVITY * supported by the National Natural Science Foundation of China 'Tel:86 027 87684026, Fax:86 027 87882661 SPIE Vol. 3559 • 0277-786X/981$10.00 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/23/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx