Simulator for computer-aided design of holograms

Abstract

A simulator for the computer-aided design of holograms is developed. The direction and intensity of the reconstructed beam are calculated using the Kirchhoff diffraction integral and Kogelnik's coupled- wave theory. Grating distortions induced by physical changes in the re- cording medium are evaluated using the diffraction integrals, and imag- ing characteristics are analyzed using ray tracing. Simulator results can be used to evaluate wavefront aberrations of the reconstructed images, and holograms that compensate for aberrations can be designed by the simulator. Examples are given where recording and reconstruction wave- lengths are different and where the grating is distorted by nonuniform shrinkage of the medium. Also, to illustrate practical application, a holo- graphic optical element lens and a wavelength demultiplexer are de- signed and evaluated.9 © 2001 Society of Photo-Optical Instrumentation Engineers. Holographic optical elements ~HOEs! are useful for assem- bling compact optical systems. Since a hologram is a kind of diffractive optical element, the position of the recon- structed image is changed and aberrations are induced when the reconstruction conditions are different from the recording conditions. Also, the intensity of the recon- structed beam is reduced when the physical properties of the recording medium are changed during the development process. Therefore it is necessary to take the reconstruction and imaging characteristics into consideration when design- ing holograms. The reconstruction characteristics of holograms can be analyzed using the Kirchhoff diffraction integral 1 or coupled-wave theory. 2 The imaging characteristics of holo- grams can be analyzed using wavefront matching 3-5 or ray tracing. 6,7 However, it is difficult to design holograms by analytical methods because of the nonlinearity of the evalu- ation function, but computer-aided design can be effective. Latta's ray-tracing program can be used to design holograms, 8,9 but is inconvenient because of its specializa- tion for the analysis of imaging characteristics. Sweatt has presented the ultra-high-index method 10,11 for designing ho- lograms using general optical design tools. However, com- mercially available tools are not suitable because they em- phasize the design of bulk-type lenses. Therefore a computer-aided design tool specialized for holography is needed.