Wavelength-multiplexing diffractive phase elements: design, fabrication, and performance evaluation

We report on the wavelength-multiplexing diffractive phase element (WMDPE) capable of generating independent spot patterns for different wavelengths. The iterative method proposed by Bengtsson [Appl. Opt. 37, 1998] for design ing a kinoform that produces different patterns for two wavelengths is exte nded to tile WMDPE for multiple wavelengths (more than two wavelengths). Ef fectiveness of the design algorithm is verified by design and computer simu lations on the WMDPE's for four and nine wavelengths, The WMDPE for three w avelengths (441.6, 543.5. and 633 nm) is designed with five phase levels an d is fabricated by electron-beam lithography. We observed that the individu al spot patterns are reconstructed for the design wavelengths correctly. Pe rformance of the WMDPE is evaluated by computer simulations on the uniformi ty error. the light efficiency, and the contrast. On the basis of the resul ts, the characteristics of the WMDPE's are discussed in terms of various co nditions of fabrication and usage. (C) 2001 Optical Society of America.