Abstract

Diffractive optical elements constructed as phase only computer generated holograms (CGHs) are attractive for numerous applications in photonics and optoelectronics. A conventional diffractive optical element (DOE) has a maximum phase delay of 2π between pixels. Therefore, the required etch depth is, in general, shallow (< wavelength λ, see Fig. 1a). These DOEs are relatively insensitive to the polarization and wavelength of the reconstruction field compared to volume gratings. Previously we demonstrated polarization selective diffractive optical elements using two birefringent LiNbO₃ substrates with different diffractive microstructures on the interior.^1,2 The required etch depths on both substrates are deeper than that in a conventional DOE because the substrates birefringence is relatively small (see Fig. 1b). Another approach to achieve the same functionality is based on deep etch structure (see Fig. 1c) that corresponds to multiple periods of phase delays (also called modular 2mπ) using a single birefringent substrate, as first proposed in reference 1 and later in reference 3. This approach may reduce the cost and simplify the fabrication process of such polarization selective diffractive optical elements. In the following we report the design, fabrication and characterization of multiple order delay (MOD) holograms that posses dual functionality in polarization or color.

© 1996 Optical Society of America