Design considerations of stacked multilayers of diffractive optical elements for optical network units in optical subscriber-network applications.

The detailed design process and experimental results of stacked multilayer diffractive optical elements are reported for an optical network unit used in optical subscriber-network applications. The optical network unit accepts two incoming light beams of 1.3- and 1.55-microm wavelengths through a single-mode optical fiber. A laser diode is also placed for bidirectional communications. The optical network unit consists of five diffractive optical elements that perform the following functions: collimation of incoming beams, focusing of the outgoing 1.55-microm beam, 3-dB splitting of the 1.3-microm beam, focusing of the 1.3-microm beam onto the photodiode, and collimation of the light emitted from a laser diode. Possible cost reductions as a result of mass production and the ease of alignment of the stacked diffractive optical elements could be ideal for constructing low-cost optical network units.