Fiber array optical-coupling design issues for photonic beam formers

Novel two-dimensional (2-D) optical polarization switching array-based photonic time delay units (PTDUs) have been introduced for phased array antenna and wideband signal processing applications. The use of low loss optical fibers allows remoting of the photonic beamformer, along with providing a compact, lightweight, and low electromagnetic interference (EMI) microwave frequency signal interconnection and distribution method, such as needed for very large aperture wide instantaneous bandwidth phased array antennas/radars. However, there are losses associated with multiple fiber interconnects that limit the maximum number of array channels in these systems. Thus, accurate analysis of such losses is crucial to the design of an optimal photonic fiber-based system. In this paper, we present theoretical design and simulation results on optical fiber array interconnects for our 2-D N bit M channel photonic beamformer for wideband phased array antennas. In addition, we discuss an alignment technique for the large channel count fiber arrays proposed for our beamformer that uses V-grooved silicon wafers. Note that these precise V- groove structures are fabricated via crystallographic perfection of the substrate, accurate alignment of the etch pattern with respect to the crystal planes, and optimized etch conditions. This paper discusses these and other fiber array issues.