Role of the channel phase profile in phasing fiber optical arrays

The individual elements or apertures in a fiber optical phased array are finite in size and range from a few to many wavelengths in diameter. Therefore, the beam from each aperture cannot be characterized by a single phase. Hence, phasing a fiber optical array is actually a form of coherent beam combination and not just wavefront reconstruction. The fiber diameter and wavelength determine the angles at which the diffraction orders appear, but the illumination within an order in the near and far fields will depend on the profile from each aperture. From the path integral viewpoint, the shrinking in size of the central lobe that should result from the beam combination requires destructive interference of neighboring paths. The decoherence resulting from phase profile differences between apertures can upset the constructive addition of paths in the forward direction as well as the destructive interference to the side. Numerical results are presented.