A mode-evolution-type integrated-optical beam combiner for coherent receivers

Abstract
An integrated-optic sum-and-difference optical beam combiner for coherent receivers based on adiabatic mode evolution in an asymmetric waveguide junction is described. The device was packaged as a 2*2 fiber-compatible LiNbO/sub 3/ chip, and operated as a 180 degrees optical hybrid for combining arbitrary input polarization, exhibiting excellent balance and moderate loss. The advantage of this component over previously studied directional coupler beam combiners is the absence of a strict interaction length requirement for obtaining balanced separation. Integration of this component with a passive mode-evolution-type polarization splitter will result in polarization-diversity receivers with broad constraints on processing, design, and wavelength of operation.<>