Highly polarization-selective diffractive optical elements for use in optical interconnection and routing systems have been fabricated by the wet etching of pairs of calcite substrates and characterized experimentally. We show that when an index-matching polymer is used to fill the gap between the two substrates, substrate alignment problems are eliminated and efficiency is greatly increased. This has resulted in first-order diffraction efficiencies of 40.5% and polarization contrast ratios of 450:1 for several off-axis binary-phase elements, allowing these components to be used for practical applications.