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.
I. INTRODUCTIONThe reconfigurability of optical interconnects is often translated in polarization-selectivity. To this aim, polarizing highspatial frequency gratings in GaAs [1], polarizing holographic optical elements in DCG [21, polarization-selective computer-generated holograms in LiNbO3 [3] and polarization-selective diffractive optical elements in calcite [41 have been developed. Polarization-selective, or anisotropic, diffractive optical elements (ADOEs) implementing calcite in combination with an index-matching polymer have proven to have several advantages over LiNbO3 [41. Recently we implemented ADOEs in a free-space reconfigurable optical interconnect using liquid crystal retarders (LCR) to control polarization of light [5]. The reconfiguration rate in this case was limited by the switching speed of the LCR, which is 20Hz in the case of a nematic LCR, and 20kHz in the case of a ferroelectric LCR. Very recently electrically controlled polarization switching in VCSEL's has been demonstrated up to 50MHz [6,7] with a polarization contrast ratio of 20:1 [7]. Here we report on the implementation of these polarization-switching VCSEL's in a reconfigurable interconnect demonstrator based on ADOEs. We present reconfigurable interconnects at 30MHz, and we demonstrate the proof-ofprinciple of a data transparent reconfigurable interconnection scheme with a bit rate of 1MHz and a reconfiguration rate of 40kHz. Both the bit rate and the reconfiguration rate are limited by the available electronic source of modulation.
Diffractive optical elements (DOEs) have proven to be useful components in optical interconnection and routing systems, especially where volume, weight and design flexibility are important. We will show that it is possible to increase the functionality of DOEs by making them polarization-selective, i.e. anisotropic. Several anisotropic diffractive optical elements (ADOEs) were fabricated in calcite by means of simple wet etching technology, and characterized experimentally. Both anisotropic Fresnel lenses and gratings have been studied. First order efficiencies of more than 12% and contrast ratios of over 1 1 0: 1 have been observed for off-axis elements.To demonstrate the potential of these ADOEs we have built an electrically controlled beam deflector which consists of a liquid crystal polarization modulator and an anisotropic grating. An incident beam can then be deflected to two different pairs of points by changing the voltage applied to the liquid crystal modulator. We will show the high contrast ratios observed when simultaneously measuring the intensity in each point while the voltage on the liquid crystal is modulated.
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