Free-space reconfigurable optical interconnection based on polarization-switching VCSELs and polarization-selective diffractive optical elements

The 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.