Polarization selective hologram-based photonic delay lines

The use of polarization selective holograms as optical signal routing elements for the implementation of photonic delay lines (PDLs) is proposed. A single bit PDL using ferroelectric liquid crystal (FLC) devices as active polarization switches and polymer dispersed liquid crystal (PDLC) devices as polarization selective holograms for optical path routing is experimentally demonstrated and characterized. Different within-channel leakage noise filters for improved PDL performance are discussed and experimentally demonstrated. Record high optical signal-to-leakage noise ratios (> 45 dB) are obtained for both PDL settings using a combination of the proposed noise filters. An alternative reflective PDL architecture is also proposed. This reflective architecture requires half the physical length for each path compared with the transmissive design to obtain the same time delays. Other polarization dependent optical router designs based on birefringent-mode nematic liquid crystal (NLC) devices are also proposed.