Liquid Crystal-Based Optical Time Delay Units for Phased Array Antennas

Novel two-dimensional (2-D) spatial light modulator (SLM)·based optical time delay units (OTDU's) using free-space/solid optics and fiber delays are introduced for phased array antenna and wideband signal processing applications. In particular, the mature nematic liquid crystal (NLC) SLM technology is considered for the proposed architectures. A 1 × 2 optical switch is demonstrated using a parallel-rub birefringent-mode NLC cell, a bulk optics cube polarizing beamsplitter, and a sheet polarizer. Switch measurements taken at 633 nm show a > 3400: 1 or > 35 dB output port optical isolation. The 1 × 2 NLC switch is used to build a 1 1-bit 3.33-ns-duration free-space OTDU using mirrors and total internal reflection corner prisms. The unit demonstrated a > 30 dB optical (or > 60 dB electrical) signal-to-noise ratio for both delay and no-delay positions. A 1500 pixel NLC SLM is built, and a 128: 1 or 21 dB on/off isolation is demonstrated limited by the digital drive electronics of thin-film transistor (TFT)-based pixel control.