Innovative Photonic Time Delay Units for Radar Applications

We aim to design and demonstrate an innovative photonic true time delay solution which alleviates the fundamental problem of cascaded optical switches, and additionally offers several significant benefits. The device uses wideband spatial-spectral (S2) holographic optical memory materials to store and access several broadband time delay gratings. Broadband optical chirps are used to create these time delay gratings, and the control mechanism is an RF tone, not an optical switch. Each filter can extend over GHz of bandwidth, and can be individually programmed. Multi-casting is possible with multiple delays stored as spectral gratings. Hundreds of filters can be stored in a single small volume of S2 material (human hair sized). The delay gratings are probed by radar signal modulated onto an optical laser carrier, and the S2 material creates a true-time delayed replicas of the signal, which is then photodectected at the array element. Delays of interest are accessed by fast optical frequency switching. One S2 crystal spot per array element is needed, and many spots can be illuminated in one sugar cube sized S2 crystal, e.g., 32x32 elements.