Coherent Communications, Imaging and Targeting'72

Laboratory and field demonstration results obtained as part of the DARPA-sponsored Coherent Communications, Imaging and Targeting (CCIT) program are reviewed. The CCIT concept uses a Phase Conjugation Engine based on a quadrature receiver array, a hologram processor and a spatial light modulator (SLM) for highspeed, digital beam control. Progress on the enabling MEMS SLM, being developed by a consortium consisting of LLNL, academic institutions and small businesses, is presented. TABLE OF CONTENTS ............................................................. INTRODUCTION.. ... .................................. 1 CONCEPT DESCRIPTION.. . ........................... 1 SPATIAL IGHT MODULATOR DEVELOPMENT ..... .9 CONCLUSIONS.. .. ................................... 10 REFERENCES.. ... .................................... 11 BIOGRAPHY.. .. .................................... .l 1 LABORATORY AND FIELD DEMONSTRATIONS.. .... 4 Introduction The CCIT program is developing new capabilities in secure, very high data rate free-space communications, aberrationcompensated imaging and sensing, and targeting at very long ranges. It combines innovative concepts and integration of MEMS SLMs, which provide digital wavefront control, with photonics and high-speed electronics. A team consisting of the Lawrence Livermore National Laboratory, academic institutions, small businesses, and aerospace companies bas carried out Phase-I ' 0-7803-8155-6104/$17.0~004 IEEE IEEEAC papcr 4.0302.1500 0-7803-8155-6/04/$17.00 02004 IEEE of the program, which was completed in July 2003 (SLM development continues). The SLMs being developed have numerous applications in addition to their use in the holographic concept discussed in this paper. The CCIT concept incorporates elements of the Active Tracking System developed by Northrop Grumman under DARPA sponsorship [I]. Concept Description The holographic concept is based on a Phase Conjugation Engine (PCE) that is common to all applications. As shown in Fig.1, it consists of a coherent receiver (focal plane array, charge-coupled device), a hologram processor, and an SLM. The PCE interfaces with other system modules according to the generic architecture of Fig. 2. Part of the input field is split off and directed to a high-speed detector to provide a trigger signal for a local oscillator (LO). The remainder is interfered with a pair of LO beams that are 90 degrees out of phase with one another to form quadrature holograms. The holograms are read-out and processed, and the conjugate of the extracted phase is applied to the SLM. The calculation of phase at any pixel is independent of other pixels, allowing very high fiame rates by parallel, pipelined processing. The latency time is the s u m of the hologram read/processing/write time and the SLM response time. For a 128x128 FPA/SLM and a 25 MHz clock, the read/processing/write time is about 5 ps. For a 10 ps SLM response time, the program specification, the minimum latency time is therefore 15 ps. The holograms are also read into computer memory for application-specific processing, including system control and application algorithms.