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Development of an EO/IR Common Aperture Modular Multifunction Sensor


OBJECTIVE: To explore and develop the technologies needed to combine a number of passive and active electro-optical functions, currently being accomplished through multiple apertures, into a single aperture. DESCRIPTION: Electro-optical surveillance and targeting systems are very numerous in the DOD and involve substantial complexity. They usually consist of large focal plane imagers, lasers and electronics, and are in many cases packaged in gimbaled enclosures to facilitate flexible pointing and tracking. Many of these EO/IR systems now incorporate multi-functional capabilities that involve 2 or 3 functions combined in a given gimbaled enclosure to increase capabilities within a maximum allowed size, weight, and power (SWAP). These systems involve conventional components such as bulky glass optical lenses, conventional lasers, and multi-axis mechanical turrets. The turrets are heavy and require substantial power to operate and, in the case of turrets mounted on aircraft, must protrude into the airstream and therefore induce substantial drag. In order to circumvent these issues and provide a major advance in capability, it is desirable to develop a phased array capability in the EO/IR regime similar to that practiced in the microwave radar domain. To this end, a flat panel arrangement of optical elements needs to be developed. Such a system would require far less weight, power and space, and would eliminate the need for a gimbal mechanism such as a ball turret. This would lead to more aerodynamic and lower cross section structures and would afford higher performance by providing broader spectrum coverage in a smaller SWAP. To realize these advantages, it is necessary to develop optical phased array technology that would permit both transmission and reception of EO/IR signals by a planar, phased array optical structure that might be conformally mounted on the sides of military platforms. There exist several optical technologies in which prototype demonstrations at the basic component level have been accomplished. One example is an array of vertical cavity surface emitting lasers (VCSELs) in which the emitting elements can number in the millions. These VCSELs are in use in the telecommunication industry but they have only been phased locked (a necessary condition) in small numbers in the laboratory1-4. It is necessary to demonstrate phase locking of large arrays and at substantial powers before flat panel transmitter arrays can be realized for military use. Electronic beam control and steering control technology must also be developed further to enable useful flat panel arrays. Focal plane detector arrays exist that function effectively as incoherent receivers requiring bulky lens systems. To convert these into lens-less, phased array receivers, the same phase sensing, electronic beam control and steering control will have to be developed. Another option to develop flat panel transmitters and receivers involves the use of slotted planar waveguides using corporate feed techniques similar to those used for many years in the microwave regime. In this case, planar optical waveguides5 with appropriate out couplers are fed in columns with a laser source and the out-coupled radiation is externally phase controlled by optical phase modulators, enabling electronically-controlled beam steering. In the reverse direction, radiation is coupled into the waveguide and sensed in column fashion by a single detector per row. Given successful demonstration of these and other flat panel optical array structures, major advances in the SWAP and performance of optical systems as described above can be realized. PHASE I: Provide detailed modeling of flat panel array structures that are suitable for transmission and/or reception of phase controlled optical signals. Show that the proposed structure has the potential to be scaled to militarily useable performance. Perform a laboratory demonstration at the component level or use literature data to verify the model. PHASE II: Fabricate and test an optical phased array to verify the array design. Demonstrate the beam steering, beam control and phase sensing needed to control the array so that the array design can be fully validated. The array should be at least a 10x10 element array and the spacing of the elements close enough so that the array side lobes do not interfere with the interpretation of the data. PHASE III: Produce a 100x100 element optical phased array that performs to design specifications including minimum element spacing relative to a wavelength, accurate phase detection and control, and near theoretical beam spread. PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: The availability of optical phased array transmitters and receivers would be used to replace ball gimbaled surveillance systems widely used by the military and law enforcement. It would enable new consumer products such as digital cameras with new electronic scanning and focusing capabilities, miniature movie projectors, helmet mounted displays, and display products of various types including low cost projection televisions. REFERENCES: 1) F. Monti di Sopra, et al,"CW operation of phase-coupled VCSEL arrays", (AVALON Photonics & EPFL) APL, 77 (15) p2283 (Oct, 2000). 2) D.K. Serkland, et al.,"Two-element phased array of antiguided VCSELs,"(Sandia National Labs) APL 75 (24) p3754 (Dec, 1999). 3) B. Lucke, et al.,"Autostable injection-locking of a 4 x 4 VCSEL array with on-chip master laser,"(Stuttgart University) Proc. SPIE-VCSEL IV, 3946, p240 (2000). 4) L.D.A. Lundeberg, et al.,"Mode switching and beam steering in photonic crystal heterostrucutres implemented with VCSELs ,"(EPFL) APL, 90, 241115-1 (2007). 5) K.V.Acoleyen, et al , Off-chip beam steering with a one-dimensional optical phased array on silicon-on-insulator, Optics Letters, vol.34, No.9, pp1477-1479 (2009).
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