Low Cost Multi-color infrared (IR) sensors/focal plane arrays are required for surveillance and other homeland security applications. These sensors require multi-color focal plane arrays (FPA) that will cover 3-5 (MWIR) and 8-14 (LWIR) micron bands. There has been a significant progress in developing HgCdTe on Silicon substrates [1,2]. Two-color IR FPA eliminate the complexity of multiple single color IR FPAs and provide a significant reduction of weight and power in a simpler, reliable and affordable systems.
The state-of-the-art in infrared optics can be looked at in terms of size, quality, material or complexity. Itek has recently completed the manufacture of an optical component that presented most of these challenging requirements to the designer, the manufacturing group and the test engineer. We believe that the combination of severe asphericity, test complexity and lightweight construction are representative of the most difficult optics producible today. The mirror is a convex asphere, with only bilateral symmetry, a departure from the nearest sphere of 178 micrometers , and a maximum slope departure of 4.0 micrometers per mm. Testing required a combination of null correctors and binary optics, with extremely tight alignment tolerances. Surfacing was accomplished with small tools and computer controlled optical surfacing.
User requirements and economics demand that large optics components will have to be produced to more stringent tolerances and lower costs. While manufacturing and testing technology have been improving rapidly, the challenge will continue to be how to integrate technology improvements into industrial processes. This paper describes Itek's approach to continuous process improvement in optical manufacturing. Specific examples of process innovations show how evolutionary upgrading of the process has resulted in improved performance and reduced costs.
A Computer Controlled Optical Surfacing (CCOS) process has been developed that is in routine use for fabricating off-axis and centered aspheric mirrors. An industrial robot effects surface removal by moving a relatively small tool over the mirror surface in a path covering the entire surface. The removal is computed by the convolution of the tool work function with the path of the tool over the mirror surface. The combination of CCOS with microgrinding (grinding with fine diamond powders that produce a specular surface) allows interferometric testing at an early stage of the process. Removal rates and tool conformance to the mirror surface are enhanced by vacuum applied to the grinding and polishing tools. Surface figure accuracies better than 0.02 μm rms and finishes better than 10 Å are currently achieved.
A computer-controlled optical surface (CCOS) process has been developed that is in routine use for fabricating off-axis and centered aspheric mirrors. The CCOS process effects surface removal by moving a relatively small tool over the mirror surface in a path covering the entire surface. The removal is computed by the convolution of the tool work function with the path of the tool over the mirror surface. The combination of CCOS with microgrinding (grinding with fine tool over the mirror surface. The combination of CCOS with microgrinding (grinding with fine diamond powders which produce a specular surface) allows interferometric testing at an early stage of the process. Surface figure accuracies better than 20 nm rms and finishes better than 10 A are currently achieved.
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