Figure 1. An aircraft navigation and targeting system incorporates multi-spectral optical assemblies formed of exotic materials. (KAISER ELECTRO-OPTICS INC.)
Today, missile seeker, reconnaissance, countermeasure, avionics, and communication systems used for defense and anti-terrorism are more complex, have higher performance, and are more compact and lightweight than ever before. Many of these systems have multi-spectral sensor fusion capabilities and their requirements place enormous demands on the design and manufature by today's top level electronic-optics (E-O) suppliers.
The best approach to achieve a cost-effective design for E-O systems is to integrate low-cost fabrication technologies into the initial system architecture at the concept definition phase and then apply them during the detail design of the system's components and assemblies. Taking this approach minimizes the number of components as well as the system adjustment and alignment features.
Examples of current E-O systems that incorporate this type of integrated low-cost design approach include programs such as the Land Warrior Helmet Mounted Display (HMD), the AN/AAQ-24(V) Directed Infrared Countermeasures (DIRCM), new high-performance aircrafts infrared (IR) navigation and targeting system (see figure), and the Hyperscope, a near-IR transceiver for laser communications.
Partial implementation of this integrated low-cost design approach was made to other programs such as the Advanced Tactical Air Reconnaissance System reconnaissance cameras, satellite star trackers, infrared navigation and targeting pods, head up displays, and the Defense Meteorological Satellite Program spectrometer.
Design of multi-spectral, sensor-fused, electro-optical systems requires multi-disciplined engineering capabilities. Optical design engineers must have experience with all types of optical surfaces and element configurations. In addition, they must be familiar with materials for the ultraviolet (UV), visible, and near- and far-IR spectral regions. These materials include fused silica, calcium fluoride, high index glasses, polymethyl methacrylate and amorphous polyolefin polymers, sapphire, silicon, zinc selenide, germanium, and amorphous IR glass. Optical configurations include plano, spherical, aspherical, toric, cylindrical, diffractive, and sometimes combinations of these. To produce the most cost-effective electro optic systems, optical and mechanical engineers must be experienced with the use of state-of-the-art fabrication technologies that are consistent with the integrated low-cost approach.
Optical coating design experience is a critical step in achieving the required optical transmission of the multi-spectral systems. Included in the system design efforts are optical sensitivity analysis, finite element and thermal analysis, and tolerance analysis for all components and their interface. Any or all of these engineering capabilities can be obtained from electro-optic subsystems suppliers as a concurrent engineering service.
Concurrent engineering is the practice of applying the integrated low-cost design approach assistance to the systems developer during the conceptual design phase of the system. Assistance from a subsystems supplier familiar with state-of-the-art fabrication technologies and the integrated low-cost design approach can be obtained to provide this concurrent engineering service when required.
Manufacturing high performance electro-optical systems for defense at an affordable price is a major challenge. They require a rugged and reliable configuration to meet all military environmental conditions. This reliability requirement is accomplished by maintaining close tolerance control of components and assemblies during their fabrication cycle. Optical surface figure accuracies of λ/10 are often required. Anti-reflection (AR) optical coatings with better than 99.5% reflectance are common for each surface in the optical path. Geometric tolerances on both optical and mechanical components are often ±0.0005 inch or less.
State-of-the-art fabrication capabilities used routinely include computer-numeric controlled optical grinding and polishing, single-point diamond machining, optical coating, and plastic injection molding. These specialized fabrication processes are obtainable from industry suppliers if not available internally. Critical optical assembly operations, such as laser cavity and near-image plane assemblies, require a Class 100 clean room environment. This environment can be achieved economically using a Class 100 laminar flow booth located in a Class 10,000 clean room.
Ensuring performance reliability requires a series of vigorous tests to be performed during the development and production phases. To maximize assembly throughput and reduce cost, some assemblies and subsystems require custom designed, programdedicated functional test equipment. This facilitates 100% testing of production units to ensure performance and reliability at a reasonable cost.
The above described manufacturing concepts were used in the development of the following systems. Land Warrior, an integrated fighting system for individual soldiers and infantry units, incorporates aspheric polymer optics and a 800 x 600 SVGA Display in the HMD. DIRCM, an integrated UV and IR countermeasure system, includes optical assemblies with fused silica and silicon aspheric lenses. The Hyperscope transceiver consists of a single-point diamond machined primary aspheric mirror, and a plano secondary reflector/window incorporating a unique coating that is highly transmissive to incident radiation, yet highly reflective to internal radiation. The new high performance aircraft's Navigation and Targeting System's multi-spectral optical assemblies consist of plano, spherical, and aspherical optics. They are made from materials such as calcium fluoride, sapphire, AMTIR, silicon, zinc selenide, and germanium. Both computer numeric-controlled polishing and single-point diamond machining fabrication methods are used.
Performance and cost pressures placed on electro-optic systems will continue to increase as battlefield demands increase. By continuing to implement innovative design and fabrication techniques, however, manufacturers can rise to the challenge. oe
Benedict Mall is vice president of business development at Kaiser Electro-Optics Inc., Carlsbad, CA.
Bill Cooper is an electro-optics industry consultant to Kaiser.