In the realm of thermal imaging, the pursuit of excellence is a delicate dance. The challenge lies in crafting lenses that not only capture the essence of the unseen but also do so with unparalleled precision and efficiency. Enter the world of LWIR lens design, where innovation meets the extreme. This article delves into the intricacies of two groundbreaking lens configurations, each a masterpiece in its own right, designed to push the boundaries of what's possible in thermal imaging technology. But before we embark on this journey, let's set the stage with a brief introduction to the challenges that lie at the heart of LWIR lens design.
The Challenge of LWIR Lens Design
In the realm of long-wave infrared (LWIR) optical systems, achieving a harmonious balance between a large aperture, a compact form factor, thermal stability, and high imaging performance is akin to solving a complex puzzle. These requirements are often mutually exclusive, especially in applications demanding long-range detection, broad field coverage, and reliable performance in harsh environments. Traditional design techniques often fall short when it comes to simultaneously optimizing aberration correction, athermalization, and producibility. It's a delicate tightrope walk, and the stakes are high.
Two Lens Configurations, Two Masterpieces
Now, let's shift our focus to the two lens configurations that have emerged as shining examples of innovation in LWIR lens design. The first, a 20 mm F/0.85 ultra-wide aperture lens, and the second, a 40 mm F/1.0 high-resolution lens, are both marvels in their own right. These designs not only overcome the challenges of LWIR lens design but also set new benchmarks for performance and compactness.
20 mm F/0.85: Ultra-Large Aperture in a Compact Architecture
The 20 mm F/0.85 lens is a testament to the power of innovation. Its optical performance is nothing short of remarkable, with consistent MTF performance across the entire field of view at three representative temperatures (20 °C, -40 °C, and 80 °C). This ensures uniform contrast under fluctuating environmental conditions, a crucial feature for applications requiring reliable performance in extreme environments. The defocus response is smooth, indicating sufficient depth of focus and supporting tolerance control throughout assembly.
Aberration control is achieved through effective energy concentration in diffraction spots across the field, while distortion is held at a competitive 4.65% for a wide-angle system with such a large aperture. Relative illumination reaches 66% at F/0.85, indicating effective control of vignetting. The CRA (3.52 °) is well aligned with standard uncooled detector microlens arrays, reducing shading and ensuring consistent signal response.
The mechanical design is equally impressive, with a miniaturized housing featuring a maximum diameter of 25 mm and an overall length of 35 mm. This form factor facilitates integration into size- and weight-limited platforms, including UAVs, handheld thermal imagers, and vehicle-mounted systems. Interface configurations can be tailored to meet specific system specifications, making it a versatile solution for a wide range of applications.
40 mm F/1.0: High-Resolution Medium Telephoto Design
The 40 mm F/1.0 lens takes a slightly different approach, focusing on high-resolution detection. Its MTF performance is close to the diffraction limit across the operational thermal range, with high contrast maintained at the yquist frequency (25 lp/mm). This facilitates dependable high-resolution detection, making it ideal for medium-range recognition applications.
Aberrations, such as spherical aberration, astigmatism, and field curvature, are effectively suppressed, while distortion is limited to -2.96%, allowing precise measurement and ensuring compatibility with computer vision and AI-based image evaluation workflows. Relative illumination surpasses 81%, providing consistent brightness across the field, and the CRA (6.27 °) is optimized to achieve efficient coupling with conventional infrared detectors.
The mechanical design is robust, with a maximum diameter of 40 mm and an overall length of 48 mm, providing a balance between optical performance, mechanical durability, and temperature control. The lens maintains compatibility with conventional infrared camera interfaces, supporting operation in extreme environments, including surveillance systems, automotive platforms, and airborne payloads.
Technical Considerations
Large Aperture and Miniaturization
The designs employ a combination of aspherical surfaces and low-absorption infrared materials, such as germanium (Ge), zinc selenide (ZnSe), and chalcogenide glasses. Global optimization methods and tolerance-sensitivity evaluations are employed to preserve exceptional imaging performance within compact geometries, ensuring that the lenses are both powerful and portable.
Passive Athermalization
Athermal performance is achieved through a combination of materials with differing thermo-optic coefficients and mechanical compensation techniques. This approach facilitates stable imaging over a thermal range spanning -40 °C to 80 °C without the need for active refocusing, making it a reliable solution for applications in harsh environments.
Illumination and CRA Optimization
Managing pupil aberration and optimizing vignetting enhances edge illumination, while precise alignment of the CRA to detector microlens structures avoids non-uniformity and radiometric artifacts, ensuring consistent signal response.
Production and Assembly
Execution of these designs depends on submicron-precision aspherical machining and high-transmission infrared coatings. Accurate mechanical design and active alignment procedures guarantee repeatability and consistent performance during volume manufacturing. Environmental validation involves rigorous testing, including thermal cycling, vibration, shock, salt spray, and particulate exposure, to ensure that the lenses can withstand the rigors of real-world applications.
Typical Applications
The 20 mm F/0.85 lens is well-suited for handheld thermal-imaging systems, short-range detection and monitoring, UAV-based reconnaissance, automotive night vision, and industrial thermography. The 40 mm F/1.0 lens, on the other hand, is ideal for border and perimeter surveillance, infrared measurement systems, medium-range target detection, robotics and automation, and AI-assisted vision systems.
Customization Capability
Customization options for these lenses are extensive, including optional active focus mechanisms, spectral band optimization, manufacturing and qualification test planning, and adjustments to focal length, F-number, and field of view. Mechanical interface and back focal distance can also be tailored to meet specific system specifications, making these lenses highly adaptable to a wide range of applications.
Conclusion
In conclusion, the presented LWIR lens designs from Avantier Inc. showcase a remarkable balance between ultra-wide-aperture performance, passive athermalization, miniaturized mechanical structure, and producibility. These advancements demonstrate a systematic approach to addressing critical constraints in infrared optical design, enabling robust imaging performance across a wide range of use cases and environmental settings. As the world of thermal imaging continues to evolve, these innovations will undoubtedly play a pivotal role in shaping the future of this exciting field.
