IR lenses, large-array sensors target solar
By Ann R. Thryft, Contributing Technical Editor- February 1, 2011
This sidebar accompanied the article "Lenses in solar, flat-panel inspection."
Many manufacturers are starting to perform more inspections in the nonvisible bands while also still working in the visible light spectrum. For example, Navitar's customers are expanding into NIR (near infrared) and SWIR (short-wave infrared) bands, said Craig Fitzgerald, the company's VP of product and business development. "Images taken with lenses designed for infrared wavelengths let you detect things you can't with visible light, such as certain defects on semiconductors or solar wafers," he said.
Camera designs have become much more sensitive to nonvisible wavelengths of light, primarily because of improvements in CMOS silicon sensors, said Fitzgerald. "Sensor manufacturers have learned how to optimize their devices for specific IR or UV [ultraviolet] wavelengths, so some customers also want lenses optimized for those wavelengths," he said. Today, cameras that can see those wavelengths are a lot smaller and less expensive than the ones used 10 years ago, due to advances in their electronics.
The SWIR band, in particular, can detect low-efficiency and high-efficiency areas in solar cells, said Nicholas James, product line manager for Edmund Optics. "Some lenses sold to this market are really a visible lens with a SWIR optical coating to increase transmission frequency," he said. "But designing specifically for SWIR frequencies allows the lens maker to provide greater contrast and optimize for the camera sensors used in that band, which are larger, with larger pixel sizes, than sensors in the visible band."
Meanwhile, some camera companies are targeting solar-cell and FPD (flat-panel display) inspection with arrays that are larger than the current 12k-resolution camera, said Stuart Singer, VP of Schneider Optics. In the next generation of these cameras, arrays will be 16k and up, with very small pixels, he said. "It will be a challenge for lens makers to provide lenses with performance that is commensurate with these miniature pixels. We're making lenses with greater resolution and greater performance, such as larger apertures to let more light through, so they can keep up with the trend of ever-decreasing pixel size."