Abstract
Electro-optical imaging sensors are widely distributed and used for many different tasks. Due to technical improvements, their pixel size has been steadily decreasing, resulting in a reduced saturation capacity. As a consequence, this progress makes them susceptible to intense point light sources. Developments in laser technology have led to very compact and powerful laser sources of any wavelength in the visible and near infrared spectral region, offered as laser pointers. The manifold of wavelengths makes it difficult to encounter sensor saturation over the complete operating waveband by conventional measures like absorption or interference filters. We present a concept for electro-optical sensors to suppress overexposure in the visible spectral region. The key element of the concept is a spatial light modulator in combination with wavelength multiplexing. This approach allows spectral filtering within a localized area in the field of view of the sensor. The system offers the possibility of automatic reduction of overexposure by monochromatic laser radiation.
Highlights
Imaging sensors operating in the visible, near-infrared or thermal infrared are widely distributed devices
The application of spatial light modulators as a protection measure against dazzling light sources was already described earlier by Tomilin and Danilov, but no experimental results were given [18]. We demonstrated successfully such an approach [19]. The applicability of this method was significantly improved by the implementation of wavelength multiplexing, which allows spatial and spectral filtering in contrast to [18]
The main characteristics of the setup described above were quantified by two different measurements: (1) The attenuation for monochromatic light turned out to be 48 dB at a wavelength of 532 nm. (2) The broadband system transmission was measured to be 24% using a halogen cold-light source
Summary
Imaging sensors operating in the visible, near-infrared or thermal infrared are widely distributed devices. Current laser protection measures typically involve the use of conventional optical filters based on absorption or interference effects These devices only work in a limited wavelength range, and they may introduce a strong colour distortion in the visible spectral range. Optical power limiters are not usable as protection against laser dazzling because the activation threshold is far too high. They are intended to protect the eye or electro-optical systems against damage by laser radiation. We present a novel concept for automatic suppression of intense monochromatic light in electro-optical sensors It is based on the recognition of dazzling light and its suppression, while low power radiation is nearly unaffected. Such an active concept is definitely attractive, since the proliferation of compact continuous wave (cw) laser pointers is very high and largely uncontrolled
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