Increasing the capture volume of visible cameras while maintaining high image resolutions, low power consumption and
standard video-frame rate operation is of utmost importance for hand-free night vision goggles or embedded surveillance
systems. Since such imaging systems require to operate at high aperture, their optical design has become more complex
and critical. Therefore new design alternatives have to be considered. Among them, wavefront coding changes and
desensitizes the modulation transfer function (MTF) of the lens by inserting a phase mask in the vicinity of the aperture
stop. This smart filter is combined with an efficient image processing that ensures optimal image quality over a larger
depth of field. In this paper recent advances are discussed concerning design and integration of a compact imaging system
based on wavefront coding. We address the design, the integration and the characterization of a High Definition (HD)
camera of large aperture (F/1.2) operating in the visible and near infrared spectral ranges, endowed with wavefront coding.
Two types of phase masks (pyramidal and polynomial) have been jointly optimized with their deconvolution algorithm in
order to meet the best performance along an increased range of focus distances and manufactured. Real time deconvolution
processing is implemented on a Field Programmable Gate Array. It is shown that despite the high data throughput of an
HD imaging chain, the level of power consumption is far below the initial specifications. We have characterized the
performances with and without wavefront coding through MTF measurements and image quality assessments. A depth-of-
field increase up to x2.5 has been demonstrated in accordance with the theoretical predictions.
The military uncooled infrared market is driven by the continued cost reduction of the focal plane arrays whilst maintaining high standards of sensitivity and steering towards smaller pixel sizes. As a consequence, new optical solutions are called for. Two approaches can come into play: the bottom up option consists in allocating improvements to each contributor and the top down process rather relies on an overall optimization of the complete image channel. The University of Rennes I with Thales Angénieux alongside has been working over the past decade through French MOD funding’s, on low cost alternatives of infrared materials based upon chalcogenide glasses. A special care has been laid on the enhancement of their mechanical properties and their ability to be moulded according to complex shapes. New manufacturing means developments capable of better yields for the raw materials will be addressed, too. Beyond the mere lenses budget cuts, a wave front coding process can ease a global optimization. This technic gives a way of relaxing optical constraints or upgrading thermal device performances through an increase of the focus depths and desensitization against temperature drifts: it combines image processing and the use of smart optical components. Thales achievements in such topics will be enlightened and the trade-off between image quality correction levels and low consumption/ real time processing, as might be required in hand-free night vision devices, will be emphasized. It is worth mentioning that both approaches are deeply leaning on each other.
In this work, we present the development of a multi-sensor system for the detection of objects concealed under clothes
using passive and active millimeter-wave (mmW) technologies. This study concerns both the optimization of a
commercial passive mmW imager at 94 GHz using a phase mask and the development of an active mmW detector at 77
GHz based on synthetic aperture radar (SAR).
A first wide-field inspection is done by the passive imager while the person is walking. If a suspicious area is detected,
the active imager is switched-on and focused on this area in order to obtain more accurate data (shape of the object,
nature of the material ...).
To improve the depth of field in imaging systems, we propose a new method for designing pupil filters with the classical
approach used for computer-generated holograms. This method allows us to calculate a complex amplitude/phase filter
in order to obtain a desired distribution of intensity along the optical axis, and thus the desired depth of field.
We will compare our complex filter with binary-phase filters, which are one of the different methods already
investigated to improve the depth of field in imaging applications. This study will reveal that the complex filter is an
interesting alternative for applications where very low fluctuations of the amplitude distribution along the optical axis are
required. It is indeed as energy-efficient as a pure phase filter even with a non negligible absorption. It also ensures to
precisely tailor the shape of the focal line of an imaging lens, as the decrease of intensity is sharper outside the regions of
interest than with the binary-phase filter. Moreover, it also benefits from lower sidelobes. With these characteristics, this
new complex filter will be suitable particularly for 3D imaging applications.