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.
Thales Angénieux (TAGX) designs and manufactures zoom lens assemblies for cinema applications. These objectives are made of mobile lens assemblies. These need to be precisely characterized to detect alignment, polishing or glass index homogeneity errors, which amplitude may range to a few hundreds of nanometers. However these assemblies are highly aberrated with mainly spherical aberration (>30 μm PV). PHASICS and TAGX developed a solution based on the use of a PHASICS SID4HR wave front sensor. This is based on quadri-wave lateral shearing interferometry, a technology known for its high dynamic range. A 100-mm diameter He:Ne source illuminates the lens assembly entrance pupil. The transmitted wave front is then directly measured by the SID4- HR. The measured wave front (WFmeas) is then compared to a simulation from the lens sub-assembly optical design (WFdesign). We obtain a residual wave front error (WFmanufactured), which reveals lens imperfections due to its manufacturing. WFmeas=WFdesign+(WFEradius+WFEglass+WFEpolish)=WF design + WFmanufactured The optical test bench was designed so that this residual wave front is measured with a precision below 100 nm PV. The measurement of fast F-Number lenses (F/2) with aberrations up to 30 μm, with a precision of 100 nm PV was demonstrated. This bench detects mismatches in sub-assemblies before the final integration step in the zoom. Pre-alignment is also performed in order to overpass the mechanical tolerances. This facilitates the completed zoom alignment. In final, productivity gains are expected due to alignment and mounting time savings.
Large aspherical focusing and beam deviating square lenses will be used in the framework of the Laser Megajoules project developed by the French Atomic Energy Commission. In order to validate the associated manufacturing processes a half scale prototype lens has been manufactured and tested by REOSC (SFIM subsidiary). Specific aspherical generating process and computer controlled micro-polishing technology have been used in order to demonstrate the faisability of a mass production on an industrial basis (approximately 1300 lenses in 6 years). A 250 mm square lens in Fused Silica with a convex hyperboloid profile (250 microns difference with respect to the best sphere) has been manufactured and REOSC reached a transmitted wavefront better than 130 nm Peak-peak, 11 nm rms. Moreover residual micro-oscillations amplitudes (spatial frequency 0.5 to 30 mm) have been limited to 60 nm PTV and 8 nm rms. The total work duration for this exploratory lens remained below 60 hours.
Within the framework of a MATRA MARCONI SPACE FRANC contract for the European Space Agency, MATRA DEFENSE - DOD/UAO have developed, produced and tested 9 laser diode collimators, 52 optical components (anamorphoser, mirrors, dichroic splitters, redundancy module) and 9 interferential filters. All these space equipments must be integrated into the optical head of the SILEX (Semi-conductor Laser Intersatellite Link Experiment) bench. The SILEX experiment consists in transferring data from a low altitude satellite (SPOT 4) to a satellite in geostationary orbit (ARTEMIS) via beam generated by a laser diode (60 mW Cw). Very low emitted flux and long distance between the two satellites gives rise to the following technical difficulties: high angular (1 (mu) rad) and transverse stability requirements, requirement for high transmission and high rejection narrow band filters, in order to differentiate the transmit and receive channels, necessity of a very good optical wavefront, wavelength range 815-825 nm, 843-853 nm.
In the framework of a contract with the Indian Space Research Organization (ISRO), MATRA DEFENSE - DOD/UAO have developed, produced and tested 36 types LISS 1 - LISS 2 lenses and 12 LISS 3 lenses equipped with their interferential filters. These lenses are intended to form the optical systems of multispectral imaging sensors aboard Indian earth observation satellites IRS 1A, 1B, 1C, and 1D. It should be noted that the multispectrum cameras of the IRS 1A - 1B satellite have been in operation for two years and have given very satisfactory results according to ISRO. Each of these multispectrum LISS 3 cameras consists of lenses, each working in a different spectral bandwidth (B2: 520 - 590 nm; B3: 620 - 680 nm; B4: 770 - 860 nm; B5: 1550 - 1700 nm). In order to superimpose the images of each spectral band without digital processing, the image formats (60 mm) of the lenses are registered better that 2 micrometers and remain as such throughout all the environmental tests. Similarly, due to the absence of precise thermal control aboard the satellite, the lenses are as athermal as possible.