MARKETS / PRODUCTS
Optronics Systems & Optics : Optics

With its REOSC range of high-performance optics, Sagem is one of the world leaders in the design, development and manufacturing of state-of-the-art optomechanical equipment for all kinds of applications. REOSC was founded in 1937 by the famous opticians Henri Chrétien and Charles Fabry, and joined the Sagem world of high technology in 1999. Its products now form part of the optronic systems department.

Items developed by the REOSC engineers and technicians enjoy two major advantages: REOSC's experience in all optical fields and its capacity for innovation applied to the different stages of projects.

Sagem's participation in technically ambitious projects has also enabled it to consistently maintain its expertise and high-precision optomechanical equipment at the most advanced levels, whether it be with respect to design, development, metrology or integration.

Sagem applies the following state-of-the-art optical skills to all types of development:

Optomechanical design

With over 40 years' experience in optical development and computing for all types of equipment, the REOSC team devotes part of its time to the following fields:

• Off-axis aspherical mirrors, mirror systems and catadioptrics

• Reconnaissance optics with a high degree of athermalisation

• IR and aspherical diffractive optics

• Aberration compensators and null lenses"

• Materials with very low expansion factors, silicas and ceramics (silicon carbide).

Optics requires nanometric precision (down to a millionth of a millimeter) over several meters. The REOSC team specializes in calculating the Finite Elements of large sophisticated optical components and their mechanical structures: mirrors up to 2.7m lightweighted, giant 8m astronomy mirrors, and space or aerial reconnaissance optics, designed and developed with powerful software.

Mirror lightweighting and machining

Lense and ceramic machining and mirror lightweighting have been constantly improved since 1970. Several numerically-controlled machining centers with a capacity of up to 3 meters have enabled hundreds of components and lightweight mirrors to be developed. The 2.7m SOFIA mirror completed in 1999, after removing 2.4 tons of glass, is a world record.

Lightweighting ratios above 90% are achieved by applying HF chemical machining after mechanical machining.

The REOSC team has researched achieving lightweighting ratios of 95% or higher in hybrid mirrors.

Precision polishing

Sagem has the largest precision optics workshop in France. This enables the following to be carried out:

• Machining and polishing of all types of materials (lenses, IR materials, metal, etc.)

• Production of all types of optical surfaces (flat, spherical, aspherical, cylindrical, conformal and diffractive)

• Machining of large optics (8m and more)

• Achievement of high precision forms (under a nanometer)

• Achievement of high quality surfaces (under an angstrom)

The company has developed several generations of computer aided polishing technologies, which have contributed to the success of projects such as the Very Large Telescope (VLT), Gemini and Gran Telescopio Canarias (whose primary mirrors were polished in a workshop unique in the world).
Sagem has one of the largest flat polishing workshops in Europe, equipped with continuous polishing machines over 4m in diameter.

Machining by ion beams is another precision optical machining technology which has numerous advantages:

• High degree of precision and determinism through a perfectly controlled wear rate (convergence ratios of up to 98.5% are obtained)

• No edge effects around the parts

• No quilting on lightweighted mirrors as the procedure does not involve any contact

• Adaptation to most precision optics materials

Sagem uses several machines for finishing, one of which has a capacity of up to 2 meters in diameter.

Optical metrology

Metrology forms an integral part of precision optics development.

Previous development projects have enabled Sagem to acquire extensive expertise and master the key stages of the following operations:

• Grinding testing through spherometry

• Aspherical surface testing

• Absolute calibration of flat or spherical optical references – automatic data acquisition using several techniques and algorithms developed in-house

• Data processing using different software linking the interferometers, polishing machines, alignment benches and computing office

• Vibration and air turbulence testing for large optics

High performance processing and etching

Sagem is also an expert in thin optical coating technologies and all metallic and multi-dielectric coating on any substrata up to 1.5m in diameter. Engineers design and optimize theoretical thin-film layers and select the best coating technology according to the desired optical function:
anti-glare/mirrors/dichroics/selective band pass/high-power laser coating.

Integration/alignment and tests

The REOSC technicians are masters in standard alignment techniques (laser, theodolite, etc.) for complex multiple-item systems and ensure they are accurately and securely assembled in the required mounts and mechanisms.

For space optics requiring greater levels of precision, software and methodology have been developed for computer-aided interferometric alignment. For large optics, the entire instrument together with its tooling is placed in a vacuum in order to reduce the effects of air turbulence.

> See the PDF brochures of REOSC:
Brochure 1 - Brochure 2