Assembly Technique for Miniaturized Optical Devices: Towards Space Qualification

Key members

The TRIMO-SMD technology (Three Dimensional Miniaturized Optical Surface Mounted Device) developed by Leica Geosystem [1] is a packaging technology for assembling complex passive optical micro-systems. TRIMO-SMD is based on a laser soldering technique. The optical components fixed in holders are actively aligned using a high-precision manipulator with six degrees of freedom. Upon completion of the alignment, all degrees of freedom are frozen at once by soldering the holder on a metal baseplate with a hard solder by means of a laser.

The TRIMO-SMD technology is already used in the industrial production environment. In the frame of the project SQUATOS (Space Qualified Assembly Technique for Optical System), its associated manufacturing methodologies and performances were assessed in the context of space applications. Two types of experimental demonstrators were conceived. Several copies were manufactured and tested in various situations reproducing space environmental constraints, like launch and operational conditions.
Based on LTF’s knowledge and involvement in the project, a laser rubidium frequency reference was developed around a saturated absorption scheme, representing a sub-part of the possible next generation of Rb atomic clock [2, 3]. This demonstrator was operated at different temperature (10-60°C), under vacuum and in micro-vibration conditions, as typically found in a satellite environment. The second type of demonstrator, simpler than the previous one, was placed in strong environmental constraints that might potentially destroy the device under test (e.g. high thermal constraints and strong vibrations as similarly found during a rocket launch). No dysfunction of the demonstrators was detected. Results indicate that misalignments due to the applied environmental loads are usually smaller than the soldering accuracy [4].

This project was financed by the SSO (Swiss Space Office) and was led in collaboration with CSEM, Leica Geosystem and micos Engineering.

Laser frequency stabilization device built around an LTF home-made rubidium cell and assembled using the TRIMO-SMD technology. Dimensions : 71 x 24 mm.

1.    L. Stauffer, F. Wälti, U. Vokinger, K. Siercks, “High precision surface mount assembly of micro-optical components per laser reflow soldering – positioning accuracy and thermal stability”, Proceedings SPIE, vol. 5454, pp 85-95 (2004)
2.    C. Affolderbach, G. Mileti, “A compact laser head with high-frequency stability for Rb atomic clocks and optical instrumentation”, Review of Scientific Instruments, 76, 073108 (2005)
3.    C. Affolderbach, F. Gruet, R. Matthey, G. Mileti, “A compact laser-pumped Rb clock with 5x10-13 T-1/2 frequency stability”, Proceedings of the Joint Meeting of the European Frequency and Time Forum (EFTF) and the IEEE International Frequency Control Symposium (FCS), San Francisco, May 2-5 2011
4.    R. Matthey, L. Stauffer, P. Giaccari, A. Pollini, L. Balet, G. Mileti, “Assembly Technique for Miniaturized Optical Devices: Towards Space Qualification”, Proceedings of the International Conference on Space Optics (ICSO), Ajaccio (F), October 9-12 2012