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One of the key features of the photonic payload concepts investigated in the frame of Optima is their flexibility, and adaptability. This is enabled thanks to an Optical Switch Matrix.

Sodern, (a recognized space equipment provider) is working in partnership with HUBER+SUHNER Polatis Ltd, (the worldwide leader in optical switch solution) to adapt their so called DirectLight® switching technology to satellite applications.

The principle of such switches is illustrated in figure 1.

  • Each input and output fibers are terminated with an optical collimator to generate parallel beams.

  • Figure 1

  • Collimators of input and output beams are pointed to each other via 2D piezoelectric actuators. The orientation is controlled by a local controlled closed loop using an integrated position sensor.
  • The link between two ports is established when input collimator and output collimator are aligned facing each other.

    The architecture of DirectlLight® switch product is based on a modular component named “slice” composed of 12 fibered collimators with corresponding piezo-actuator and proximity EEE components as shown in the figure below. The integration and alignment of several slices enables to build a large switch matrix up to 384 x 384.

    Sodern and Polatis' objectives are to define a scalable architecture of a Space Switch that makes the best compromise between SWaP (Size Weight and Power) and reliability, but also to guarantee functionalities and performances within the GEO environment. The major requirements underlying the space Optical Switch development are as follows:

    - working wavelength 1.55 µm
    - insertion loss, (fiber connector excluded): 1 dB typ. (2.5 dB max)
    - a scalable number of ports from 24x24 to 96x96
    - a modular electronic architecture to reach high reliability
    - a reduced SWaP adapted to ports number from 24x24 to 96x96
    - performances guaranteed in thermal range -10 °C / +60 °C, qualified for mechanical loads (sine at 20g, random at 18.4g RMS, shocks at 1300g SRS [3000 10 000Hz]), and resistant to radiations 30krad, 60 MeV.cm²/mg
    - without disturbing others light path.

    In the frame of the Optima project, three main activities have been addressed at switch level :

    - Evaluation of Switch technology compatibility with Space Environment

    Sodern has evaluated the compliance of DirectLight® Slice materials and manufacturing processes with respect to European Space Standards (ECSS) and SODERN Standards applied for the Space Telecom market. Analyses have concluded that only minor adaptations are required.

    - Evaluation of the opporunity to reuse the piezo-driver ASIC of DirectLight® switch.

    In the DirectLight® switch the piezo-actuators are driven by a dedicated high voltage ASIC originally designed by iMinds for Polatis. Sodern and iMinds have performed an extensive campaign of radiation testing of the existing ASIC that concludes that it is not able to survive in GEO environment. Since the existing ASIC cannot be reused as is for Space application, iMinds and Sodern are investigating the development of a new ASIC version with radiation hardened structures.

    - Design and environmental testing of a switch breadboard

    Based on an in depth finite element mechanical analysis confirmed and correlated by environmental testing at slice level, Sodern and Polatis have designed a switch breadboard (see figure below) to demonstrate its ability to withstand mechanical and thermal environments mentioned above. The success of the environmental test campaign has demonstrated the ability of the DirectLight® technology to face mechanical and thermal environments.

    Activities and results of Optima at switch level have been presented at the :

    - International Astronautical Congress (IAC) (see R. Le Goff, 2018, Optical switches of photonics payload)
    - International Conference for Space Optics (ICSO) (see K. Ravel, 2018, Optical Switch Matrix development for new concepts of Photonic based flexible Telecom Payloads).

    Based on the outputs of the OPTIMA switch activities, Sodern and Polatis are working on a roadmap to reach qualification of a switch product to address the emerging market of photonic geostationary telecom satellites.

  • Design and picture of the switch breadboard manufactured in the frame of Optima

    Layout of DirectLight modular building block named Slice