February 7, 2017

VIS Instrument

The Visible and Near Infrared Imaging Channels instrument (VIS) provides high-quality images in the visible spectrum. It is optimized to fulfil the needs of its primary scientific goal, weak lensing. Euclid Instrument Channels starts after the beam-splitting mirror M3.

The focal plane of VIS is composed of 6 x 6 CCDs with 12 µm pixels (baseline e2v CCD203-82 CCD with optimized packaging for field of view gap) that cover the 0.5 deg² visible field of view. The CCDs are full-frame types of 4096 x 4096 pixels. The dimensions of this focal plane of about 600 million pixels are nearly 50 cm x 50 cm. The detectors are kept at a temperature near 150 K.

Detection bloc of VIS instrument
Detection unit of VIS instrument

The architecture of the proposed electronics to control and read out the 36 CCDs has been developed from experience with previous projects, most notably Gaia. Unlike Gaia where the CCDs are all operated independently, Euclid's VIS CCDs are all operated in synchronism. This simplifies the sub-system design. Each CCD is served by a proximity electronics module (PEM) and each row of PEMs is served by an interconnect module (IM). Because an individual clock sequence generators for each CCD is not needed for Euclid, it is beneficial to combine the PEM & IM functions into one unit. This unit is called a Read Out Electronics (ROE) unit.

In order to meet the image quality requirements, the focal plane is made of silicon carbide (SiC) and thermally and mechanically coupled as much as possible to the instrument through thermal shields (Thermal Shields 1 & 2) and flexible connectors.

The Power Supply Unit (PSU) ensures the power supply of the focal plane and its read-out electronics.

  • The calibration unit (CU) is dedicated to supplying a perfectly known light source during the flight in order to calibrate the instrument. It is composed of an integrating sphere supplying a uniform illumination of the whole focal plane.
  • The shutter is placed before the focal plane. After each integration (a few hundreds of seconds), it is shut to prevent the stray light effects during the accumulated signal reading.
  • Two electronics units are associated to the instrument but located in the service module: the Control and Data Processing Unit (CDPU) and the Power and Mechanisms Control Unit (PMCU).

From left to right: Calibration unit - Shutter - CDPU - PMCU