Test & measurement
European Space Agency uses Yokogawa instruments to achieve precise laser tuning for satellites
T
he European Space Agency (ESA) is using the precision of Yokogawa’s optical wavelength meters to ensure
accurate tuning of lasers used in Earth to space communications. ESA operates a network of geostationary
satellites known as the European Data Relay System (EDRS). These satellites communicate with a constellation of European Low Earth Orbit (LEO) satellites called Sentinels, used for Earth monitoring applications. The EDRS satellites use radio
communication to upload the LEO satellites’ images and other data to terrestrial servers. The challenge is that the growing amount
of information from LEO and geostationary satellites and from satellite constellations will mean that the available bandwidth from radio
communication links will soon be too low to meet ESA’s data transfer needs. Optical, laser-based communication is the
obvious answer, a technique already used to transfer data between the LEO satellites and the EDRS network. Optical communications is a proven technology on Earth and forms the backbone of the internet. However, optical communications in free
space between the Earth and a satellite calls for special laser technology. This is because optical signals transmitted between the Earth and space are subject to interference from various sources, such as clouds or other weather phenomena.
In addition, optical signals in
free space cannot be shielded from external sources of optical interference by the physical medium through which they travel, such as an optical fibre on Earth. Optical communication
systems need to achieve a sufficient signal-to- noise ratio to maintain the link between transmitter and receiver. In the ESA’s EDRS, signals are transmitted at a very precisely specified infrared wavelength of 1,064.625nm (nanometers) ±11pm (picometers), with almost zero variance in the peak wavelength. This allows the receiver to lock on to the transmitted narrowband signal and to eliminate interfering signals. With this technology, the EDRS satellite can operate even when the sun is in its line of sight. ESA is implementing
optical Earth-to-satellite communications technology in its optical ground station (OGS) on the Spanish island of
52 February 2022 Instrumentation Monthly
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