Optical Filters and Coatings for Satcom Applications

The need for low latency, secure, high capacity, uninterrupted internet connectivity exists everywhere on earth, at all times. This has resulted in considerable growth in the satellite communications (satcom) market.

Iridian is a designer and manufacturer of custom wavelength selective windows and transceiver filters, with the goal of improving these systems’ signal to noise. The company possesses more than two decades of experience delivering industry leading optical telecommunication and datacom filters designed for use in terrestrial systems. This communication filter expertise is coupled with space heritage, providing filters flown in satellite applications such as earth observation. The dedicated Aerospace and Specialty Optics group guides customers from initial specification and design through to full volume production from Iridian’s Ottawa, Canada facility.

Satcom and Optical Filters

Commercial satcom networks are made of constellations, each containing 100’s to 1,000’s of satellites, communicating via an interconnected low earth orbit (LEO) mesh.

A number of these systems depend on optical intersatellite link (OISL) architecture, which is designed to connect satellites using laser based optical communications. Optical filters are responsible for providing wavelength selectivity to these systems, accommodating functional needs which range from beam steering wavelength selective dichroic filters to solar rejection windows.

Solar rejection windows (SRW) facilitate the transmission of the communication band (usually around 1550 nm) between satellites, while simultaneously blocking background solar radiation. This offers enhanced signal to noise while minimizing solar heating inside the satellite itself.

Optical SRW filter performance requirements usually include:

  • High transmittance in signal band: generally 1550 nm, though wavelength is customizable
  • Low transmitted wavefront error (TWE)
  • Broad deep blocking of solar spectrum
  • Large (up to 150 mm) windows

Dichroic filters allow the receiver to selectively pick up particular wavelength bands of interest. These may form stand-alone clean-up filters, or work in series to direct different signals to specific detectors in the optical train.

Optical dichroic filter requirements in these settings include:

  • Steep edges
  • High transmittance and high reflection
  • The need to preserve polarization (for QKD encryption signals)

Optical Filters and Coatings for Satcom Applications

Space Heritage

Iridian has supplied both individual filters and multi-spectral elements, and these have been tested and qualified as suitable for a wide range of space environments and orbits.

Furthermore, Iridian is a registered participant in the Canadian Controlled Goods Program, offering filters and coatings for space, with multi‐zone filter arrays currently in LEO orbit for several commercial customers. These include:

  • Assembled arrays; up to 10 zones with dark seam coatings, designed to provide isolation between color bands
  • Large format NIR band-pass filters for NASA LADEE free space communications test, Lunar Laser Communication Demonstration (LLCD)
  • Large, highly uniform narrow band-pass filters and SRW for MTG-Lightning Imager at 7 nm (geosynchronous orbit)
  • Light absorbing coatings on International Space Station (LEO at 350 km)
  • 532/1550 nm partial reflectors and AR coatings for Fabry ‐ Perot etalons used on NASA’s ICE Sat‐2 satellite (LEO at 500 km)
  • AR coatings on NASA’s Solar Dynamics Observatory (SDO) (geosynchronous orbit)

Completed Space Environment Tests

Radiation exposure including:

  • Thermal shock/survivability: multiple liquid N2 dips
  • Laser damage testing: in excess of 1 MW/cm2
  • Thermal vacuum cycling testing from 50 K to 450 K
  • Vibration testing (customer performed)
  • Reliability as per MIL‐C‐48497A
  • Outgassing testing (ASTM‐E595)
  • Gamma, proton, combined solar UV and electron

This information has been sourced, reviewed and adapted from materials provided by Iridian Spectral Technologies.

For more information on this source, please visit Iridian Spectral Technologies.

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