Satcom and Optical Filters
The desire for low latency, high capacity, secure, uninterrupted internet connectivity everywhere on earth, at all times has driven explosive growth in the satellite communications (Satcom) market. Iridian designs and manufactures custom wavelength selective windows and transceiver filters to improve the signal to noise in these systems.
Commercial Satcom networks will consist of constellations of 100’s to 1000’s of satellites in an interconnected low earth orbit (LEO) mesh. Many of these systems rely on optical intersatellite link (OISL) architecture to connect satellites via laser based optical communications. Optical filters provide wavelength selectivity to these systems addressing different functional needs from solar rejection windows to wavelength selective signal clean-up filters and beam splitting/combining dichroic filters.
Solar Rejection Windows (SRW) allow the transmission of the OISL communication band (typically around 1550nm) between satellites while blocking the background solar radiation, providing improved signal-to-noise while helping minimize solar heating inside the satellite.
Typical SRW optical filter performance requirements include:
- ? ? ? high transmittance in signal band
- typically 1550nm; wavelength is customizable
- ? ? ? broad deep blocking of solar spectrum
- ? ? ? typically large (up to 150mm diameter) windows
- ? ? ? low transmitted wavefront error (TWE)
Dichroic Beam Splitters/Combiners enable the receiver to selectively receive specific wavelength bands of interest.?These may be used as stand-alone clean-up filters or in series to direct different signals to different detectors in the optical train.
Typical Dichroic filter requirements include:
- ? ? ? high transmittance (Tx) and high reflection (Rx)
- ? ? ? steep edges to provide a sharp transition from Tx to Rx
- ? ? ? may need to preserve polarization (for QKD encryption signals
Band-pass “Clean-up” Filters ensure high signal to noise in the transmitted and received signal bands (often two or more wavelength bands carrying signal).
Typical Band-pass filter requirements include:
- ? ? ? narrow bandwidth (FWHM or passband)
- ? ? ? high Tx and high Rx – maximizing isolation of channels from each other
- steep edges to provide a sharp transition from Tx to Rx
- ? ? ? low TWE
Iridian has produced individual filters and multi-spectral elements that have been tested and qualified for a range of orbits and space environments. Iridian is a registered participant in the Canadian Controlled Goods Program.
Examples of space environment testing and qualification that our filters have passed include:?
- ? ? ? Radiation exposure (gamma rays, protons, combined solar UV and electrons)
- ? ? ? Thermal cycling/shock/survivability including liquid N2 to boiling ethanol dips
- ? ? ? Vibration testing
- ? ? ? Laser damage testing in excess of 1 MW/cm2
- ? ? ? Thermal vacuum cycling testing from 50K to 450K
- ? ? ? Outgassing testing as per ASTM-E595
- ? ? ? Reliability as per MIL-C-48497A
Iridian has over 20 years of experience producing industry leading optical telecommunication and datacom filters for terrestrial systems. This communication filter expertise is combined with a space heritage providing filters flown in satellite applications such as earth observation and is supported by a dedicated Aerospace and Specialty Optics group to guide customers from initial specification and design through to full volume production from our Ottawa, Canada facility.