Coherent Optical Receiver (CORX) for Satellite and Space Communication

Why Space Communication Programmes Test the Receive Side on the Ground

Optical links for space communication, whether satellite-to-ground, inter-satellite or free-space links between terminals, are increasingly built around coherent detection. Before a terminal is integrated and qualified, research teams need to know how its signal behaves at the receiver: how clean the constellation is, how the error rate changes as received power falls, and which modulation format gives the best balance between data rate and margin.

Those questions are answered on the ground, in a lab, long before any flight or field test. The receiver used for that work has to be stable and well characterised, so that changes in the results come from the terminal and the link conditions rather than from the test equipment.

The Coherent Optical Receiver in a Space Link Test Bench

The CORX coherent optical receiver recovers all four components of a dual-polarisation signal, XI, XQ, YI and YQ, using a built-in tunable local oscillator, a polarisation-maintaining 90° optical hybrid, balanced photodetectors and integrated TIAs. Its outputs feed a real-time oscilloscope, which then shows the constellation, EVM and bit-error rate.

In space communication research, it serves as the reference receiver for terminal prototypes and for modulation and DSP studies, so results can be compared from one test campaign to the next.

Why Received Power and Format Matter

Space links work with changing distances and limited received power, so ground tests usually step through three variables:

• Received power: the CORX’s 10 dB variable optical attenuator, with an amplifier in the path when needed, lets the lab step the power reaching the receiver.
• Modulation format: comparing QPSK, 8-PSK, 16-QAM and 64-QAM shows how much margin each format leaves for a given link.
• Long sessions: the built-in LO holds its frequency to ±0.3 GHz over 24 hours, so long measurement campaigns stay on channel.

Built for Space Research Laboratories

The receiver is a 1U, 3 kg instrument designed to stay on the bench through a whole development programme.

Local oscillator inside the receiver

The tunable LO covers 1528 to 1568 nm with 10 to 16 dBm output on PM PANDA fibre, so the receive side needs no separate oscillator laser.

Bandwidth chosen at order

The CORX is factory-configured at 20, 40 or 60 GHz, matched to the symbol rates of the terminal designs being studied. Its integrated TIAs give a 600 mV swing into 50 Ohm for the oscilloscope.

Low timing error between channels

IQ skew is held to ±3 ps and XY polarisation skew to ±5 ps, so the recovered constellation reflects the signal rather than the receiver. Optical return loss is 27 dB at 1550 nm.

Scripted test campaigns

USB and Ethernet with SCPI commands, a built-in web server and a browser GUI allow power and format sweeps to run as automated sequences.

Building a Complete Space Link Test Bench

Reference signals in each format come from the Optical Multi-Format Transmitter, which has its own built-in bias control. When the team tests its own terminal transmitter, the Automatic Bias Control System keeps that prototype’s modulators locked. The PM EDFA sets the signal level in the C-band as a booster or pre-amplifier ahead of the coherent optical receiver, and the ID OSA Optical Spectrum Analyser confirms spectral shape and channel placement.

Who Uses It

• Space research centres and satellite communication programmes
• Optical terminal and free-space optical communication developers
• Defence research laboratories working on optical links
• Photonics groups at IITs, universities and research institutes
• Satellite communication companies and start-ups

Supply and Support in India

United Spectrum Instruments (USI), Chennai, supplies the CORX in India together with the ID Photonics Optical Multi-Format Transmitter, Automatic Bias Control System and ID OSA, and the PM EDFA.

Sourcing the bench from one supplier gives space communication teams a single point of contact for bandwidth version, oscilloscope matching, installation and after-sales support, with pre-sales guidance on the formats and power ranges to be tested.

Request a Configuration

Download the brochure from this page, use the Enquire Now button, write to sales@unitedspectrum.in, or call +91 93631 83748 / +91 97899 04948. Please mention:

• The link type: satellite-to-ground, inter-satellite or free-space terminal
• The modulation formats and symbol rates to be studied
• The received-power range you want to emulate on the bench
• Your real-time oscilloscope model and bandwidth