Coherent Optical Receiver (CORX) for Defence & Secure Communication

Why Secure Communication Programmes Validate Links In-House

Defence and secure communication networks increasingly use coherent optical links to carry large volumes of data over fibre. Before a new transmitter, DSP design or link configuration goes to field trials, research teams need to measure it in their own laboratory, under conditions they control and can repeat.

Real links rarely carry one channel. A secure communication backbone is usually loaded with many DWDM channels, so a receiver test that only works on an isolated signal does not show how the design behaves among its neighbours. The lab needs a receiver that can pick out each channel in turn on a fully loaded link.

The Coherent Optical Receiver on a Loaded-Link Bench

The CORX coherent optical receiver mixes the incoming light with its built-in tunable local oscillator in a polarisation-maintaining 90° optical hybrid, detects the result with balanced photodetectors and passes four outputs, XI, XQ, YI and YQ, to a real-time oscilloscope.

Because the local oscillator is tunable across the C-band, the receiver is set to the channel being studied. Moving to the next channel is a matter of retuning the LO, so one instrument can work through every channel on the bench.

Why Channel Selection Matters

On a multi-channel test link, three receiver properties decide how well each channel can be studied:

• Tunable local oscillator: the LO covers 1528 to 1568 nm, so the receiver can be set to any channel in that range on the link.
• Frequency stability: the LO holds its frequency to ±0.3 GHz over 24 hours, so a long campaign stays on the chosen channel.
• Polarisation handling: a polarisation-maintaining hybrid and PM PANDA fibre on the LO keep both polarisations of the signal well defined.

Built for Defence Research Laboratories

The receiver is a 1U, 3 kg instrument that stays on the bench through a programme of tests.

Bandwidth chosen at order

The CORX is factory-configured at 20, 40 or 60 GHz bandwidth, matched to the symbol rates of the systems under study. Integrated TIAs give a 600 mV swing into 50 Ohm, with a 1 MHz low-frequency cutoff and below 5% THD.

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 link rather than the receiver. A 10 dB variable optical attenuator sets the input level, and optical return loss is 27 dB at 1550 nm.

Low-noise local oscillator

The built-in LO has a linewidth below 100 kHz, 25 kHz typical, with 10 to 16 dBm output and a PER above 20 dB.

Repeatable, scripted runs

USB and Ethernet with SCPI commands, a built-in web server and a browser GUI let measurement sequences be repeated in the same way from one session to the next.

Building a Complete Loaded-Link Test Bench

Neighbouring DWDM channels come from the Multi-Channel Tunable Laser Sources, and the Polarization Maintaining Multiplexer combines them onto one PM fibre at 50 or 100 GHz spacing. The channel under test is generated by the Optical Multi-Format Transmitter, with its own built-in bias control, and the ID OSA Optical Spectrum Analyser confirms channel placement before the coherent optical receiver measures each channel in turn.

Who Uses It

• Defence research and development laboratories
• Secure network and communication system developers
• Aerospace and defence electronics organisations
• Photonics groups at IITs and national research institutes
• Indian optical communication equipment makers

Supply and Support in India

United Spectrum Instruments (USI), Chennai, supplies the CORX in India together with the ID Photonics Optical Multi-Format Transmitter, multi-channel CoBrite lasers and ID OSA, and the PM multiplexer.

Sourcing the bench from one supplier gives secure communication teams a single point of contact for bandwidth version, channel plan, oscilloscope matching, installation and after-sales support, with pre-sales guidance on matching the receiver to the link being studied.

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 number of channels and channel spacing on your test link
• The modulation formats and symbol rates to be measured
• Your real-time oscilloscope model and bandwidth
• Whether the work is research, link validation or pre-trial testing