Coherent Optical Receiver (CORX) for Telecommunication and Optical Networks

Why Optical Networks Labs Need a Calibrated Coherent Receiver

Coherent transmitters for optical networks encode data in amplitude, phase and polarisation. To see whether a new transmitter, module or IQ modulator is working, a lab has to recover all four signal components, XI, XQ, YI and YQ, and look at the constellation, EVM and bit-error rate.

Building that receiver from a separate optical hybrid, photodiodes, amplifiers and a local oscillator laser takes time, and every part adds its own skew and imperfections. A turn-key coherent optical receiver gives the lab a front-end whose behaviour is known, so differences in the measurement can be traced to the transmitter under test.

The Coherent Optical Receiver as a Measurement Front-End

The CORX coherent optical receiver mixes the incoming signal with its built-in local oscillator in a polarisation-maintaining 90° optical hybrid, detects the result with balanced photodetectors and amplifies it with integrated TIAs. Its four outputs feed a real-time oscilloscope, which then works as a coherent signal analyser.

It handles QPSK, 8-PSK, 16-QAM, 64-QAM and higher-order dual-polarisation formats, for DWDM testing, coherent transceiver and module qualification, IQ modulator characterisation and DSP algorithm development. Because the same receiver can stay on the bench from early R&D to production test, results remain comparable as a transmitter design moves towards volume.

Why Skew and Local Oscillator Quality Matter

In a coherent receiver, timing and the local oscillator decide how faithfully the signal is recovered:

• IQ and XY skew: a timing difference between channels distorts the constellation; the CORX holds IQ skew to ±3 ps and XY polarisation skew to ±5 ps.
• Local oscillator linewidth: phase noise in the oscillator adds to the measured phase noise; the built-in LO has a linewidth below 100 kHz, 25 kHz typical.
• Frequency stability: the LO holds its frequency to ±0.3 GHz over 24 hours, so long measurement runs stay on channel.

Built for Optical Networks Test Benches

The receiver is designed to sit in a rack beside the oscilloscope and to be driven from the bench software.

Three bandwidth versions

The CORX is factory-configured at 20, 40 or 60 GHz bandwidth, chosen at order to match the symbol rates the lab needs to measure.

C-band local oscillator inside

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

Matched to the oscilloscope

Integrated TIAs give a 600 mV swing into 50 Ohm, with a 1 MHz low-frequency cutoff and below 5% THD. A 10 dB variable optical attenuator sets the input level, and optical return loss is 27 dB at 1550 nm.

Ready for automation

USB and Ethernet with SCPI commands, a built-in web server and a browser GUI let the CORX run in scripted test sequences, in a 1U chassis of 3 kg.

Building a Complete Coherent Transmitter Test Bench

The transmitter under test takes its optical carrier from the Narrow Linewidth Tunable Laser Source. Where the transmitter is a team’s own prototype, the Automatic Bias Control System keeps its modulators locked. The Optical Multi-Format Transmitter, with its own built-in bias control, provides a known-good reference signal for checking the coherent optical receiver and comparing results, and the ID OSA Optical Spectrum Analyser confirms spectral shape and channel placement.

Who Uses It

• Coherent transceiver and module developers
• Telecom equipment makers and production test teams
• IQ modulator, silicon photonics and PIC developers
• Coherent DSP and algorithm development teams
• Optical communication research groups at IITs and research institutes

Supply and Support in India

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

Sourcing the bench from one supplier gives telecom and optical networks teams a single point of contact for bandwidth version, oscilloscope matching, installation and after-sales support. Pre-sales guidance helps choose the bandwidth for the line rates you need to measure.

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 symbol rates and line rates you need to measure
• The modulation formats, from QPSK to 64-QAM or higher
• Your real-time oscilloscope model and its bandwidth
• Whether the receiver is for R&D, module qualification or production test