Coherent Optical Receiver (CORX) for Coherent LiDAR

Why Coherent LiDAR Research Needs a Calibrated IQ Receiver

Coherent LiDAR measures distance and velocity by mixing the light returned from a target with a reference, then reading the beat signal. In FMCW designs the transmitted light is chirped, and range and Doppler information sit in the frequency and phase of that beat. Research teams developing these systems need to see the received field in detail, not just a single intensity signal.

Building a receive chain from separate hybrids, photodiodes and amplifiers makes it hard to tell whether an odd result comes from the LiDAR design or from the receiver itself. A calibrated, turn-key receiver gives coherent LiDAR labs a fixed reference point on the receive side.

The Coherent Optical Receiver in a LiDAR Test Bench

The CORX coherent optical receiver mixes the incoming light with its built-in local oscillator in a polarisation-maintaining 90° optical hybrid, detects it with balanced photodetectors and amplifies it with integrated TIAs. It delivers four outputs, XI, XQ, YI and YQ, which a real-time oscilloscope or DSP software can process.

In coherent LiDAR work it is used to study heterodyne detection, chirped waveforms from modulator-based transmitters, receiver bandwidth and the interaction between laser and receiver, as part of a modular bench with other ID Photonics instruments.

Why IQ Detection and Low-Frequency Response Matter

For LiDAR studies, three receiver properties shape what can be measured:

• In-phase and quadrature outputs: recording both I and Q gives the full amplitude and phase of the received field, rather than intensity alone.
• Dual polarisation: returns can arrive in either polarisation, and separate X and Y outputs capture both.
• Low-frequency cutoff: the CORX passes signals from 1 MHz upwards, which should be checked against the lowest beat frequencies in the LiDAR design.

Built for Coherent LiDAR Laboratories

The receiver is a 1U, 3 kg instrument that sits beside the oscilloscope and stays on the bench through a research programme.

Local oscillator inside

The tunable LO covers 1528 to 1568 nm with 10 to 16 dBm output on PM PANDA fibre and holds frequency to ±0.3 GHz over 24 hours, so no separate oscillator laser is needed on the receive side.

Bandwidth chosen at order

The CORX is factory-configured at 20, 40 or 60 GHz bandwidth, matched to the chirp bandwidth and signal rates of the LiDAR architecture being studied.

Matched channels

IQ skew is held to ±3 ps and XY polarisation skew to ±5 ps, with below 5% THD and a 600 mV swing into 50 Ohm from the integrated TIAs. A 10 dB variable optical attenuator sets the input level, and optical return loss is 27 dB at 1550 nm.

Scripted measurements

USB and Ethernet with SCPI commands, a built-in web server and a browser GUI let measurement runs be automated alongside the rest of the bench.

Building a Complete Coherent LiDAR Test Bench

The optical source for the experiment comes from the Narrow Linewidth Tunable Laser Source. Where the team modulates that light with its own modulators or photonic chip, the Automatic Bias Control System keeps them locked. The Optical Multi-Format Transmitter, with its own built-in bias control, generates AWG-defined reference waveforms for checking the coherent optical receiver, and the ID OSA Optical Spectrum Analyser confirms the spectrum of the transmitted light.

Who Uses It

• Coherent and FMCW LiDAR research and development teams
• Photonic integrated circuit and silicon photonics LiDAR developers
• Aerospace and defence R&D groups working on optical sensing
• Photonics groups at IITs, universities and research institutes
• Laser and optical sensing start-ups

Supply and Support in India

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

Sourcing the bench from one supplier gives coherent LiDAR teams a single point of contact for bandwidth version, oscilloscope matching, installation and after-sales support, with pre-sales guidance on matching the receiver to the LiDAR architecture.

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 LiDAR architecture: FMCW, heterodyne or another coherent scheme
• The chirp bandwidth and the range of beat frequencies you expect
• The operating wavelength and any polarisation requirements
• Your real-time oscilloscope or DSP set-up