Automatic Bias Control for Mach-Zehnder Modulators

Why Mach-Zehnder modulators need bias control

A Mach-Zehnder modulator splits light into two arms, applies a voltage-dependent phase shift and recombines them. Its transfer function is a raised cosine, and the DC bias sets where on that curve the modulator operates: quadrature for intensity modulation, or null for IQ and coherent formats. In lithium niobate and other materials the optimum bias drifts with temperature, ageing, photorefractive effects and optical power. Uncorrected drift reduces extinction ratio, introduces IQ imbalance and quadrature error, and raises EVM and bit error rate.

Why IQ modulators are especially demanding

An IQ modulator contains two child MZMs (I and Q) plus a phase section that sets the 90° quadrature between them. A dual-polarisation IQ modulator doubles that to six bias points. All six must be held simultaneously, and the quadrature angle is especially sensitive: a few degrees of error visibly distorts a 16QAM or 64QAM constellation.

What makes the ID-ABC different

Many bias controllers derive their feedback from the RF data signal itself. When the modulation format or drive amplitude changes, the feedback changes too, and the controller must be re-tuned or may lock incorrectly. The ID-ABC, developed in-house by ID Photonics over more than ten years, does not depend on the applied format or RF amplitude. It tracks the optimum operating point for QPSK, 8-PSK, QAM-xx, Nyquist-shaped and other signals without parameter tweaking, which keeps operation stable even when formats are switched.

In ID Photonics’ application examples, the ID-ABC found and held the optimum bias of a dual-polarisation LiNbO₃ IQ modulator within 45 seconds for 128 Gb/s DP-QPSK and within one minute for 256 Gb/s DP-16QAM, starting from an arbitrary point. A single-polarisation 56 Gb/s QPSK test showed no penalty compared with careful manual optimisation.

One unit, many configurations

The ID-ABC is reconfigured in software rather than hardware. The same unit can control a single- or dual-polarisation IQ modulator, single- or dual-polarisation intensity modulators, or up to two single-polarisation modulators at once, covering 12 Mach-Zehnder configurations. It supports electro-optic and heater-based bias electrodes, so it works with bulk and thin-film lithium niobate (TFLN), InP, GaAs and silicon photonics devices.

Supported Configurations

We will confirm whether the 1-channel (ABC-BPC-13) or 2-channel (ABC-BPC-14) feedback version suits your modulator.

Independent of Modulation Format and RF Amplitude

The ID-ABC does not rely on the data signal for feedback, so it locks reliably for QPSK, 8-PSK, 16QAM, 32QAM, Nyquist-shaped and custom signals at any drive amplitude. Switching formats needs no re-tuning.

Fast, Penalty-Free Locking

From an arbitrary starting point, the ID-ABC settles in about 45 seconds (under 3 minutes maximum) and holds quadrature error below ±0.5° on average. ID Photonics’ tests show performance equal to careful manual optimisation by an experienced researcher.

One Unit, 12 Modulator Configurations

Single- or dual-polarisation IQ modulators, intensity modulators, or two single-polarisation modulators at once: all are selected with a click in software, so the same hardware serves future projects instead of needing a new controller.

TFLN-Ready, Multi-Material Support

Support for electro-optic and heater-based bias electrodes covers bulk and thin-film lithium niobate, InP, GaAs and silicon photonics modulators, including the latest TFLN devices.

Six Bias Channels up to ±30 V

Six channels drive every bias point of a dual-polarisation IQ modulator. Outputs reach ±30 V differential or ±5 V single-ended high current, with a user-settable software voltage limit to protect sensitive devices.

Built-In Optical Feedback Taps

The ABC-BPC-13 and ABC-BPC-14 include 10% optical tap detectors with 26 dB dynamic range across the O-, C- and L-bands, so no external photodiodes or monitor wiring are needed.

Plug-and-Play with OIF Modulators

An included adaptor board connects directly to OIF-PMQ-TX-01.1 standard IQ modulators. Further adaptor boards are available for SMA outputs and other modulator types.

Zero-Noise Mode

For the most sensitive measurements, the zero-noise feature mutes the control signals and freezes the bias at its optimum, removing any contribution from the controller.

Touch Display, Web GUI, SCPI and LabVIEW

Operate locally from the front touch display, from any browser via the installation-free web GUI over USB or Ethernet, or by SCPI-style commands with supplied LabVIEW drivers.

See the full overview of automatic bias control applications, or explore the uses below.

Coherent Transmitter Development

Telecom R&D teams building their own coherent transmitters for telecommunications and optical networks use the ID-ABC to keep DP-IQ modulators locked while testing QPSK, 16QAM and higher formats, without retuning between experiments.

Custom Modulator Setups with AWGs

Labs that already own IQ modulators and RF drivers add the ID-ABC to build a stable transmitter around their AWG. For a fully integrated alternative, the OMFT transmitter uses the same ID Photonics bias control technology.

Modulator Characterisation and Production Test

In opto-electronic packaging and modulator manufacturing, the ID-ABC holds devices at their correct operating point during burn-in, characterisation and final test, and its software reconfiguration handles different device types on one station.

Thin-Film Lithium Niobate and Silicon Photonics Research

Researchers developing TFLN and silicon photonic modulators, including for quantum photonics, use the ID-ABC’s heater and electro-optic electrode support to stabilise new devices during experiments.

DWDM Comb Modulation

When a PMUX combines a CoBrite MX laser array into one channel comb, a single MZM modulates all channels. The ID-ABC keeps that modulator locked for long-running loaded-system tests.

Single-Sideband, LiDAR and Microwave Photonics

Single-sideband modulation for coherent LiDAR, frequency shifting and microwave photonic links all depend on precise IQ bias; the ID-ABC maintains it automatically.

Space and Defence Optical Terminals

Teams developing satellite and space communication and defence optical terminals use the ID-ABC to stabilise modulators during long environmental and link tests.

Official Authorised Distributor in India

United Spectrum Instruments is the authorised Indian distributor for ID Photonics, so you receive a genuine ID-ABC backed by the manufacturer.

Help Matching the ABC to Your Modulator

We review your modulator type, material, connector and bias voltage requirements and recommend the right ID-ABC variant and adaptor board, so it works with your device from day one.

Experience with Indian Research and Industry

We work with IITs, CSIR laboratories, defence establishments, telecom companies and photonics start-ups across India and understand their procurement and documentation requirements.

Delivery and Local Technical Support

We deliver anywhere in India and provide after-sales support for setup, modulator connection, SCPI and LabVIEW integration, and troubleshooting.

A Complete Transmitter Test Chain

Alongside the ID-ABC, we supply CoBrite tunable lasers, OMFT transmitters, CORX receivers and optical spectrum analysers, so your full coherent setup can come from one partner.

Contact Us

Phone: +91 93631 83748 / +91 97899 04948
Email: sales@unitedspectrum.in