Automatic Bias Control (ABC) System for Telecommunication and Optical Networks

Why Optical Networks Development Needs Stable Modulator Bias

Every transmitter in modern optical networks depends on Mach-Zehnder modulators held at the right bias point. When a team builds its own transmitter, from discrete lithium niobate modulators or a silicon photonics chip, that bias point does not stay put. Temperature changes, ageing and changes in RF drive all shift it.

A modulator that drifts off its operating point gives a distorted constellation and a worse bit-error rate, even when the rest of the design is sound. On a test bench, manual re-adjustment between runs costs time and makes results hard to compare from one day to the next. Development teams need the bias held automatically, so measurements show the behaviour of the design rather than the drift.

The Automatic Bias Control System on the Bench

The Automatic Bias Control (ABC) System from ID Photonics locks the bias of the modulators in a transmitter under development. It applies a small, low-frequency dither to each bias voltage, reads the response in the optical output and adjusts each bias point continuously.

Automatic bias control is intended for the team’s own modulators. The ID Photonics OMFT already has bias control built in, so on a shared bench the ABC looks after the prototype while the OMFT serves as the reference transmitter.

Why Bias Drift Matters

Three sources of drift make manual bias setting unreliable over a working day:

• Temperature: small changes in the lab or inside the package move the modulator transfer curve and shift the best bias point.
• Ageing: the best bias point creeps slowly as a modulator is used over hours and days of testing.
• RF drive and format changes: moving between formats or drive amplitudes changes the best operating point, so a fixed setting no longer holds.

Built for Optical Networks Test Labs

The ABC is configured in software, so one unit can follow a project from first modulator tests to a complete coherent prototype.

Every MZM type on one bench

The same controller handles single-polarisation intensity MZMs, dual-polarisation intensity modulators, IQ-MZMs and dual-polarisation IQ-MZMs, on lithium niobate and silicon photonics platforms.

Holding the point through long runs

Bias precision is below 0.1 mV and the response to drift is below 100 ms, with a bias adjustment range of, for example, ±10 V depending on the modulator.

Formats from OOK to QAM

The ABC supports OOK, BPSK, QPSK, QAM and Nyquist-shaped signals, across 1260 to 1625 nm, so the same unit serves O-band and C-band work.

Rack or module format

It comes as a 1U rack unit or a module card, with USB or Ethernet control depending on the model, a 5 V or 12 V DC supply and an operating range of −10 to +70 °C.

Building a Complete Modulator Test Bench

The optical carrier for the prototype transmitter comes from the CoBrite DX2 Dual-Port Tunable Laser Source, whose second port can serve as a local oscillator. With the ABC holding the prototype’s bias, its output can be compared directly with the Optical Multi-Format Transmitter as a known-good reference. The CORX Coherent Optical IQ Receiver measures constellation, EVM and BER on the receive side, and the ID OSA Optical Spectrum Analyser confirms spectral shape and channel placement.

Who Uses It

• Coherent transceiver and transmitter developers
• Silicon photonics and photonic integrated circuit design teams
• Modulator and optical component manufacturers
• Telecom equipment makers and operator test laboratories
• Optical communication research groups at IITs and research institutes

Supply and Support in India

United Spectrum Instruments (USI), Chennai, supplies the Automatic Bias Control System in India as the distributor for ID Photonics, together with the CoBrite tunable lasers, OMFT, CORX receiver and ID OSA.

Sourcing the bench from one supplier gives telecom and optical networks teams a single point of contact for modulator configuration, interfaces, installation and after-sales support. Pre-sales guidance helps match the ABC model and format to the modulators you are building.

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 modulator types to be locked: intensity MZM, IQ-MZM or dual-polarisation IQ-MZM
• The platform (lithium niobate or silicon photonics) and the wavelength band
• The modulation formats and symbol rates you are working with
• Whether you need a rack unit or module card, and USB or Ethernet control