Polarisation-Maintaining Multiplexer for Defence & Secure Communication

Why Secure Communication Links Must Be Proven Under Load

A secure communication link that performs well alone on a dark fibre has only passed half its test. In service, it will share fibre and amplifiers with dozens of other wavelengths, and those neighbours bring crosstalk, nonlinear interaction and amplifier noise that a single-channel bench never shows.

Defence and research laboratories therefore need a way to surround the link under test with a realistic DWDM spectrum. Building that spectrum from many separate lasers is the easy part; keeping it under control is harder, because every channel has to arrive at the next stage with a known, stable polarisation.

The Polarisation-Maintaining Multiplexer’s Role: A Controlled Channel Load

The polarisation-maintaining multiplexer (PMUX) from ID Photonics combines individual laser channels into one dense wavelength comb on a single polarisation-maintaining output fibre. Inside is a polarisation-maintaining arrayed waveguide grating built with PANDA fibre throughout, so each channel keeps its linear polarisation from its own input to the combined output.

The result is a channel comb that emulates the spectral loading of a deployed DWDM network, ready to be modulated, amplified or sent through the system under test without a polarisation alignment step.

Why Polarisation Extinction Ratio Matters on Every Channel

A standard multiplexer combines wavelengths efficiently but lets each channel’s polarisation wander with birefringence and temperature. For secure communication test setups, that wandering becomes a hidden variable.

• Modulator efficiency: Mach-Zehnder and IQ modulators respond to polarisation alignment, so a drifting input changes extinction ratio and drive requirements from one channel to the next.
• Clean comparisons: with a polarisation extinction ratio of at least 16 dB (20 dB typical) held on all channels at once, changes in link performance can be traced to the system under test rather than the load.
• Repeatable records: a stable, characterised comb lets a qualification run be repeated weeks later under the same conditions.

Engineered for Long, Unattended Test Campaigns

Secure communication programmes often run measurements over many hours or overnight, so the channel load has to stay put without supervision.

Precise grid placement

Channels sit on the ITU-T G.694.1 grid with a centre offset of ±0.04 nm and a 0.55 nm 3 dB passband at 100 GHz spacing, leaving margin for laser frequency accuracy while keeping adjacent channels apart.

Fixed or flexible grid

Fixed 50 GHz or 100 GHz grids cover standard DWDM emulation. Flexible-grid versions, chosen at order, allow non-uniform and sub-50 GHz spacing for elastic network and super-channel studies.

Low, even loss across the band

Insertion loss stays below 6 dB with 1 to 1.5 dB uniformity across the band, so a high channel count does not demand a steep power budget.

Nothing to recalibrate

The solid-state design has no moving parts and needs no periodic realignment between 0 and 50 °C. It fits a standard 19-inch rack beside the laser mainframe.

From Laser Channels to a Loaded Link

The channels themselves come from the Narrow Linewidth Tunable Laser Source, in CoBrite chassis that scale from a few ports up to 48 channels in an MX rack. After combining, the Polarisation-Maintaining EDFA restores comb power without giving up its polarisation alignment, and the ID OSA Optical Spectrum Analyser confirms grid placement, channel power flatness and OSNR before each run. At the far end, the CORX Coherent Optical IQ Receiver recovers the channel under test after it has travelled with the full load, showing what the neighbouring channels have cost the secure link.

Who Uses It

• Defence R&D laboratories working on secure optical links
• Government research organisations in optical and quantum communication
• Photonics groups at IITs, universities and research institutes
• Telecom equipment developers building encrypted or secure optical transport
• Optical component makers qualifying amplifiers, filters and transceivers under DWDM load

Supply and Support in India

United Spectrum Instruments (USI), Chennai, supplies the polarisation-maintaining multiplexer in India as the distributor for ID Photonics, together with the narrow linewidth laser, PM EDFA, ID OSA and CORX receiver.

Sourcing the complete secure communication test setup from one supplier gives defence and research teams a single point of contact for channel spacing, grid type, connector choice, installation and after-sales support. Pre-sales guidance helps match the channel count to the network the programme needs to emulate.

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:

• Channel spacing (50 GHz, 100 GHz or flexible grid) and band
• Number of channels to combine and the lasers that will feed them
• Preferred connectors (FC/APC, FC/PC or SC/PC)
• What the channel load is for: link testing, component qualification or network emulation